Improving the Seismic Performance of Existing Buildings and Other Structures

Seismic hazard assessment is based on two primary components: (1) establishing the likelihood of earthquake occurrence and (2) quantifying earthquake effects, particularly the distribution of strong shaking. The seismically active western United States has relatively young crust that is actively deforming, and in some cases uplifting, part of a broad plate boundary with the Pacific Plate. This on-going deformation is measured directly with GPS instrumentation and generates relatively frequent large earthquakes. In contrast, the central and eastern U.S. resides on older, generally stable crust that is not rapidly deforming. Large earthquakes can occur in this stable crust (e.g., 1811–1812 New Madrid or 1886 Charleston, South Carolina earthquakes), but they are much less frequent than in the western U.S. However, the older (and colder) crust beneath the central and eastern U.S. transmits seismic energy much more efficiently than in the western U.S, so despite lower rates of earthquake occurrence, the potential effects of equivalent sized earthquakes in the eastern and central U.S. is larger than in the West. Furthermore, effects such as directional fault rupture or geologic subsurface complexity, such as the existence of a large basin filled with soft sediments, can locally greatly amplify shaking levels. A variety of earthquake scenarios will be used to demonstrate the regional variations in seismic hazard around the U.S and provide examples of some of these effects on ground motion. The risk posed by these scenarios is described in terms of both estimated total economic losses and insured losses for each event. Regional variations in the ratio of insured to total economic loss around the country is one factor influencing resiliency and post-event recovery.

Development of performance-based seismic design initiated in the 1980s as a tool to solve the problem of existing seimsically-hazardous buildings. With the publication of national rehabilitation guidelines in the late 1990s, and standardization of these guidelines in 2006, the practice of performance-based design has become widely practiced throughout the United States and been implemented in the evaluation and retrofit of thousands of buildings. Today we are on the threshold of a new era of performance-based earthquake engineerin technology that will combine advanced structural simulation capability, building information modeling and probabilsitic evaluation to enable true performance-based design.

The progress on mitigating the seismic risks from existing buildings in the U.S. will be summarized based on published information and an informal telephone poll. In order to identify a manageable scope, information will be given only for states having high Annualized Earthquake Loss or Annualized Earthquake Loss Ratios. Programs have been sought that systematically identify, evaluate, and or mitigate buildings by occupancy (schools, hospitals) or structural type (unreinforced masonry). Code requirements or practices that require seismic rehabilitation when triggered by change-of-occupancy or structural alteration are also identified. Lastly, a general description of the extent of voluntary seismic rehabilitation accomplished by private industry in various regions will be given.

Assessment and retrofit of 3 parking structures in accordance with the ASCE 41 standard is discussed in this paper. All were built between the mid 70-s and early 90-s, and are of cast-in-place reinforced concrete construction. Together with configurational anomalies, columns that are not part of the seismic force resisting system, and are not detailed for deformation compatibility, generally limit the performance of these structures. During design Supplement 1 to ASCE 41 was developed and published, and adopted on the project. Changes to the column modeling and acceptance criteria affected design decisions, and early adoption of the provisions provided a more economical design meeting the requested performance objectives. Foundation flexibility effects are included in the analysis to better predict displacement demands, and confidently assess the acceptability of the performance.

Engineering systems in a building provide services to maintain functionality within the building. In hospital buildings, these systems are required to support critical lifesaving functions and continue to function during and after an earthquake and hence they are to be carefully designed and constructed to maintain their operational continuity. To understand the potential problems and inadequacies with existing engineering systems within critical facilities, three hospitals in Wellington region were surveyed. The survey focused on `essential' systems required to sustain the operational continuity of hospitals. The study revealed that most of the components have been provided with some degree of restraint. The `adequacy' of the mode of supporting systems has been examined against the latest New Zealand standards, NZS 4219:2009 (SNZ, 2009). The paper highlights the observations in terms of the vulnerability of the components, the existing scenario of their restraints and their impact on seismic safety. Finally, a brief note is made on the current practice within consultancy firms towards the seismic design and installation of engineering systems.

The 1994 Northridge earthquake exposed the vulnerability of steel moment frame structures to seismic damage. This paper summarizes the performance-based seismic retrofit of a three-story steel moment frame building in the San Francisco Bay Area of California. The building is located within a few hundred feet of the Hayward fault and serves as an essential service facility. ASCE 41 was used in conjunction with FEMA 351 to assess the anticipated performance of the existing building and to evaluate several retrofit options. Retrofit options included: connection upgrades, the addition of either energy dissipation or buckling restrained braces, and combinations of these approaches. Various performance objectives were studied and varied from Life-Safety to Immediate Occupancy and included the evaluation of both structural and non-structural systems. Schematic level plans and associated estimate of probable cost were developed for each of the six schemes. After extensive discussions with the owner, an Immediate Occupancy level of performance at the DBE emerged as the desired objective for the retrofit. The strengthening scheme is currently in design development and will include the combination of connection upgrades and new buckling restrained braces. The design phase will employ non-linear static and dynamic analyses to evaluate the efficiency of the retrofit.

Buckling-restrained braces may be used for both new design and retrofit applications where increased seismic performance levels are desired relative to traditional buckling braces. As a retrofit technology, buckling-restrained braces may be used to augment strength, stiffness, or damping in an existing lateral force resisting system. In the case of the seismic rehabilitation of the steel-framed hospital building at the Department of Veterans Affairs Seattle campus, buckling-restrained braces were used as a direct replacement of the existing braced frame braces. Where possible, the new braces were connected to the existing gusset plates. This implementation technique may be applied in future rehabilitation projects where ductile details are lacking or increased performance levels are desired. This paper focuses on the unique challenges encountered during the analysis, design, and construction phases of the seismic rehabilitation. Analysis topics will include the development of buckling-restrained brace nonlinear hinge properties and the use of performance-based design techniques to verify seismic performance while minimizing demands on the existing columns and connections. Design phase topics will include brace to gusset connection design and reframing at the existing interstitial floor to allow for brace erection. Construction phase topics will focus on maintaining the continued operation of the hospital functions, which was an important consideration during the entire project.

This paper summarizes the seismic analysis and rehabilitation design of a fifteen story steel moment resisting frame building constructed with connection details that were found to be vulnerable to fracture in the 1994 Northridge earthquake. This building is located in Oakland, California, less than five miles from the Hayward Fault. Previous testing of the existing moment connections demonstrated that the beam flange to column flange complete joint penetration groove welds were vulnerable to fracture, and consequently the building presented a risk to life safety in the event of a major earthquake. Seismic rehabilitation to meet the requirements of the State of California, Department of General Services resulted in a retrofit scheme including a combination of moment connection strengthening and addition of viscous dampers. To meet the proposed requirements, two phases of sophisticated analysis techniques were performed in the rehabilitation design. First, to estimate the necessary connection strengthening and damping, multi-mode two-dimensional nonlinear pushover analyses were performed along with single-degree-of-freedom nonlinear dynamic time-history analyses. Then to refine the scheme and perform final checks, nonlinear time history analyses of building frames were performed. These models included a nonlinear fiber element that approximated the fracture behavior observed in the existing connection tests and incorporated results from the test program to model the strengthened connection behavior. Concurrent with the analysis portion of the work, various connection modification schemes were studied, designed, and subjected to full-scale laboratory testing. Available design procedures contained in the AISC/NIST Design Guide 12 were modified to include column and panel zone deformation and adapted to alternate strengthening configurations.

The implementation of linear elastic procedures for the seismic evaluation and retrofit design of existing structures has been developed with great detail in ASCE 41. Although the procedures are intended to cover the most important aspects of the evaluation and design process, some specific aspects may not be as transparent as needed for adequate results, and may require modifications or comment clarifications in upcoming editions of the standard. This paper is intended to highlight the pros and challenges of implementing linear static procedures for seismic evaluation and retrofit design of structures, particularly when compared with the use of more advanced non-linear based analysis techniques.

A design example is presented to illustrate the creative solutions implemented to achieve Immediate Occupancy (IO) performance for a voluntary seismic rehabilitation of a high-tech manufacturing facility, which is required to remain fully operational during construction. The owner desired to design for Immediate Occupancy performance per ASCE 41 for several reasons including risks associated with the use of hazardous chemicals and the crippling cost of a production shutdown. In addition to the challenge of retrofitting an operational manufacturing facility, the myriad of building utilities located throughout and around the building made locating strengthening elements a major challenge, and led to unusual and unique design features. The facility is located in the Silicon Valley, less than two miles from the Hayward Fault. The building is split level, with a two-story portion that is 45,000 square feet in plan, and a one-story portion that is 91,000 square feet. The entire ground floor of the building is occupied by operating clean rooms. The original lateral system of the building consists of exterior tilt-up concrete panel shear walls and steel concentrically braced frames with wood-framed roofs. A seismic evaluation concluded that the building did not satisfy IO acceptance criteria. The rehab design required careful consideration of the owner's objectives to upgrade the building while minimizing costs and providing continued operations. The upgrade utilizes exterior steel frame and concrete shear wall buttresses in conjunction with buckling restrained braces and link elements to improve seismic performance without interrupting operations. The new exterior buttresses limit the drift demands to the existing braced frames and gravity columns, while the buckling restrained brace elements provide ductility and limit demands to buttress foundations and collectors. Design and analysis of the building followed the ASCE 41 procedures for linear static, linear dynamic, and nonlinear static analysis procedures. The analysis confirmed that the external buttresses efficiently enhance the building performance to achieve the owner's desired performance level while minimizing impacts to the operating clean room.

Nonlinear response history analysis provides a robust analytical approach to estimate and evaluate existing building performance but it is sensitive to the characteristics of input ground motion. ASCE 7-05 provides guidelines for selecting and scaling from individual ground motion records. Recently, researchers developed an alternative method called "modal-pushover-based ground motion scaling procedure" (MPS) that considers the strength and higher mode effects of the individual building in its selection and scaling methodology. A 24-story steel moment frame building with "pre-Northridge" connections is chosen as a case study to compare the response predictions of the ASCE 7-05 method and the MPS method. Based on comparison the inter-story drift ratios, the MPS method resulted in significantly lower demands than the ASCE 7-05 method. The case study includes a re-evaluation of the structure after a conceptual rehabilitation. Implications of the rehabilitation on the scaling of ground motion records when utilizing the MPS method are discussed.

This paper presents the seismic design and remodeling of Santa Monica Place mall and its seismic strengthening following the guidelines of ASCE 41-06. The original building was designed as a closed roof mall based on the 1976 Uniform Building Code. The remodeled mall is designed to be an open roof mall with about same plan dimensions as existing mall. The existing mall is a steel frame with inverted Chevron (V-type) concentric braced frames in the N-S direction and CMU shear walls in the E-W direction. A nonlinear two-dimensional push-over analysis is conducted on representative braced frames to demonstrate nonlinear post-buckling capacity of Chevron braced frames. It is found that plastic rotation of the beam, where two braces intersect, at target displacement is less than the limits defined by ASCE 41-06. It was found that the existing braced frames have a lateral load carrying capacity greater than the demands according to the 1976 UBC and ASCE 41-06. To improve the seismic performance of the inverted braced frames, the beam in each frame that is intersected with the braces was strengthened. The strengthening scheme ensures that the expected post-buckling lateral load capacity exceeds the lateral shear demands.

"What gets measured gets done" is an aphorism that could be more routinely applied in earthquake risk management. This paper draws lessons from three mitigation programs in California and describes ways to measure mitigation progress that can be adapted for future use.

Seismic evaluation of Pre 1973 hospital buildings using conventional procedures outlined in the SB-1953 regulations resulted in over 90% of these buildings not meeting the minimum life safety standard as specified in the regulations, and hence being classified as SPC-1. These buildings are considered at risk of collapse in the event of an earthquake or other natural disaster and are required to be retrofitted, replaced or removed from providing acute care services by 2013. The Office of Statewide Health Planning and Development (OSHPD) began a search for an alternate solution which possibly reclassifies some of these hospital buildings to a higher structure performance category based on seismic risk. HAZUS which stands for Hazards United States, a general all purpose software available through FEMA for estimating damage, and losses to buildings and communities through a variety of natural disasters including floods, earthquakes, and wind was selected to achieve this goal. SPC-1 buildings being reclassified to SPC-2 if they met specified criteria using this new risk based analysis procedure would results in hospital buildings originally licensed to provide acute care services to the 2008/2013 seismic deadline to a 2030 deadline.

As part of major renovation projects at Department of Defense facilities, the seismic evaluation and possible retrofit of the existing structure may be required. Structural engineers need to adhere to specific Unified Facilities Criteria documents that govern the seismic analysis and retrofit of existing structures. In addition, Antiterrorism and Force Protection criteria specific to the Unified Facilities Criteria documents may significantly impact the choice and implementation of seismic retrofit measures for Department of Defense structures.

Non-Ductile Concrete Buildings (NDCBs) are particularly vulnerable to earthquake damage. These buildings have stiff reinforced concrete frames that do not bend when shaken or twisted, which increases the likelihood of structural failure during an earthquake. A major earthquake striking the City of Los Angeles would present particularly high risks to the occupants of NDCBs. It is likely that there are around 2,000 such buildings in the City of Los Angeles, yet no inventory exists, and they are virtually unidentifiable from the outside. Seismic rehabilitation would reduce the potential human and economic loss caused by shaking, yet building owners are reluctant to bear the costs. Through a probabilistic model of earthquake impacts, we analyze the human and economic costs and benefits of policy interventions to encourage private sector seismic rehabilitation of NDCBs. We project building owner action under distinct policy options such retrofitting mandates and public information placards. We find that although mandates would be most cost-beneficial — saving $56 million and avoiding 5 deaths — they are less politically feasible than other options. We conclude by recommending ways in which policy makers, engineers, and relevant business owners can collaborate to prevent loss and save lives.

A new decision-support model is developed for making well-informed retrofit decisions in seismic-risk management of structures retrofitted with passive control devices (PCD). Optimal design of passively damped structures in highly seismic environments requires not only choosing the most cost-effective approach from a series of alternatives but also defining the risk associated with each retrofit alternative. Thus, unlike previous works in PCD optimization, the proposed decision-support tool uses multi-criteria genetic algorithm to maximize the overall economic benefit of structural control system through different measures of risk that reflects physical and economical uncertainties, as well as the attitudes of decision makers. Risk measure characterizes the risk tolerance of the decision makers and allows the evolution of rational design or retrofit strategies that depend upon the level of risk aversion to low probability-high impact events. Through a review of different risk measures, a uniform and robust multi-criteria decision tool is created to: (1) provide a systematic and efficient approach for quantifying and evaluating the trade-offs between key decision components (i.e., benefit, cost, performance level, and risk) and deciding on optimal design /retrofit alternatives, therefore suggests a more efficient investment allocations for mitigation of existing structuxes (2) enable a decision maker to more accurately assess how the risk preferences affect the overall design/retrofit alternatives Besides presenting an outline of the risk-based computational framework, the paper includes numerical simulations to emphasize the financial benefits of using passive control devices to make retrofit decisions regarding seismic safety.

The Federal Emergency Management Agency has produced a series of documents aimed at specific building occupancies that details a means for incorporating seismic rehabilitation through discreet actions or steps. Termed, Incremental Seismic Rehabilitation, or ISR, this method helps building owners, risk managers, maintenance personnel and design professionals formulate a means to move toward greater seismic safety for buildings. A companion manual titled "Engineering Guideline for Incremental Seismic Rehabilitation, FEMA 420/Decemeber 2008" (as developed under Applied Technology Council project ATC-68) is intended as a technical resource for design professionals who are implementing incremental seismic rehabilitation on their projects or advocating its use. It explains the concept of incremental seismic rehabilitation as a strategy, discusses maintenance, capital improvement and decision-making processes, summarizes available engineering resource documents, and outlines the overall engineering process for incremental seismic rehabilitation of buildings. This paper will discuss the purpose of the FEMA 420 document; it's relationship to the entire FEMA ISR series; and the underlying presumptions. It will discuss the role of the engineer as a consultant on ISR projects and the rehabilitation process.

Integrated Incremental Seismic Rehabilitation (IISR) is a methodology developed specifically to overcome the primary obstacles to implementation of seismic rehabilitation: costs of physical strengthening and costs of business or functional interruption. The IISR methodology breaks down the process of building rehabilitation into discrete increments, which can be implemented independently over an extended period of time. In combination these increments accomplish the objective of reducing seismic risk, but do so without an unacceptable initial cost or major disruption of building function or income stream. Furthermore, the identified increments can be integrated into normal, programmed building maintenance and capital improvement activities to further reduce project costs and interruption of building function.

This study uses cost-benefit assessment to evaluate the cost-effectiveness of replacing existing seismically deficient reinforced concrete frames to improve their seismic safety. This assessment is based on a set of typical older California reinforced concrete frame structures, whose seismic performance, measured in terms of the risk of earthquake-induced collapse, fatalities and repair costs have been evaluated in previous studies (Liel et al. 2009, Liel and Deierlein 2008). The cost-benefit assessment accounts for the costs of replacement and the benefits of these actions, including improved seismic safety and reduced earthquake damage and repairs. While the assessments show that replacing these vulnerable structures can significantly reduce the life safety and repair cost risks, the cost-benefit rates (assuming a value of life saved of $2 million) are generally greater than one, suggesting that the costs outweigh the benefits. The breakeven point in the cost-benefit analyses (for building replacement) occurs at a cost per life saved of approximately $5 million. Alternatively, if building retrofit could achieve comparable life safety to a new building, it would be cost effective (assuming a value per life saved of $2 million) for retrofit costs less than $98 per square foot of building (on average).

Roble Hall is a historic, three-story dormitory, originally built in 1918, that houses 310 students on the Stanford University campus. Discovered in 1987 to be a non-ductile concrete frame with hollow clay tile infill, it was deemed to be a high seismic risk, students were moved out during the middle of the school year, and a fast-track seismic rehabilitation project was completed in 1989. The goal for that work was to significantly reduce the risk to life safety (primarily from collapse) at a reasonable cost. In 2005, a reevaluation of the building was completed using Stanford's latest performance-based standards, and additional rehabilitation work was implemented as part of an overall capital improvement program. Roble Hall provides an excellent case study in the evolution of seismic analysis procedures, performance-based thinking, and rehabilitation techniques. The following paper describes the criteria, analyses, performance objectives, and key decisions in each rehabilitation project, and it explores the challenges and opportunities that complicated, historic structures can present in providing practical, cost effective seismic rehabilitation solutions.

A new technique for the strengthening of existing R.C. structures, based on the application of a high performance fiber reinforced jacket, is investigated herein. Aim of the research is to study the possibility of using this technique for the seismic retrofitting of existing columns. A full scale test has been performed on a column-foundation element. The specimen has been loaded with static cyclic action having increasing amplitude, up to failure. The results shows that with the adoption of this technique it is possible to significantly increase both bearing capacity and ductility of the existing R.C. structure.

In 2004, the Province of British Columbia, on the West Coast of Canada, announced a 10–15 year, $1.5 billion seismic retrofit program for the province's 750 at-risk public schools. The purpose of this earthquake preparedness initiative is to accelerate the upgrading of school public safety in the moderate and high seismicity regions of the province. Given the magnitude of the mitigation program, the province's Ministry of Education made a commitment to support the development of state-of-the-art performance-based seismic engineering technology for achieving optimum safety within a cost-effective mitigation framework, which could not be achieved based on current practice. This paper describes a non-linear performance-based methodology that has been developed to provide the framework for the drafting of these technical guidelines. This methodology is the culmination of more than five years of applied research and extensive and intensive peer review.

ASCE/SEI 41, the standard for seismic rehabilitation of existing buildings, proposes seismic evaluation procedures for concrete buildings. In-situ test results of existing school buildings in Taiwan can be used to verify the evaluation methodology in ASCE/SEI-41 Supplement 1. This paper reports on one in-situ specimens, 2-story 2-classroom building frames, subjected to reversed-cyclic and pseudo-dynamic loading. The experimental program, test setup and test results will be presented in this paper. The methodology for seismic assessment in ASCE/SEI-41 Supplement 1 will be applied to evaluate the seismic capacity of the existing school building, and the results of the evaluation and in-situ tests will be compared. A methodology proposed for the seismic assessment of concrete school buildings in Taiwan will also be discussed.

Delhi, India faces substantial earthquake hazards from both distant, large-magnitude earthquakes in the Himalayas and smaller, local events. Delhi has many seismically vulnerable school buildings, in both government and private schools. GeoHazards International (GHI) has been working for several years with the Government of the National Capital Territory of Delhi and private sector partners, in order to reduce the earthquake risk to Delhi's schools. In the course of these efforts, GHI encountered a type of "semi-permanent," unreinforced brick school building with a particularly vulnerable type of roof constructed from steel I-beams and heavy, flat stone slabs. The stone slabs and beams are not attached to each other or to the supporting brick walls so that the building could, theoretically, be dismantled and moved to a new location. However, this lack of connection means that during strong shaking, stones could fall on students and teachers. This paper describes the unique design problem that these unusual semi-permanent buildings pose and the retrofit and conceptual new construction solutions that could reduce the earthquake risks that the buildings pose to students and teachers.

A task committee comprised of local structural engineers and earthquake engineering experts from abroad was formed to assess the seismic performance of public schools in under auspices of this group; a guideline has been developed better assess the existing conditions and develop retrofit options for school and hospital buildings in Istanbul. The project is financed by a World Bank (WB) loan and is implemented through the Istanbul Special Provincial Administration (ISPA). The ISMEP project started on 1 February 1, 2006, and is expected to be completed by the end of 2010. The Istanbul Project Coordination Unit (IPCU), established under ISPA, is responsible for implementing the ISMEP. The Guideline is based on provisions of the ASCE 41 and Turkish earthquake code and is purposed to address the seismic design requirements for hospital and school facilities in Istanbul and recommends effective retrofit measures. Many such buildings were constructed prior to adoption of seismic codes and use non-ductile concrete moment frames and unreinforced masonry walls to resist earthquake loading. Recent earthquakes in Indonesia (2007) and China (2008) have shown that this type of construction is particularly sensitive to earthquake damage and even complete collapse due to the inadequate design and construction practices. Such vulnerability caused loss of life of thousands of students in China. The provisions of the guidelines are written to be easy to follow and implement. The engineer is charged with condition assessment, followed by analysis and determination of deficiencies. Both conventional and state-of-the-art retrofit measures are discussed in detail. The document also provides suggested retrofit measures for different building groups. It is hoped that the implementation of this guideline will drastically reduce the level of damage and loss of life in the public buildings during the next earthquake.

Non-ductile reinforced concrete frame buildings constitute an important part of the vulnerable buildings in seismic regions of the world. Collapse of non-ductile multi. story concrete buildings during strong earthquakes in the past resulted in severe casualties and economic losses. Their rehabilitation through retrofitting is a critical issue in reducing seismic risks worldwide. A displacement based approach is presented in this study for the seismic retrofitting of medium height non-ductile concrete frames. The deformation capacity of the existing critical columns control design. A minimum amount of shear walls are added for maintaining the deformation levels below the critical level dictated by the existing columns, which are usually at the ground story. Detailing of shear walls are based on conforming to the reduced deformation demands of the retrofitted frame/wall system. Member-end rotations are employed as the parameters for performance evaluation. Initial results obtained from the proposed displacement based approach have revealed that jacketing of columns and confining the end regions of added shear walls are usually unnecessary compared to the conventional force-based approach, where excessive force and deformation capacities are provided regardless of the actual deformation demands.

The government of Turkey is involved in a major undertaking to improve the seismic performance of Istanbul's public buildings under the Istanbul Seismic Mitigation and Emergency Planning (ISMEP) project. The Istanbul Project Coordination Unit (IPCU) and its consultants have faced many challenges implementing this program. This paper presents the experience of two consultants who have been involved in two major retrofit design projects, one involving the assessment and upgrade of 13 major hospitals, and the second involving 124 school campuses and social service centers located throughout Istanbul. The paper discusses a number of the challenges experienced during the management of these two projects including implementing a new Turkish building code, which had been completely revised and updated to incorporate aspects of performance based engineering design. Code application examples are given along with comparison of approaches between those in the Turkish and those in U.S. The methods used to determine the makeup of the existing construction (most buildings had no existing documentation), including site surveys; material testing: and material investigations are presented. Analysis methods used (both rapid and detail) are presented along with representative retrofit schemes.

Seismic performance evaluation and retrofitting / strengthening of 142 public school buildings in Istanbul have been implemented within the World Bank funded Istanbul Seismic Risk Mitigation and Emergency Preparedness (ISMEP) Project. The most common retrofitting techniques applied to the school buildings following their seismic performance assessments in accordance with the national (Turkish Earthquake Resistant Design and Retrofitting Code-2007, [3]) and the international standards (FEMA273, FEMA356, ASCE41-06) are the reinforced concrete jacketing of the existing columns and shear walls and, the construction of new shear walls. In this study, a parametric evaluation of the retrofitting techniques applied to the school buildings is carried out. The amounts of RC jacketing (i.e. concrete and steel quantities) and the number of the newly added shear walls are statistically evaluated and the changes in the stiffness, fundamental period and the mass of the buildings as well as the resulting base shears are compared with the existing cases.

The accuracy of estimating the performance levels of a deficient RC frame using linear elastic and nonlinear dynamic analysis is evaluated in this study. This was achieved by comparing the response of a structure tested with pseudo-dynamic testing and estimated by the linear elastic assessment procedures along with nonlinear dynamic analysis. The test structure (three bay-two storey planar frame) is a 1/2 scale reinforced concrete frame having masonry infill walls in the central span. The test frame contains a number of structural deficiencies such as low concrete compressive strength (7MPa), lack of transverse reinforcement detailing at potential plastic hinge regions and beam-column joints. Tests were conducted for the NS component of 7.14 magnitudes 1999 Duzce Earthquake for three different scale levels. Test results indicated that drift deformation demands estimated using nonlinear dynamic analysis were within 15% of those observed in the tests. On the other hand, damage estimations of TEC and FEMA 356 were found to be conservative resulting in retrofit decisions. It was also observed that although nonlinear dynamic analysis provided reasonable estimations for inter-storey displacements, local demand parameters such as column curvature demands were estimated with less accuracy.

The most commonly used code provisions for retrofit of soft story woodframe residential buildings are found in Appendix Chapter A4 of the International Existing Building Code. For practical reasons these provisions continue the practice of modifying the code for new construction to make it suitable for evaluation and retrofit. As policy and technical questions have arisen about this approach, and as more jurisdictions begin in earnest to address this vulnerable building class, the Structural Engineers Association of Northern California has convened a committee to study the issues and to advise local engineers and code officials. This paper reports on the committee's initial study regarding the sufficiency of ground story retrofit and the implications of code-based approaches. Using nonlinear response history analysis of a two-dimensional model, the study finds that code-based approaches can fail to properly balance the stiffness and strength of different stories, leading sometimes to under-design in the ground story or to damaging effects in stories above. A proposal to size the retrofit system instead based on mitigation of irregularity and on relative stiffness and strength appears to offer a more productive approach.

Several cities throughout California's high seismic regions have expressed concern over the large number of existing soft-story buildings and the risk they pose. Many city building departments are actively developing guidelines for retrofit of these structures because of their documented risk of collapse during a major seismic event. Officials have the difficult task of enacting mandatory retrofit requirements that will mitigate the risks, while still being flexible enough so building owners can economically implement the requirements. A common solution to address the potential risk of collapse at the first floor (soft-story level) of an existing building is to add a lateral-force resisting element in the direction(s) where the deficiency exists. The system can vary based on the level of desired performance the owner and designer have agreed upon or the code standard that is being used which will determine strength, stiffness and ductility requirements of the system. While this added lateral-resisting element could be a shearwall or a braced frame, steel moment resisting frames are a preferred retrofit strategy in light-framed, soft-story structures since they do not impact the open space at the first level. Two common types of open spaces that create a line of deficiency in the building, thus defining the first story as "soft" are tuck-under parking and retail space. These types of soft-story structures often have residential occupancies in the stories above. The moment frame solution allows the building owner to maintain the open space for which the use is intended while providing the necessary lateral-force resistance to mitigate the soft-story problem.

Chapter A4 of the International Existing Building Code has played an important role in providing national model building code provisions to communities interested in improving seismic resistance of vulnerable soft-story wood-frame buildings. There are, however, many aspects of Chapter A4 that could be substantially improved to better serve the engineers and communities that rely on the document. Two important issues that need to be better addressed by these provisions include: 1) identification of vulnerable buildings, and 2) direction to design professionals regarding seismic strengthening design requirements. These subjects have also been addressed, directly or indirectly, by shake table testing, analytical studies, and building case studies from the CUREE-Caltech Woodframe Project, the NEESWood project, and others, which have provided further understanding of the contributions of various building materials to overall seismic resistance, the distribution of force and deformation demands in wood-frame buildings, and the implications of seismic strengthening. Drawing from research and analysis efforts, more direct methods to identify and strengthen vulnerable buildings are suggested.

Wood-framed residential structures with soft, weak, or open-front walls are common in areas of high seismicity like the west coast of the United States. Parking below the residential portions of the building, or "tuck-under" parking, is particularly problematic in many buildings built in the 1960s through the 1980s, when stucco and gypsum board were widely used to resist lateral loads in two-, three-, and even four-story structures. The 1994 Northridge earthquake demonstrated the problematic nature of these types of structures, as a number of these structures experienced significant damage and even collapse. Standards for designing strengthening measures for wood-framed structures with soft/weak stories were adopted into Appendix Chapter 4 of the International Existing Building Code (IEBC). This paper addresses problems with these provisions in the IEBC, including what the authors believe are excessive engineering analysis requirements as well as excessive design force levels, neither of which is conducive to economical designs or inducement to owners. Several case studies are presented to demonstrate problems with the current provisions in the IEBC and to demonstrate how, if engineering judgment is used, reasonable solutions can be implemented in actual buildings in what the authors believe to be an effective and economical manner (i.e. significant reduction of risk for a reasonable cost and a reasonable amount of engineering effort). Issues regarding owner reticence to invest in structural strengthening are also discussed, and possible modifications to the IEBC are suggested.

The Vincent Thomas Bridge, a long span suspension bridge connecting the city of San Pedro and Terminal Island of Los Angeles Port, carries an overwhelming number of port traffic. Concerns regarding the seismic safety of the bridge have gained significant attention after the finding that the main span of the bridge lies directly over the Palos Verdes Fault, which has the capacity to produce an earthquake of magnitude 7.25 (M_w) with a return period of 1000 years. The bridge was thus retrofitted in spring 2000. In this study, a three dimensional finite element (FE) model of the Vincent Thomas Bridge are developed using a widely used software. In order to show the appropriateness of the model, eigenproperties of the bridge model are evaluated and compared with the results of system identification from ambient vibration and the 2008 Chino Hills earthquake response data. A new simulation technique is developed to generate spectrum-compatible spatial variable ground motions. The response of Vincent Thomas Bridge under spatially varying ground motion is evaluated by nonlinear time history analysis. Using spatially variable motions, it is found out that the response in some locations on the bridge deck, may be under predicted even if the motion with maximum intensity is uniformly applied at all supports. Therefore, to be more realistic in assessing the seismic performance of long span suspension bridge, the spatial variability of the ground motions should be considered in the analysis.

For a port facility to maintain serviceability after an earthquake, individual port structures must maintain serviceability. Past earthquakes have demonstrated that important port structures such as quay wall and container cranes are highly vulnerable to damage during strong earthquakes. This paper focuses on seismic performance evaluation of a typical container crane located on a quay wall. At first, a representative numerical model of a typical gravity-type quay wall is developed and considering a large number of scenario earthquakes with various hazard levels, nonlinear time history analysis is performed assuming the ground motions to be known at the bedrock level. After that using a numerical model of a typical container crane, time history analysis is performed using the motion obtained at the base level of the crane (i.e., top of the quay wall). To assess seismic performance of the crane in the framework of performance-based design, the damage criteria for the crane are established based on the post-earthquake serviceability. Finally, seismic performance of the crane is evaluated in terms of fragility curves.

This paper describes existing bridges in service with Orthotropic steel decks that have performed well in earthquakes. A table of Orthotropic Bridges in California and Korea is provided. The seismic performance of bridges with lightweight orthotropic decks is definitely a consideration when considering new structure types or solutions for deck retrofit in areas where seismic loads are a concern.

The ATC-58 project seeks to develop the next generation of guidelines for performance-based seismic design and evaluation. This includes the development of seismic fragility functions for commonly employed building systems. These fragility functions define the likelihood that the system will exhibit a specific level of damage and thus require a specific type of repair when subjected to earthquake demand as defined by maximum story drift. The research presented here uses data from laboratory tests to develop fragility functions for one type of building system: reinforced concrete frames.

This paper describes the performance based seismic rehabilitation of a historic 1920's vintage 6-story non-ductile concrete shear wall building which is being remodeled to be reused as an abused/homeless women's shelter. The building is located in the blighted "skid-row" district of downtown Los Angeles and is part of the City's adaptive reuse and redevelopment program. The retrofit objective was to obtain a Life Safety performance level under BSE-1. The work followed the relevant requirements of ASCE41-06, LABC 2008 and the LADBS Adaptive Reuse Ordinance (ARO). The analysis consisted of a Linear Dynamic Procedure (LDP) used as a baseline followed by a Nonlinear Static Procedure (NSP) to capture nonlinear behavior. The retrofit scheme was implemented by adding a couple of new cast-in-place concrete shear walls and shotcreted shear walls at certain existing wall locations. Other measures included foundation augmentation, gravity column fiber-wrapping along with some roof mass reduction.

Advanced Seismic Assessment Guidelines, developed by researchers at Stanford University and tested by practicing structural engineers, offer improvement over previous methods for seismic evaluation of buildings where post-earthquake safety is a concern. This new method allows engineers to evaluate, before an earthquake, how safe it will be to occupy a building after the earthquake. The method measures building performance in terms of the post-earthquake occupancy classifications "Green Tag," "Yellow Tag," and "Red Tag," defining these performance levels quantitatively, based on the structure's remaining capacity to withstand aftershocks. The authors have used this methodology to perform seismic assessments for several buildings in the Pacific Gas & Electric Company (PG&E) utility network, including electrical substations and other facilities in Oakland, Berkeley, San Francisco, and Vacaville. Analytical and probabilistic features of the method are also applicable to more typical seismic evaluation and retrofit projects, where evaluation of post-earthquake occupancy tagging is not needed.

Since 1984, the Federal Emergency Management Agency (FEMA) has sponsored efforts to address problems of seismically hazardous existing buildings. Much of this work has been accomplished through FEMA's Existing Buildings Program (EBP). With the release of the seismic evaluation and rehabilitation standards ASCE 31 (Seismic Evaluation of Existing Buildings, ASCE/SEI 31-03, ASCE, 2003) and ASCE 41 (Seismic Rehabilitation of Existing Buildings, ASCE 41-06, ASCE 2006), the EBP reached a logical reflection and re-engagement point. The EBP has been guided from its inception, by action and strategic plans that have drawn on the opinions of experts in the existing buildings' community to define goals, objectives and strategies addressing fundamental obstacles to more widespread evaluation and rehabilitation of seismically hazardous buildings. In 2004, the Applied Technology Council (ATC) was awarded a contract by FEMA that included the task "Update Seismic Rehabilitation Guidance, Program Definition and Guidance Development." This task was designated the ATC 71 project and resulted in the development of an action plan to guide EBP efforts over the next decade. The recommendations contained in this document "Existing Buildings Program, Action Plan 2009–2019 (publication pending) were developed to address the highest priority needs identified from review of past EBP guidance documents, interviews with members of the existing buildings' community, and the NEHRP Workshop on Meeting the Challenges of Existing Buildings held in September of 2007.

The FEMA P695 Methodology, developed through the recent ATC-63 Project, incorporates ground motion guidelines that include a so-called Spectral Shape Factor (SSF). This SSF adjusts the predicted collapse capacity of the building to account for the spectral shape of ground motions. This paper explains how aspects of this new FEMA P695 Methodology could be adapted for use in refining the target displacement equation (i.e. inelastic displacement demand) in the ASCE/SEI 41 Nonlinear Static Method to account for spectral shape. The final result would be an additional coefficient (termed the "spectral shape coefficient") that would reduce the target displacement for sites where the ground motion is expected to have a less damaging spectral shape. This paper outlines how one would compute this spectral shape coefficient for any site and building of interest, and then explains the additional work needed to implement this new coefficient into ASCE/SEI 41. An example is provided to illustrate the effect that the new coefficient has on the computed target displacement. For a 2% in 50 year motion at a San Francisco California site, application of the spectral shape coefficient results in a 40% reduction in the target displacement.

This paper presents the results of an ongoing investigation aimed at evaluating the Coefficient Method (CM) for the seismic assessment of existing buildings built on soft soil conditions. In the first part of this investigation, error statistics of target roof displacement demand predicted by the CM with respect to peak inelastic roof displacement demand of two frame models representative of exterior steel moment-resisting frames when subjected to 18 earthquake ground motion recorded on soft soil sites found in the San Francisco Bay Area were obtained. In the second part of this study, a statistical study of the ratio of peak inelastic displacement demand to peak elastic displacement demand (i.e. coefficient C₁) of elastoplastic single-degree-of-freedom systems when subjected to 118 soft-soil records is reported. Error statistics of coefficient C₁ were also obtained from the statistical results. A functional form that takes into account the frequency content of the ground motion is proposed to estimate coefficient C₁ when evaluating existing buildings built on soft soil sites.

Earthquake resilience, the ability to respond to and recover from a damaging event, is gaining currency as a performance metric even for non-"essential" facilities. Resilience can be measured as the time needed to restore basic operations. Yet our standards for seismic evaluation do not explicitly address recovery time. This paper proposes new evaluation criteria to address questions of resilience. The proposed criteria will help distinguish and prioritize likely seismic deficiencies, grouping them by their impact on recovery time. The criteria use the standard known as ASCE 31 as a platform, building on its procedures and terminology and extending its use to resilience planning.

In order to observe the interaction of structural elements at the onset of collapse, four frame specimens were tested at the National Center for Research on Earthquake Engineering (NCREE) in Taiwan in spring 2009. Each specimen consisted of a 1/2.25 scaled model of a two-bay and two-story reinforced concrete frame. The specimens were tested under moderate and high gravity loads to investigate the influence of axial loads on the collapse vulnerability of the structures. These tests will also be employed to study the interaction of the beams, columns and joints as collapse is initiated. The current paper presents the observations during the tests and comparison of the behavior of the frame specimens.

A novel model capable of simulating shear strength degradation of pre 1970's reinforced concrete columns detailed for gravity load resistance and subjected to large seismic loads is presented. The model can account for both in-cyclic as well as cyclic shear damage up to complete loss of lateral strength and stiffness. The model has been implemented in the open source analysis software OpenSees and tested with a large column database. The proposed model utilizes localized column end-rotations, axial loads, and pertinent column properties to assess column shear capacity and trigger shear failure. Once shear failure is triggered, the analytical model modifies the column response by introducing softening and cyclic degradation in the constitutive properties of a zero-length shear spring element. The zero-length shear spring can be attached in series to any column element. Past investigitions have demonstrated that axial collapse in gravity detailed reinforced concrete columns will only occur after damage has become extensive and the shear strength is almost exhausted. Thus accurate column collapse assessment necessitates adequate modeling of shear strength degradation up to the critical limit that initiates axial collapse. The proposed shear failure model is capable of accomplishing this task and has been developed with the objective of improving the accuracy of collapse risk assessment efforts targeting pre 1970's reinforced concrete columns detailed for gravity load resistance.

The full-scale shaking test of three-story reinforced concrete school buildings was carried out at E-Defense, the world largest three-dimensional shake table, from Sep to Nov 2006. Two specimens were tested: one was a bare frame building with old design and construction practices, and the other was strengthened with attached steel braces. A dynamic progressive collapse of the bare frame specimen occurred associated with shear and axial failure of short columns under the JMA Kobe motion. A method for the detailed analytical simulation of the shake table test was developed with columns members, in which shear deteriorating behavior after flexural yielding was incorporated. The Axial-Shear-Flexural Interaction Model is adapted in order to evaluate ultimate deformation capacity of the columns. Three-dimensional nonlinear static frame analysis was carried out with the column model considering shear deterioration. Axial and lateral hysteretic responses of the inner column in test are compared with the analytical responses to verify the model.

Reinforced concrete columns with insufficient transverse reinforcement and non-seismic details are vulnerable to shear failure and loss of axial load carrying capacity in the event of an earthquake. In this study, the application of two macro models is examined using previously tested shear critical reinforced concrete columns subjected to lateral loads. One of the approaches simulates lateral load-deformation response by estimating deformation components due to flexure, reinforcement slip and shear individually and then combing them according to a set of rules specified for each category. The columns classified into categories based on comparison of their predicted shear and flexural strengths. The other approach, Axial-Shear-Flexural Interaction method, considers the interaction of axial deformations and concrete compression softening to couple shear and flexural mechanisms while satisfying compatibility and equilibrium conditions in average stress-average strain field. Capabilities of both models are evaluated in terms of predicting mode of failure, ultimate lateral loads and drifts, and post-peak responses. Based on the comparison of experimental and analytical results, conclusions are drawn to improve response estimation by either of the models. Implementation of suggested analytical procedure results in satisfactory response envelope curves which can be used for development of cyclic response models.

Axial failure of columns can lead to collapse of a building. Reinforced concrete columns in buildings constructed before modern seismic design codes were enforced may contain inadequate transverse reinforcement. Columns with these ties may experience simultaneous shear/axial failures when subjected to displacement reversals similar to those caused by earthquake ground motions. In order to prevent the collapse of buildings during an earthquake, engineers must be able to identify columns that may experience simultaneous shear/axial failures. The standard for evaluation of existing buildings, ASCE/SEI 41-06, outlines guidelines to estimate drift levels associated with axial failure for reinforced concrete columns. However, when the procedure outlined by this standard was used to evaluate the reinforced concrete column specimens of several research studies it was found that the standard failed to identify columns prone to simultaneous shear/axial failures. Due to the limited number of known specimens in the literature that have suffered simultaneous failures there is a need for additional testing of specimens that will exhibit this type of behavior. This need is being addressed by the ongoing NEESR Grand Challenge Project "Non-ductile Reinforced Concrete Buildings."

This paper describes the motivation for the development of a new Guide for Seismic Rehabilitation of Existing Concrete Buildings based on the concrete provisions of ASCE/SEI 41. By enabling rapid inclusion of results from ongoing research on the seismic performance of existing concrete buildings, this Guide will be a valuable resource for engineers and is expected to serve as a source document for future updates to ASCE/SEI 41. The approach described below may also serve as a model for updating the other material sections of ASCE/SEI 41.

This paper summarises improvements to the ASCE/SEI 41 concrete provisions considered for implementation in the new ACI 369 Guide for Seismic Rehabilitation of Existing Concrete Buildings. The paper is intended to inform the structural engineering community on the approach being taken by ACI 369 to provide engineers with the latest modeling approaches and acceptance criteria for the assessment and rehabilitation of existing concrete buildings. Through the removal of unnecessary conservatism, it is expected that these modifications will make the seismic rehabilitation of concrete buildings more cost effective.

In reinforced concrete frames, earthquake loading results in damage to beam-column joints that reduces frame stiffness and strength. This can significantly impact frame performance. Joints in existing frames may be subjected to large shear stresses, have large bond stress demands, and have little or no transverse reinforcement. To assess the seismic performance of existing concrete frames, engineers require models that can accurately predict the behavior of joints with a wide range of design parameters and that are easily implemented in commercial software. In this study, a database of 45 planar interior beam-column joints was used to evaluate two types of joint models. First, rigid offset models, which are acceptable for linear analyses, were considered. The rigid offset models recommended in the ASCE/SEI Standard 41-06 were evaluated, and a modified approach to provide improved prediction of the yield displacement was evaluated. Second, a nonlinear model was developed to enable simulation of progressing stiffness and strength loss using commercial design/analysis software; this model was verified for a range of joint designs. In the proposed nonlinear model, the beam-element plastic hinge is assumed to represent two nonlinear hinges in series. The first hinge represents the flexural response of the beam, and the second represents the nonlinear response of the joint. The beam flexural hinge is defined by the traditional moment-curvature response of the beam section and a newly developed rotation limit at which strength loss is predicted. The joint hinge is bilinear, with stiffnesses calibrated to accurately predict measured response, and includes a rotation limit at which strength loss initiates in the joint. Using this approach, nonlinear joint response is, ultimately, simulated by modifying the beam-element plastic hinges. The proposed model accurately predicts the load-displacement response of frame sub-assemblages including accurately predicting the mechanism that determines response: flexural yielding of the beam or failure of the joint.

Rehabilitation techniques for seismically deficient reinforced concrete elements were developed more than 20 years ago. At that time, lateral-load response of rehabilitated elements was deemed satisfactory if significant strength degradation did not occur at a target displacement demand (typically large). Large economic losses in recent earthquakes have highlighted the importance of evaluating element response at other performance levels, such as those associated with smaller displacements. In order to accurately estimate the global response of rehabilitated reinforced concrete buildings, a thorough understanding on the response of individual rehabilitated components must be developed. ASCE/SEI Standard 41-06 — Seismic Rehabilitation of Existing Buildings, provides engineers with a much needed resource to incorporate performance-based concepts in seismic rehabilitation projects. Within ASCE/SEI 41-06, guidelines to develop backbone curves for modeling typical reinforced concrete elements, and acceptance criteria of these elements based on their calculated deformation are provided. The document, however, does not explicitly include information that can be used for elements that have been rehabilitated by methods such as jacketing. A need to examine the performance of these elements using a multi-level performance perspective is therefore warranted. In this paper, a comparison of the laboratory performance of jacketed reinforced concrete columns with modeling parameters in ASCE/SEI 41-06 is presented. This information is part of ongoing activities taking place within ACI Committee 369 — Seismic Repair and Rehabilitation, that focus on an evaluation of existing guidelines for the seismic rehabilitation of concrete buildings. Existing laboratory tests found in the literature are used to compare the plastic deformation capacity of jacketed reinforced concrete columns with the corresponding modeling parameters in ASCE 41-06. The three primary types of jacketing materials that have been used to date (concrete, steel, and fiber-reinforced polymers) are included in the study. Particular attention is paid on whether plastic drifts in jacketed columns compare favorably with modeling parameters in ASCE/SEI 41-06.

The term PML, or Probable Maximum Loss, has been employed for many years in the insurance, lending and engineering industries as a means to define the monetary risk — expressed as a percentage of replacement value — associated with a particular property experiencing an earthquake. PML studies have mostly been used to facilitate real estate transactions. Over time, a number of definitions of the PML have appeared. Most often, PML estimates are generated by engineering firms utilizing shorthand "black box" methods implemented by commercially available computer software. Generic characteristics of the property such as structural type, number of stories, age and more are input and a PML is output. Notwithstanding the authors' suspicions about the validity of such shorthand methods — particularly in light of the technical definition of the PML, more rigorous engineering and cost estimating methods can also be used to explicitly estimate building response and damage distribution, develop repair scopes and methodologies, and derive costs. However, such explicit methods — while capable of generating substantially more rational and defensible estimates than shorthand black box software — also fall short because they are incapable of yielding answers consistent with the technical definition of PML. The discussion herein explores the vagueness of the definition of PML and the obvious inconsistencies between the explicit statistical significance embedded in the definition of PML and what the engineering methods traditionally used to conduct seismic response assessment can deliver, with foci on the ground motion side, on the capacity side of engineered materials and systems, and on the fragility of nonstructural systems. Many of these inconsistencies are applicable to both "shorthand" and explicit PML estimation methods. Included, for example, are discussions of selection and scaling of ground motion records — a first step in any explicit assessment — as this pertains to definition of a design event upon which the PML estimate is based.

How will my building respond in an earthquake? Will it be safe? Will I be inconvenienced? How long until it is back to normal? How much better would my building be with a seismic upgrade? This paper previews a system under development by the SEAONC Existing Buildings Committee (Building Ratings Subcommittee). Savvy owners and tenants in earthquake country want to know their seismic risk. Although a typical engineering report can provide technical information for a single building, there is an unmet need for qualitative information to compare seismic performance among multiple buildings, and for terminology to support real-world decision making. Like other rating systems customarily used in transactions, such as the Building Owners and Managers Association (BOMA) method of rating office space, SEAONC's Earthquake Performance Rating is proposed to be strictly voluntary, and presented so that its meaning is easily grasped by non-technical personnel, providing a common vocabulary of seismic risk. The intent is to have a rating system that utilizes many of the existing evaluation methodologies but translates their results into a format that will be easily understood by building owners and the general public. Phase 1 of the project was completed in January 2008. This paper will summarize the Phase 1 results and will include work completed to date on the translation matrices for the various methodologies that are a key part of Phase 2. Feedback from potential users, including conference participants, is essential for delivering a system that is credible, workable, and informative since a key first step is to develop a system that structural engineers can agree upon. If we are successful in this effort within the structural engineering community our next step is to engage the broader building community for their input.

Probable Maximum Loss (PML), Scenario Expected Loss (SEL), and Scenario Upper Loss (SUL) earthquake damage estimates are being indiscriminately developed, used, and abused by the engineering profession and by the parties who commission and utilize PMLs. Owners may pressure engineers to obtain specific PML, SEL, and SUL values that they desire to meet insurance or lending requirements, and engineers often capitulate. Engineers use "black box" software and obtain either the desired values or values that are not representative of the actual structure. Black box software, which can "produce" PMLs at a small fraction of the cost required to actually understand the seismic behavior of the structure, has lowered the bar. Engineers who do not provide the desired values at a very low price tend to get cut out of the process. Meanwhile, the insurance companies and lending institutions, as third parties, blindly rely on the PML, SEL, and SUL values obtained by building owners to set insurance rates for the buildings in question or as the basis for deciding whether to issue financing — setting up a clear conflict of interest on the part of the owners and the engineers. In some cases, building owners even appear to be using the PML, SEL, and SUL values to determine the policy limits for the property casualty insurance that they purchase, never realizing that the values are not appropriate for such a decision for an individual building. The authors examine the multitude of problems inherent in the PML, SEL, and SUL procedures being used by most of the profession, provide case studies, propose a more logical way of determining PML values, and present limitations and caveats for owners and other interested parties.

This paper summarizes the results of a comprehensive study of floor acceleration demands on nonstructural components. The study is based on analytical studies on buildings responding elastically and nonlinearly to earthquake ground motions. Buildings analyzed range from 3 to 18 stories. Parameters evaluated include: fundamental period of vibration, lateral resisting system, damping ratio, level of ground motion intensity relative to the intensity that triggers nonlinear behavior. The study included the following aspects: (1) parametric study of peak floor acceleration demands in buildings responding elastically; (2) parametric study of floor response spectral ordinates in buildings responding elastically; (3) development of response spectrum analysis for estimating peak floor acceleration demands; (4) dynamic interaction between primary and secondary systems; and (5) peak floor acceleration demands in buildings responding nonlinearly. Results indicate that the amplitude of acceleration demands in buildings and their variation along the height are strongly dependent on the period of vibration, lateral resisting system and damping ratio of the building and therefore, current US recommendations that compute acceleration demands that are independent of the period, damping and lateral resisting are inadequate. It is also shown that alternative code procedures based on linear response spectrum modal analysis are equally inadequate. The most important trends are summarized.

A response spectrum method to estimate peak floor acceleration demands of multistory buildings subjected to earthquakes and responding elastically is presented. Available response spectrum methods and modal combination rules such as SRSS or CQC have been used for estimation of relative displacement and inter-story drift demands but cannot be directly used for estimation of peak absolute (total) floor acceleration. The proposed response spectrum method not only considers the correlation between modal accelerations, but also takes into account the correlation between ground acceleration and modal accelerations. The formulation for estimation of peak floor acceleration is presented. Closed form solutions for correlations between the modal accelerations as well as modal accelerations and ground accelerations have been derived for filtered white noise inputs. Empirical equations for correlations are presented. To verify the results, a continuum model of building consisting of a shear beam connected laterally to a flexural beam previously studied by the authors has been used and combined with the presented closed form and empirical formulations for the purpose of parametric analysis. It is shown that results of the proposed response spectrum method match with the time history analysis with great accuracy.

This paper addresses the quantification of peak component acceleration demands for acceleration-sensitive nonstructural components attached to or suspended from inelastic structural wall and moment-resisting frame structures. Under certain conditions, for a given ground motion hazard level, inelasticity of the primary structures increases the peak component acceleration demands when compared to the accelerations experienced by the component if the primary structure behaves in the linear elastic range. These conditions include nonstructural components located near the bottom of the structure with periods of vibration that are between the higher modal periods of the supporting structure. This amplification of peak component acceleration demands increases with a decrease in the damping ratio of the component and is more pronounced for structural systems that exhibit a concentration of inelastic behavior near the bottom of the structure. A short discussion on the relevance of these results in the context of current seismic strength demand estimation for nonstructural components is included.

The International Building Code [ICC, 2006], and the attendant structural design standard ASCE/SEI 7-05 Minimum Design Loads for Building's and Other Structures [ASCE, 2006] provides the structural criteria for buildings, as well as the seismic design requirements for nonstructural components, equipment, and systems. Over the years this criteria has been expanded from essentially nominal design requirements (2 pages) to an entire chapter of content dedicated to nonstructural components in ASCE 7-05, not including additional referenced industry standards for certain components. With this additional design complexity, are we really sure that we will achieve the expected earthquake performance intended for nonstructural components, equipment, and systems, or are there other issues affecting desired performance that require greater attention? This paper will present issues that compromise achieving the expected nonstructural component earthquake performance that the codes and standards intend by examining several case examples of projects in the Midwest. Specifically, four (4) construction projects will be examined where enhanced seismic performance and standard code compliance performance levels were used for design of the building structure and nonstructural components. The paper will present the issues affecting the seismic performance of nonstructural components from initial design, development of contractor implemented seismic design performance criteria, contract language, contractor seismic design implementation, contractor construction, and monitoring construction quality. As the paper will conclude, achieving enhanced earthquake performance for nonstructural components, equipment, and systems is difficult, but not impossible. Suggested solutions are offered for improved earthquake performance of nonstructural components on future projects.

To investigate the effect of elastomeric snubber properties on the seismic response of vibration-isolated nonstructural components, a numerical study is conducted on six different vibration-isolated nonstructural components mounted on the roof of six different buildings located in areas with different levels of seismicity. The dynamic model used for the numerical study considers the effects of thickness and hardening of elastomeric snubbers. Transient dynamic analysis is conducted with an explicit state-space approach to determine the response of the Single Degree-of-Freedom (SDOF) system representing the vibration-isolated nonstructural component under the action of historic roof motions scaled to match with a target response spectrum defined per the seismic design requirements of the IBC 2006 for nonstructural components.

For commercial construction such as office buildings, hotels, and hospitals, the nonstructural components and contents typically represent 80–90% of the capital investment at risk during an earthquake. Not surprisingly, post-earthquake reconnaissance following recent earthquakes in the U.S. shows that the majority of losses are the result of damage to nonstructural components and contents. Many nonstructural components also represent a life safety risk to building occupants. Recent studies by EERI and FEMA have found that, with some notable exceptions, there is still relatively poor compliance with code provisions that address nonstructural components and most contents are not covered by code provisions; thus, most nonstructural components and contents remain vulnerable to earthquake damage. In order to improve compliance, these studies recommend better education regarding nonstructural hazards and effective design solutions, more detailed design aids to assist those responsible for designing nonstructural restraints, and clarification of the parties responsible for the design and construction of nonstructural seismic restraints. FEMA E-74, Reducing the Risks of Nonstructural Earthquake Damage — A Practical Guide, has been recently revised and published as an electronic document and is intended to help improve compliance with nonstructural restraint requirements. FEMA E-74 explains the sources of nonstructural damage and provides practical methods for reducing the potential risks by providing extensive visual information in the form of photographs of earthquake damage to nonstructural components and contents, photos of properly installed nonstructural restraints, and drawings and details of appropriate nonstructural restraints. The updated edition includes illustrated mitigation examples for 50 nonstructural items as well as an example seismic code block now in use in some jurisdictions to define design responsibility for nonstructural restraints.

Large global energy companies rely on the safe operation of data centers that are scattered around the world. These data centers sometimes consist of a few server racks supported on raised access floors installed in various types of buildings and located on various floors of the building. The data centers can also contain several thousands of square feet of raised computer floors housed in one or two stories of large commercial buildings, which are normally existing structures designed to meet the local building codes for office buildings (applicable at the time of construction). Often these centers are located in zones of moderate to high seismicity. Past earthquakes have demonstrated that data centers experience severe damage and loss of operations even in moderate, more frequently occurring earthquakes (Gould et al. 2003). This paper describes several approaches that have been assessed to enhance the post earthquake safety of data equipment. This includes designs that incorporate building seismic base isolation, passive energy dissipation devices, computer floor isolation, individual rack isolation and more conventional methods which rely on direct bolting of equipment. The advantages and disadvantages of each approach are summarized.

Performing a typical Nonlinear Static Procedure requires the use of a nonlinear computer analysis program. Presently, computer program PERFORM 3D is most often used in structural engineering offices for this purpose. The concepts used in Nonlinear Static Procedure (NSP) are simple, and it would be desirable to develop an approach in which the results of linear analysis can be used to determine the nonlinear demands in different components of a building. This paper presents a procedure for using the demand capacity rations (DCR) obtained from a linear analysis to approximate component nonlinear demands. Two examples are presented to demonstrate the application of this process. One example is a one story shear wall building in which wall shear controls performance. The second example is a 15 story concrete shear wall building in which deformations in coupling beams and flexural yielding at the base of walls control performance.

The development of cheap, whilst effective and relatively non-invasive structural retrofit techniques for existing non-ductile reinforced concrete (RC) structures still remains the most challenging issue for a wide implementation on a macro scale. Seismic retrofit is too often being confused as purely structural strengthening. As part of a six-years national project on "Seismic retrofit solutions for NZ multi-storey building", focus has been given at the University of Canterbury on the development of a counter-intuitive retrofit strategy for earthquake vulnerable existing rc frame, based on a "selective weakening" (SW) approach. After an overview of the SW concept, this paper presents the experimental and numerical validation of a SW retrofit strategy for earthquake vulnerable existing RC frame with particular focus on the exterior beam-column (b-c) joints. The exterior b-c joint is a critically vulnerable region in many existing pre-1970s RC frames. By selectively weakening the beam by cutting the bottom longitudinal reinforcements and/or adding external pre-stressing to the b-c joint, a more desirable inelastic mechanism can be attained, leading to improved global seismic performance. The so-called SW retrofit is implemented on four 2/3-scaled exterior RC b-c joint subassemblies, tested under quasi-static cyclic loading at the University of Canterbury. Complemented by refined 3D Finite Element (FE) models and dynamic time-history analyses results, the experimental results have shown the potential of a simple and cost-effective yet structurally efficient structural rehabilitation technique. The research also demonstrated the potential of advanced 3D fracture-mechanics-based microplane concrete modelling for refined FE analysis of non-ductile RC b-c joints.

The FEMA 440 report, Improvement of Nonlinear Static Seismic Analysis Procedures (FEMA 2005), was commissioned to evaluate and develop improvements to nonlinear static analysis procedures used in prevailing practice. Recommendations contained within FEMA 440 resulted in immediate improvement in nonlinear static analysis procedures at the time, but many difficult technical issues remained unresolved. The FEMA-funded ATC-62 Project was commissioned, in part, to further investigate the issue of component and global nonlinear degrading response, including cyclic and in-cycle degradation of strength and stiffness. The result was the publication of a supplemental report, FEMA P-440A, Effects of Strength and Stiffness Degradation on the Seismic Response of Structural Systems (FEMA 2009a). The FEMA P-440A report includes an extensive summary of available research on modeling of degradation, a database of analytical results documenting the effects of a variety of parameters on the response of structures with degrading components, and recommendations for improving nonlinear analysis techniques in current practice.

The nonlinear static procedures (NSP) in FEMA-440 are evaluated by comparing, for five instrumented buildings, predictions with estimates of the structural response obtained from an observer. Differences in the predictive ability between the various NSPs in FEMA-440 are found unimportant from a practical perspective. The scaling needed to ensure that predictions have no more than a 10% chance of being un-conservative are found to be around 1.7 and 2.7 for story shears and for drifts, respectively. NSP predictions in the lower half of the buildings, due to stronger contribution of the lower modes, are found significantly more accurate than the average over the full height.

This paper illustrates the results of experimental tests and numerical simulations carried out on full scale reinforced concrete (RC) existing frames retrofitted with buckling restrained braces (BRBs). Experimental tests were performed on two sample full scale RC building structures designed for gravity loads only. Such frames were subjected to cyclic pushovers to investigate their structural performance under earthquake ground motions. The results of the experimental tests show the efficiency of using BRBs to retrofit RC frames designed for gravity loads only. Such results were also confirmed by comprehensive non linear static and response history analyses carried out on an existing RC school framed building designed for gravity loads only and retrofitted with BRBs similar to those adopted for the tested full-scale frame. In such sample building the BRBs are placed along the perimeter of the existing frames to minimize the interruption of the functionality of the school and for easy of maintenance in the aftermath of major earthquake ground motions. The seismic performance assessment of the retrofitted structural system is illustrated in a detailed manner. Local and global response quantities are presented. The cost-effectiveness of the adopted retrofitting scheme is emphasised and further needs for the application of BRBs are highlighted.

A simple performance-based evaluation approach is presented based on interactions of axial, shear, and flexure mechanisms to estimate the axial and lateral deformation and load capacities of reinforced concrete columns. The developed model is based on a simplification of a consistent but relatively more complex approach known as the axial-shear-flexure interaction (ASFI) method, which is able to predict the full load-deformation response of reinforced concrete columns subjected to axial, flexure and shear force. The analytical model was developed by coupling an axial-shear model, which is a biaxial shear model, and an axial-flexure model, which is the traditional section analysis. Axial deformation interaction is the main compatibility condition taken into account in this approach. Equilibrium conditions are satisfied through a simple shear and flexure stress relation. A series of reinforced concrete columns subjected to axial and lateral loads, tested by various researchers, were evaluated by the simple developed approach and the results were compared with the test data; consistent correlation and agreement were achieved. This paper describes the formulation, implementation and verification of the modified approach. A future attempt is to modify the ASFI method for response estimation of reinforced concrete columns in fire under axial load and lateral deformation induced by thermal expansion.

Seismic evaluation of structures generally involves determination of displacement demands from which story drifts, and component forces and deformations for specified hazard levels can be obtained for comparison with available capacities. A number of methods have been proposed by investigators in the past some of which are also used in current practice, such as MPA, FEMA 440, and Capacity Spectrum. Those methods generally involve non-linear pushover analyses. This paper presents adaptation of an energy based method that has been recently developed and successfully used by Goel et al., for design purposes, called Performance-Based Plastic Design (PBPD) method. In the PBPD method the design base shear for selected hazard level is determined by equating the work needed to push the structure monotonically up to a selected target drift to the corresponding energy demand of an equivalent SDOF oscillator. It turns out that the same work-energy equation can also be used to estimate seismic demands for existing structures. In this approach the skeleton force-displacement (capacity) curve of the structure is converted into energy-displacement plot (E_c) which is superimposed over the corresponding energy demand plot (E_d) for the specified hazard level to determine the expected peak displacement demand. The drift demands of two 20-story RC and steel moment frames as computed by the proposed energy spectrum method were in excellent agreement with those obtained from inelastic dynamic analyses using representative ground motion records.

Concentrically braced frames (CBFs) are stiff, strong, and were commonly used for seismic design in existing construction, but their inelastic seismic behavior is not easily evaluated, because it is dominated by tensile yield and post-buckling deformation. Recent research to better understand and evaluate CBF behavior for a range of construction eras is summarized. These results are combined with historic experimental results to develop fragility curves, which can be used to estimate seismic performance and to evaluate repair and retrofit strategies. Evaluation of seismic performance also requires analytical models to predict deformation demands due to seismic excitations, but current models provide limited accuracy. Recent developments in modeling and analyzing CBF performance and seismic demands and improved prediction methods are presented. The seismic performance of CBFs is strongly dependent upon the gusset plate connection design and performance as well as brace cross-section and configuration, and these details have a major impact on the seismic damage expected from a given CBF system.

This paper presents a practical displacement-based evaluation procedure for the seismic assessment of low-height regular confined masonry buildings. First, the Coefficient Method established in ASCE 41-06 Standard and several FEMA documents is adapted to obtain rapid estimates of inelastic roof displacement demands for regular confined masonry buildings. For that purpose, a statistical study of constant relative strength inelastic displacement ratios of single-degree-of-freedom systems representing confined masonry buildings is carried out. Second, a nonlinear simplified model is introduced to perform pushover analysis of regular confined masonry buildings whose global and local behavior is dominated by shear deformations in the masonry walls. The model, which can be applied through the use of commercial software, can be used to establish the capacity curve of such buildings. Finally, the evaluation procedure is applied to a three-story building tested at a shaking table testing facility.

Ultimate Strength based Design (USD) method is a major seismic design method in Japan. Ductility Related Force Modification (DFM) Factor is the most important factor in USD method. Procedures obtaining DFM factors of dual or combined systems are not described in the code. But strengthening design need to calculate DFM factors of dual or combined systems, because those are often strengthened by different systems other than original systems. This paper proposes a Stiffness- Potential Energy Addition (SPEA) method in order to calculate lateral strength of stories with shear walls of different ductility. This method needs only two design lateral strengths for each type of shear walls in Damage Limit State and Safety Limit State. SPEA method also provides DFM factors of storied with shear walls of different ductility. SPEA method uses elastic stiffness and potential energy of each shear wall in a story.

In May 2004 the Ministry of Education of British Columbia (Ministry) announced a $1.5 billion seismic mitigation program for public K-12 school buildings. The goal of this program is to achieve the seismic mitigation of the most hazardous school buildings within a reasonable length of time. The development of innovative, cost effective assessment and mitigation design is being prepared under contract with the Ministry through a cooperative agreement between the Association of Professional Engineers and Geoscientists of British Columbia (APEGBC) and the Department of Civil Engineering of the University of British Columbia (UBC). The unique approach to develop a new cost effective seismic mitigation program within a reasonable period of time is a real challenge. The basic concepts of the approach and preliminary data were generated and released to the design community in November 2006. Internally this document is referred to as the Bridging Guidelines. However, the official title of the copyrighted document is Performance-Based Seismic Assessments and Retrofit Design Concepts — Second Edition. In March 2007 the Ministry announced the availability of $254 million in funding for capital construction. The Ministry required that the funds for this program be utilized for the assessment and structural seismic retrofit designs of the school buildings. Non-structural seismic mitigation was in a separate program. APEGBC and UBC are continuing the program development. The concepts and ideas given herein are a combination of those released in November 2006 and more recent developments. This paper is intended to be consistent with the new, significantly improved version of the program. However, as new concepts continue to be developed this paper cannot assure the reader that what is presented will be the final approved program.

A new retrofit technique for unreinforced masonry infills in non-ductile reinforced concrete frame structures is being investigated. The proposed technique uses a thin layer of sprayable, ductile fiber-reinforced mortar material referred to as Engineered Cementitious Composites, or ECC. The aim of the retrofit is to hold the masonry wall together to delay infill and frame strength degradation and enhance system ductility. Proof-of-concept experiments on retrofitted masonry prisms and beams demonstrated large increases in strength and ductility. Quasi-static, in-plane, cyclic testing of small-scale frames with masonry infills including 3 retrofit designs demonstrated a 10x increase in ductility in one design relative to the unretrofitted system. Results were used to design a retrofit for a 2/3-scale, in-plane test, where a 2.6 x increase in ductility was achieved. Several finite element modeling approaches are under investigation for use in system predictions and further retrofit analyses.

This experimental work focuses on enhancing the seismic performance of reinforced concrete (RC) columns by using innovative active confinement technique. Spirals made of Shape Memory Alloys (SMAs) are utilized to provide the active confining pressure. The proposed technique is investigated experimentally through the testing of two reduced-scale columns under quasi-static cyclic loading. One of the columns is confined passively using glass fiber reinforced polymer (GFRP) sheets while the other is confined using a reduced number of GFRP sheets in addition to prestressed SMA spirals. The confining pressure on both columns is designed to be the same. The results show significant increase in the energy dissipation and ductility of the column wrapped with SMA spirals compared to that with GFRP sheets.

The first application of seismic isolation in the world that permits the vertical expansion of an existing structure by introducing isolation bearings between the existing structure and the addition is presented. In essence, the isolated addition acts more like a tuned mass damper than an isolated structure. The existing building which serves as the base for the isolated addition is about 825 ft long and 110 ft wide with two expansion joints at approximately the third of the length. The new addition is a continuous structure that bridges over the expansion joints and utilizes concentric braced frames for its lateral strength. This is truly a unique application of the base isolation technology where the plane of isolation has been moved from the base of the building to the roof of an existing building. A 3D non linear analysis using site specific time histories was used to demonstrate the adequacy of the base structure and extract the design parameters for the new addition.

The mid-story isolation design method is recently gaining popularity for the seismic protective design of buildings particularly located at highly populated areas. In a mid-story isolated building, the isolation system is incorporated into the mid-story rather than the base of the building. In this paper, the dynamic characteristics and seismic responses of mid-story isolated buildings are investigated using a simplified three-lumped-mass structural model for which equivalent linear properties are formulated. It is found that the nominal frequencies of the superstructure and the substructure respectively above and below the isolation system have significant influences on the isolation frequency and equivalent damping ratio of a mid-story isolated building. The mass and stiffness of the substructure are of greater significance than the superstructure in affecting the dynamic characteristics of the isolated building. Moreover, based on the response spectrum analysis, it is noted that the higher mode responses may contribute significantly to the story shear force of the substructure. The adverse effect arising from the coupling of higher modes on the acceleration responses of the superstructure is presented numerically and experimentally. A simple method to guarantee the mid-story isolation design against the modal coupling effect attributed to the improper design of the substructure and superstructure is proposed. Consequently, the equivalent lateral force procedure of design codes should carefully include the effects of higher modes.

The seismic isolation system is a structurally applicable construction method for existing buildings, for the purpose of preserving them for future generations. Such retrofitting is relatively new and is vital for the reinforcement and safety of buildings in the event of earthquakes. It is not only effective for historical and culturally important properties, but also for all types of buildings. A lot of new seismically isolated buildings have sprung up in Japan, totaling approximately 2,200 at present. Retrofitting accounts for approximately 4 % of that. The National Museum of Western Art in Tokyo was the first building retrofitted with seismic isolation. The features of some of the others are shown in our paper. The "operate-under-construction method" of retrofitting accounts for one-third of the whole. By this method, occupants in the building can continue their operations during retrofitting by this method. Another method is the "move-out method", which_requires occupants to temporarily relocate during retrofitting. If it is decided to renovate a building, it is necessary to consider what kind of procedures should be adopted, and to decide what type of retrofitting method to use. We discuss them in our paper. In addition, other important matters for retrofitting are explained with a flow-chart, while showing an example of buildings retrofitted with seismic isolation (SI).

The landmark Theme Building at the Los Angeles International Airport was evaluated for seismic loading. This structure is comprised of a reinforced concrete annular core and four steel arches placed at 90-degree orientations. Performance based engineering was used to assess the seismic performance of the concrete core. A detailed mathematical model of the structure was analyzed using site-specific acceleration histories. Analysis showed that the concrete core had insufficient flexural and shear capacity to resist the seismic loading. A comprehensive retrofit strategy consisting of increasing the capacity and lowering the demand was employed. The focus of the seismic retrofit is a tuned mass damper placed at the roof of the structure to reduce the seismic demand. Additional strengthening for flexure and shear are also incorporated in design. The retrofitted structure met its performance goal. Confidence analyses were conducted to assess the probability of reaching non-ductile limit states.

Three important projects of application of the seismic isolation to existing buildings are described in the paper. The first project is located in Naples and consisted in a reinforced concrete structure of 125 x 170 x 20 meter, belonging to the Municipality of Naples. The construction started in year 1976 and was stopped in year 1979 when all the foundations and the reinforced concrete frame was completed. In year 1999 the Municipality decided to complete the building but in the meantime the Italian Seismic Standard was changed and the already built structure was no more adequate for the newly defined seismic action implying a PGA of 0,25g. Seismic isolation was found to be the best and more economical solution to provide the building with the necessary resistance, minimizing at the same time the necessary strengthening to the existing structure and foundation. The seismic isolation has been provided through the application of 636 High Damping Rubber Bearings with equivalent viscous damping of 10%. The use of HDRB allowed to shift the period of the structure from 0,7 to 1,75 s and reducing the acceleration from 0,42 to 0,14g. To cut the columns ALGA developed special steel clamps, applied over and under the location of the cuts by use of prestressed bars in order to generate a friction suitable to support the load transferred by the concrete column. After the application of the clamps the vertical load of the column was released by use of hydraulic jacks, the column cut, the isolator installed and the clamps removed. The second application has been made to the airport structure of Antalya, Turkey. The job consisted in cutting the reinforced concrete columns and applying 358 LRB. During the cutting phase the vertical loads were transferred to an auxiliary steel structure applied below the beams by use of hydraulic jacks. The base isolation allowed to shift the period to 2,69 s, reducing the acceleration to 0,1g, being the design PGA 0,4g. Peculiar aspect was the fact that the retrofitting has been performed without interfering with the airport activity. The last project described, currently in progress, is the Justice Palace of Avellino, near Naples. For this project the use of sliding pendulum isolators has been foreseen as this was the only possible solution allowing to shift the period to 3,5 s and therefore reduce the acceleration below 0,07 g. In this way was possible to retrofit the structure avoiding any additional reinforcement to the upper structure. To reduce the dimensions of the isolators and to reduce the eccentricity caused by the design displacement, sliding pendulum with 2 spherical surface has been foreseen. The total number of sliding pendulum isolators is 220.

Performance-based earthquake engineering relies on accurate prediction of seismic demands from structural systems under given hazard conditions. In the past-decade, numerous approaches in predicting engineering demand parameters (EDPs) from structural systems were established. Some of these methods were implemented into the design guidelines and building codes. Among them, nonlinear static procedures (NSPs) have found a wide usage in practice for checking new designs and evaluating performance of existing structures. Today, there is a paradigm shift towards using nonlinear response history analysis (RHA) in lieu of NSPs to predict EDPs. The pre-requisite to nonlinear RHAs is a set of ground motions to be selected and scaled appropriately so that analyses results would be accurate (unbiased) and efficient (having relatively small dispersion). Considering that ground motions may show significant variability in frequency content and amplitude, small dispersion (variability) of EDPs is desired since it provides a confidence. There are currently many different methods in scaling and selecting records to be used in nonlinear RHAs. Since there are no experimental validation studies available up to date, the effectiveness of these methods can only be assessed using numerical simulations. These simulations require development of realistic computer models. In this respect, structural monitoring plays a key role in providing recorded motions on existing structures which can be used to create their well-calibrated (in terms of modal periods, damping etc.) computer modes. This paper shows how the recorded earthquake data from the 52-story high-rise building located in Los Angeles is utilized to create a realistic three-dimensional computer model. This model is also used to assess the accuracy and efficiency of the ASCE-7 ground motion scaling method in predicting the building's nonlinear response. It is concluded that the ASCE-7 method results in significantly high dispersion of EDPs despite the fact that median EDPs are well estimated.

A simplified method to estimate the seismic performance of existing steel moment resisting frame buildings is presented. Emphasis is placed on the estimation of the level of damage in beam-to-column moment connections. The proposed method makes use of fragility functions for pre-Northridge moment connections that allow the estimation of the probability of reaching or exceeding various damage states as a function of the peak interstory drift ratio. The fragility functions were developed based on a statistical study of a large number of experimental data on the testing of welded beam-to-column moment connections to cyclic loading. Of particular interest is the estimation of the probability of fracture in pre-Northridge welded beam-to-column connections. In the proposed method peak interstory drift ratios at each story are estimated by using a simplified continuous model consisting of a flexural beam laterally coupled to a shear beam. The method is evaluated by estimating the seismic performance of two instrumented building that recorded the 1994 Northridge earthquake and experienced different levels of damage. Estimated performance is then compared to observed performance documented in detailed reconnaissance reports. Results show that the method provides relatively good results by providing an indication of the level of damage in the building and of the stories where damage may have occurred.

This study reports the experimental findings on the upgrading of deficient reinforced concrete frames with externally installed structural components. Specimens strengthened with an external reinforced concrete shear wall, external steel frame, steel plate shear wall, and one as-built reference portal frame specimens having a 1/3 scale were tested under constant gravity load and increasing cyclic displacement excursions. The RC frames had deficiencies such as low concrete compressive strength (8MPa), lack of transverse reinforcement detailing at potential plastic hinge regions and beam-column joints that mimic the existing deficient building stock in Turkey. The test results showed that the external upgrading can increase the lateral stiffness and strength allowing a minimum of 3% drift ratio. On the other hand, it was found that the cyclic behavior of specimens including pinching and energy dissipation capacities was found to be quite different for different strengthening methods.

Fluid viscous dampers have been extensively used in new construction and seismic retrofit. They provide a reliable mean of dissipating seismic energy. In practice, the dampers are designed and sized using the procedures outlined on ASCE 7 for new structures and ASCE 41 for retrofit of existing buildings. These guidelines provide a factor of safety for damper design. In typical applications, the engineers analyze structures with dampers without consideration for the damper limit states and instead count on the abovementioned safety margins. However, the limit states of viscous dampers have a significant effect on the response of the building to which they are attached to. To address this issue, a refined model of viscous dampers has been developed based on the force-displacement-velocity constitutive relations of the damper components and incorporating the damper limit states. The model incorporates both displacement and force limit states. Simulations were conducted to check the limit state activation for the model. Experimental data were then used to verify the accuracy of such limit states. Finally, a sample structure was analyzed to assess the effect of limit states on the building response and to evaluate the safety margins..

This paper presents a case study of the seismic rehabilitation of an existing high school building in Southern California. The two-story 1968 building has extreme soft and weak story irregularities. Its second story concrete and masonry full perimeter shear walls sit on non-ductile reinforced concrete moment frames at the first story. The voluntary seismic rehabilitation falls under the jurisdiction of California's Division of the State Architect (DSA). The authors describe and compare a code-based elastic solution to an ASCE 41 nonlinear, displacement-based solution. The elastic solution involved adding steel concentric braced frames with sufficient stiffness to eliminate the first story irregularities. The nonlinear solution involved adding steel tube braces to provide additional initial stiffness, selectively cutting reinforcement to protect shear critical beams, and jacketing columns to increase deformation capacity. Friction dampers were included in the new tube braces to protect existing non-ductile elements from overload and provide desirable post-yield behavior of braces. The nonlinear approach dramatically reduced construction costs, by significantly decreasing the required structural steel tonnage of braces, easing the ability to connect braces to the existing structure, eliminating the need to strengthen diaphragm collectors, and eliminating the need to add drilled piers to existing pile groups.

This paper presents a new technique for optimizing the design of viscous dampers when they are used to improve the seismic performance of existing buildings. The technique uses a genetic algorithm optimization routine that is applicable to the highly complex and nonlinear relationship between damper properties, building response and cost. The paper describes the use of nonlinear static analyses in a manner that significantly reduces the amount of analysis required to determine building response. This makes the genetic algorithm highly efficient and reduces the time required to obtain an optimized solution. The method is illustrated with two buildings — a four-story reinforced concrete moment frame building and a nine-story steel moment frame building. Analyses of the buildings shows that the method produces excellent results, even after relatively few iterations. Typical values of optimization parameters that give good convergence are recommended. The paper also suggests criteria that can be used to determine when a near optimum design has been achieved.

This paper describes the structural investigations and subsequent structural renovations that were performed on the twin 17-story State Office Buildings 8 and 9 located four blocks south of the State Capitol in Sacramento, California. The renovation designs conform to a performance criteria established by the California Department of General Services (DGS) with the intent that structural damage would be moderate and Risk to Life would be minor during a large earthquake.

When considering social function of railway viaduct as infrastructure, less damage control is demanded even against significant earthquake. Response control technique with damping device is highly expected as alternative solution. In responding, authors have developed Arc Shaped Dampers. In order to investigate applicability of the proposed damper to moment frame type rail way viaduct structures, seismic retrofit design, nonlinear analysis and experimental loading tests have been conducted to verify present technique. Following results were obtained: the existing structure is failed in post yielding shear, while retrofitted structure assures flexural yielding ductile behavior with higher damping effect.

Seismic protection of critical facilities such as hospitals, emergency response centers, and schools is crucial as these buildings must remain in full service after major earthquakes. A new modular, multiple-panel infill system made of a ductile, high performance fiber reinforced concrete (HPFRC) is currently under investigation with a focus on protecting such critical facilities wherein the primary structural system is a steel, moment-resisting frame. The primary objective of this paper is to compare the proposed HPFRC infill panel retrofit system with the alternative retrofit techniques of buckling-restrained braces (BRBs) and viscous dampers for seismic protection of existing steel moment resisting frames. The effectiveness of the three seismic retrofit techniques is evaluated based on analytical simulations after retrofitting the SAC 3-story structure. It is shown that the HPFRC infill panel system when installed in an existing steel moment resisting frame designed prior to major earthquake events (Northridge, 1994, Kobe, 1995) limits residual story drifts as well as frame damage at a design and a maximum considered event. Its seismic response is very comparable with the state-of-the art BRB and viscous damper retrofitting techniques.

Building Façade has various functions, not only being suitable for placing additional seismic reinforce elements, but affecting on architectural appearance and running energy efficiency. For improving all of these performances, the authors have proposed the concept of "Integrated Façade", which treats structural design, façade design and environmental design combined together, including improvements on seismic performances using seismic energy dissipation devices. The practical application of this concept to the 40-years aged building is reported, which requires improvement in seismic performance allowing continuous tenant occupancy along the retrofit works.

A retrofit system of prestressed concrete rocking walls and steel dampers is used to control the seismic damage mode and increase the strength and energy dissipating capacity of an 11 story steel reinforced concrete frame in Japan. Important details of the retrofit design are introduced. The seismic performance of the structure before and after the retrofit is evaluated through extensive nonlinear time history analysis. Results show that the rocking system can significantly reduce both the seismic responses to different earthquake ground motions and their scattering. This makes the damage mode and the seismic performance of the retrofitted building more predictable, leading to a possibility of more reliable performance-based seismic design.

The concept of the hybrid passive control system is studied analytically by investigating the seismic response of steel moment-frame structures. A hybrid passive system combines a rate-dependent damping device with a rate-independent energy dissipation device. The innovative configuration exploits individual element strengths and offsets their weaknesses through multi-phased behavior. A 9-story, 5-bay steel moment-frame was used for the analysis. Six different seismic resisting systems were analyzed and compared. The conventional systems included a plain special moment-resisting frame (SMRF) and a dual SMRF-buckling-restrained brace (BRB) system. The four hybrid configurations utilize a BRB and either a high-damping rubber damper or viscous fluid damper. The results demonstrate the capabilities of hybrid passive control systems to improve structural response compared to conventional lateral systems and to be effective in performance-based earthquake engineering. Each hybrid configuration improved some aspect of structural response with some providing benefits for multiple damage measures. The multi-phased nature of the device improves performance for small, moderate and severe seismic events.

To investigate the seismic behavior of the fully isolated (slitted) non-structural reinforced concrete walls using dowel bars, authors performed the static loading tests and seismic response analysis. According to the results, such walls had no negative effects on the stiffness balance or deformation capacity of the building structure and consumed energy mainly by the damaged dowel bars under small and mid scale earthquakes. The lateral strength and the hysteretic energy absorption of the non-structural walls with only horizontal slit face could be calculated as the cumulative increase of the performance of each dowel bar. The results show that non-structural walls have potentials to be incorporated into actual buildings as a new passive control device. It can be considered to be reserves for the seismic performance of the building, which would contribute to re-appreciation of the asset value of existing buildings.

To adopt damper devices easily to Japanese Post and Beam wooden houses, a new damper device are developed. The mechanism of the new damper device is simple and the manufacturing cost is low. The high damping rubber is used for the damper device. To evaluate the basic performance of a brace with the new developed damper device as well as a brace with a normal fastener, static shear loading tests of a wood frame with the damper braces and normal braces were done. Secondly, shaking table tests were conducted. Finally, time history earthquake response analyses were carried out to evaluate the performance of the brace with the damper device under several earthquakes. Moreover, the seismic response of two-storied wooden house with normal braces and the damper braces was predicted. From these tests and analysis, it was found that the new damper device is effective for Japanese Post and Beam wooden houses.

Nonlinear static procedure (NSP) or pushover analysis is becoming a popular tool for seismic performance evaluation of existing and new structures. It is believed that the pushover analysis will provide adequate information on seismic demands imposed by the design ground motion on the structural system and its components. Nonlinear pushover analysis was recommended by FEMA 356 — Prestandard for Seismic Rehabilitation of Buildings, which currently adopted into a standard called ASCE 41-06 — Seismic Rehabilitation of Existing Buildings, in assessing the seismic performance of buildings for a given earthquake hazard representation. This purpose of the paper is to examine the effectiveness and benefits of nonlinear static procedure for seismic response analysis of reinforced concrete buildings. This study focuses on one of the low-rise hospital buildings located in Orange County, California. This building was constructed in the early 60's with a reinforced concrete shear wall system and it is a non-compliant building per current building code. In order to meet the code requirements, the building was analyzed and retrofitted based on the results from nonlinear pushover analysis. By implementing this advanced analysis approach, structural performance was better understood which led to the more efficiently use of retrofit methods.

FEMA 356 backbone relations tend to provide conservative estimates of the available strengths and deformation capacities of reinforced concrete components, leading to costly seismic rehabilitation solutions for California hospitals. The conservatism is driven by the lack of test data for older, typically poorly detailed, structural components. Although FEMA 356 does provide for building specific component testing, this approach is not common due to cost concerns and/or schedule constraints. However, a test program on lightly-reinforced, poorly-detailed wall segments was undertaken at UCLA in 2004–2005 to support seismic rehabilitation projects on several southern California hospitals. Presented test results are compared with FEMA 356 backbone relations to highlight the advantages associated with building-specific test programs. In general, the test specimens revealed more strength and deformation capacity than assumed by FEMA 356, and more gradual strength deterioration. The test results, when coupled with the FEMA 356 Nonlinear Static Procedure (NSP) and Nonlinear Dynamic Procedure (NDP), enabled the development of more rational and substantially more economical rehabilitation solutions. The test results were used to help develop new backbone relations that were incorporated into ASCE-41-06 Supplement #1.

Traditional geotechnical engineering practice typically utilizes a wide variety of empirical correlations which contain varying degrees of epistemic and aleatory uncertainty. The source of the uncertainty varies from the use of poorly controlled field test methods to sample disturbance prior to laboratory testing. When accounting for uncertainties such as these, the geotechnical engineer may be influenced by a desire to give "conservative" values or "better" values to the structural engineer. However, when considering performance-based design, rather than accounting for the uncertainties in empirical formulae and test results through the use of poorly understood and inconsistently applied factors of safety, there is a need for a reduction in the uncertainties themselves. This can be accomplished through the use of high quality field and laboratory testing methods. It is important that the uncertainties in the geotechnical parameters are reduced and that arbitrary safety factors not be applied so that the actual performance of the structure can be accurately modeled by the structural engineer. The best estimate of geotechnical. performance is what is required. Overly conservative or overly aggressive foundation stiffness and/or bearing capacity values, which may seem desirable to some engineers, can lead to the incorrect predicted failure mechanism of the structure and result in a misguided retrofit scheme. Accurate estimates of geotechnical parameters and reduced uncertainties can help owners build safety and cost savings into the analysis and retrofitting of existing buildings. A case history is presented where performance-based design concepts were utilized in obtaining geotechnical parameters for the nonlinear analysis of an existing hospital building.

Structural systems of reinforced concrete (RC) frames with unreinforced masonry (URM) infill walls are common building systems, especially for historical buildings. In this study a one-story reinforced concrete building was simulated until collapse scaled records of ground motion, before and after retrofitting the URM infill wall using Fiber Reinforced Polymer (FRP) bars. The nonlinear behavior of the URM-infilled RC frame was modeled using the general purpose finite element (FE) software ABAQUS, to shear-deformation behavior of the infill walls. The infill walls were then idealized using a calibrated strut-and-tie model of the wall. The infill walls were then modeled, along with the RC frames, using the open source FE code OpenSEES (Open System for Earthquake Engineering Simulation). The OpenSEES (Mazzoni et al, 2004) modeling uses a direct element removal procedure which accounts for sudden loss of brittle elements taking into account dynamic equilibrium and the transient change in the structural system kinematics. Static and dynamic analytical simulations were conducted, on the one story building model, to study the effect of retrofitting the infill walls on the overall behavior of the building system. Finally, the overall building performance after retrofitting was compared to the as-built building system. This study concludes that, after retrofit of the infill walls with FRP bars, the overall displacement ductility and the building system performance were enhanced, without significant increase in the stiffness of the lateral resisting system.

This paper reports the results of an investigation on the efficacy of using rocking spines of strengthened infill walls as a retrofit measure for non-ductile reinforced concrete (RC) frames with unreinforced masonry (URM) infill walls. The study examines the effects of spines of strengthened URM infill walls on the behavior of the RC frame, with particular emphasis on whether spines could reduce the tendency to form a soft story mechanism. For this purpose, a nine story frame with five bays is selected to represent complex multi-story behavior, where the collapse of stiff infill walls may lead to the formation of a soft story mechanism. The effect of the proposed retrofit is investigated through nonlinear static and dynamic analyses. Fragility relationships are obtained for the frames using pseudo-acceleration corresponding to the first mode as the intensity measure and maximum interstory drift ratio as the response variable. For the analyses, a progressive collapse algorithm, previously developed and implemented into the object-oriented open system for earthquake engineering simulation (OpenSees) is utilized and the interaction between the in-plane strength of the infill wall and its out-of-plane strength is taken into consideration. Analyses show that infill retrofit with rocking spines provides significant improvement in the seismic performance of non-ductile RC frames.

New infill units made of the Carbon Fiber Reinforced Polymer (CFRP) have been developed for one of the seismic retrofit technologies. The CFRP shear wall consisted of the CFRP units by epoxy resin bonding. The thickness and the weight of the wall are about 100mm and 41 kg/m². As for the connections between CFRP shear wall and existing concrete, boundary steel plates are installed with epoxy resin. Three types of reinforced concrete frames with CFRP shear walls were tested under axial and cyclic lateral loads. The parameters of the specimens were anchorage bond strengths and with/without splice plates on unit joints. From the test results, the average shear strength of CFRP shear wall was over 3.5 N/mm² without splice plates and over 6.4 N/mm² with splice plates. These values can be enough for the strength of seismic rehabilitation. As for the ductility, the story drift of the wall without splice plates was 0.26 %, that with splice plates 0.74 %. In the additional case of slipping along the anchorage connection, the story drift of the specimen with splice plates was about 2.0 %. From the viewpoints of strength and ductility, the CFRP shear walls with splice plates are better suited for the strength resistant type of seismic rehabilitation.

This paper summarizes some of the findings of a research project that investigates the seismic performance of masonry-infilled, non-ductile, RC frames, including the development of reliable analytical methods for performance assessment and effective retrofit techniques. Quasi-static tests were conducted on small and large-scale, single-story, single-bay, RC frames infilled with brick masonry walls with and without openings. Some of the infill walls were strengthened with an engineered cementitious composite material. Furthermore, two 2/3-scale, three-story, two-bay, masonry-infilled, RC frames were tested on a shake table. One was tested with no retrofit measures, and the other had infill walls strengthened with the engineered cementitious composite and fiber reinforced polymeric material in the first and second stories, respectively. The tests have demonstrated the effectiveness of the retrofit measures. Computation models that combine smeared and discrete cracks have been developed and validated by the experimental data. Some of the experimental and numerical results are presented in this paper.

Istanbul is most vulnerable city because of its seismic-prone location nearby the North Anatolian Fault, and its high population and commercial/industrial densities. Taking into consideration that the probability of a major potential earthquake in next years will bring mass destruction in physical environment and economic sector with a high risk of life loss to Turkey, there is an urgent need to shift existing faith-oriented, reactive and recovery based policies into proactive, mitigative and preventive approaches. Istanbul Seismic Risk Mitigation Project (ISMEP) is a significant attempt to implement essential principles of comprehensive disaster management financed by the World Bank and European Investment Bank. The main objectives are to improve the city of Istanbul's preparedness for a potential earthquake through enhancing the institutional and technical capacity for disaster management and emergency response, strengthening critical public facilities for earthquake resistance, and supporting measures for better enforcement of building codes and land use plans. Accordingly, ISMEP Project consists of three (3) sub-components which are implemented through Istanbul Special Provincial Administration, Istanbul Project Coordination Unit.

India's fast-growing capital city of Delhi, home to over 14 million people, faces substantial earthquake hazards from both distant, large-magnitude earthquakes in the Himalayas and smaller, local events. The Delhi metropolitan area contains an amalgam of existing building types: old and recently constructed, illegally built and well-designed, humble brick houses and gleaming new high-rises. Many of these buildings are seismically vulnerable and will threaten the lives of Delhi's inhabitants, if a major earthquake strikes. To help reduce Delhi's earthquake risk, GeoHazards International (GHI) conducted a project to build the capacity of the Delhi Public Works Department (PWD) to assess and seismically retrofit vulnerable existing buildings that have important post-earthquake functions. Improved seismic performance of these buildings both protects the government employees working there and enables them to respond more effectively to disastrous earthquake events. GHI utilized a practical learning approach, in which a peer review panel from India and the United States mentored Delhi PWD engineers as they seismically retrofitted government buildings.

Ever since the Napier earthquake in 1931, New Zealand has taken earthquake engineering seriously. Developments in design standards and seismological knowledge over the years have resulted in a current building stock with a wide variety of expected performance when compared with new building standards. This paper traces the main developments in design since 1935 and the efforts to address deficiencies in older buildings, from the first legislation in 1968, which covered masonry buildings, to the latest experiences with the implementation of the Building Act 2004. The 2004 provisions cover all buildings except small residential building and define the level at which and existing building is regarded as earthquake-prone and thus could be subject to a requirement to "reduce or remove the danger". The Act required each of New Zealand's 73 territorial authorities to develop a policy on earthquake-prone buildings, to consult publicly before adopting it, and to submit it to the Department of Building and Housing. The approach, priorities and details of policies were up to each territorial authority. The paper outlines how New Zealand has sought to reduce earthquake risk in existing buildings over the last 40 years and to deal with the complex mix of technical, social, heritage and economic issues involved. It is hoped that this examination of the New Zealand experience will be instructive to those in other countries seeking to address the risks represented by existing buildings.

San Francisco is in the process of doing something revolutionary: the City is heeding the warning of the moderate damage caused by the Loma Prieta earthquake, and may mandate strong rehabilitation measures for soft-story buildings to prevent catastrophe in future quakes. A study for the City, the Community Action Plan for Seismic Safety (CAPSS), recently estimated the consequences of several moderate to large Bay Area earthquakes on multi-unit, soft-story wood-frame dwellings. The project estimates that tens of thousands of residents of these buildings would be displaced from their homes, many for years, after a large earthquake, but retrofits would greatly reduce these impacts. Remarkably, it was building owner and tenant groups, not structural engineers, who actively led the discussion about whether mandatory mitigation makes sense. The project, with support from many community groups, calls for mandatory retrofit of the most vulnerable of these buildings.

The 1989 Loma Prieta Earthquake and the 1991 East Bay Hills Firestorm had roughly the same order of magnitude impacts on the City of Oakland, California. The long-term recovery aspects of the two disasters, however, were not similar; the earthquake damaged more apartments for more low-income residents, while the fire destroyed homes in the hills of more wealthy residents. Starting in 1992, the Association of Bay Area Governments (ABAG), the regional planning agency for the San Francisco Bay Area, began to make projections of impacts of earthquakes on housing. These projections, based on a variety of existing data and statistical inventories, predict over 150,000 uninhabitable housing units, 350,000 people forced from their homes, and over 100,000 people requiring publicly-provided shelter in a major earthquake on the San Andreas or Hayward fault. Despite the severity of this risk, it has taken 15 years for that general earthquake-impact information to be converted to policy. Part of the delay has been related to data on inventories of different types of residential building construction, including building a consensus on what to inventory and the accuracy of the resulting list. Part of the delay has been developing a consensus on the expected damage to and relative hazard of mobile homes, single-family homes with cripple-wall problems, and potential soft-story multifamily buildings. Other delays have been related to competing priorities on city staff and elected official priorities. Yet from 2006–2009 there has been a major change in the attitude toward housing and its impacts on recovery, as well as an acceleration in housing mitigation policies. It can be argued that one of the major sources of this change has been the impact of housing damage in the Northridge and Kobe Earthquakes, and, most recently, after Hurricane Katrina in New Orleans. This paper discusses the history of this transformation, as well as ideas on how to convert the experience into change for other types of existing buildings and in other areas.

Prompted by high economic losses from the 1994 Northridge, California, earthquake, the City of Los Angeles initiated a program to develop, test, and implement standardized procedures for the seismic evaluation and retrofit of single-family wood-frame dwellings (ATC-50 project). The primary products of the project include: 1) a seismic evaluation and grading system that considers damage or collapse potential in a manner that is consistent and useful to owners, purchasers, insurers, lenders, contractors, design professionals, and regulatory officials; 2) a seismic grading form that enables a certified inspector to evaluate a detached single-family wood-frame dwelling and assign a seismic grade, ranging from A through D, with each grade representing an expected range of damage (expressed as a percentage of replacement cost), should the 475-year MMI (Modified Mercalli Intensity) occur in the zip code containing the inspected dwelling; 3) seismic rehabilitation guidelines comprised of prescriptive methods, simplified engineering methods, and fully engineered methods that allow for a revised resistance grade; and (4) a report that provides guidance on how to develop and implement a market-driven, incentives-based program to induce homeowner use of earthquake performance evaluation forms and rehabilitation guidelines produced by the ATC-50 Project. The procedures were tested in a pilot program involving evaluation and grading of approximately 500 detached single-family wood-frame dwellings in the Los Angeles area, and rehabilitation (or retrofit) of approximately 50 dwellings with inadequate earthquake resistance. The ATC-50 project was conceived with input from the banking and insurance industries, was performed by the Applied Technology Council for the City of Los Angeles, and was funded by the Federal Emergency Management Agency through a Hazard Mitigation Grant Program award from the California Office of Emergency Services (now the California Emergency Management Agency). Additional funding for the 50 retrofit projects was provided through a grant from the U.S. Department of Housing and Urban Development.

As part of a study for the City of San Francisco entitled Community Action Plan for Seismic Safety (CAPSS), we estimated the consequences of 4 large Bay Area earthquakes for large soft-story woodframe dwellings in San Francisco to inform City risk-management policy. A survey by the City's Department of Building Inspection found 2,800 residential woodframe buildings with 3 or more stories and 5 of more housing units with soft-story conditions. As proxies for these 2,800 unique buildings, four index buildings and three retrofits for each building were designed and analyzed. We developed nonlinear pseudostatic structural models for each building and retrofit. From lab tests and other observations, we created fragility functions for straight-sheathed woodframe walls, lath and plaster interior wall finish, brick veneer, and stucco veneer, and related the observed damage to HAZUS-MH damage states. We estimated the distribution of drift at which buildings would likely receive a red tag under ATC-20 post-earthquake safety inspection procedures. From observations of similar buildings in the San Francisco Marina District after the 1989 Loma Prieta earthquake, we estimated the transient drift associated with collapse. Using a procedure based on the HAZUS Advanced Engineering Building Module, we estimated the economic loss, ATC-20 safety tag color, and collapse probability for each of the 2,800 buildings in each of the 4 scenario earthquakes. Loss estimates were reviewed by an expert panel. We conclude that, in a M7.2 rupture of the San Andreas Fault, between 30 and 50% of the 2,800 buildings would be rendered unsafe to enter or occupy (i.e., they would be red-tagged), and an additional 10 to 30% would collapse. Seismic retrofit costing $11,000 to $17,000 per dwelling unit could reduce red tags to between 6 and 12% of the subject buildings, with 0.3 to 0.7% collapsing—substantial improvements on both counts—though repairs would still be costly.

Recent earthquakes have demonstrated the weakness of light-frame construction buildings that rely on gypsum drywall sheathing as shear walls. Seismic design codes now limit the use of gypsum sheathing to resist seismic loads and therefore have created a large inventory of seismically suspect buildings — including many two- three- and four-story residential apartment buildings constructed between 1950 and 1980. Potential earthquake damage to these buildings may be heavy enough to require vacating these buildings for repair. The required displacement would impact the residents and the surrounding communities significantly. The conventional method to seismically upgrade these buildings has been to remove existing gypsum sheathing, install new structural plywood, upgrade sill bolting and hold-downs, and then re-apply gypsum and finish. This approach is expensive and intrusive, resulting in very few buildings being retrofitted. A test program at the University of California Irvine (UCI) was developed to investigate the performance of gypsum sheathed shear walls reinforced with glass fiber-wrap material epoxied to the gypsum, and using glass fiber anchors to connect the system to the foundation. The test specimens had 1/2-inch and 5/8-inch gypsum wallboard sheathing, and framing and nailing that simulate typical light-framed construction from 1950 to 1980. The test program included 9 half-scale (4 ft x 4 ft) and 8 full-scale (8 ft by 8 ft) wall specimens loaded cyclically to obtain the force/displacement relationships and strength parameters for use in retrofit design. All testing was conducted using computer-controlled, cyclical test protocols [ASTM E 2126-07]. Half-scale tests to validate the capacity of the glass-fiber anchors followed a force-controlled protocol, while full-scale tests for overall panel strength used a displacement-controlled protocol. This paper presents experimental results including: (a) composite anchor strength results and failure modes; (b) control and retrofitted panel strength results, force-displacement relationships and failure modes; and (c) preliminary concepts and recommendations for application in seismic retrofit design.

Existing wood-panel, sectional, overhead garage doors have been shown in preliminary proof-of-concept testing to be effective as load transfer and energy dissipation elements in soft-story, wood-framed buildings. Such doors performed surprisingly well and, with further development of uplift restraint devices and additional testing, may be recommended for soft-story reinforcement in certain buildings.

This panel presentation examines some of the many complex issues associated with understanding the earthquake risk represented by older, nonductile concrete buildings. A volunteer-based initiative, the Concrete Coalition, has formed to address these issues, and is actively working with some cities in California, particularly Los Angeles, to better understand all the dimensions of the problem. With funding from the National Science Foundation, the Grand Challenge Project aims to identify how many such buildings are in Los Angeles, to understand what makes these buildings most vulnerable, and to explore effectiveness and implementation of possible retrofit options. There is another component, based entirely on a volunteer effort of the engineering community in northern and southern California, to estimate how many such buildings exist in the high risk counties, primarily along the coast, in California. Once the size of the problem is understood more clearly, it becomes possible to identify and implement retrofit solutions.

Following a major earthquake, one of Caltrans' most critical tasks is to assess the condition of all potentially impacted bridges and roadway corridors in the state highway system. Timely response is important to ensure public safety, guide emergency vehicle traffic, and re-establish critical lifeline routes. In the past, bridge inspection teams had difficulties setting priorities immediately following an earthquake, because they lacked precise information about where the worst shaking and, most likely, the greatest damage had occurred. In 2005 Caltrans initiated a contract with the United States Geological Survey (USGS) to develop and implement a Caltrans-specific version of their ShakeCast system, a post-event software analysis tool that was anticipated to change the way Caltrans responds following a major earthquake. ShakeCast is a web-based application that automatically retrieves measured earthquake shaking data, analyzes it against individual bridge performance characteristics, and generates inspection prioritization emails and other web-based products for emergency responders within minutes of an event. Benefits have already been realized over the course of the test deployment phase. The ShakeCast system has proved to be a valuable tool for post-earthquake response for Caltrans during real events as well as for scenario planning exercises.

Following the 1994 Northridge earthquake, the Los Angeles Unified School District (LAUSD) faced three key challenges; to determine the extent of damage on its properties; to return students to schools as quickly as possible; and to maintain a documented link between initial damage reports and subsequent mitigations to ensure proper reimbursement from state and federal disaster funds. Were a similar seismic event to take place today, the District would face the same challenges, but would be able to draw on resources that were not available 15 years ago. Through the wider adoption of standards in seismic risk awareness, coupled with advances in mobile communications and electronic data storage and transfer, an earlier and more complete picture of potential losses can be provided to decision making teams along with more robust tracking of the actual damage suffered. This paper will highlight the promise of these advances by drawing comparison to the response in 1994. It will also examine the challenges faced by a large urban school district of implementing an end-to-end program to improve seismic risk awareness, mitigation and post-earthquake response using the HAZUS-MH model and the suite of technology products that have been produced to compliment it. These challenges are a combination of different types; from the sheer number of buildings under consideration; to the implementation of multiple software products in a non-standard technical infrastructure; to the institutionalization of a training program. All these hurdles must be overcome within a cost-conscious administrative structure that is typically reactive rather than pro-active.

The US Federal Emergency Management Agency and the US Geological Survey have developed a suite of free software for cities, building owners, and others to manage their seismic risk, before, during, and after earthquakes. FEMA's Rapid Observation of Vulnerability and Estimation of Risk (ROVER) is open-source software that operates on a Windows Mobile device (a smartphone) to quickly gather field information about the buildings subjected to seismic risk, before an earthquake occurs. It automates and enhances the FEMA 154 methodology, Rapid Visual Screening of Buildings for Potential Seismic Risk, which has been successfully used on tens of thousands of US buildings, and adapted for use in other countries as well. ROVER also has a free open-source database server component that operates on a Windows or Linux PC to compile the data collected in the field by one or more mobile devices. After an earthquake occurs, ROVER has yet another module that automates and enhances the ATC-20 methodology, Procedures for Post-earthquake Safety Evaluation of Buildings. Using the ROVER ATC-20 module, field safety workers can use a smartphone to carry out the de facto international standard for post-earthquake safety evaluation of buildings. ROVER is linked to two additional seismic risk software packages: HAZUS-MH (NIBS and FEMA 2003) and ShakeCast (Wald et al 2008). After an automated ROVER data export to FEMA's HAZUS-MH Advanced Engineering Building Module, the user can perform scenario or probabilistic seismic risk analysis on the portfolio of buildings examined with ROVER. ROVER's data also interacts with the USGS's ShakeCast software. After an automated ROVER data export to ShakeCast, the user can automate the monitoring of the buildings for damaging earthquakes. When one occurs, ROVER users are automatically notified of shaking and likely damage at each site, including an automated estimate of the likely ATC-20 tag color, which the field user can then verify or update at will. ROVER's server and all its data can be remotely and securely accessed via a Web browser, allowing the field or office user to seek outside expert advice, in real time, about buildings currently under investigation, while the user is still in the field examining the building. All the software—ROVER, HAZUS-MH, and ShakeCast—are free, and can reside securely on the user's own computers. No data need to be shared with anyone else or stored on a computer out of the user's control, although services are available for the user with limited IT resources. This paper focuses on ROVER.

The seismic hazard analysis for Quetta and surrounding area was carried out by using the probabilistic approach. The analysis considers seismicity occurring in the study area, tectonics and expected ground motion in terms of peak ground acceleration (PGA). The area is seismically very active and due to this disturbance cities of Quetta and Kalat were completely destroyed during the 1935 earthquake. To mitigate the consequences of future possible earthquakes, seismic hazard analysis for the area is carried out. On the basis of seismotectonics and geological features, seven seismic sources are recognized in this region and significant sources among them are established. Expected PGA with return periods of 50 and 100 years for the cities of Quetta, Chaman, Kalat and Ziarat are 0.27g, 0.16g, 0.21g, 0.26g and 0.29g, 0.20g, 0.25g, 0.27g respectively. Probabilistic PGA maps for 90% probability of non-exceedance in 50 and 100 years are also compiled.

Recent earthquakes have provided several examples of the devastating effects of earthquake surface fault rupture on buildings. Numerous examples of satisfactory performance of buildings have also been observed. These examples of satisfactory performance indicate that similar to other forms of ground movement, effective design strategies can be developed to address the hazards associated with surface fault rupture. Advancements in surface fault rupture hazard mitigation lag behind those for other forms of ground failure, because of the overreliance on avoidance. However, not all faults can be avoided, and not all faults require avoidance if engineering design techniques can be shown to be effective in mitigating the ground deformation resulting from fault movements. Potentially effective design measures include establishing non-arbitrary setbacks based on fault characteristics and site conditions; constructing reinforced earth fills to absorb partially underlying ground movements; using slip layers to decouple ground movements from foundation elements; and designing strong, ductile foundation elements that can resist imposed earth pressures.

Built in 1927 from reinforced concrete, Bowles Hall is the oldest dormitory at University of California, Berkeley campus. In 2007 a fault-displacement hazard analysis commissioned by the University found that two corners of the structure sit atop a potentially active western fault trace of the Hayward fault. Rutherford & Chekene Structural and Geotechnical Engineers (R&C) evaluated the structure's seismic performance for shaking and for fault offset. To understand how buildings respond to ground offset, R&C reviewed reports of earthquakes where surface fault rupture occurred under structures. Based on the evaluation and retrofit design of Bowles Hall for earthquake fault offset, and on the review of research on fault-offset effects on structures, the authors have developed recommendations for designing for such a hazard. The recommendations include a general evaluation procedure, a consideration of influential variables, an identification of mitigation strategies, and draft building code requirements and commentary. Retrofit measures for Bowles Hall, constructed in July and August 2009, include new retaining walls at the hillside behind the building to limit soil pressure against the structure, and new foundation slabs over the fault zone. These measures are designed to allow surface fault displacement to occur without causing significant damage to the building.

UC Berkeley's California Memorial Stadium, constructed in 1923 and designed by the renowned architect John Galen Howard, sits directly over the northern segment of the Hayward Fault. After many years of analysis, politics, litigation and even an 18 month much-celebrated tree sitting protest, the campus authorized the advancement of the seismic safety corrections for the Stadium. Situated at the opening of Strawberry Canyon, with the eastern half of the stadium literally carved into the hillside, the non-ductile concrete frame western stadium bowl will be seismically retrofitted and modernized with new seating bowl framing, a new press box, and with the preservation and restoration of the historic perimeter concrete wall. The truly unique aspect of the retrofit design is the approach to the sections of the stadium positioned over the north-to-south running, right-lateral Hayward Fault. The planned retrofit design creates separate "fault rupture zone blocks", gapped and separated by joints from the adjacent sections of the stadium. The FRB's will be reinforced with stiffening concrete shear walls bearing on a monolithic flat mat slab foundation, all bearing on a plastic membrane to reduce friction and thus facilitate the independent twisting and tilting that may result from the predicted 6 feet of horizontal fault rupture displacement and 2 feet of vertical fault rupture displacement. An adjacent crescent-shaped building named the Student Athlete High Performance Center, currently under construction, and the retrofit of California Memorial Stadium are designed in strict compliance with the State of California's Alquist-Priolo Seismic Zonation Act (APZA).

The aim of the study is to evaluate the earthquake performance of two historical buildings located in Istanbul exposed to a M+7 earthquake expected to hit the city and, to propose solutions for their structural rehabilitation and/or strengthening. Both of the buildings are unreinforced clay brick masonry (URM) structures built in 1869 and 1885, respectively. The first building is a rectangular-shaped structure rising on four normal floors and the second one has an L shape with one basement floor and three normal stories. They survived the 1894, Ms7.0 Istanbul earthquake, during which widespread damage to URM buildings took place in the city [3]. No information could be reached whether and in what way they were affected by this earthquake. Although, there can be seen some cracks on some perimeter as well as secondary walls of the buildings. Determination of the site-specific performance assessment and retrofit design basis earthquake ground motion is achieved through deterministic seismic hazard assessment. The buildings are modeled and analyzed as a three-dimensional assembly of finite elements using SAP2000 v11 (Static and Dynamic Finite Element Analysis of Structures) [8] software package. The linear dynamic analysis procedure of FEMA 356 and ASCE41-06 [1, 2] is followed for the seismic assessment of the buildings. In order to improve earthquake resistance of the buildings, reinforced cement jacketing of the main load-carrying walls and application of fiber reinforced polymer (FRP) bands to the secondary walls are proposed.

The paper is devoted to historical masonry buildings protection against the destructive influence of earthquakes. Strengthening such buildings that were not originally designed to resist seismic actions became a common practice in structural engineering in Romania. Seismic retrofitting of the cultural heritage, especially of the historic buildings, requires compliance with the severe restrictions of the Romanian legislation related to the preservation of the original artistic and structural features. That's why the technical assessment, the strengthening followed by the rehabilitation of an old heritage building became an engineering "art" with a firm "scientific base". After a very short presentation on the evolution of the masonry buildings in Romania, the paper deals with the study of a prototype of such a building in Constanţa city, within which "The National History and Archeology Museum" is located. To perform the technical assessment of the above mentioned building a theory of damage and failure of unreinforced masonry walls was applied. This theory was conceived by the Romanian engineer Emilian Ţiţaru when he studied the behavior of masonry buildings in Karpoš district, after the July 26, 1963 Skopje earthquake. For the strengthening of the museum building the concept of "spectral position" was used. Some information on the use in Romania of the concept of "base isolation" is also given.

In this paper, the main results of an experimental, theoretical and numerical study on the rocking behaviour of full scale barrel vaulted structures undergoing cyclic horizontal loading is discussed. The main scope of the paper is to provide some evidence of the rocking mechanism experienced by these structures when subjected to horizontal forces. The comprehension of the behaviour of such structural systems is fundamental for their seismic vulnerability assessment, as well as for the design of any possible strengthening technique. Different strengthening solutions are presented and compared: traditional techniques, such as extrados thin concrete slab, or masonry spandrel wall; and an innovative solution with an extrados thin lime slab reinforced by means of glass fiber mesh. The experimental results are used to validate both numeric and analytical models for the prediction of the structural response of masonry vaulted structures subjected to rocking of the abutments, as well as for the proportioning of the strengthening solutions.

Unlike conventional concrete, High Performance Fiber Reinforced Cementitious Composite (HPFRCC) materials exhibit strain hardening behavior after first cracking. This unique characteristic translates into greater structural ductility and enhanced shear and flexural member responses. HPFRCC materials hold great promise for earthquake engineering applications, which has motivated researchers to explore their use for replacing traditional concrete in critical elements of a structure. To date, most research on the behavior of HPFRCC structural components has been experimental and only limited efforts have been made to develop HPFRCC constitutive models for computational simulation of member and system responses. This paper presents a validated plane-stress, orthogonal, mixed rotating/fixed-crack constitutive model that can be used for modeling the 2-D behavior of HPFRCC structural members and systems subjected to reversed cyclic loading.

As an approach to the problem of the seismic vulnerability evaluation of existing buildings using the predicted vulnerability method, analytical procedures are applied to produce vulnerability curves for different building classes. For some building types, mainly masonry structures, the development of those curves will be complicated and time consuming if a Finite Element-based method is used. Therefore, the Applied Element Method is used here to develop fragility curves for those challenging building classes. The incremental dynamic analysis of a 6-storey industrial masonry building built in 1906 in Montreal, Canada has been carried out using 14 sets of synthetic and real ground motions representing three M, R categories. Intensity and damage measures are pointed on the IDA curves at three structural performance levels, immediate occupancy, life safety, and collapse prevention, for each ground motion. The statistical analysis of those points is then carried out to develop fragility curves for the masonry building at each performance level. To show the effect of the building typology, those fragility curves are compared with the fragility curve provided by NIBS in HAZUS-MH MR1 Technical and User's Manual for masonry buildings.

This paper compares the nonlinear seismic response of an 10-story reinforced concrete shear wall building located in Montreal, Canada that was designed according to four different editions of the National Building Code of Canada: 1975, 1985, 1995 and 2005. The design seismic loads and detailing requirements used for the four designs are discussed and compared. The study focuses on the shear force demand in the wall and on the potential for inelastic flexural response in the upper levels due to higher mode response. Two different 2D models are used in the study: a plane stress finite element model using the VecTor2 software and a fiber element model using the OpenSees program.

Wood and/or iron tension members in the form of either tie bars (both wood and iron) in historic masonry arches or externally applied tension rings (iron) of masonry domes have been used in historic buildings especially in the areas that are vulnerable to severe earthquake excitations. Earthquake reconnaissance investigations revealed that masonry arches and domes with tension members showed satisfactory behavior under earthquake loading. To investigate their effectiveness on behavior, three case studies are analyzed from Turkey. The first one is a 16^th century mosque having major structural cracks on its 25m-diameter brick masonry dome. Combined steel and CFRP sheets as tension members at several dome levels are proposed as a seismic retrofit measure. Significant improvement is obtained in response, leading to maximum 60% reduction in stresses. The second case study is a stone masonry vault having damaged wooden tie bars. Similarly, numerical results show that stresses as well as deformations can be reduced up to 50% by replacing the old ties with the new wooden tie bars. The third one is a 508-year-old tomb having a nearly collapsed brick masonry dome. At the support level of the dome, externally applied steel rings were used as tension members to limit stresses and deformations. Similar amounts of reductions in stresses are obtained. This study also shows that both traditional and contemporary retrofit strategies can be used in the same project when required.

Floor diaphragms may provide an effective solution for reducing the seismic vulnerability of masonry buildings. Unfortunately, diaphragms are usually not present in historical building with wooden floors but often they are non present even in old R/C buildings where floors were made without shear reinforcement. A possible strengthening technique could be based on the application of a thin concrete plate reinforced with a welded mesh. In order to reduce the thickness of the plate, some suitable solutions may be obtained by using Fiber Reinforced Concrete (FRC) since the minimum concrete cover is no longer required because the reinforcement (fibers) is spread all over the concrete matrix. The adoption of FRC floor diaphragms is proposed and discussed in this paper; the early results from a preliminary numerical study are analyzed in order to asses the feasibility of this new strengthening technique and better organize an experimental program that is currently in progress.

A study was carried out on the assessment of the residual strength and lateral/seismic load capacity of reinforced concrete columns after fire exposure. The mechanical properties of concrete after fire exposure, such as residual tension and compression strength, stiffness and constitutive responses, were reviewed. A nonlinear finite element analysis program, developed for three-dimensional reinforced concrete structures, was employed to estimate the post-fire axial and lateral performance of two full-scale reinforced concrete columns, tested previously at the National Research Council Canada. The results of the axial load-deformation response obtained from the analysis were compared and verified successfully with the test data. The lateral load and deformation responses of the specimens were then estimated using the numerical program. The results showed that both the lateral/seismic load capacity and ductility of the two reinforced concrete column specimens decreased noticeably due to the fire exposure. Studies are suggested on fire damage mitigation and post-fire shear strength recovery of reinforced concrete columns.

In this paper a new enhanced Nonlinear Static Procedure (NSP) is presented and evaluated. The steps of the proposed methodology are quite similar to those of the well-known displacement modification method (ASCE 41-06). However, the determination of the characteristics of the equivalent single degree of freedom (E-SDOF) system is based on a different concept. Specifically, the E-SDOF system is determined by equating the external work of the lateral loads acting on the multi-degree of freedom (MDOF) system under consideration to the strain energy of the E-SDOF system. After a brief outline of the method, a series of applications to single storey R/C buildings is presented. Considering the results obtained by nonlinear time-history analysis as the reference solution, a comparison between the proposed and the conventional NSPs is conducted, which shows that the proposed method gives, in general, better results.

Steel bar fracture of reinforced concrete (RC) column under strong cyclic load has been tested. On the basis of the test results, the steel bar fracture of specimen is considered as the very low cycle fatigue behavior and the calculation method of steel bar fracture is derived by the use of Coffin-Manson equation and the Palmgren-Miner rule. The obtained damage ratio equation of steel bar fracture can be easily applied to the seismic response damage analysis of multi-story RC frame under extremely strong ground motion. By the use of the derived damage analysis method, the effects of design conditions on the seismic response damage of RC frame are investigated.

The trend in construction leans toward maximizing land usage by constructing buildings as close to each other as possible. Without serious and careful consideration this could lead to damage due to structural pounding. The objective of this research therefore is to investigate by stimulation the pounding effect between two adjacent buildings caused by three levels of ground acceleration, as well as the utilization of liquid dampers to mitigate the effect of structural pounding. The two investigated buildings stand, respectively, 171 meters and 45 stories high, and 155.5 meters and 42 stories high. First, the pounding forces, displacements, and accelerations at the 40^th story of the two buildings were investigated. The results show that maximum displacement increased, and abrupt pulse accelerations occurred intermittently, due to the pounding effect. The dampers and gap elements were then simulated at three locations per floor in two cases. In Case-1, 63 liquid dampers were simulated, three on each even floor from the 2^nd to the 40^th floor. In Case-2, 33 dampers were simulated at the same locations on each even floor from the 30^th to 40^th floor. In both cases, due to the dampers, the maximum displacements of one of the buildings under three levels of ground acceleration were reduced by approximately 80%, 60%, and 90%, respectively. Moreover, pulse accelerations were eliminated, which in turn reduced the impact forces on the structures.

Nowadays, various methods of passive energy dissipation are widely used in designing structures. Using shape memory alloys is one of these methods. Their super elasticity properties can be utilized to design lateral load resisting systems. An innovative system consisting of SMA and cable is introduced in this paper. The system behavior under dynamic loading is analyzed and described in detail. Finally, the numerical study is conducted on the compound system and the results are qualitatively and quantitatively compared with the conventional bracing system.

This is an experimental study on a new seismic retrofitting method of a longitudinally over reinforced reinforced concrete beam-column joints. The objective of the retrofit is to increase the story shear capacity with externally placed CFRP composite to ensure a strength of beam-yielding mechanism by shifting the critical part from the joints to the beam ends. Four one third scale reinforced concrete interior beam-column joint subassembleges were constructed and subjected to statically cyclic lateral loading simulating earthquake. The main parameter of the test is with and without a retrofit. Externally placed CFRP composite for seismic retrofit of beam-column joints has been considered as challenging because the presence of transverse beams and floor slab limit the accessibility to the joint in actual three-dimensional frame. The method in this study overcomes the difficulty by placing only four CFRP bundled strands vertically at the four corners of a column. Due to its simplicity it is applicable to most types of three dimensional beam-column joints with transverse beams and floor slab despite of architectural restrictions. Test result shows that a joint shear failure was altered to a beam-hinging mechanism and the story shear increased to the shear at flexural capacity of beams. It is verified that the new retrofitting method is one of the practical solutions for seismic retrofits of critical beam-column joints.