Improving the Seismic Performance of Existing Buildings and Other Structures 2015

Building 431 at the Puget Sound Naval Shipyard & Intermediate Maintenance Facility in Bremerton, Washington houses the primary machine shop used to maintain the Navy ships and submarines on the West Coast. The historic 640,000 square foot steel, concrete, wood, and masonry building was constructed in 1935, underwent significant additions during World War II, and has been continually modified since that time. KPFF was the structural engineer on the design team tasked by the Navy to design seismic strengthening for the building that would satisfy the enhanced performance objectives required for this mission-critical structure. The design for the seismic retrofit of the structure began in 2013 using the ASCE/SEI 41-13 Standard (ASCE-41). KPFF employed several interacting design methods to achieve the required performance goals, including nonlinear response history analysis (NLRHA), selective weakening of existing perimeter walls, and 71-foot-long buckling restrained braced frames (BRBFs) added to the building’s exterior.

The award winning Starbucks Reserve Roastery & Tasting Room serves as Starbucks flagship store in Seattle and, per Starbucks CEO Howard Schultz, “reflects everything the company has learned about coffee”. The creation of the Reserve Roastery & Tasting Room required that the existing 1920s auto row building with the adjacent parking garage undergo both a full life-safety seismic upgrade as well as tenant improvements required to install the new roasting equipment, retail fixtures/finishes and an independent restaurant.

This paper discusses the background and methodology associated with the seismic upgrading of a large multi-unit residential project. The advantages of using a rigid diaphragm analysis for the design and retrofit of this type of structure are demonstrated. The development of a computer spread sheet analysis tool greatly aided in the design of the retrofit project. Detailed construction management allowed for an efficient system, which provided for continuous occupancy of the individual units during the construction project, resulting in significant cost savings.

This paper presents the three-dimensional finite element analysis of squat RC walls using a continuum constitutive model for concrete developed at ANATECH. The concrete model is based on the smeared-cracking concept and an elastic-plastic formulation that permits the simulation of cracking and other particular response characteristics of concrete. The laws governing the normal and tangential stresses on a crack are suitable for the simulation of shear failures and crack closing and re-opening under load reversals. Finite element models have been developed to reproduce experiments on squat walls found in the literature. These tests were conducted on walls with rectangular and non-rectangular sections subjected to cyclic lateral loading. The finite element models provide a good representation of the nonlinear response and shear failure of these walls. Results of a blind simulation of a five-story shear wall building tested on a shake-table, in which a diagonal shear failure was well predicted, are also presented.

Vertical collapse performance of existing multi-story buildings has been investigated through field experiments and computational simulations. Four reinforced concrete (RC), two masonry, and three steel frame buildings have been tested in recent years. During the experiments, single or multiple first-story columns were physically removed from the buildings, which were demolished immediately after the experiments. Due to lack of full-scale building test data, the data produced in this research has been a valuable addition to the state of knowledge on gravity collapse of buildings. The main goal of field experiments was to simulate the structural dynamic and static response of buildings that may experience collapse after sudden loss of column(s) due to, say column shear failure in a reinforced concrete building. Another objective was to investigate how the internal forces are redistributed within the building after each column is removed. In this study, two- and three-dimensional models of the buildings were used to simulate the building performance and collapse potential. Computational models and simulations were examined and compared to the experimental data from the field tests. It is noted that the current nonlinear modeling and progressive collapse assessment guidelines (GSA 2013) use nonlinear analysis parameters found in the seismic assessment of existing buildings (ASCE/SEI 41, 2013), e.g., performance limit states and m-factors to evaluate nonlinear performance. This study showed robustness of existing buildings and contribution of different structural components to collapse resistance.

The research presented here seeks to advance nonlinear analysis of reinforced concrete flexure-controlled walls to improve understanding of the earthquake behavior of these components as well as to provide tools to support performance assessment. Previous research shows that fiber-type force-based beam-column elements can provide accurate simulation of the cyclic response, including drift capacity, of walls exhibiting flexure-controlled response. Accurate simulation of drift capacity and flexural failure modes requires regularization of concrete material response in compression and specification of a strain at which reinforcement loses strength due to buckling. For walls with high shear stress demand, which are not shear critical and exhibit flexural rather than shear failure, shear influences the flexural failure mode. Flexural walls with high shear exhibit a compressive-shear failure that is less ductile than a compression- or tension-controlled flexural failure. Compression-shear interaction and the compression-shear failure mode cannot be captured by the fiber-type beam-column element model. Here, flexure-shear interaction and compression-shear failure are investigated using continuum analysis. The results of continuum analyses indicate that high shear stress demands result in a diagonally oriented strut across the wall height that elongates the compression zone beyond that determined by a plane-sections-remain-plane analysis; elongation of the compression zone is exacerbated by increased wall cross-sectional aspect ratio. This response mechanism results in walls with high shear stress demands being vulnerable to web and boundary element crushing, which induce the compression-shear failure and compromise drift capacity.

Shear failures in reinforced concrete (RC) or reinforced masonry (RM) components can negatively affect the lateral strength and inelastic deformation capacity of building structural systems subjected to cyclic lateral loads. Such failures can occur in both old and new construction. The determination of the safety of RC and RM structures critically hinges on the capability to capture the strength and stiffness degradation induced by shear failures. This study uses nonlinear truss models to capture the response of shear-dominated RC columns and RM walls under cyclic loading. The material laws for the concrete/masonry material and for the steel reinforcement and the procedure to establish the geometry of a truss model are described. The modeling scheme is validated using the results of quasi-static and dynamic tests on reinforced concrete columns and reinforced masonry walls. The combination of accuracy, conceptual simplicity, and computational efficiency establish truss models as an attractive method of assessing the performance of shear-critical structural components and systems.

Historic and heritage have sustained severe damage and collapse in recent earthquakes, including in Italy (2009), Haiti (2010), and New Zealand (2011). The same has been in case in California in previous earthquakes. The main vertical and lateral load bearing members for these buildings are typically comprised of unreinforced masonry walls. These walls have experienced both in-plane and out-of-plane failures leading to the collapse of the structures. Given that the walls have little lateral capacity, it is critical to limit the input forces acting on them. In addition, these structures do not have a well-defined load path or diaphragm for seismic loading. A proposed mitigation strategy combining seismic isolation and superstructure intervention is discussed to address these deficiencies. Advanced nonlinear global and local finite element analysis is used to assess the efficiency of the proposed retrofit. The proposed method significantly reduces the level of seismic excitation acting on the existing walls and limits the superstructure retrofit, and thus preserves the historical features of the structures. Application of this technique to Miragoane Cathedrals in Haiti is presented construction.

As a result of the Mineral, Virginia earthquake on August 23, 2011, a number of historic masonry structures throughout the Baltimore-Washington, DC area sustained varying degrees of damage. Following the earthquake, Keast & Hood had numerous opportunities to provide structure engineering services as part of the post-disaster response, assessment, and recovery of historically sensitive structures. This paper provides a case study of a successful earthquake recovery and reinforcement project at the Sherman Building in Washington, DC.

Previous experiences exposed the urgency to re-think the methodological and technical approaches to seismic vulnerability of historic buildings, on the grounds of the adverse impact induced by the inadequacy of preventive measures applied in the past often too intrusive, cost-inefficient, and unreliable. This paper presents a new integrated methodology, developed within the European project NIKER, which establishes a wider, multi-disciplinary framework of activities including essential steps complementary to the execution of interventions. Such methodology formalizes four different interrelated phases namely the investigation, intervention, evaluation, and management phases. The paper closely explores the intervention stage providing a review of the main techniques developed and tested during the project. More specifically, it discusses the developed technologies and tools including optimum interventions for vertical and horizontal elements and building connections as well as advanced instrumented dissipative devices. The impact of the project results on the expert and non-expert communities is also discussed.

The Pacific Earthquake Engineering Research (PEER) Center has expanded its Tall Building Initiative project to include the seismic performance of existing tall buildings. A candidate 35-story steel building with representative details from that era was analyzed. Pushover analysis and nonlinear dynamic response history results for the as-built building are discussed in a companion paper. In this paper, a potential retrofit approach using viscous dampers is presented. The performance criteria for the retrofit focused on reducing story drifts and accelerations to promote continued occupancy in moderate earthquakes. The retrofit feasibility study starts by selecting damper locations within architectural constraints. The overall effective damping ratio is calculated in order to satisfy a target roof drift limit based on the pushover analysis of the existing building. Three conventional damper placement methods are proposed, and the structural responses including story drift ratio, floor acceleration, and damper responses are compared. Possible improved schemes are investigated taking into account of performance-related and cost-related factors. In the end, a refined damper design scheme is proposed based on an overall cost-benefit analysis.

This paper presents a new retrofit method that employs gravity-frame connections to improve the seismic performance of buildings by enhancing the lateral-force resisting capacity of conventional shear-tab connections. In the retrofit method, proprietary T-stub flange connectors used in the Simpson Strong-Tie Strong Frame Special Moment Frame are installed adjacent to the shear tab connections to create a ductile partially restrained beam-to-column connection. Beam flanges and buckling restraint plates are used to force the reduced-width segment of the T-stub stem into high-mode buckling and to act as a “structural fuse” in an earthquake. The collapse safety and seismic serviceability performance was predicted for a set of archetypical office buildings with ductile or non-ductile (pre-Northridge) moment connections by employing the FEMA P-695 and FEMA P-58 methodologies. The results indicated that the seismic collapse safety and serviceability performance of retrofitted buildings was generally superior compared to conventional buildings. The retrofit method decreased interstory drifts and reduced repair cost and downtime, although retrofitted buildings were stiffer and experienced higher roof accelerations in some scenarios.

The 1994 Northridge earthquake caused widespread damage to steel moment-resisting frames including brittle fractures of beam-to-column welded moment connections. The damage was in the form of brittle failures at the interface of the beam and column members and was detected in multi-story buildings. Improvements to these pre-Northridge existing connections are often required as part of an overall strengthening scheme, particularly when higher performance levels are desired. To improve the behavior of moment resisting connections, the SidePlate connection was designed and began to market as an alternative moment connection. The SidePlate connection technology uses a pair of parallel full-depth side plates to connect the beam to the column, thereby eliminating the traditional welded connection between the end of the beam and the face of the column flange. While the SidePlate technology has been largely used in the construction of post-Northridge buildings, its application in the retrofitting of existing buildings has been limited to date. In this paper, a new generation of SidePlate connections is proposed, which is applicable for retrofitting purposes and can improve the performance of existing steel structures. It is believed that the new technology may lead to the best way for retrofitting existing building moment frame systems instead of adding concrete shear walls and/or bracing elements. The proposed detail aims to minimize the disturbances of existing building usage situation and at the same time improves the performance of the system by increasing the rigidity of panel zone region and the stiffness of the beam segment between the column face and plastic hinge location. A case study including two multi-story steel moment frame structures was conducted to show that the proposed technology can largely upgrade the performance level of existing structures. Nonlinear analysis was performed to evaluate the vulnerability of the existing structures first, then the proposed detail was implemented to the connections, and new performance levels were obtained by means of nonlinear static analysis. The results showed that the plastic hinges are always formed in beams instead of the columns. It has also been shown that the application of the proposed details reduces the target displacement and improves the performance level of the structures. It can be concluded that depending on the performance level of existing buildings, the proposed detail might be considered as an efficient and optimized way of retrofitting those structures.

Backbone curves were constructed following the procedures of ASCE41-07 and the ASCE41-13 for retrofitted reinforced concrete columns and masonry wall, which were previously tested until receive severe damage. Carbon fiber reinforce polymer (CFRP) sheets and anchors, for jacketing in columns and diagonal tension ties on the masonry wall; and mechanical splices, providing continuity to reinforcement; were used for retrofit techniques. ASCE41-07 and ASCE41-13 provisions are compared using these backbone curves by shear resistance values and ductility, where it was found that ASCE41-07 provisions are adequate for new structures and ASCE41-13 provisions for retrofit. Then, idealized force-displacement curves and elasto-plastic curves, based on the ASCE41-13 backbone curves, normalized with respect to load at yield obtained from the idealized curves and converted data is presented to be use in computer models. These idealized curves are aimed toward calculating the seismic vulnerability of various structures using the state-of-the-analytical procedures and providing test data that will help designers to make decisions regarding the use of innovative techniques for rehabilitation of structures. Such information is needed for fully implementing performance based seismic design procedures.

According to a Los Angeles Times report in Oct. 2013, by the most conservative estimate, as many as 50 old concrete buildings in the city of Los Angeles would be destroyed in a major earthquake, exposing thousands to injury or death. To address this concern, the City of Los Angeles recently proposed instituting what are arguably the most ambitious seismic safety regulations in California’s history; regulations that would require building owners to retrofit thousands of building deemed to be at risk of collapse during a major earthquake. Non-ductile concrete buildings built before 1980 were singled out as one of two particularly vulnerable structural types requiring attention. This paper presents a case study of seismically retrofitting a historic concrete building located in Los Angeles, California. Designed in 1916, the building originally housed the Willy’s Overland Company car dealership and assembly plant, which later became a Desmond’s department store warehouse. After the retrofit, the five-story warehouse will be transformed into high quality, creative office space with a ground floor cafe and the addition of a 7,000-square-foot sixth floor that will bring the total size of the building to 82,000 square feet. The retrofit project is currently under construction with full occupancy expected in the summer of 2015. When it is complete, it will be the first of many potential renovations of historic properties located in the South Park district for creative office use. This case study presents an innovative but rigorous approach taken to enable the addition of a story to the existing building by not exceeding the gravity load and lateral force change triggers in Chapter 34 of the 2011 Los Angeles City Building Code necessitating retrofit. Although demonstrated to not be required by code, a seismic retrofit was nevertheless instituted; this while continuing to ensure that the changes in force effects in retained existing structural members did not exceed code retrofit triggers. All structural modifications made since the building was originally constructed using very low strength concrete were considered in the evaluations and retrofit design.

Protection of cultural heritage buildings against strong seismic events is one of the most challenging tasks modern engineers are called to tackle. Masonry structures are complex with regional and historical diversities rendering extremely difficult defining generalized rules. A holistic approach that involves interdisciplinary collaboration and a full package of engineering from monitoring to testing is a necessity. The sources for assessment, strengthening, and preservation are not enough for the entire inventory of heritage buildings, thus there always exists need for conducting risk studies to estimate the seismic risk these structures are exposed to. The main ingredient of seismic risk studies is the definition of the structural limit states, which is one of the most challenging topics since the historical structures rarely possess similarities among them while their response is characterized by complex interaction of structural components. This paper presents a scientific project funded to contribute to the mitigation of seismic risk in the historical peninsula of Istanbul where Eastern Rome, Byzantine, and Ottoman structures populate almost every street. A complete approach has been followed in the project, the main activities of which consist of creating a wide strong ground motion and ambient vibration network, building and testing large-scale specimens to define limit states of the masonry heritage structures and combining the monitoring an testing findings with analytical modelling tools. The project resulted in a master plan in which steps to be taken to protect the existing heritage buildings in the historical peninsula of Istanbul is proposed and discussed.

Historic preservation allows society to maintain and keep relevant for future generations the buildings and neighborhoods that have played a meaningful role in our past. Preserved buildings can range from humble residences to grand monuments. Allowing continued use and reuse while retaining character defining features of these older buildings requires different building code considerations than those used for non-historic buildings. Fundamental to historic preservation is a balance between maintaining existing historic materials, building systems and configurations, and the need to make alterations or repairs to allow continued use. California is unique in that it has an adopted building code specifically developed for historic preservation. This paper discusses some of the ways that the California Historical Building Code (CHBC) can be used to preserve existing historic buildings, while also presenting some of the more commonly misunderstood and misused provisions so that readers can gain a better understanding of the correct use the CHBC. Several case studies are presented to illustrate the intent and use of the CHBC. Also presented are recommendations for future improvements to existing CHBC language to ensure that the intent is clear, with a focus on seismic concerns and upgrades. This is the second of two companion papers that address the CHBC; the first paper provides an introduction to the CHBC, discussing history and intent.

California is unusual in that it has developed and adopted a building code specifically intended for historic preservation. The California Historical Building Code (CHBC) was developed nearly forty years ago in response to the problem that “restoration is frequently made difficult by the unnecessarily rigid interpretation of building…codes”. Despite the passing of significant time, many engineers and architects are still completely unaware of the existence of the CHBC and its context in the suite of California codes. Even those aware of its existence are sometimes prone to misconceptions regarding its content and use. This paper will discuss the history of the CHBC and its purpose and intent. A summary of use of the CHBC will be presented, along with its application — and its differences with the regular code — for repair, additions, and alterations; change of use; and seismic upgrades. This is the first of two companion papers that address the CHBC. A complimentary paper provides examples of beneficial use of the CHBC and cautions regarding potential misuse.

When a building with shallow foundations experiences a seismic event, the footings can uplift. This rocking behavior can have a profound impact on the building response. Specifically, allowing the footings to uplift can significantly reduce shear deformations in the lateral system. We validated this concept through our design and analysis of the San Francisco War Memorial Veterans Building. The results of this case study can be valuable in evaluating, retrofitting, and designing buildings in areas of high seismic risk.

Bowles Hall is a reinforced concrete building of approximately 55,000 square feet on eight levels. The structure was designed in 1927 as the first residence hall in the University of California system. Designed by the architect George W. Kelham in the Collegiate Gothic style, the building is designated a landmark for the City of Berkeley and is listed in the National Register of Historic Places. A western trace of the Hayward earthquake fault passes underneath two corners of the building. In 2015, the renovation and restoration of the structure plus the construction of an addition was undertaken to revitalize the building’s character and usefulness. The new work revises the dormitory room layout to include bathrooms within units, adds wheelchair accessibility, replaces or upgrades all building utilities, restores and protects historic features, corrects life safety deficiencies, restores dining, and adds conference capabilities. The renovation and retrofit are being carried out through a public-private partnership, and the dormitory will re-open as a coeducational “residential college.” As described in a recent newspaper article, there will be “new keepers of the castle”. The remodel affords the opportunity to address remaining seismic deficiencies. Selective retrofit work had been done in 1977, and measures to accommodate earthquake fault-offset were constructed in 2009. Structural and seismic measures in the current construction include addressing discontinuous structural walls and constructing new building spaces, elevators, and stairways in a way that augments seismic resistance. Non-structural retrofit work includes developing secure attachment of historic tiles on the steeply pitched roofs and providing support for existing historic ceilings in the main dining and common rooms. Challenges of the project include a number of unique structural details, and development of an appropriate analysis strategy for a hillside structure in a location of extreme seismicity.

A six-story hospital stair tower with a single level of basement, integrated within an existing two-story administration services structure, provides emergency egress and access between two acute care wings of a hospital. The tower is located at the corner of an L-shaped plan. The tower and adjacent hospital wings are separated from one another by a two to three inch gap. A peer reviewed nonlinear analysis of the structure identified the possibility of global instability due to pounding between buildings, potentially leading to collapse of the stair/elevator tower. In order to accurately model realistic behavior, we explicitly modeled pounding in our analysis. Additionally, we modeled the effect of rocking behavior and sliding foundations. ASCE 41-06’s Nonlinear Dynamic Procedure permitted a minimal retrofit for tower, significantly reducing projected construction cost and schedule relative to our previous design based on linear analyses, while still satisfying SPC2 requirements.

An increasing number of high rise steel buildings, particularly of the “pre-Northridge moment frame” era, are being evaluated and retrofitted in the San Francisco Bay Area. In addition to addressing the well understood vulnerabilities associated with the moment frame connections, the evaluations are also frequently identifying apparent column deficiencies when applying ASCE 41 criteria. ASCE 41 currently classifies any steel column with an axial compression ratio greater than 0.5 as force-controlled, which does not permit any flexural yielding. Nonlinear dynamic analyses of three case-study high rise steel moment frame buildings typical of the “pre-Northridge” era demonstrate that these force-controlled criteria cannot be satisfied for design level events, and frequently govern the performance measure prior to expected onset of the pre-Northridge moment frame connection failure. However, examination of column results typically indicates that plastic rotation demands are extremely low (<0.01 radian) with axial compression ratios less than unity. Other standards, such as the New Zealand Steel Structures Standard (NZS 3404), permit limited flexural hinging in columns with axial load ratios of up to 0.8. Recent testing at the University of California San Diego indicates that the force- controlled limitations of ASCE 41 are generally overly conservative for seismically compact steel columns, with little evidence of significant strength or stiffness degradation. The testing also suggests that the ASCE 41 plastic rotation limits may be non-conservative for columns with low levels of axial compression. Based on a review of other national standards, testing and the research used to derive the force-controlled limits in ASCE41, the authors propose a set of alternative modeling and acceptance criteria for steel columns.

The seismic renovation of the historic 1932 Clinical Sciences Building on the UCSF Parnassus Campus will be examined. When the renovation is complete, the seven story steel framed structure with board-formed concrete façade will serve as functionally critical office space for the Moffitt Hospital staff. Because of the linkage with the hospital UCSF mandated that higher than seismic performance be achieved, but at a cost similar to conventional construction. The retrofit concept selected uses cast-in-place post-tensioned concrete shear walls with external buckling restrained brace dampers. The scheme was selected on a “best value” basis after evaluating several schematic-level designs. The paper will emphasize: development of the project-specific design criteria, application of nonlinear response history analysis techniques, performance-based detailing of articulation joints between walls and floors, and seismic interface considerations related to adjacent buildings.

The seismic remediation of pre-Northridge steel moment-resisting frames has been primarily focused on resolving the lack of ductility of beam-column connections, with particular attention to the area between the beam bottom flange and column. In contrast, much less attention has been focused on possible problems with welded column splices of pre-Northridge moment-resisting frames. In fact, observation of column splice failures in seismic events has been infrequent. This paper will address potential column splice connection issues with two recently evaluated pre-Northridge steel moment frame structures, including a mid-rise and a high-rise example. The paper will focus on these main issues: existing evaluation and acceptance guidelines for pre-Northridge column splices, fracture mechanics considerations, column splice demand evaluation methodology, column splice weld specimen removal and testing, and splice weld remediation.

Welded steel moment resisting frames with non-ductile beam-column connections are common among high rise buildings and have been studied at length. What is often under-emphasized is the effect that non-ductile column splices may have on the expected seismic performance and collapse potential. There is also room for improvement in common approaches to improving these buildings that leverages detailed nonlinear response history analysis to foster effective yet economical retrofit design. This paper is a case study on a 17-story office building constructed around 1975 and which has recently been retrofitted. Details of the analysis and subsequent design are discussed noting discoveries that were somewhat surprising. Illustrations of the design approach and the effect of the retrofit are shown.

Buildings with concentrically braced frame (CBF) lateral force resisting systems constitute a large proportion of existing steel infrastructure in seismically vulnerable regions. However, many were constructed in the era preceding critical milestones in seismic design, including the codification of capacity design and geometric limits on members of the seismic resisting components. These are included in current design of special CBFs, but the engineering community has recognized the vulnerability of older frames. Here, these are termed nonductile CBFs (NCBFs). International research collaboration was undertaken to identify the scope and scale of deficiencies, evaluate as-existing performance, and develop and validate minimally invasive retrofit schemes. The research described herein focuses on experimental evaluation of NCBFs. Initially, frames were tested to simulate the as-existing condition. Then, retrofit schemes that were both practical and effective were implemented. The results show the retrofitted frames have improved performance.

A full-scale multi-wythe unreinforced masonry (URM) wall constructed with a parapet and a flexible diaphragm was subjected to out-of-plane loading on a shake table to investigate the seismic behavior and vulnerability of older existing URM buildings. Several common retrofit techniques were implemented in the specimens to assess their effectiveness. This paper describes the testing program and presents key experimental results, including the hysteretic behavior of the parapet and demands in the floor-to-wall connections. The URM wall sustained shaking consistent with the 2011 Virginia earthquake with minor damage but failed when subjected to a ground motion recorded in the 2011 New Zealand earthquake scaled to a peak ground acceleration of 0.36g. An unexpected sliding failure was observed at the connection of the floor diaphragm to the wall. A comparison of the experimental data and results of analysis of numerical models of the timber diaphragm, floor-to-wall connections and masonry walls indicates the out-of-plane response of URM assemblies can be well predicted.

In recent years, there is an increasing need to quantify earthquake-induced losses throughout the expected life of a building in order to evaluate alternative design options such that we can minimize repairs in the aftermath of an earthquake. This paper discusses an analytical study that quantifies the expected economic losses in a portfolio of archetype steel frame buildings designed with perimeter special moment frames or special concentrically braced frames in urban California in accordance with current seismic provisions in the U.S. The expected economic losses associated with repair are computed based on an established loss estimation framework within the context of performance-based earthquake engineering. It is shown that repair costs in the aftermath of earthquakes vary significantly depending on the employed lateral load-resisting system, seismic design considerations as well as the analytical model representation of the archetype frame building itself.

During moderate seismic events, it is local masonry failures rather than global building responses that provide the bulk of damage. The paper suggests that one can understand the vulnerability to these local failures by analyzing collapses of vernacular structures, especially those that had occurred under non-extreme conditions. Four cases of collapse of unreinforced masonry buildings are presented in the context of the history of building accidents and empirical classifications of collapse mechanism. These accidents occurred in the absence of significant environmental loads and were the result of the walls’ geometric instability that had developed after adjoining demolitions interrupted the continuity of the building block. Aging, shortcuts during erection and especially the plane shape of the buildings’ structure contributed to the failures and should be given a larger weight in seismic risk analysis. Evaluations of non-extreme condition may help lead to efficient solutions of retrofit of large classes of buildings.

Past earthquakes have shown that seismic events may incur large economic losses in buildings. FEMA P-58 provides engineers, a practical tool for the performance seismic assessment of buildings. In this study, FEMA P-58 is applied to a typical Italian pre-1970 reinforced concrete frame building, characterized by plain rebars as steel reinforcement and masonry infills and partitions. Given that suitable tools for these buildings are missing in FEMA P-58, specific fragility curves and loss functions are first developed. Next, building performance is evaluated following a time-based assessment approach. Finally, the expected annual loss of the selected building is derived and compared with results from past PEER-PBEE applications to old RC frame buildings representative of the U.S. building stock.

Structural design consultants and building owners should rethink the way that they retrofit existing structures and develop new facilities in light of a recent seminal California lawsuit: the Myrick case. Many owners adhere to the platitude that they are automatically immune from legal liability if they choose to design, build or operate a structure in accordance with minimum building code standards. This concept was toppled by the published court opinion entitled Myrick v. Mastagni, when the trial judge, the jury and the court of appeal all found that a building owner can have legal liability for the poor seismic performance of a structure even if its management and use is in accordance with the minimum standards of local ordinances and building codes. A statute, ordinance or regulation ordinarily defines a minimum standard of conduct and mere adherence to that minimum standard “does not preclude a finding that a reasonable person would have taken additional precautions under the circumstances.” How a building owner can manage this seismic risk in the legal arena will often involve early seismic performance target choices under the auspices of ASCE 7-10 and ASCE 41-13. In most scenarios, the owner’s structural design consultant will provide essential technical input on the predicted seismic performance of the facility in light of the functional uses selected by the owner, which in turn can determine the legal risk profile that the owner will assume when proceeding with the project. In most scenarios, the design professional will need to describe the costs and benefits of designing above code minimum thresholds. This usually involves the often painful consideration of spending more than the bare minimum for improved structural performance. Practical approaches to solving this problem are illustrated in a hypothetical San Francisco project where the developer wants to retrofit and reconfigure an existing urban campus, and its structural consultant helps the owner manage its seismic risk inherent in the project.

Structural design consultants and building owners should rethink the way that they retrofit existing structures and develop new facilities in light of a recent seminal California lawsuit: the California Supreme Court opinion in the Beacon case. Many design professionals adhere to the platitude that they are automatically immune from legal liability to a party with whom they have no contractual relationship, who claims he or she was injured by poor performance of the designer’s facility after completion of construction. The California Supreme Court toppled this platitude when it published the Beacon opinion (2014), holding that design professionals can have a non-statutory duty to avoid design flaws that may harm third parties with whom they have no contractual relationship. Most courts will extend the logic of this rule to structural consultants whose flawed designs cause poor performance in a foreseeable earthquake. In this situation, choices by owner concerning the performance targets for retrofitted structures and new facilities can determine the legal risk profile of the design professionals. In a hypothetical San Francisco project where the developer wants to retrofit and reconfigure an existing urban campus, the structural engineer of record should consider what his or her testimony would be in the event that a retrofitted reinforced concrete (RC) structure fails to perform elastically in a service level earthquake (say peak ground acceleration on the order of 0.20 gravity) and bystanders are severely injured by spalling concrete and falling non-structural components (say HVAC assemblies) when it sustains a partial collapse. Following the Beacon opinion, most judges would allow the injured bystanders to allege that the structural engineer owed them a duty of care to avoid unacceptable performance during a foreseeable earthquake that was smaller than the 1906 San Francisco earthquake. Needless to say, the structural engineer’s ability to manage its risk in the legal arena is enhanced if he or she can truthfully testify that the design was intended to exceed the minimal standards of San Francisco’s building code in light of the owner’s choices for seismic performance targets specified in ASCE 7-10 and ASCE 41-13.

Case law has shown that in seismically active areas, owners of potentially vulnerable structures should have an understanding of the ability of their property to perform satisfactorily in foreseeable earthquakes. In the case of an existing building, that understanding should be informed by evaluations performed by structural consultants utilizing professional judgment augmented with available rating systems, guidelines and methodologies. The structural consultant should be able to answer important questions about anticipated seismic performance, including identifying specific vulnerabilities and available mitigation measures that improve seismic performance, which very often consist of partial, incremental, or vulnerability-based seismic retrofits. For new buildings, the structural engineer of record may be the one asked to provide such predictions for their own design, as well as options for improving the design’s anticipated seismic performance to meet the owner’s expectations. In their typical role, the structural consultant is an advisor with no authority to implement their recommendations. However, in the event of poor structural performance in an earthquake, the advice and actions of the structural consultant, as well as the building owner, will be scrutinized. While the engineering profession understands that a collapse prevention retrofit will not prevent property damage or possible injury, that “subtlety” may be lost on owners and injured parties in the post-event search for scapegoats. How can structural consultants simultaneously serve the public good by working to improve seismic performance of our building stock in a cost effective manner without becoming liable for foreseeable damage in an actual event?

Structural retrofitting targets to improve seismic performance of a building, however, it might be difficult for structural engineers to demonstrate and persuade building owners that the retrofitting is cost efficient without experiencing or at least expecting a real earthquake. There are three main reasons that contribute to this. First, earthquakes, as well as structure seismic responses, are random process in both time-wise and intensity-wise. It is difficult for engineers to explain the deterministic structural design or analysis results to non-engineering people, given the uncertainty nature of earthquakes. Second, owners are more interested in the fiscal loss or fiscally related issues, such as injury or usage down time, while engineers only focus on structural behavior. Third, once the minimum requirement in building code is met, there is no more incentive for owners to spend money in their structures. In recent years, there are great efforts to advocate performance based earthquake engineering (PBEE) and more resilient structures. Two of them are the FEMA P-58 project and SEAONC’s EPRS. FEMA P-58 (by FEMA and ATC) provides methodology for probabilistic structure seismic analysis and tools for estimating the monetary loss and down time. EPRS is a rating system of building seismic safety, repair and recovery, and it has already been adopted by Los Angeles City. Predictably, it assists local authorities to request retrofit on buildings and it may impact building seismic insurances rates. This study utilizes FEMA P-58 and EPRS to evaluate retrofit of a building selected from SAC Steel project. It demonstrates that FEMA P-58 is helpful for incorporating probability into the structural analysis and correlating the structure’s performance and fiscal loss. The benefit of retrofit can be demonstrated by the criteria either in FEMA P-58 or EPRS.

An engineer providing structural engineering design services for the seismic evaluation and rehabilitation of existing buildings and other structures may be subject to claims made for professional negligence if those facilities do not perform as expected. If professional negligence is proven, the engineer may be liable for costs caused by that negligence. For a professional negligence claim to be proven, the engineer must be shown to have failed to meet the “standard of care.” This paper presents the definition of the standard of care as determined by case law, and discusses the process used to determine the standard of care. It outlines instances or circumstances where and when an engineer may be seen as negligent in the engineering of seismic evaluation and rehabilitation of buildings and other structures, and how a practitioner may avoid or defeat such claims.

The last decade has seen growing interest in probabilistic portfolio-level (regional) seismic risk assessment. State-of-the-art methods build on established performance-based earthquake engineering methods for individual buildings, in combination with robust treatment of spatial correlations of ground motion intensity, building response, and collapse, which complicate the analysis significantly. Consequently, these methods are practically out of reach for many potential users. Relationships between advanced portfolio risk assessments and a second set of risk assessments that are based on the summation of risks for individual buildings are examined. Results for a sample region show that a simple sum of the risks for each individual building within a portfolio under-estimates the values of small frequent losses and over-estimates the values of large rare losses. Since their differences are systematic, a simplified procedure to estimate portfolio-level seismic risks based on assessments of individual buildings (or building types) within the portfolio is feasible in the future.

The paper provides a contribution for the assessment of economic losses in masonry buildings, following a component-based approach, to be implemented within the modern probabilistic seismic risk analysis. It is based on the computation of proper decision variables as the potential economic losses due to the direct repair cost, in order to improve the resilience to a seismic event. An application to a three-story unreinforced masonry building is illustrated, focusing on the computation of structural losses. Nonlinear dynamic analyses have been adopted, following the multiple stripe analysis method.

This paper is focused on assessing the earthquake induced horizontal floor accelerations in wood shear wall buildings. While building design codes have provisions for estimating horizontal seismic design force that might occur at different story levels in a building, these procedures are empirical and do not differentiate between various types of structural systems. The research discussed in this paper evaluates the floor acceleration demands in a variety of FEMA P-695 wood-frame shear wall index models, with different damping levels and earthquake ground motion characteristics. These computed floor acceleration demands are compared against the different design demands for rigid and flexible non-structural components as recommended in the seismic design provisions of ASCE 7. The results from this study show that for the wood-frame index models studied, maximum floor accelerations frequently occurred at first floor level, which is different than the height-wise distribution of acceleration demands computed using ASCE 7 design provisions.

In the past U.S. earthquakes, lay-in panel suspended ceilings have suffered significant damage. However, there has been scant evidence of damage to the drywall suspended ceilings. Consistent with such observations, the building codes in the U.S. have specific prescribed design requirements for lay-in systems; however, for drywall systems the codes typically refer to engineers to verify the design. Drywall suspended ceilings have been damaged in past earthquakes in Japan and in the U.S., leading to the question of whether the U.S. code language is adequate for the drywall systems. To investigate the seismic response of drywall suspended ceilings, a broad study was recently completed. The study was comprised of: (1) examination of drywall systems in the U.S. and abroad, (2) shake table testing of suspended drywall system, (3) static tests of the key components of the drywall system, and (4) finite element analysis of a drywall system. The investigation revealed that the drywall suspended ceiling systems are more robust that the lay-in panel units and thus can sustain much larger seismic event prior to experiencing damage.

Lay-in panel suspended ceilings have suffered significant damage and collapse in moderate and large earthquakes in U.S. and abroad. This has led to blocking of egress and financial losses and business interruptions. The building codes in the U.S. have been updated to incorporate design and installation requirements for these components. In recent years, the major grid manufacturers in the U.S. have used shake table testing to certify alternate installations. Shake-table testing of suspended ceilings as part of a grand challenge project in the U.S. to investigate the response of the building environment have also been completed. The authors have conducted static and shake table testing of components and systems with the following objectives: (1) development of seismic qualification test standard incorporating performance metrics and amplitude thresholds, (2) assessment of the prescribed code capacity provisions, and (3) estimation of the performance of ceilings of larger footprint not suitable for shake table testing. Experimentation included the direct measurement of force in grid members and correlation to member capacities. The main findings were confirmed in the authors’ survey of the seismic performance of the lay-in suspended ceilings following the 2014 South Napa Earthquake.

The FEMA P-807 (2012) guideline titled Seismic Evaluation and Retrofit of Multi-Unit Wood-Frame Buildings with Weak First Stories is a new approach for building retrofit. It goes beyond current building codes and standards by quantifying performance in probabilistic terms. This commentary provides an overview of the P-807 approach with emphasis on key aspects that users should be aware. The objectives are to provide design professionals and building officials with a better understanding of the P-807 benefits/limitations as well as important P-807 seismic safety implications that can be discussed with building owners so informed decisions can be made about the best retrofit approach for particular projects.

Applications of isolation/energy dissipation devices for the seismic protection of equipment and components in multistory buildings are limited, and experimental evidence on the effectiveness of these applications is lacking. This paper summarizes the developments of experimental studies to assess the seismic performance of different isolation/energy dissipation platforms for the protection of equipment under three-directional seismic floor accelerations of multistory facilities. The experimental studies consisted of earthquake simulation tests of different isolation/energy dissipation platforms under three directional shaking. The experimental studies included five different platforms based on energy-absorbing wire ropes, hinge-rubber bearings, lead-rubber bearings, among other isolation/energy dissipation mechanisms. The platforms supported full-scale equipment and simulated equipment with different properties; including relatively heavy and rigid simulated equipment and relatively light-weight tall frames that held computer equipment. The different platforms supporting a piece of equipment were subjected to seismic shaking that intended to simulate a variety of floor accelerations of different multistory buildings under earthquake shaking of varying intensities. This paper includes the summary of outcomes of the experimental studies and concludes on the performance of the platforms for the seismic protection of equipment under floor acceleration at different building levels, and discusses further research directions.

Architectural precast concrete (APC) cladding system is a critical nonstructural component of commercial real estate buildings. The design of this system is based upon the building code, which specifies both the design forces for components as well as the expected inter-story deflection that the system will be expected to accommodate. APC systems have gone through significant changes over the past thirty years, in particular with the changes in design displacement requirements during the 1990s, which significantly changed the displacement demands that the systems were required to accommodate. The Pathways project, part of the National Science Foundation’s NEES research initiative, conducted a series of experiments on architectural precast concrete (APC) cladding which was designed to modern building code requirements. A significant finding from the study was that the system performed well while loaded to inter-story deflections below the design deflection of the cladding. This paper will discuss the types of damage observed when the applied displacement exceeds the design deflection. Using the information obtained from the Pathways experiments, the authors will adjust the findings to provide performance expectations for extant APC systems with varying levels of initial design displacement.

Contained is a study into the effects of pounding on the collapse performance of midblock wood-frame “soft-story” buildings. Various pounding situations were analyzed, and it was confirmed that pounding can change the collapse risk when compared to the risk of the same building having no adjacent buildings. The key parameters affecting building response due to pounding are explained and implications for design and public policy are discussed. The objectives are to provide design professionals and building officials with a better understanding of the effects of pounding on the expected performance of retrofitted buildings as well as the benefits of systematic retrofit programs that upgrade adjacent buildings within reasonable timeframes to have similar relative strengths.

San Francisco’s mandatory soft-story building retrofit program names three alternative design criteria for the retrofits: FEMA P-807, ASCE 41, and IEBC Appendix Chapter A4. This paper presents example case studies on the retrofit of two buildings using the three alternative design criteria according to the San Francisco ordinance (total six example retrofits). The objectives are to provide design professionals with insights about: how the P-807 performance-based guideline differs from more traditional methods such as ASCE 41 and IEBC A4, the different retrofit outcomes that result from using the alternative criteria, and which criteria can best serve client needs.

Architectural precast concrete (APC) cladding is composed of separate panel units, each one with its own mass, stiffness, and natural modes. If a natural frequency of the panel is particularly low (< 20 Hz), the corresponding mode could be activated during an earthquake, creating amplification of accelerations in the panel and forces in the connections. To clarify this issue, a study of the dynamic characteristics of connected panels was performed. Numerical models of panels were created using SAP2000 and validated thorough experimental data from a seismic test on a full-scale building incorporating APC cladding. Since these models revealed able to predict the experimental frequencies of the panels, they were used to perform further investigations. Namely, a sensitivity study was conducted to determine the effects of the stiffness and location of the connections, geometry of the panels, and stiffness of the concrete on the dynamic behavior of the panels.

A full scale three-dimensional model of a consultation room is constructed and tested dynamically by using the shaking table facility of the University of Naples, Italy. The outcomes of the tests have been utilized to derive fragility curves based on a systemic approach. Simplified finite element models of the tested components are implemented in a commercial computer platform for numerical calibration and simulation of the dynamic response. It is demonstrated that simple models are able to adequately simulate the dynamic properties of sample medical components and can be employed in the earthquake response analysis of healthcare facilities. Preliminary studies on the fragility of rigid blocks highlight that PGA and PGV can be selected as good candidates for efficient intensity measures for rocking and collapse damage states, respectively.

Performance based design with seismic protection devices such as viscous dampers have fundamentally altered the landscape of earthquake engineering and design. Structures designed and built without such devices typically use a code-prescribed design that implies extensive structural damage, loss of operation, and likely replacement at design-level earthquake. In contrast, performance based design incorporating earthquake protection devices leads to a combination of best engineering practice and reducing life-cycle costs. These devices are robust, cost-effective, and have a proven exceptional performance record in past earthquakes. In most cases, initial cost of their utilization is neutralized by reduction in cost of other structural members. The long-term performance is the key parameter used for evaluation. Structures properly designed with these devices will likely only require minimum post-earthquake inspection and can be fully operational within hours of a seismic event. When utilized for critical structures, such performance reduces the need for use of natural resources by eliminating post-earthquake repair or reconstruction and thus improving the community resiliency. Example cases are presented.

This paper presents the seismic evaluation and retrofit design of an airport passenger terminal building, which was constructed in 1981. The main objective of the work was to evaluate and enhance the structural performance of the building to satisfy the “collapse prevention” structural performance level under the strong earthquake events, which are probable to occur rarely in the remaining lifetime of the building. The seismic retrofit design was carried out to enhance the structural performance, minimizing the potential of collapse during the strong earthquake events. As the 32-year old passenger terminal building has a relatively shorter remaining life, compared to a new building, it was decided to carry out seismic evaluation against the earthquake with the return period of 1,146 years (approximately 4% of probability of exceedence in 50 years), as opposed to new buildings that are typically evaluated for 2,475-year return period earthquake (2% of probability of exceedence in 50 years).

This study focuses on vibration-based system identification of an actual structure located in El Centro, California. The structure had already been subjected to four earthquakes with epicenters in close proximity and was to be demolished due to the extended damage. Four damage levels were introduced to the structure by gradually removing four perimeter infill walls. A series of dynamic tests were conducted in each damage state using an eccentric mass shaker. The ambient vibration of the structure was also recorded through an array of 60 accelerometers mounted on the structure. The system identification discussed in this paper was conducted using the ambient vibration recordings. Moreover, a preliminary finite element model of the building was created to estimate numerically the dynamic characteristics of the structure. These were compared to the properties obtained from the system identification. The results indicate that the frequencies estimated by the model overestimate those obtained from the system identification results, while the experimentally and numerically obtained mode shapes are in good agreement.

The results of four cyclic tests on full-scale beam-column joints with typical pre-1970s deficiencies are presented. The challenges incurred by the presence of a floor slab and transverse beams in retrofitting deficient specimens are often ignored, but are here fully taken into account in the experimental set-up. A realistic repair and retrofit scheme using carbon fibre-reinforced polymer (CFRP) sheets is proposed. The scheme aims to improve the ductility of the deficient joints, while providing continuity of the flexural strengthening through the joint. The results highlight that the proposed retrofit can successfully increase the ductility of the joint by activating the beams. The presence of the slab has a significant effect on the global behaviour of the sub-assembly, which ultimately does not reach failure in the beams due to the stiff slab limiting rotation. Despite significant pre-damage, the repair scheme is very efficient, with only minor differences in terms of initial stiffness and lateral strength compared to the retrofit.

Buckling-restrained braces (BRBs) are an important addition to the structural engineer’s seismic design toolkit and are in widespread use in high seismic regions throughout the United States. Recently, designers and researchers have begun considering alternative bracing configurations to capture the benefits provided by BRBs in a fundamentally different way. The buckling-restrained braced mast (BRBM) frame is one such alternative configuration. The BRBM frame consists of yielding BRBs in series with a stiff elastic wide-flange mast frame that is able to pivot about its base. This mast redistributes brace forces between stories, fundamentally changing the kinematics of the system, producing a more uniform distribution of interstory drift, and eliminating the possibility of inelastic weak-story mechanisms. The BRBM system inherently provides for increased redundancy, reducing the number of frames required and providing enhanced seismic performance and better architectural compatibility at a lower cost than conventional brace-frame systems.

Claddings serve architectural purposes and at the same time act as protective or insulating layer in prefabricated RC structures. Postulating that claddings are non-structural elements, their complexity due to the variability in material, shape, configuration, connection etc. is often overlooked despite numerous failures observed in past earthquakes. The research work presented here suggests that a structural role for the cladding system may be reasonable as long as it is taken into account during the design process. Such a consideration presupposes that the response of the cladding system is known and successfully controlled during an earthquake by means of using appropriate advanced connectors, capable of dissipating energy, the structural features of which are well established. A dissipative connector is the type of device that exhibits enhanced properties in terms of ductility and damping and constitutes a key element in the new concept of designing the cladding system participating in the response. This work thus proposes a displacement-based methodology for the design of RC precast structures with claddings that is validated with analyses results from nonlinear time-history analyses.

Los Angeles lies at the precipice of a long-awaited, devastating earthquake, yet much of its building stock remains uninvestigated for the structural integrity to endure such forces. An obstacle standing between the city and preparation is that building owners simultaneously overestimate the stability of their structures and underestimate the strength of a potential earthquake. An interactive seismic webmap would bring an unprecedented and comprehensive amount of seismic and building information to the fingertips of the public and would help policy makers, code officials, building owners and engineers alike to develop cost effective measures to minimize future losses. We outline the approach and methodology behind creating an interactive seismicity and building response map of Los Angeles that uses data visualization techniques to engage and empower the community. Built through ArcGIS, this online tool would allow users to navigate through Los Angeles’ seismic past, present, and future. By integrating diverse datasets that include specific building characteristics, instrumentally recorded and interpolated past ground motions, and earthquake scenarios, this proposed freely accessible public resource offers to communicate risk for building owners in a novel, personalized manner.

Guidance developed in 2013 is intended to improve barricading and stabilization practices for damaged buildings. It includes advice for obtaining situational awareness after disasters, clarifying whom, among multiple government agencies, should be in charge of barricading and stabilization decisions, and making transitions from an emergency to installing and maintaining long-term barricades for safe recovery.

This study investigates a seismic retrofit method for existing reinforced concrete (RC) frame by using steel plate shear wall (SPSW). The SPSW resists the lateral forces primarily through the tension field action of the slender infill panel. In order to minimize the interruptions to the use of the existing buildings during the retrofit, all the components in the proposed SPSW are connected by bolts. All the components are so light weight that can be transported conveniently within the existing building before assembling. The connections between the SPSW and RC frame are made by post-installed adhesive anchors. Cyclic tests of two full-scale one-story one-bay RC frames retrofitted using the proposed SPSWs were conducted. Test results demonstrate that the retrofitted RC frames possess a lateral load-carrying capacity approximately 4∼5 times greater than that of the bare RC frame and perform in a satisfactorily ductile manner.

This paper presents seismic retrofit of one typical single-story industrial-type precast reinforced concrete building structure located in Turkey using rotational friction dampers. This project consist of retrofitting twelve precast reinforced concrete buildings and it is considered to be the first fully engineered and completed application of supplemental energy dissipation devices for retrofitting purpose in Turkey. In Turkey, precast concrete is one of the most preferred type of construction for all type of industrial structures due to their low cost, fast construction, and availability in rural areas. Unfortunately, most of these structures constructed before “Specification for Buildings to be Built in Seismic Zones (2007) (TEC)” are not well-engineered and are expected to have very poor performance when exposed to a major seismic event. One of the importand official instutions of Turkey decided to undertake a major project to retrofit their single story precast concrete buildings. It is required that buildings will not be vacated during retrofit and disturbance to the building operation will be the minimum. Existing building structures are examined and reviewed in detail, and based on the comparison of several retrofitting schemes, it was concluded that seismic retrofit with energy dissipation devices is a feasible option for the subject buildings. Rotational friction dampers are selected as the supplemental energy dissipation device. ASCE 41-06 is employed for the damper design and performance evaluation. The most effective damper configuration and capacities are selected after an intensive iterative trial-and-error linear study. Finally, nonlinear time-history analyses are performed for seven pairs of historical ground motion acceleration data and it is shown that proposed retrofit scheme satisfies the desired performance goals for both DBE and MCE events. In overall, it is considered that proposed retrofit scheme with dampers provides a viable solution to the stakeholders of the project from performance, design, constructability, and economical points of view. Some application photos were presented and methods are explained in detail in the paper.

Out-of-plane mechanisms induced by earthquakes are typical of many masonry structures and their seismic assessment requires proper methods of analysis and verification. Different displacement based assessment (DBA) procedures have been already adopted in many codes, to take into account the dynamics of rocking mechanisms, but a systematic comparison of their results has not been provided, yet. In this framework, the paper presents a review of the DBA procedures proposed by different national and international codes. In particular, the attention is mainly focused on the out-of-plane mechanisms developed at the upper parts of the buildings; thus, a comparison between the different expressions actually proposed in standards for the floor spectra definition is firstly provided and then a new expression is proposed and validated through experimental results. Finally, the differences and analogies among the different formulations are critically discussed with the support of a reference case study building.

Under the auspices of the World Bank, a multi-step risk assessment project has been recently completed for metropolitan Manila, Philippines, the country’s primary commercial and business center, the 11th most populous metropolis in the world, with 12 million. This area is susceptible to multihazard natural disasters such as earthquakes, floods, and typhoons. To address this vulnerability, a risk assessment and mitigation program was undertaken. A prioritization and seismic retrofit program was developed and focused on public schools and hospitals that have suffered disproportional damage and casualties in past disasters worldwide. The key steps in the program were to: (1) prioritize vulnerable structures, (2) conduct cost-benefit analysis to assess retrofit options, and (3) prepare a seismic retrofitting guidelines including design examples and details. Approximately, 4,000 structures were evaluated. The probabilistic evaluation platform was utilized and retrofit options were developed based on the state of art but simple seismic retrofit methods and modified for local construction.

The recent earthquakes in New Zealand have highlighted the vulnerability and risk to life safety of some of the existing building stock across the country. It is important for New Zealand to satisfactorily address risk to life safety from earthquakes within the social, heritage, and economic context in order to develop an appropriate response to address this issue. For many years, New Zealand has had legislation providing for nationwide seismic assessment of existing buildings and minimum seismic retrofit levels in buildings. While the legislation historically has worked successfully in conjunction with recommended practice promulgated by the New Zealand Society of Earthquake Engineering for the seismic assessment and retrofit of buildings experience from the Canterbury earthquake sequence and other recent earthquakes has led to the need to reconsider some aspects of both the legislation and the guidance provided for engineers assessing and retrofitting buildings. This review has led to the questioning of some aspects of previous practice. In this paper, the authors briefly discuss the history relating to earthquake risk buildings in New Zealand, the issues that have arisen as a result of the earthquakes and the manner in which these are likely to be addressed. The paper discusses approaches being used in New Zealand to identify and assess large numbers of buildings throughout New Zealand. The concept of relating existing building seismic resistance/performance to new building standards is explored illustrating how structural engineers are engaging with building owners, policy makers and the general public to communicate seismic risk.

In 2004, the Province of British Columbia (B.C.) announced a 10–15 year, $1.5 billion seismic retrofit program for the province’s 750 at-risk public schools. The purpose of this program is to quantify the seismic risk of the provinces school buildings and to expedite the seismic upgrading of the most at-risk schools. In order to provide a safe and cost effective implementation of this program, the Association of Professional Engineers of British Columbia (APEGBC), in collaboration with the University of British Columbia (UBC), has developed a performance-based probabilistic method and guidelines for the seismic risk assessment and retrofit of low-rise buildings. The guidelines: the Seismic Retrofit Guidelines, (SRG), are currently moving towards their 3^rd edition, to be published in 2016. This paper summarizes the current state of the province-wide retrofit program and introduces the performance based methodology that has been used to assess and retrofit school blocks. Some of the methodology changes that will be implemented in SRG3 are also introduced. These changes include revisions to the seismic hazard, a new ground motion selection and scaling procedure, and new retrofit prototypes and modeling approaches.

The notion that there is a disconnect between the anticipated performance of buildings in a major earthquake, and what the public understands or expects, is not new. Bridging this communication gap has been discussed in a number of different forums, including U.S.-Japan workshops. The idea of a building rating system has arisen on a national level in the NEHRP Workshop on Meeting the Challenges of Existing Buildings Prioritized Research for Reducing the Seismic Hazards of Existing Buildings and Grand Challenges in Earthquake Engineering Research, A Community Workshop Report. Input on creating such a rating system was obtained in the FEMA-funded Workshop on a Rating System for the Earthquake Performance of Buildings. The thought was that if the public could be made more aware of their potential seismic risk, they could be expected to make better-informed decisions on owning and leasing properties, and market forces would eventually drive the building design, management, and procurement process into more resilient seismic design. Seismic performance assessment techniques have reached level of sophistication and maturity that we now feel capable of distilling complex measures of performance into meaningful sound-bite information that is expected to be useful to owners, developers, tenants, lenders, and insurers in their building procurement transactions. Efforts to develop a building rating system have included many technical and philosophical challenges, but USRC has formed a diverse coalition of technical organizations, engineering firms, individuals, industry supporters, and government agencies to develop a consensus-based approach to solving these challenges. This paper describes the need for a building rating system, the potential users, the information it provides and the measures that will be used to maintain the long term credibility of the system. Another paper in this session covers the goals and objectives, organization, and founding principles of the USRC. Two additional papers describe the two evaluation methodologies that will initially be used to determine the earthquake ratings.

Building on the work of the SEAONC Existing Buildings Ratings Committee over the past eight years, and the recommendations of an Applied Technology Council (ATC) User’s workshop, in 2011 the U.S. Resiliency Council (USRC) was formed as a 501(c)3 nonprofit organization to be the administrative vehicle for implementing a rating system for buildings subjected to natural and man-made hazards. Measuring and improving the resiliency of the country’s building stock is a national imperative. Current methods to define and evaluate resiliency are often inconsistent and lack both standardization and verification. The USRC will issue either transaction or verified ratings, much like the US Green Building Council issues LEED ratings. Ratings will benefit building owners, lenders, tenants, and government jurisdictions by increasing the value of well-designed properties and providing a means to quantify risk. Policy makers will use USRC ratings to compare and prioritize relative risks and to form a basis for developing long-term resilience policy. This paper describes the goals and objectives, the organizational structure, and the founding principles of the USRC. Another paper in this session discusses the need for a building rating system, the potential users, the information it provides, and the measures that will be used to maintain the long-term credibility of the system. Two additional papers describe the two evaluation methodologies that will initially be used to determine the earthquake ratings.

FEMA P-154 Rapid Visual Screening of Buildings for Potential Seismic Hazards: A Handbook and the companion publication FEMA P-155: Supporting Documentation provide a methodology for rapid visual screening of buildings for potential seismic hazards. The Handbook provides a “sidewalk survey” approach that enables classification of buildings into two categories: those that appear to be adequately safe and those that may be seismically hazardous and should be evaluated in more detail. The first edition of the Handbook was published in 1988, and it was updated to the second edition in 2002. The methodology has been used extensively throughout the United States by private sector organizations and government agencies to screen buildings, and it has served as a model for similar efforts in other countries. In a project funded by FEMA, the Applied Technology Council updated both FEMA P-154 and FEMA P-155. Major enhancements in the third edition include improvements in the screening form; an added optional more detailed level of screening; updates of the scoring methodology; more refined seismicity regions; new reference guides for vertical and plan irregularities; additional building types; improved consideration of additions, adjacent structures, and retrofits; an optional electronic scoring methodology; new insight into risk; and more detailed discussion on how to run an effective screening program.

The U.S. Federal Emergency Management Agency (FEMA) and the ROVER Development Consortium (RDC) have released a new version of software for communities to manage earthquake risk. FEMA’s Rapid Observation of Vulnerability and Estimation of Risk (ROVER) Version 2 is free mobile software for pre-and post-earthquake building screening that automates the de facto paper-and-clipboard standards FEMA 154 2nd Edition and ATC-20. FEMA ROVER works through a smart device’s browser via cellular data service. RDC has released the complementary ROVER ATC-20 app that implements ATC-20 for offline tagging, when Internet service is congested or unavailable. Local governments can benefit from ROVER and ROVER ATC-20 because: (1) they produce 25% more building safety inspections per day; (2) they reduce the effort to coordinate evaluations; (3) they provide faster situational awareness; (4) tenants and owners return to safe buildings sooner; (5) FEMA ROVER is free; and (6) ROVER training can be free. The nonprofit ROVER Development Consortium offers additional optional support such as data hosting and training.

Although several self-centering seismic systems have been developed, their use in practice has been relatively limited. Complicated or unusual field construction, perceived initial cost premiums, and deformation incompatibility with the gravity framing are some of the issues that may be factors. A self-centering beam moment frame (SC-BMF) has been developed that mitigates several of these issues. The SCB-MF can be shop fabricated with self-contained restoring force, which eliminates deformation incompatibility and allows conventional field construction methods. The main focus of the paper is the development of a two-dimensional computational model in OpenSees, which can capture the salient behavioral features of the SCB-MF and its components. In addition to the development of the computational model, this paper also describes the SCB-MF concepts followed by a brief description of a large-scale experimental program conducted to validate the performance and study the global and local behavior of the SCBs in depth. Finally, the computational model is validated by comparing the important response quantities of the SCB-MF with the experimental data.

Controlled rocking steel braced frames (CRSBFs) are emerging as a promising solution for achieving an enhanced level of seismic resilience relative to traditional systems. In a CRSBF, selected columns are designed to uplift from the foundation in response to seismic loads, resulting in a reduction in lateral stiffness. This rocking action limits the maximum structural forces in a way that can avoid both residual deformations and also damage to main structural members. The response of a CRSBF can be controlled using a combination of post-tensioning and supplemental energy dissipation. This paper gives an overview of the behavior of CRSBFs before presenting three case studies of buildings that have been built in New Zealand recently. The paper introduces a New Zealand Design Guide for CRSBFs and also discusses some potential advantages and design considerations for CRSBFs in retrofit applications.