Structures Congress 2017: Business, Professional Practice, Education, Research, and Disaster Management

This paper explores some of the key challenges and risks faced by structural engineers when working with existing building structures as well as identifies potential cost- and schedule-saving approaches that can streamline the design process and maintain the integrity of the anticipated scope and project quality. Often times, structural engineers enter into the design phase with incomplete existing documentation and limited access to carry out the full-scale site investigations needed to observe and record the existing structural conditions. Utilizing a case study of the recently completed $54 million Logan International Airport Terminal C to E (C2E) Connector project, this paper explores various approaches that structural engineers can use during the design phase to expedite the building systems coordination through the use of building information modeling (BIM) tools, laser scanning, and selective localized demolition. These approaches can help minimize unforeseen conditions when the construction begins, thus ultimately helping to mitigate costly change orders and schedule delays that would be required to accommodate these unknown conditions. Successful completion of the C2E project required in-depth understanding of the original construction, subsequent renovations of both terminals (C and E), coordination between adjacent concurrent construction projects, and collaborative construction sequencing to ensure minimal disruptions to airport operations, while maintaining containment of post-security areas. Additionally, early engagement and integrated project team collaboration with the Contractor can serve to identify critical enabling packages and project milestones. This facilitates efficient and timely completion of the structural design and the complex phasing required to satisfy operation of a fully active project site open to the public and coordination with overlapping scope of adjacent projects. Throughout this paper, a number of project-specific items are explored to further support the impact of the above-described design approaches and efforts as a way to minimize the challenges and risks faced by structural engineers when working with existing building structures.

OpenBIM is a universal approach to the collaborative design, realization and operation of buildings based on standard format files and open workflows. This technology supports a transparent and open workflow, allowing all project members to participate in a coordinated and simultaneous mode, regardless of the software tools they use. This way of working is different to that proposed in workflows based on traditional BIM tools, through which the project is carried out on a single model. In the new openBIM workflow proposed by CYPE, the project is solved in an iterative mode by progressively solving its different models (structures, mechanical, electrical, plumbing, etc.).

Since the beginning of this century is a tendency in building and construction industry to perform structural engineering with computer programs based on 3D models with graphical, digital and supplementary data of the structure. This kind of structural engineering covers 3D modeling of physical construction and structural system evaluation, code-based loading assignments, numerical structural analysis, and design after specific codes of various materials with required drawing production and final detailing. With “Open BIM” (building information modeling) technology follows nowadays the integration of the architectural and structural engineering workflow by neutral file standard “IFC2x3”. After file loading are architectural model verification, the “BIM-tools” aligning and creation structural elements of beams, columns and slabs with connection. After the above described structural analysis with code-design follows often a model change for cost effective construction. After structural engineering solution comes the evaluation of results and following the model export to architect or other planner as revised neutral file update.

Today’s global work environment and social media technologies offer more interactions among experts, team members, partners, and clients across physical boundaries. Although literature suggests that knowledge collaboration is the key to successful expertise development, due to globalization, the more complex work environments impose challenges in such behavior. Understanding those challenges and factors that lead to successful knowledge collaboration and expertise development is critical to company or organization leaders seeking to implement effective knowledge collaboration programs to develop the future structural engineers. The qualitative case study results suggest that internal knowledge collaboration and external knowledge collaboration tend to positively influence expertise development of structural engineers. Readers will learn about (1) the barriers that prevent knowledge collaboration in a global work environment, (2) the enablers that encourage the future structural engineers to explore their areas of interest and pursue deeper into those areas, and (3) implications for companies to develop knowledge collaboration strategies.

Four structural engineering elective courses at San Jose State University have been revised to use project-based learning to educate undergraduate and graduate students in both technical content and workplace skills. These courses include introduction to steel design, timber design, advanced steel design and advanced seismic resistant design. The courses were originally transitioned to project based learning starting in 2009 and several years of pedagogical experience have shown benefits to students. Projects include design of a truss bridge, design of a glulam beam roof system, design of a soft-story retrofit, pushover evaluation of a bridge bent using FEMA 356 and a fiber hinge, evaluation of the lateral load path of a woodframe structure, elastic analysis of a 3d concrete moment frame structure, and a written term paper about drift-demands of steel frame structures. Adjustment of pedagogical strategies to address differentiated learning styles, student/faculty ratios over 30, conversion from two meetings per week to a single three-hour design studio and reduction of traditional lecture format instruction have been successfully modeled. Assessment of group and individual achievement is conducted for overall projects, individual contributions, and written examination.

This paper describes a bridge engineering outreach activity developed for a science, technology, engineering, and math (STEM) expo event. The hands-on building activities are designed to engage kids and teenagers quickly (10-15 minutes) by introducing them to basic structural engineering. The objectives of the outreach activity are to spark interest in engineering among participants and to increase their awareness of engineers’ contributions to society. Bridge model kits, consisting of paint-mixing sticks, binder clips, chains, S-hooks, and large bottles of water for load testing, are used by participants to assemble simple structural models of tied arch, cable-stayed, and suspension bridges. Participants are guided by engineers and are challenged to think critically about how the structure works. All items in the kit are easily procured, inexpensive, and compact. The novelty and utility of this engineering outreach activity lies in its expeditiousness, minimal use of space and resources, simplicity of concepts, and connection with real engineering design. The author hopes that other engineers will use and adapt this outreach activity to organize their own outreach program.

In the architecture and construction world, a capstone is the final stone placed at the apex of a stone arch. In undergraduate engineering education, a capstone is a culminating major design experience that requires the engineering student to synthesize and apply knowledge and skills gained in previous curricula to solve a significant technical challenge. Engineering education uses the architecture and construction imagery to imply that the capstone design experience is the final building block in the student’s undergraduate engineering education. This paper inverts this model by suggesting that it may be advantageous for undergraduate engineering students to commence with a major design experience at the outset of their engineering curricula rather than waiting to complete their capstone experience during their final undergraduate academic year.

This article presents ideas on how the engineering curriculum can be improved to enable engineers to design bridges that are economical and visually elegant. The focus is on practical bridges, i.e., bridges for which owners have not allocated funds over and above what is necessary to perform the practical function. When bridges contain new ideas that advance bridge technology, economy and elegance can coexist in the same bridge. Elements of knowledge, skills, and values are proposed as enhancements to the curriculum, which will help engineers thus educated to be competent and creative designers of economical and elegant bridges.

The reform of structural engineering education is one of the seven key initiatives put forth in the 2015 Structural Engineering Institute Vision for the Future. The need to expand on this initiative, educating our future structural engineers with a broader perspective of the profession is more relevant than ever, if structural engineers are ever to see their role as more than consultants. As a profession if we are better prepared to be collaborators, then we can be part of the project vision, including how decisions as a design structural engineer are visible in the form of the building structure and the intimate scale of the details. The history of structural engineering and design with an emphasis on the role structural engineer plays in the design of the built environment are essential elements of an educational expansion that best prepares structural engineers to be in the forefront of a collaborative profession.

Traditional hazard vulnerability indices often quantify shock (hazard occurrence) and exposure (physical composition of the building stock), but fail to include resilience (recoverability from the hazard) in the assessment. This paper proposes the coastal community social vulnerability index (CCSVI) to address these limitations. Accounting for resilience within a vulnerability index is becoming crucial as coastal communities experience an influx in population and are exposed to the potential impacts climate change may have on hurricane patterns. This paper presents the methodology for developing the CCSVI, while accounting for the dynamic impact of climate change. This paper quantifies the exposure and resilience of a community and presents intermediate results for the development of the CCSVI. Ongoing work will address the quantification of shock. The CCSVI has the potential to aid in identifying communities that are in need of structural retrofit as well as ensuring that governmental resources for hazard preparedness are being allocated effectively.

In this paper we examine and compare the vulnerabilities of building and highway bridge to the combined effect of earthquake and tsunami loading. Earthquake-induced ground shaking, ground failure (e.g., landslides and liquefaction), and tsunami inundation fragility functions are combined with regional hazard data to estimate the damage and direct economic loss of building and bridge. We use the city of Seaside, Oregon, as a case study site, because it is one of the most vulnerable coastal cities in the Pacific North United States given the threat of an extreme nearfield Cascadia Subduction Zone earthquake and resulting tsunami. We test sensitivity of damage levels using various fragility curves. For the fragility curve analysis, we consider flow depth, velocity and momentum flux ad the intensity measure to estimate the probability of a certain damage level based on the known structure type and characteristic tsunami and earthquake intensity. We also evaluate the disaster resilience. The results indicate that when ground failure and tsunami inundation are considered, there is an overwhelming increase in the loss estimates when compared to the estimates obtained when ground shaking alone is considered.

Wind speeds and velocity structures in tornadoes are largely unknown, since direct measurements are difficult and rare. Structural engineers, atmospheric scientists, and catastrophe modelers must therefore utilize “proxy” methods (such as the estimation of structural resistances that have been exceeded) to better assess tornado and other windstorm risks to achieve safe yet economical designs. Damage to simple engineered structures is of particular interest, since the resistance of such structures can often be readily estimated. Such determination requires accurate measurement of structural member sizes, which can be prohibitive due to time, site access, and safety issues. A late-2015 intense tornado outbreak severely damaged a group of engineered structures at an industrial facility near Pampa, TX. This facility contained multiple engineered structures for which structural resistances could be estimated, thereby enabling the estimation of tornado wind speeds required to cause the observed damage. Due to safety and security liability concerns, facility owners restricted access to the site. Investigators were, however, permitted to acquire remote-sensing data to preserve the damage scene for subsequent detailed analysis. Ground-based LiDAR scanning and terrestrial digital imaging from the property line as well as aerial and satellite imaging provided effective solutions for rapidly, safely, and accurately preserving the damage scene. The multi-platform data collection has facilitated and evaluation of remote-sensing platforms for their utility in rapidly capturing and preserving damage scenes via 3D models and visualization.

Accelerometers in smart devices have been used to measure seismic activity by researchers. Taking smart devices to the next step and using them to characterize building seismic damage in a quantitative manner is a complex undertaking with multiple challenging dimensions. Among the top challenges are: (1) how can accelerometer data be used to obtain an accurate measure of inter-story drift, and (2) can smart devices determine if their data is meaningful before feeding it to a centralized processing station based on which electronic safety tagging can be achieved? This paper will highlight these and other challenges and describe ongoing research to address them. An analytical error model for MEMS-based accelerometers that are ubiquitous in smart devices is adopted in an attempt to understand the errors that could potentially contaminate their measurements. In addition, research is presented on how a smart device can decide if its motion is representative of the motion of the floor underneath or whether it is tainted by excessive sliding action. Computational simulation results are used to demonstrate the concepts discussed in this paper.

In seismic assessment of existing reinforced concrete buildings, the plastic behavior of beams and columns are typically represented by concentrated plastic hinges at the end of the members and the beam-column joint is considered rigid or partially rigid. This approach; however, does not account for the joint deterioration caused by cyclic seismic loading as observed during past earthquakes and also in experimental tests. The observations indicate that the potential for joint deterioration is higher in older concrete buildings. In this paper, the seismic behavior of a full-scale reinforced concrete beam-column connection extracted from an earthquake-damaged building is evaluated using structural testing and also numerical analysis. Cyclic testing is performed up to a column drift of 3%. Two analytical models of the connection are developed considering the joint flexibility; one model considers the rigid end offset approach recommended by ASCE/SEI 41, and the other model uses a lumped-plasticity joint spring model which is calibrated using the experimental test results. The test results show that the plastic mechanism of the connection is controlled by the joint flexibility in shear and that slippage of the beam bottom bars occurred after plastic hinges developed at the beam ends. These results are validated using the analytical model with joint lumped-plasticity. The model with end offsets, on the other hand, fails to adequately represent the specimen behavior. These findings indicate that nonlinear modeling of beam-column joints is critical in seismic assessments of older reinforced concrete buildings.

On-shore flow during tsunami events can transport a significant amount of debris as was evident from recent events such as the Japan 2011, Chile 2010, and Indonesia 2004. Tsunami-generated debris can place extreme loads on the structures they impact, particularly in the case of large debris items such as shipping containers and shipping vessels, where impact can result in the collapse of a system if not properly designed. The 2016 publication of the ASCE 7 Standard, Minimum Design Loads for Buildings and Other Structures, includes a new chapter entitled Tsunami Loads and Effects, which provides design engineers with guidance to protect tsunami prone regions of the U.S. against the forces that can be generated during tsunami events. The new tsunami loads chapter requires debris impact to be considered in the design of structures located in the tsunami inundation zone. The goal of this paper is to familiarize design engineers with the procedures required to calculate the impact demands on structures in tsunami prone regions. A case study of a tsunami prone region of the U.S. is used to demonstrate the impact demands that can be generated at a building site from common debris types such as: wood poles, empty and fully loaded shipping containers and passenger vehicles. As part of this case study three different methods are used to estimate the flow velocity and flow depths needed to determine the impact force and location at which the force is applied to a structural component. The modified energy method is recommended for flow characteristic approximations. For calculating impact force in the inundation region the standard provides two approaches that design engineers can utilize: (1) a conservative, prescriptive load specification, and (2) impact force and duration equations that utilize the approximated velocities. It was determined the main advantage in using the impact force and duration equations comes from the fact that a dynamic response factor can be determined based on the debris type and impacted structural component, which can potentially reduce the calculated debris impact static load. It is recommended that when applying the impact force to the structural component, further load cases should be explored for the impact force and duration equation as this can further improve the accuracy of the impact demands potentially allowing for more economical sections to be utilized.

Building codes evolve as engineers and scientists learn more about the destructive capability of natural phenomena and how to design structures to effectively withstand these extreme events. The 2012 building and residential codes published by the International Code Council have recently seen significant updates to the wind hazard and design criteria, and have generally decreased the design wind speeds along much of the hurricane-prone East and Gulf Coasts. Catastrophe models, which integrate a stochastic hazard with views of building vulnerability in order to provide reliable risk estimates, can be used to quantify the impact of spatial and temporal building vulnerability changes. This study quantifies the impact of the building code related changes in a catastrophe modeling framework using a sophisticated hurricane model and an actuarial metric: average annual loss. A resulting discussion is provided detailing the implications of this study.

Lessons learned from previous earthquakes and the results from some analytical research studies have indicated that basic building code equations for seismic forces on nonstructural components may not return sufficiently accurate force values under certain circumstances. Floor accelerations and their effects on nonstructural components can be highly variable due to characteristics such as varying structure nonlinearity, building-specific dynamic characteristics, input ground motions, and geometric configurations. Ensuring that nonstructural components meet specified building code performance criteria is important for maintaining the safety of structures during and after a design-level seismic event. The seismic performance of nonstructural components may be of increased concern for high-importance facilities that must remain operational following an earthquake. As a result of lessons learned from recent earthquakes, more attention has also been paid to the seismic performance of nonstructural components in low-level seismic events that do not cause structural damage. The results of nonstructural seismic analyses of two west coast pre-Northridge steel moment frame buildings are presented. Nonstructural component spectral accelerations were calculated from the floor acceleration results of nonlinear response history analysis models. Nonstructural component accelerations were numerically calculated across a range of periods to develop response spectra. The analysis results obtained from the nonlinear response history analyses are compared against equations from ASCE 7-10 Minimum Design Loads for Buildings and Other Structures and ASCE 41-13 Seismic Evaluation and Retrofit of Existing Buildings. The implications of assumed nonstructural component damping are also discussed. The information presented highlights some questions for designers and academics to consider for use in practical design. In addition, the results highlight some challenges in conducting computationally intensive, detailed analysis on nonstructural components using current code provisions.

Two full-scale architectural precast concrete cladding panels were tested in 2011 on a full-scale five-story steel frame building at the E~Defense shake table facility at Miki. Japan. Two full-height column cover panels were tested: a return cover 3D shape, and the matching half-width flat panel. The cladding specimens represented one type of standard U.S. cladding façade design where cladding is designed to accommodate inter-story drift though racking of individual panels. A 50 mm vertical seismic joint was installed between the two panels. The panels and connections were designed according to common U.S. practice and the connection hardware was fabricated in the U.S. as a subcontract to a California precast fabrication company. Due to the expense of shipping full concrete panels, the panels were cast in Japan with final installation overseen by U.S. personnel. Two issues evaluated during the experiments were: (1) the effect of three-directional ground acceleration on the cladding panels, and (2) the effectiveness of the current slotted-bolt sliding connection to allow for inter-story earthquake motion. Instrumentation measured the acceleration of the panels and the movement of the slotted connections. The panels were mounted on the 4^th floor of the steel frame structure, which was then shaken at the foundation with both fixed-base connections between the structure and foundation and two alternative isolation systems. The primary findings was that slotted connections were able to slide while being accelerated in a full scale 3D seismic motion and no damage was seen in the panels at inter-story drift ratios as high as 0.0075 radians. Detailed study of the panel performance for the fixed-base experiments is reported in the paper. Torsional twist of the structure was found to be significant thus drift of the panels was determined using the displacement of the floor plates at the perimeter of the structure rather than considering the panel drift to be equivalent to the drift of the center of mass of each story. Review of the accelerations recorded on the panels was inconclusive. High-frequency vibration resulted in spikes of acceleration well above the value expected to cause damage. Additional study is required to correlate the acceleration readings with panel performance. The results of the experiments indicate that modern detailing and construction practice should produce facade systems which will perform suitably in future earthquakes.

Accurate prediction of peak floor accelerations is a crucial step in developing simplified methods for the seismic analysis and vulnerability estimation of acceleration-sensitive non-structural components (NSCs) attached to buildings subjected to earthquakes. A particular characteristic of seismic floor accelerations is that they increase along the building height, with a maximum amplification at the rooftop level. While the amount of horizontal acceleration amplification currently suggested in most modern building codes is empirical, the amount of vertical acceleration amplification is not fully addressed yet in most building codes. This paper discusses the amplification of horizontal and vertical rooftop accelerations based on the analysis of recorded accelerations in 7 buildings during the 1999 Chi Chi earthquake in Taiwan. The ratio between vertical and horizontal rooftop accelerations and spectra is also discussed. Evaluated parameters affecting the amplification of vertical accelerations include: the building vertical period of vibration, the number of stories, and the location of the building relative to the fault. Findings are discussed and compared to provisions currently proposed in the ASCE 7, the NBCC 2015, the CSA S832 and the Eurocode 8. The most significant trends are highlighted.

This paper investigates the effect of balconies on wind loads of residential mid-rise buildings and the wind loads on balcony glass handrails. Large-scale experiments were performed in Wall of Wind facility at Florida International University. A 15-story mid-rise building was selected for the experiments. Two sets of experiments were performed by using building models without and with balconies. Wind effects on both continuous and discontinuous balconies were studied. In order to study the scaling effects, in each set of experiments, pressure measurements were performed on three models with scales 1:180, 1:67 and 1:25. The results showed that the balconies can change the flow pattern around the building and consequently the pressure distribution on the walls. The pressure coefficients on the balcony structures provided in this paper provide useful information for more reliable design guidance for balcony glass railings that will improve safety of the residents.

This paper aims to investigate the effect of adding carbon nanotubes (CNT) to latex modified mortar (LMM) with 0 wt% to 1.5 wt% of latex on the mechanical characteristics of LMM. Various types of samples were prepared. It was found that adding CNT enhances the mechanical characteristics of LMM. While it is important to assess the significance of using CNTs to improve the resistance of mortar to different environmental conditions, two types of thermal cycles were applied to the samples. That is, the samples were subjected to a number of freeze-thaw cycles according to ASTM C-666 to simulate winter outdoor condition in the US northern area; the samples were subjected to thermal fatigue cycles from 16^oC to 40^oC to simulate the summer outdoor condition. Some of cube and cylinder samples were tested after 50% of the total number of cycles in order to assess the effect of the number of cycles on the sample performance. After all cycles were completed, all the remaining cubes and cylinders samples were tested. The effectiveness of adding CNTs was evaluated by comparing between the performance of control LMM samples and the samples with different CNT content.

Cross-laminated timber (CLT) is an innovative wood product that has been introduced recently to engineering practice; CLT members have a wide variety of applications in engineering practice, these include primarily building and architectural applications as structural members that support gravity and lateral load. Although CLT practices have been gaining popularity in building applications, this research explores new applications and focuses on investigating the CLT members for Industrial applications which include, crane mats, access mats, temporary bridges etc. The authors have established an experimental program to obtain strength parameters of CLT members built from Southern Yellow Pine members to help engineers design such members for the applications mentioned above. The experimental program consists of testing 10-15 in. x 216 in. x 5 layers of 2x8 members’ specimens in bending (Group 1), and 10-15 in. x 53 in x 5 layers of 2x8 members specimens in shear (Group 2), 10-48 in. x 216 in. x 5 layers of 2x8 members specimens in bending (Group 3) and 10-48 in. x 53 in. x 5 layers of 2x8 members specimens in bending (Group 4). The test dimensions were selected per ANSI PRG-320-2012 and were performed at the Forest Product Laboratory in Madison, WI. The specimens were tested to failure and load deflection curves were obtained. The test clearly identified the behavior of the CLT members up to failure as well as their failure modes. Additionally, non-linear finite element analysis was performed for the different tests to help validate the tests and understand the behavior of the CLT members. The results from the experimental program and from the finite element analysis were used to obtain the bending and shear strength parameters for CLT members and recommendations have been made to design such members. The methodologies used in this analysis and the failure modes observed in the laboratory provide behavioral characteristics of CLT’s that can be applied to the design of CLT’s for buildings.

Increased frequency and intensity of coastal storms as well as the restructuring of flood insurance policies has renewed interest in the structural performance of coastal residential homes under wind, flooding and storm surge hazards. Varying construction techniques and environmental deterioration often results in nailed connections that are weaker than the structural members they join. Therefore, global performance of light framed residential structures is found to be greatly dependent on the performance of individual connections. Nonlinear behavior of these connections could further complicate accurate characterization of the connection response in the structural system. Traditional finite element approaches such as using multiple nonlinear springs to define directional stiffness often neglect the coupling effects of the multidirectional connection response. Furthermore, the implementation of nonlinear spring connector elements along the corners and edges of a structure could be difficult and time consuming for the user since additional nodes or elements and coupling functions have to be built or used in the modeling process. In the present study, an innovative connection modeling scheme is proposed to model nailed connections using an equivalent beam element. Experimental data and a nonlinear material model is used to define a single parameterized beam element to represent a connection between structural members. The parameterized beam element retains an intrinsic coordinate system for ease of meshing and couples the axial and transverse connection response for a more conservative displacement solution.

Structural topology optimization is a free-form design tool that allows for a systematic search of the design space for optimizing both the structural connectivity and member sizing. This search could be used to eliminate engineering guess-work especially in the preliminary structural design conceptualization, and obtaining high-performance designs. Although many steel structural designs are primarily driven by controlling stress and buckling, the currently developed structural topology optimization algorithms mainly focus on controlling structural stiffness, which is often carried out via controlling displacements in a predefined set of points within the structure. This limitation should be alleviated for better integration of topology optimization with structural engineering. An efficient algorithm for topology optimization of steel frame structures that seeks designs in a safe region of elastic stress, buckling load factors and displacements is presented in this work. Stress-based performance of the structure is optimized by evaluating the von Mises yield criterion in a set of predefined points within the structure and controlling the maximum of these stresses within the optimization algorithm. Moreover, under the assumption of linear buckling, an Eigenvalue problem for determining buckling load factors and the corresponding modes is solved, and the minimum buckling load factor is controlled. Designs suggested by the proposed algorithm are compared with conventional designs and changes in their topologies and performances are discussed.

This paper investigates the fatigue behavior of reinforced concrete beams at low temperatures compared to similar beams tested in fatigue at room temperature. Four large-scale steel reinforced beams (200 mm x 400 mm x 4200 mm) were fabricated and tested under cyclic load to failure. This study showed that the fatigue life of the reinforced concrete improved at low temperature and this improvement was much more pronounced when shear reinforcement was not present. In fact, low temperature changed the mode of failure of the reinforced concrete beams without stirrups from shear to flexural fatigue failure as a result of the higher shear strength and stiffness of the reinforced concrete, the lower number of cracks with smaller widths, and improved fatigue properties of steel at low temperature. The results showed that the fatigue life of the reinforced concrete beam without shear reinforcement at room temperature primarily depended on the concrete and concrete to steel bond while fatigue lives of the other beams depended on the stresses in the tensile reinforcement. The findings of this study showed that the contribution of concrete to the performance of the beam under either static or cyclic load becomes more pronounced at low temperature.

This study was performed to show the effects on properties of concrete when incorporating different gradations and different percentages of crumb rubber into a concrete mix. Millions of used tires are disposed of every year in the United States. As a remediation to this negative environmental impact, the environmental engineering community, the materials engineering community, as well as the structural engineering community have been working to use scrap rubber tires in engineering material modification projects to improve their properties and move into a more sustainable direction. In this study the effects of the crumb rubber, obtained from processed used tires, on axial compressive strength and flexural strength of unreinforced concrete was investigated. Different percentages of varying gradations of crumb rubber were used as an aggregate in concrete. The results of this study show that the addition of crumb rubber to concrete as a percent replacement of the fine aggregate is detrimental to the overall strength of the specimen, but not so much that it may not be used in small amounts.

This paper presents a hysteretic damage model for response simulation and damage assessment of structural components. The model extends existing models with its ability to describe the degrading hysteretic response of components on the basis of a continuous damage evolution. The formulation is based on classical continuum damage mechanics theory and relates any two work-conjugate variables, such as force-deformation, moment-curvature, and stress-strain. The strength and stiffness deterioration is based on two damage variables that are continuously updated based on internal energy dissipation. The model consistently accounts for cyclic degradation and damage interaction between response under positive and negative deformations. The model is validated against a collection of cyclic experiments of steel and reinforced concrete components. The simulations demonstrate that the model is able to describe well the component degrading hysteretic behavior with consistent sets of parameters. The study also highlights the ability of the model to utilize the damage variables to assess accurately the progressive degradation of components under different load histories.

The use of bamboo as a structural material in construction has recently become a topic of interest for researchers. Bamboo is a natural resource that is highly renewable, and its manufacturing process demands low energy consumption. Bamboo has excellent mechanical properties making it a promising nonconventional material for construction. However, there is much variation in the size and the material properties of the individual bamboo culms, which have traditionally been used in construction in various regions of the world. In recent years, the bamboo culms have been cut into strips and glued together to form laminae sheets. The laminae sheets are then glued together to form boards, or glued laminated guadua bamboo. This development has the potential to overcome the abovementioned limitations, and pave the way for the use of bamboo in the construction of structural elements. This paper presents the development of a three dimensional finite element model (FEM) for a bamboo composite I-shaped beam. The I-shaped beam was constructed with boards of glue laminated guadua bamboo. The flanges and web were connected with a combination of steel bolts and angles. The FEM was compared with experimental data. The deflections predicted by the FEM are in good agreement with the deflections obtained through physical testing. The goal of this research is to develop a tool for further research in the design of sustainable structural elements and their connections. There is a lack of standardization and design criteria for bamboo in construction; this paper presents the possibility for glue laminated guadua bamboo to be considered in the design of different structural elements. The inclusion of bamboo in the construction industry results in an excellent sustainable alternative for conventional structural materials, such as steel and concrete.

One important aspect of performance-based earthquake engineering is developing structural models that can accurately capture key characteristics of dynamic responses up to structural collapse. This in turn requires the solution algorithm to be capable of capturing large displacement responses through appropriate use of geometric nonlinearity. Small-displacement-based solution algorithms possess this capability in the analysis with high computational efficiency and relatively good accuracy; while large-displacement-based finite element analysis algorithms address geometric nonlinearity through satisfying equilibrium in the deformed position which capture large displacement accurately but with poor computational efficiency. The objective of this research is to investigate the impact of epistemic uncertainty in small-displacement-based algorithms for capturing large displacement responses. Consistent models of steel moment frames are developed for analysis using various solution algorithms based on different geometric nonlinearity formulations. Response history analysis is performed under the same input ground motions. Analysis results show that some formulations address the geometric nonlinearity more appropriately with less uncertainty than others.

Regional risk assessment of bridge classes necessitates the grouping of bridge classes. Although HAZUS categorizes bridges and is compatible with the National Bridge Inventory, it suffers many drawbacks such as grouping based on traditional subjective approaches, doesn’t adequately consider the difference in bridge performance, failure in explicitly addressing the evolution in seismic design philosophy and the effect of number of spans, to name a few. This paper uses a performance based grouping technique called analysis of variance to improve the HAZUS grouping of bridge classes. The proposed approach is able to identify the bridge parameters which have a significant influence on the seismic demand and the fragility curves. The paper improves the HAZUS grouping of box-girder bridges in California accounting the effect of various design attributes such as abutment-type, number of spans, number of frames, span continuity, design philosophy, and pier type.

A new finite element model based on a fiber beam element formulation that considers large displacements is presented. The element is used to model fiber reinforced concrete members. The element uses a displacement based formulation and has the capability to model reinforced concrete members strengthened with carbon fiber sheets under different loading conditions. The element is developed within a two-dimensional Lagrangian corotational beam formulation. Both the element internal and external geometric stiffness matrices are considered. The transformation between the corotational and the global system is made using an enhanced transformation matrix that takes into consideration the current angle of the co-rotating frame with respect to the global coordinate system. When steel fibers are added to the concrete mix, the properties of the concrete are improved such that the tensile strength of the concrete increases and the tension softening stiffness is also modified. The new element can precisely simulate the effect of steel fibers while taking into consideration the second order analysis. Two verification examples commonly used in the literature are first presented to verify the capability of the element to model the non-linear material behavior and the geometric non-linear formulation. The first verification example is the William’s toggle frame and the second is a cantilever beam with a vertical load at the tip. In both examples, the cross section used is steel. It was found that the proposed element results are in good agreement with the analytical solution of the two examples. Later, the new element is employed to model the experiment of a reinforced concrete column hinged at both ends that encounter large displacements, where carbon fiber reinforced polymer (CFRP) sheets are used to strengthen the column. Results show that the element can precisely depict the strengthening effect when the structure is simulated using a second order non-linear analysis.

With increased use of welded aluminum light poles along highways and in industrial service applications such as parking lots, harbors, stadiums, etc., it is important that they are sustainable and resist fluctuating wind induced stresses or fatigue loading. Forty-one welded aluminum shoe base light poles were fatigue tested in the structures laboratory of the University of Akron. The fatigue life of the test specimens was considered and used to develop a design S-N curve for the specific shoe base details used on the light poles. The proposed S-N curve derived from the test results, including the endurance limit in high cycle regime, was compared to the Aluminum Design Manual’s (2015) category F1.Among forty-one aluminum shoe base light poles, twenty-six specimens failed (63.4%) and the remaining survived (run-outs). Crack development in the specimens was observed on the surface primarily along the weld toe between the tube and cast shoe base. The lower bound S-N curve was extracted and provides approximately 97.5 percent probability of survival for the shoe base detail and is in a good agreement with category F1 of Aluminum Design Manual (2015). Additionally, the run-out data for the fatigue test results, which is taken to be 10 million cycles for the older tests and 20 million cycles for new test group, is in good agreement with the British Standard Institute 8118 and the Aluminum Design Manual (2015). The S-N curve is useful for investigating the fatigue behavior of the light poles during analysis for wind induced loadings.

The American Institute of Steel Construction (AISC) Manual provides equations for calculating the capacity of a W-shaped steel member to resist concentrated forces applied to its flange. In the case of flange local bending, the capacity equations were primarily formulated for an interior point along the member, which is defined to be at a distance larger than ten flange thicknesses away from the member’s end. When a concentrated load is applied within ten flange thicknesses from the member’s end, AISC requires a fifty percent reduction to be applied to the flange bending capacity. This reduction, however, is not supported by any research. In this study, finite element modeling is used to investigate the actual reduction in capacity near the end of such a steel member. The results indicate that the AISC equation for flange local bending is quite conservative for forces applied at less than ten flange thicknesses from the member’s end and a new equation is suggested for the evaluation of available flange local bending capacity within that distance.

The use of cross-laminated timber (CLT) in residential and non-residential buildings is becoming increasingly popular in North America. While the 2016 supplement to the 2014 edition of the Canadian Standard for Engineering Design in Wood, CSAO86, provides provisions for CLT structures used in platform type applications, it does not provide guidance for the in-plane stiffness and strength of CLT shearwalls. The research presented in this paper investigated the in-plane stiffness and strength of CLT shearwalls with different connections for platform-type construction. Finite element analyses were conducted where the CLT panels were modelled as an orthotropic elastic material, and non-linear springs were used for the connections. The hysteretic behaviour of the connections under cyclic loading was calibrated from quasi-static tests; the full model of wall assemblies was calibrated using experimental tests on CLT shearwalls. A parametric study was conducted that evaluated the change of strength and stiffness of walls with the change in a number of connectors. Finally, a capacity-based design procedure is proposed that provides engineers with guidance for designing platform-type CLT buildings. The philosophy of the procedure is to design the CLT buildings such that all non-linear deformations and energy dissipation occurs in designated connections, while all other connections and the CLT panels are designed with sufficient over-strength to remain linear elastic.

In order to reduce the environmental impact of the construction industry, structural high-rise solutions using sustainable construction practices and renewable materials need to be developed. This study investigated a novel hybrid structural system comprised of concrete and timber where concrete slabs at every third story provide the necessary stiffness and strength to resist gravity and lateral loads and the intermediate floors are constructed using light-frame wood modules to create the living spaces. Apart from reducing the building’s carbon footprint, the weight of the building is reduced considerably and, as a result, the seismic demand on the lateral load resisting system is reduced. The research presented in this paper evaluated the feasibility of the proposed hybrid concept and compares it to an ordinary concrete frame structure. A linear finite element model of the system captured the model response in terms of inter-story drift, base shear and the seismic demands in accordance with the design requirements of the National Building Code of Canada (NBCC 2010). It indicates that the system meets the NBCC design performance requirements and has a lower seismic demand in terms of floor displacement and interstorey drift.

A new type of mass timber structural system has been developed in New Zealand over the last decade. Timber members made of engineered wood products are used in combination with post-tensioning cables to produce highly efficient structural components suitable for multi-story moment resisting frames or shear wall-based lateral load resisting systems. Both systems are particularly useful in structures designed in high seismic regions. The post-tensioning also ensures self-centering of the components and the structural systems after a seismic event. In addition to the post-tensioning, the systems can use energy dissipating devices within the connections that further enhance the ductility of the systems and make them good candidates for low damage structural applications. Extensive experimental and numerical studies have been conducted to determine the performance of these systems and design procedures have been developed for practical applications. In an effort to bring this system closer to the North American designers, this paper contains a summary of the evolution of the concept and the most important research projects and findings to date. In addition, a number of applications within and outside New Zealand are reviewed to demonstrate the applicability of the concept. Finally, potential and recent initiatives for adoption of the technology in North America are discussed.

Most civil infrastructure today was built during the second half of 20^th century and is nearing the end of its service life. With increasing infrastructure demand that cannot be met with current resources for new supply, replacement of all aging infrastructure is an unsustainable solution. Asset management decisions such as repair, improvement and extension of existing infrastructure are enhanced through monitoring since most structures have much reserve capacity. Recent advances in sensing and computing technology enables multiple-model data interpretation for structural identification and capacity prediction. In this paper, the application of error-domain model falsification for fatigue-life prediction is presented when data from a weigh-in-motion station and strain gauges is available. The application of this methodology is illustrated on a highway steel-concrete composite bridge having four spans with a total length of 219.8m. It is concluded that a reduction in uncertainty is justified and this leads to longer predictions of remaining fatigue life. This methodology enables condition assessment and fatigue-life prediction without interrupting the functionality of the bridge.

A significant proportion of North America’s aging infrastructure has surpassed its intended design life. This includes a large number of concrete structures that are located in Canada or northern parts of the US with prolonged freezing seasons and high temperature fluctuations. One potential solution to assess the condition and performance of a structure and ensure its resilience is to use structural health monitoring (SHM) techniques. Fibre optic strain sensors (FOS) and digital image correlation (DIC) are two SHM breakthrough techniques providing more comprehensive performance data than conventional techniques. Although these SHM techniques are reasonably well developed, there is still a gap between the monitoring data and serviceability and reliability indicators due to uncertainty of measurements caused by parameters varying with time, e.g. temperature. In this work, FOS and DIC were used to measure strains and crack widths for eight large-scale reinforced concrete beams tested under static and fatigue loading at 15°C and -25°C. In addition, to evaluate the accuracy and precision of these technologies with temperature variations, calibration tests were conducted to measure temperature related strain errors that are induced in these systems. The results showed that both FOS and DIC are affected by temperature changes, and their measurements need to be corrected for temperature when they are used for measuring strains. This study also showed that DIC technique is capable of measuring crack widths with a very high accuracy, and external fibres can measure the strains in the concrete in compression with a reasonable accuracy, and can give an indication of the strains in the tensile reinforcement prior to reaching the cracking load of the reinforced concrete.

Temperature-driven assessment has the potential to advance our understanding of long-span bridge behavior. The novel approach researched as part of this study is the identification and monitoring of a long-span cantilever truss bridge using the input-output temperature relationship. The goal is to use this relationship to identify and monitor unknown quantifiable information with regard to an existing structure using the structural identification process (e.g. boundary conditions, continuity conditions, force distribution, etc.). Since many structural parameters on long-span bridges are highly sensitive to temperature loads, a structure such as the Hurricane Bridge is a prime candidate for this type of monitoring. The Hurricane Bridge is a four-span, cantilever truss bridge over the Caney Fork River in DeKalb County, Tennessee, with a total length of approximately 1787 feet. It was built in 1949 and rehabilitated in 2011. The rehabilitation included widening the deck, strengthening various truss members, and installing a “catch system” consisting of four stainless steel rods around each vertical at the cantilever locations. This critical structure has a great deal of uncertainty related to performance and remaining service life. Therefore, a temperature-driven monitoring system has been designed and implemented to reduce the uncertainty associated with the: “catch system”, pin and hanger effects at cantilever locations, and bearing mechanisms. The sensing technology of this system is comprised of fifty-six vibrating wire strain gages, eight vibrating wire displacement gages, and sixty-four thermistors. Long-term data collection is on-going; however, preliminary results are presented and tasks for future research are explored.

Corrosion is a serious issue causing damage in power transmission lattice towers of steel that can lead to outages. In spite of initial galvanization, periodic repainting and usage of weathering steels, corrosion is experienced in lattice structures at locations with constant exposure to moisture and inaccessibility to repaint. In the present day there are a huge number of transmission towers built of carbon and weathering steels with corrosion posing serious threats to their bearing capacity and durability. Timely inspection and repair is essential to avoid unprecedented structural failures. Employing non-destructive methods of manual inspection for large number of towers to detect corrosion and related damages is time consuming and expensive. In addition to this, the drawbacks include error due to inaccurate human judgment questionable safety of inspector to climb structures possibly weakened by corrosion. In such a situation non-contact approach of automated visual inspection for corrosion and related damage detection through image processing of aerial or ground based images is a viable option. A combination unsupervised and supervised classification methods is used to identify corroded regions in power transmission tower images using various color features of the image. The image is segmented into clusters based on the colors in L*a*b* color space using K-means clustering algorithm. These segments are tested against the conditions of hue obtained from statistical analysis of hue values corresponding to a set images of corroded surfaces to identify the segment of the image with corrosion. This approach lays a foundation for content based image retrieval in the domain of corrosion detection that is the ability to identify corroded structures from a large database of inspection images.

This paper proposed a method to identify dynamic characteristics and system matrices considering uncertainties of modal and ambient excitations. Three algorithms are integrated into this procedure: stochastic subspace identification (SSI), mass change modal scale (MCMS), and finite element model updating method (FEMU). Using only the output response of the structure measured under unknown ambient vibration, the SSI algorithm is used to identify the mode shapes, natural frequencies, and damping coefficient. In typical operational analyses, the mode shapes are not correct (i.e., unscaled mode shape). A mass change modal scaling algorithm is used to identify true mode shapes (i.e., scaled mode shape). With scaled mode shapes and frequencies, a FEMU method is used to determine the mass and stiffness matrices. By analyzing the changes of mode shape, coefficients on each node can detect and locate the damage. Numerical simulation shows that under different types of excitation and with white noise influence on the response, the damage detection method exhibits high sensitivity towards changes in mass and stiffness matrices. An experimental verification of this method is carried out with a small-scale cantilever beam. A high-speed camera is used to acquire the displacements of the elements. Finally, the proposed algorithm can be used to extract frequencies and scaled mode shapes in conjunction with displacements measured over time by passive non-contact optical methods through video.

In the U.S., the challenges of an aging infrastructure network, coupled with requirements for maintaining continuous functionality of this network, highlights the need for innovative, and multi-disciplinary solutions aimed at the timely detection and remediation of defects and deterioration before serious failure situations materialize. Considering the constant and widespread interactions of citizens with urban infrastructure systems, and the increasing ubiquity of mobile and personal electronic devices equipped with onboard sensing capabilities (e.g. camera, accelerometers, GPS, etc.), the concept of leveraging crowd-sourcing provides a promising data-driven solution for urban infrastructure monitoring. In this approach, the vision of the “citizen engineer” is introduced by empowering citizens to become “active human sensors” at the source of defect detection and data collection, thus extending the role of citizens from passive infrastructure users to active infrastructure monitors. In the proposed method, volunteers are motivated and instructed to use mobile devices to capture and send geo-tagged images of defects (e.g. cracks, corrosion, trip/slip hazards, potholes, etc.) that they observe in an urban infrastructure environment, including a short description and severity rating. The collected photos and descriptions are processed using object recognition techniques. Defects are identified and extracted from the photos and quantified, whereas additional information about the defects and their perceived severity are obtained from the description field. Beyond the local condition measures, the aggregate data provides responsible authorities with a quantitative analysis of the detected defects as well as a measure of importance and severity (i.e. heat maps), as perceived by the citizen, that can be used to inform maintenance decisions. While the challenges of this framework are discussed in detail, it is expected to be a highly promising departure from the traditional top-down infrastructure monitoring approaches.

This paper aims to develop a new methodology for damage localization and estimation, through an algorithm that utilizes the ambient vibration data. More precisely, the data collected from sensors are analyzed with a subspace system identification algorithm (SSID) to retrieve frequencies and mode shapes of the structure. This information is then used to construct reduced order stiffness matrices for the system, using two different types of order reduction techniques; Guyan and SEREP. Using these matrices and the retrieved frequencies of the system, optimization functions are constructed and then analyzed with a particle swarm algorithm to locate and estimate the damage. To validate the proposed algorithm, a simply supported reinforced concrete (RC) girder was simulated. The obtained results show that the method is capable of estimating both the position and the severity of the damage in the system with a high accuracy.

Reinforced concrete (RC) structures constitute a significant portion of the building inventory. The quantitative performance assessment for such structures under extreme loading events is necessary to characterize the vulnerability of built communities to natural hazards. Three-dimensional finite element analysis of RC structures has been gaining popularity, due to its capability to capture the damage accumulation and the interaction of various mechanisms ultimately leading to structural collapse. This presentation is aimed to provide an insight on the use of three-dimensional, continuum-based models for the analysis of structural components under cyclic lateral loads, such as those experienced during an earthquake. A recently developed triaxial constitutive model for concrete is combined with a material model for reinforcing steel which can account for rupture due to low-cycle fatigue. The strain penetration effect is also explicitly accounted for in the models. The reinforcing steel bars are represented with nonlinear beam elements to explicitly account for buckling of the reinforcement. The modeling scheme is implemented in an explicit finite element program, which includes large-deformation formulations and element removal techniques to capture loss of concrete cover and rebar rupture. The analytical tools are validated with the results of experimental static and dynamic tests on RC columns and walls. The validation analyses are supplemented with a discussion elucidating modeling aspects, such as the well-established spurious mesh size effect for softening material response with the corresponding regularization procedures, and the significance of accurately modeling the bond-slip of the steel reinforcement.

For vertical containment structures which do not have significant ductility, a design that utilizes plastic yielding of the anchor bolts used to connect the structure to its foundation can be used to provide structural ductility to the system. One type of vertical containment structure is a dry storage cask (DSC), which is used to store spent nuclear fuel (SNF) rods from nuclear power plants (NPPs). DSCs are a temporary storage solution which may be licensed for operation periods up to 60 years. DSCs are being re-evaluated as a potential mid-term storage solution, where operating periods may be extended to 300 years. The potential extension of DSC compliance period increases the seismic hazard, resulting in very large horizontal accelerations and destabilizing effects from vertical accelerations. DSCs are typically unanchored, but units located in moderate to high seismic regions may slide and/or tip over, damaging the cask internals. This research focuses on the benefits of seismic anchorage of DCSs using stretch length anchors. A steel ring designed to clamp the DSC on a concrete pad is investigated as part of the anchorage system. Two types of anchor bolts are being investigated for the steel ring: (a) conventional bolt details with steel chairs using designs adopted from anchoring liquid storage tanks, and (b) stretch length bolt details with steel chairs, which performed very well during the 2010 Maule, Chile, Earthquake. In the first phase of the study, single anchor tests were performed using both conventional and stretch length bolts under dual actuator cyclic tension and shear. The evaluated stretch lengths are equivalent to four, six and eight bar diameters. Two thicknesses are also considered for the plates of the steel chair: (i) 6.35 mm and (ii) 12.7 mm. In the second phase, a group of anchors using the steel ring to clamp the cask were tested for a 1:2.5 scaled DSC under quasi-static horizontal cyclic loads. The experimental results are presented and compared for conventional and stretch length bolt details, as well as the scaled DSC in terms of load, displacement, and hysteretic energy capacity. It is shown that stretch length bolt anchorage details provide superior seismic performance compared to conventional bolt anchorage details.

The seismic behavior and design of industrial structures and high rise buildings is typically governed by the performance of the corresponding reinforced concrete (RC) or steel-plate composite (SC) shear walls. During a realistic earthquake event, these walls may be subjected to combinations of in-plane and out-of-plane shear forces or moments. However, current design codes and standards do not consider the interaction of in-plane and out-of-plane forces on the design and seismic performance of these RC or SC walls. This paper discusses the findings from a research project focused on the interaction of in-plane and out-of-plane forces on the design of structural walls. Experimental investigations were conducted first to evaluate the influence of out-of-plane shear forces (and moments) on the cyclic in-plane shear behavior of structural walls. Detailed 3D finite element models were developed and benchmarked using the experimental results to gain additional insight into behavior. The benchmarked models were used to conduct parametric studies, add results to the database, and gain additional insights into behavior and design. The paper focuses on the development and validation of an analytical approach and numerical tool that was used to conduct the fundamental axial force-axial strain-bending moment-curvature response analysis of the wall cross-section subjected to combined axial force, in-plane and out-of-plane moments. The numerical tool can be used to track the development and evolution of strains and stresses in all steel and concrete components of the walls cross-section. The model was verified using results from the experimental database for SC Walls subjected to combined in-plane and out-of-plane forces. The verified model will be used to conduct analytical parametric studies, and gain additional insight into the interaction of in-plane and out-of-plane forces, and their influence on the design of structural walls. Finally, the model will be used to formulate design recommendations for wall structures subject to combined in-plane and out-of-plane force demands. The recommendations will enable engineers and designers to consider interaction effects directly.

This paper presents an experimental investigation aimed at measuring the increases of damping produced by buckling-restrained braces (BRBs) working within their linear-elastic range. For that purpose, five one-storey one-bay steel frames, working in parallel, were tested on a shaking table. First, the frames were tested without BRBs and then BRBs were provided to form dual systems. A test with a conventional brace was also included for comparison purposes. The values of the damping ratio were calculated for each case. The results show that the BRBs increase the damping ratio on structures significantly. This happens even under linear-elastic behaviour. The contribution of each BRB to the damping is quantified and presented in this paper. The findings of this study are significant because they show that BRBs start dissipating energy at very small displacement levels, and this energy dissipation must be taken into account in the context of performance-based seismic design, in order to estimate the behaviour of BRB-equipped structures reliably.