This award is an outcome of the NSF 08-519 program solicitation, "George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES) Research (NEESR)" competition and includes the University of Washington (lead institution), University of Minnesota (subaward), and University at Buffalo, SUNY (subaward). This project will utilize the NEES equipment sites at the University of Minnesota and University at Buffalo and has strong international collaboration with large-scale experiments to be performed at the National Center for Research in Earthquake Engineering (NCREE) in Taiwan. The goal of this project is to develop a smart and resilient steel plate shear wall (SR-SPSW) system with the potential to transform seismic design in areas of moderate and high seismicity. The system strategically combines the benefits of self-centering and steel plate shear wall technologies to create a robust, ductile, and easily repairable system that will reduce life-cycle costs for buildings. Most traditional seismic load resisting systems will suffer structural damage during seismic events; the cost and downtime associated with repair of that damage has led to staggering economic losses. The proposed SR-SPSW system could drastically reduce those losses. SPSWs are excellent candidates for the application of self-centering technology; they have high strength and elastic stiffness and require low re-centering forces. The buckling and yielding behavior of the web plate will also be leveraged to develop self-sensing concepts such that post-event decisions regarding web plate replacement can be made with minimal disruption. SPSW behavior under earthquake loading is highly nonlinear, and complex component interactions exist; of particular complexity are the interactions between the web plate tension field action and the forces in the re-centering mechanisms of the proposed SR-SPSWs. Large-scale testing using advanced experimental techniques and instrumentation will generate data to be used to develop numerical models anchored in physical behavior. Application of those tools in parametric analyses of SPSW systems will provide a new level of understanding of the system response and help to eliminate overly conservative design processes. To ensure that the new SR-SPSW system will be implemented, and to increase the use of conventional SPSW systems, this research will also seek to fill critical knowledge gaps in SPSW system behavior including the understanding of coupled SPSW behavior and the expected distribution of yielding in multistory SPSW. The project also includes a series of activities that will advance the NEES education, outreach, and training goals. Through collaboration with Seattle-MESA, the project will engage high school students from underrepresented minorities in structural engineering and laboratory experimentation, ultimately helping to promote diversity in engineering and science. The project team also includes faculty and undergraduates from Seattle University, a predominantly undergraduate institution, who will contribute to the research endeavor. The project will excite K-5 students about science and engineering through the development of the Wicked Walls program; a hands on learning activity showing students the benefits of walls for seismic resistance. Finally, outreach to practicing structural engineers will occur through the Seismic Provisions committee, conference presentations, and seminars with the cooperation of AISC. The research team experience in developing national and international codes ensures that research outcomes will have an immediate impact on design practice. Data from this project will be made available through the NEES data repository (www.nees.org).
This project is documented in the NEES Project Warehouse #631: https://nees.org/warehouse/project/631 Team: Jeffrey Berman, PI, University of Washington; Laura Lowes, co-PI, University of Washington; Larry Fahnestock, co-PI, University of Illinois, Urbana-Champaign; Michel Bruneau, co-PI, University at Buffalo; K.C. Tsai, Collaborator, National Taiwan University. Steel plate shear walls (SPSWs) have become an economical seismic force resisting system that offer excellent performance relative to other steel and reinforced concrete systems. The SPSW system comprises a steel frame with thin steel infill plates, referred to as web plates, that are allowed to buckle in shear and develop tension field action under lateral loading. These web plates provide significant stiffness, strength, and energy dissipation. The structural properties of the system and its architectural flexibility make it especially attractive in high seismic regions. Despite these advantages of SPSWs, their implementation in U.S. construction is limited. Further, like conventional lateral load resisting systems, SPSWs rely on structural damage to dissipate the input energy of earthquakes. There is a need for new system concepts that limit damage to easily repaired elements, reducing earthquake losses. This research project investigated key knowledge gaps that are limiting SPSW implementation and also extended the technology to develop a resilient SPSW system that has the potential to minimize post-earthquake downtime and repair costs. Image 1 shows the overall themes and areas of research concentration. A mixture experimental and computational methods were used. NEES computational resources and the unique capabilities of two NEES facilities, NEES@Buffalo and NEES@Illinois, were leveraged. Critical knowledge gaps in SPSW design and behavior were addressed by: Studying the behavior of tension field action as the web plate yields, as occurs in large earthquakes, using small-scale experiments and advanced computational modeling (Image 2). Results were used to develop more accurate models of the behavior to be used by structural engineers when designing SPSWs, which should improve their design economy. The results are also being used to draft changes to building provisions for SPSW design. Developing a database of past results from SPSW experiments which was used to develop performance-based seismic design tools. This advance will allow SPSWs to be designed using state-of-the-art methods that are beginning to be used in practice. Studying coupled SPSW behavior for the first time in the U.S. using the unique multi-axial loading capabilities of the NEES@Illinois laboratory. Two half-scale coupled SPSWs were tested (Image 3). The results of the experiments and corresponding computational analyses were used to develop building code recommendations for coupled SPSWs, which would greatly expand their implementation. The resilient SPSW system developed as part of this project utilizes post-tensioned beam-to-column connections that allow the system to re-center itself following an earthquake, enable the beams and columns to remain essentially undamaged, and ensure the damaged web plates can be easily replaced. As illustrated in Image 1, the development of the system and corresponding design recommendations required computational analysis and large-scale experiments. Tests on subassemblages of the beam-to-column connections were conducted at the University of Washington, quasi-static and dynamic shake table tests were conducted in the NEES@Buffalo facility on three resilient SPSW designs that featured different beam-to-column connections (Image 4), and a final validation of the concept was completed through full-scale tests on two different resilient SPSW systems at the National Center for Research in Earthquake Engineering in Taiwan (Image 5). A performance-based seismic design was procedure was developed whereby the structural engineer can target various levels of seismic performance (in terms of damage and overall system deformation) for specific levels of seismic intensity. Computational analysis of prototype resilient SPSW systems, performed on NEES allocations of TerraGrid resources, demonstrated the performance targets could be achieved. The final full-scale validation tests performed in Taiwan further validated the design procedures as post-earthquake re-centering was achieved and damage was limited to only easily repaired web plates (Image 6). The research conducted will help improve building seismic performance and reduce earthquake losses. Several advances have resulted in proposed modifications to the buildings code. The project involved undergraduates in the research through collaboration with Seattle University (a predominantly undergraduate institution) where a team of students helped to develop, design and analyze prototype SPSW systems and through Research Experiences for Undergraduates. A series of summer internship experiences in the UW structural research laboratory for high school students were undertaken in collaboration with Seattle-MESA to reach groups underrepresented in STEM fields. A total of twelve students participated and all have gone on to college, several choosing engineering fields. Significant contributions to workforce development were made. Four Ph.D. students wrote their dissertations on aspects of the research. Two of them are now Assistant Professors at major research universities and two are in practice. Three students completed master’s thesis research on the project, one continued on to a PhD., and two are in practice at large firms in Chicago and Seattle.
