NEESR-SG: Seismic Performance Assessment and Retrofit of Non-Ductile RC Frames with Infill Walls

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ABSTRACTUnreinforced masonry in fills are frequently found as interior partitions and exterior walls in buildings, and are normally treated as non-structural elements. However, unlike most non-structural components, they can develop a strong interaction with the bounding frames when subject to earthquake loads and, therefore, contribute significantly to the lateral stiffness and load resistance of the structure. In spite of the research that have spanned several decades, the performance of these structures in a severe earthquake remains a major controversy among structural engineers and researchers today. The main aim of the proposed research is to develop rational and reliable methodologies for assessing the seismic safety and performance of masonry unfilled RC frames, and develop practical and effective techniques for the seismic retrofit of these structures using conventional as well as innovative materials. The project will include the development of reliable analysis tools that range from advanced computational models to simple analytical methods that can be used in engineering practice. The project will take advantage of the vast computational resources and experimental facilities provided by NEES. The analysis methods and retrofit techniques will be first validated with medium-scale experiments to beconducted with the NEES Fast Hybrid Test facility at the University of Colorado at Boulder. Final proof-of-concept tests will be conducted on a 3/4-scale three-story RC frame using the NEES Large High Performance Outdoor Shake Table at the University of California at San Diego. Stanford University will focus on the development of sprayable high-performance fiber-reinforced cement-based composites for infill retrofit. The work will be carried out as a multi-institutional, inter-disciplinary effort by a diverse research team with expertise in professional practice, structural design, structural testing, structural analysis, computational mechanics, and composite materials. Understanding and assessing the seismic performance of masonry-infilled non-ductile RC frames presents a most difficult problem in structural engineering. Currently, there are no reliable engineering guidelines for this. Analytical tools to evaluate the complicated frame-infill interaction and the resulting failure mechanisms need to be built on the fundamental principles of mechanics and sound engineering judgment. It is far more challenging than analyzing a pure RC or masonry structure. This research will fill a major gap in the modeling and performance assessment of this class of existing structures that can be frequently found in regions of high seismic risk and the development of effective retrofit strategies to prohibit the undesired failure mechanisms from a system perspective. The project will involve the development of new design and assessment techniques, new materials, and cutting-edge computational methods, which will be intellectually stimulating. The leverage provided by the successful programs on education and outreach that are already in place at UCSD, CU, and Stanford, and the additional resources that will be secured outside NEES will reinforce the common education and outreach goals of NEESinc. The proposed round-robin studies and outreach activities using the collaboratory tools, and the telepresence and data archiving and mining capabilities provided by the NEESgrid will assure timely dissemination of information to the broad engineering and lay communities. The advanced computational models developed in this project will be readily applicable to many new and existing structures and provide a 3-D model-based simulation capability that can potentially replace physical experiments in a foreseeable future. The implementation of the advanced computational models in a public-domain software, OpenSEES, which is supported by the NEESgrid, will benefit the earthquake engineering community at large. The retrofit techniques explored can potentially lead to significant savings by building owners and enhance the seismic safety of a large number of existing structures. The simplified analytical tools, design and assessment methodologies, andexperimental data will provide the much needed information and tools for the next-generationperformance-based seismic design guidelines on this class of structures. The integration of design, computation, and experimentation in this project provide a unique experience for the training of future earthquake engineers on performance-based engineering.