GOALI: Development of a Seismic Design Methodology for Precast Floor Diaphragms

University Of Arizona, Tucson AZ

Investigators

Abstract

Development of a Seismic Design Methodology for Precast Floor Diaphragms -- CMS 0324522 PI: Robert Fleischmann, Arizona A consortium comprised of the University of Arizona (UA), the University of California San Diego (UCSD), and Lehigh University (LU), together with the Precast/Prestressed Concrete Institute (PCI) proposes a collaborative research project to develop a comprehensive, accurate, and efficient design methodology for precast concrete floor diaphragms in buildings under seismic loading. To this collaboration, the universities bring knowledge of critical issues for precast floor diaphragms under seismic loads, as well as the required analytical and experimental expertise and facilities. PCI, which represents the precast concrete industry nationwide, brings knowledge of industry practices, standards, and economics, as well as project co-funding. Using closely integrated experimental and analytical simulations, the project will significantly advance knowledge of the seismic behavior of precast floor diaphragms and develop information on the stiffness, strength, and ductility capacity of critical precast diaphragm elements. Integrating these results with industry knowledge, the project will produce an appropriate seismic design methodology. The project is proposed to the NSF.s Grant Opportunities for Academic Liaison with Industry (GOALI) program as an Industry-University Collaborative Project. The development of an appropriate seismic design methodology for precast concrete floor diaphragms is challenging and addresses several critical issues: (1) the seismic force levels developed in diaphragms depend on dynamic interaction between the diaphragms and the primary lateral force-resisting elements (e.g., shear walls and moment resisting frames); (2) the dynamic interaction depends on the elastic and inelastic behavior of both the diaphragms and the lateral force systems; (3) as a result of items (1) and (2), simple, accurate estimates of design forces for diaphragms are difficult to make; (4) the inelastic behavior of precast diaphragms, including the internal force-resisting mechanisms, and the deformation demands and capacities of critical elements, is complex and poorly understood because of the jointed nature of these diaphragms; (5) details to anchor the diaphragms to the lateral force-resisting elements are needed; and (6) accurate methods to estimate the lateral drift demands on the building's gravity-force resisting systems due to the flexibility of precast floor diaphragms are needed. To address these issues, the consortium's research will integrate the following: (1) large-scale experiments to determine the flexibility, strength, and ductility of critical diaphragm elements by applying both simple cyclic force patterns and histories, and complex (multi-degree-of-freedom) force patterns and histories; (2) detailed finite element (FE) analyses of complete floor diaphragms (under seismic load) to determine critical force patterns and histories for diaphragm elements that will be applied in the experiments and used in developing diaphragm design requirements; (3) nonlinear time-history dynamic analyses (NTDA) of prototype buildings to determine diaphragm seismic force levels; (4) quasi-static diaphragm tests and shaking table tests of entire structures to verify the FE and NTDA results and provide added input into the large-scale experiments on critical diaphragm elements; and (5) industry knowledge of precast construction methods and economics, design practices, and design code development issues. Intellectual Merit. The project will develop new knowledge of the dynamic interactions between floor diaphragms and the primary lateral force-resisting elements under the conditions where the diaphragm flexibility is not negligible and inelastic behavior of the diaphragm is likely. The project will also develop new knowledge of the inelastic behavior of precast diaphragms, which is complex owing to the jointed nature of the precast system and the flexibility and limited deformation capacity of the reinforcement across the joints. To accomplish these goals, the project will advance the state-of-the-art in integrating large-scale experimental simulations with analytical simulations, and this integration will be accomplished across institutions, with UA providing the analytical simulations to drive experiments at LU and UCSD. Broader Impact. The project will directly impact seismic design practice and codes for precast concrete buildings. The interest of industry is evidenced by the number of industry participants and advisors, and PCI's financial contributions ($426,000) to the project. The project results, when deployed, will result in safe and economical precast diaphragm designs. In addition, the project will support 4 graduate students, who will be educated by the research and the interactions with industry practitioners. The research results will be utilized in graduate curriculum at the participating universities and in short courses for industry practitioners.