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More than 30 years have passed since the 1994 Northridge earthquake, which exposed vulnerabilities in precast concrete structures. Since then, engineers have made great strides in working to ensure buildings better withstand seismic forces– including a recent study that resulted in new models showing how critical structural elements in buildings behave during earthquakes.

By using U.S. National Science Foundation (NSF) ACCESS allocations on Expanse at the San Diego Supercomputer Center, part of the UC San Diego School of Computing, Information and Data Sciences, the multi-institutional Steel Diaphragm Innovation Initiative (SDII) team created the models to better understand the behavior of concrete-filled deck floor diaphragms during a tremblor.

The SDII project is led by Prof. Ben Schafer from Johns Hopkins University and Prof. Jerome Hajjar from Northeastern University. They established the project to investigate and improve the design of both bare and concrete-filled steel deck diaphragms. Hajjar, who is the Northeastern University Distinguished Professor, CDM Smith Professor and Department Chair in the Civil and Engineering Department, said that initial findings after Northridge revealed that elastic diaphragm force demands in some types of buildings could be much higher than U.S. building codes had previously suggested. He said that this decades-old revelation prompted continued extensive experimental testing and computational modeling to explore the strength and ductility of various floor systems under seismic stress, with the SDII project specifically focused on floor diaphragms in steel building structures.

“Early phases of the SDII project included push-out tests to assess local responses of steel connectors under cyclic loads, as well as cantilever diaphragm tests to understand system-level behavior with simplified conditions,” Hajjar said. “However, the culmination of our most recent study used SDSC’s Expanse for simulating a full-scale experimental test of a concrete-filled steel deck diaphragm experiment that replicated realistic construction practices, force distributions and boundary conditions.”

He said that their work was the most comprehensive test of its kind and evaluated two primary failure modes: connector shear failure and diagonal tension cracking. As part of this research, Hajjar is leading a team to do a large parametric investigation on Expanse to investigate the detailed fracture behavior of connector shear studs.

“The diaphragm ultimately demonstrated significant strength before succumbing to diagonal tension cracking,” Hajjar said. “The data gathered from this test offers critical insights into how forces flow through steel diaphragms during earthquakes and our findings are now being used to support new design provisions aimed at making steel deck diaphragms more resilient in seismic events.”

The team recently shared their work at the 18th World Conference on Earthquake Engineering. Additional academic institutions involved with the SDII include include Iowa State University and Virginia Polytechnic Institute and State University. Computational support was provided by NSF ACCESS (allocation no. BCS110001).