Advancing Earthquake Engineering of Cast-in-Place Concrete Diaphragms with Openings

University Of Washington, Seattle WA

Investigators

Abstract

In reinforced concrete buildings, cast-in-place floor slabs, or “diaphragms”, must resist both gravity loads, the weight of the structure and building contents, and horizontal loads, caused by wind or the inertia of the floors during earthquakes. For the building to function, these floor diaphragms also must contain openings for stairs, elevators, and mechanical systems. Although the presence of these openings is accounted for when designing the structure for gravity loads, there is little research or understanding of how they affect the building’s behavior during earthquake loading. The potential consequences of this lack of understanding were recently demonstrated during earthquake simulator tests on a five-story reinforced concrete building. Unexpected diaphragm damage during testing indicates that openings adjacent to walls and columns contribute to collapse risk and could preclude or delay the return of a building’s functionality after a seismic event. This Disaster Resilience Research Grants (DRRG) project will develop a fundamental understanding of the behavior of cast-in-place concrete diaphragms with openings and develop tools for their design and for probabilistically quantifying their expected performance during an earthquake. The research will be complemented by an online class curriculum focusing on accurate simulation approaches and their validation, for both students and practitioners, as part of the recently established earthquake engineering certificate program and outreach to engage underrepresented minority and first-generation college students in research. This award will focus on advancing science-based tools and technologies, through simulation-driven experimental testing and nonlinear finite element analysis of prototype buildings under multiple hazard intensities, for the collapse-resistant and recovery-based earthquake engineering of cast-in-place concrete diaphragms with openings. This research will investigate (1) accurate load paths, including fanned collection patterns from regions of low stress to struts, which form the primary load path; (2) the impact of openings and establishing protected zones to mitigate damage that could lead to partial collapse; and (3) damage states and fragility curves that quantify diaphragm performance for inclusion in functional recovery methodologies. Several fundamental research questions will be answered, including (1) what is the inertial load path through the diaphragm, and how are these load paths affected by openings; (2) how does the slab thickness, reinforcement, and the presence of openings affect the capacity of diaphragm elements subjected to complex in-plane stresses; (3) how does the presence of openings modify the effective stiffness of diaphragms, and what is the effect on engineering demand parameters; (4) what is the relationship between engineering demand parameters, ground motion intensity measures, and diaphragm damage; and (5) how does diaphragm damage around openings affect safety, story access, and tenet functionality. Equally important, this project will form the foundation for additional research to fully investigate the lateral force resisting system, including slab-wall and slab-column connections, using pseudo-dynamic and earthquake simulator testing. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.