Design of gravity force-resisting systems accounting for seismic displacement demands

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The structural system in a building must be designed to resist both vertical loads from gravity, as well as lateral loads imposed by wind or seismic action. It is common in structural design for the structural frame to consist of two separate systems: a gravity force-resisting system and a lateral force-resisting system. While seismic codes have traditionally focused on the design requirements of lateral force-resisting systems, ground shaking due a seismic event will cause the entire structure to deform, i.e. it will impose deformation demands both in the gravity and the lateral force-resisting systems. In this regard, the latest edition of the concrete design standard in Canada recognizes that failure of gravity frames is one of the most common causes of building collapse during an earthquake. Thus, the code introduced a new requirements intended to ensure adequate levels of strength and ductility in elements that are not part of the seismic force-resisting system, but are subjected to seismically induced deformations. Conventional structural design relies on equivalent linear elastic analysis models to replicate anticipated nonlinear response in buildings. However, this new requirement of the concrete design standard in Canada does not address how to accurately develop this equivalent linear elastic analysis model for the seismic design of gravity frames. To address this challenge, Glotman Simpson is partnering with the University of British Columbia to develop a procedure that provides consistent and trustworthy results to facilitate these new design checks of gravity frames per the latest code requirements. This work will facilitate the continued delivery of safe and economical designs.