System Level Seismic Performance of Steel Gravity Framing

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In typical steel buildings in the United States, the lateral force resisting frames designed to resist lateral seismic loads comprise a relatively small portion of the structural system, while the remainder of the structural system is designed to resist gravity loading only. This gravity framing normally consists of composite beams with concrete on metal deck flooring, which are connected to the building columns via simple shear connections. The gravity framing, while not explicitly designed to resist lateral seismic loads, can provide significant lateral load resistance, particularly due to the large number of gravity frames in a building. The large deformation capacity and reserve strength provided by the gravity framing can play an important role in preventing collapse of steel buildings under very large earthquake ground motions, particularly for existing buildings that may not have been built to the current standards required for construction of buildings in high seismic regions. The largest impact of this research is expected to be on advancing evaluation procedures of the seismic safety of existing steel buildings, where inclusion of the gravity system in the evaluation may preclude the need for costly seismic retrofit measures. Such comprehensive evaluation procedures will allow limited resources for seismic retrofit to be used more efficiently. This research will also inform best practices for the design and detailing of the gravity system in new buildings that will further enhance the gravity system's ability to serve as a "back-up" to the primary lateral force resisting system, thereby enhancing the seismic safety of new buildings. Seismic-resistant buildings will promote post-earthquake national welfare, health and prosperity by reducing building damage, economic and human losses, and injuries. Data from this project will be archived and publicly available in the Natural Hazards Engineering Research Infrastructure Data Depot (http://www.DesigSafe-ci.org). The overall goal of this research is to investigate the role of gravity framing systems on the seismic performance and collapse resistance of steel buildings through large-scale, system-level testing and robust numerical simulations. Through testing of large-scale, multi-bay, multi-story steel gravity framing systems, this research will create new experimental data on the response of steel gravity systems with composite floor systems, including considerations of the interactions and restraint provided by surrounding bays of gravity and lateral framing. This experimental data will lead to better understanding of the force-resisting mechanisms in steel gravity framing systems, including contributions from connection components, metal decking, and concrete flooring. This data, along with existing data in the literature, will be used to develop more realistic component level models for steel gravity framing connections to support seismic simulations of steel building performance up to collapse. These new connection models, which will be disseminated to the engineering practitioner and research communities, will also be employed in parametric computational studies of a variety of archetype buildings with variations in lateral and gravity framing designs to investigate the role of gravity framing systems in reducing the seismic collapse risk of steel buildings.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.