NEESR-CR: Assessment of Punching Shear Vulnerability of Slab-Column Connections with Shear Stud Reinforcement

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This award is an outcome of the NSF 09-524 program solicitation "George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES) Research (NEESR)" competition and includes the University of Michigan (lead institution), the University of Minnesota, Twin Cities (subaward), and the University of Minnesota, Duluth (subaward). This project will utilize the NEES equipment site at the University of Minnesota (Twin Cities). Structural systems that consist of slabs directly supported by columns or flat plate frame systems are widely used in concrete construction because of their architectural appearance, functionality, and economy. In regions of high seismic hazard, they have been used in structures of up to 60 stories, in combination with structural walls or moment resisting frames. Because of their potential for punching shear failures during earthquakes, shear reinforcement is often provided in the form of headed shear studs. Results from a test conducted as part of a prior NEESR project (NSF award 0421180), however, have raised serious concerns about the effectiveness of this reinforcement for punching shear resistance. Given the large number of flat-plate structures with headed reinforcement built in the last decade, these test results could be an indication of a latent major problem that could surface in the next large earthquake on the west coast. If this is indeed as serious of a problem as the prior NEESR test results seem to indicate, the earthquake engineering community should act with diligence and prevent a situation similar to that observed with welded steel connections during the 1994 Northridge, CA earthquake.This project involves a group of researchers from three U.S. universities and the Universidad Nacional Autónoma de México (UNAM). The main research objective is to estimate the vulnerability of existing slab-column connections by evaluating the efficiency of typical headed reinforcement designs used in practice. Large-scale slab-column subassemblies will be tested under combined gravity load and biaxial lateral displacements at the University of Minnesota NEES-MAST Laboratory. These tests will allow the evaluation of the vulnerability of slab-column connections with headed stud reinforcement during strong ground motions. Shake table tests of a flat-plate structure will also be conducted at UNAM for evaluation of the response of connections with headed reinforcement under dynamic excitation.Intellectual Merit: This research will generate needed information that will allow practicing engineers and building officials to identify vulnerable flat-plate construction with headed reinforcement. This is one of a very few instances in which experimental research has prompted major concerns about the safety of modern structures before those concerns are confirmed by a major earthquake. Thus, the knowledge developed in this project could have a major impact in terms of protecting lives and reducing financial losses associated with potential failure or collapse of flat-plate structures during an earthquake.Broader Impacts: The education and outreach program targets undergraduate and pre-college level students. Through the use of the teleparticipation capabilities at the University of Minnesota NEES equipment site, these students will have the opportunity to witness the various steps of the experimental program and remotely attend lectures on the basics of earthquakes and design of concrete structures for ground motions. Data from this project will be archived and made available to the public through the NEES data repository.