NEESR-CR: An Innovative Seismic Performance Enhancement Technique for Steel Building Beam-Column Connections

North Carolina State University, Raleigh NC

Investigators

Abstract

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). 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 North Carolina State University (NCSU, lead institution) and the University of North Carolina at Pembroke (UNCP, subaward). This project will utilize the NEES equipment site at the University of Minnesota to experimentally validate an innovative technique for enhancing the seismic performance of steel building beam-column connections. Intellectual Merit: The proposed seismic enhancement technique involves heat treating sections of beam flanges by exposing these sections to a very high temperature for certain amount of time before slow air cooling. Such a heat treatment process reduces the strength of steel in the heat treated areas of the flange. Consequently, under seismic loading, a plastic hinge develops at the heat treated beam section (HBS). A connection enhanced by this technique will have the advantages of the popular reduced beam section (RBS) connection, but the HBS will have better energy dissipation than the RBS connection. In RBS connections, "weakening" of the beam flanges induces a plastic hinge away from the welds. In HBS connections, a plastic hinge develops at the heat treated section because of the reduced strength of steel. Moreover, as the beam flange remains intact and the inelastic modulus of steel is not altered at the HBS, the lateral and torsional buckling resistances of the HBS connection will be higher than those of the RBS connection. Consequently, the HBS connection will dissipate a larger amount of energy with a minimum loss of strength or stiffness compare to the RBS connection. Through a pilot study at NCSU, the seismic performance enhancement technique is validated analytically. This project will validate the technique by conducting full-scale connection experiments. Currently, RBS is the most popular connection design because of its seismic performance and cost effectiveness. The HBS connection is anticipated to be more seismically robust and economical than the RBS connection. The research will be performed through integrated experimental and analytical studies. Material experiments of heat treated and unconditioned coupons will be conducted and data will be analyzed to quantify the influence of heat treatment parameters (peak temperature and hold time) on the reduction of strength and to determine the constitutive model parameters. Detailed structural analyses of HBS connections will be performed to determine the optimum heat treatment parameters and geometry of HBS. Beam-column connections with and without HBS will be built and tested to demonstrate seismic performance enhancement of the modified connections. Detailed measurement of strains, displacements and rotations at various locations will be recorded for investigating both the local and global failure modes of HBS connections. Experimental and analytical results will be used to refine the technique and to develop a methodology for practical application of the technique. Broader Impacts: The research results will be integrated into professional development courses, and the research will involve faculty and students from a predominantly undergraduate Native American institution in the experimental activities. A methodology for application of the novel technique will be developed and disseminated. The heat treatment concept is applicable to steel building or bridge connections; the proposed heat treatment technique will benefit industries that use welded joints. Experimental data from this project will be archived and made available to the public through the NEES data repository.