3-D Model Development of Metal Building Systems with Hard Walls

Abstract

Metal Buildings with precast concrete or masonry walls (hard walls) have been identified by analytical modeling, shake table tests, and earthquake reconnaissance as being susceptible to collapse. While the steel frames have been shown to be resilient, the potential for wall failure and possible collapse is present. There exists a large stiffness differential between the hard walls and steel frames, which in turn generates high demands on brittle connections. Also, there is very little coordination between the metal building systems (MBS) engineer and the engineer-of-record who is responsible for the connections, which can result in improper connection design. When these connections fail in a non-ductile manner, the continuous load path is lost and the wall can fall away from the structure. In order to enhance the global seismic performance and improve life safety of these structures, a new seismic force resisting system that relies on simple energy dissipating connections between the hard wall and the steel frame needs to be developed. The initial step towards accomplishing this goal, and the purpose of this research, is development of a 3-D model of metal building systems with hard walls in SAP2000 that can be used in nonlinear response history analyses. A new modeling procedure had to be developed for capturing the post-buckling behavior of a metal building frame during an earthquake. This modeling procedure included the development of a Lateral Torsional Buckling (LTB) Hinge that approximates the post-buckling behavior. The metal building frame capacities, as well as the demarcation between elastic and inelastic behavior, were determined through finite element analyses using Abaqus. Post-buckled frame behavior was modeled in SAP2000 using the newly developed LTB Hinge. Dynamic analyses were performed for 2-D planar frame models and 3-D models to assess the cyclic behavior of the LTB hinge. This 3-D model, now including post-buckling behavior, can effectively be used to analyze the global performance of a metal building system with hard walls, as well as quantify connection strength, post-yield deformation, and energy dissipation capacities required to achieve enhanced performance of these systems.