Development, Testing, and Analysis of a Rotational Friction Connection for Improving the Seismic Performance of Metal Building Systems with Hard Walls

Abstract

The use of metal building systems has become commonplace in today’s society. For well over two decades, the performance of metal building systems during seismic events has been the subject of intense research. It was revealed that the concrete/masonry hard wall cladding in metal building systems is susceptible to falling away from the structure in major seismic events. The majority of the past research efforts, both experimental and analytical, has been focused on improving the seismic performance of the metal building moment frame. In order to obtain a more complete picture of the seismic performance of metal building systems clad with hard walls, the seismic performance of the longitudinal direction (parallel to the ridge) needed to be investigated. The research presented in this dissertation focused on understanding and improving the longitudinal seismic performance of metal building systems clad with hard walls.

Post-earthquake reconnaissance following the Haiti 2010 earthquake and the Christchurch New Zealand earthquake 2011 highlighted the dangerous effects of connection failures in the hard walls of metal building systems. There exists a large stiffness differential between the hard walls and steel frames, which in turn generates high demands on brittle connections. The problem is exacerbated by little to no 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. Collapsing wall panels in metal buildings are a life safety issue, as well as an economic concern.

The research presented in this dissertation developed a simple, reliable, friction-based energy dissipating connection, the rotational friction connection (RFC). The energy dissipating mechanism of the connection is geared towards the in-plane horizontal direction, while maintaining out-of-plane strength. To assess the energy dissipating capacity and reliability of the rotational friction connection, experimental tests were performed including monotonic pushover, unidirectional cyclic, bidirectional, out-of-plane, and high cycle testing. Results show that the connection exhibits high ductility and resiliency. Replacement of the connection following a seismic event would not be required. 3-D solid finite element models were developed using Abaqus and validated using the experimental data. A parametric study was performed to expand upon the experimental dataset. A simplified component level RFC model was created in SAP2000 and calibrated using the results from the Abaqus model.

A 3-D global finite element model of a metal building system with hard walls was developed to evaluate the improvement that RFCs have on the structure’s seismic performance. Nonlinear dynamic response history analyses were performed using four levels of seismic hazard ranging from a service-level event to a maximum-considered event. A baseline metal building that does not utilize the RFCs served as a comparison with a metal building system that was equipped with RFCs. Results show that there was a reduction in the longitudinal story drifts, significant reductions in the inelastic demands in the longitudinal bracing system, as well as a slight improvement in the moment frame demands.

The results of both the experimental and analytical testing indicate the rotational friction connection shows great potential as a ductile fuse element in metal building system with hard wall cladding.