Out-of-plane dynamic response behaviour of brick veneer steel-framed walls

Abstract

© 2014 Dr. Vidal Patrick Paton-ColeThe research presented in this thesis contributes towards the body of knowledge about the out-of-plane behaviour of brick veneer steel-framed domestic structures when subjected to seismic loading. It provides a global outlook on the performance of these low-rise structures in accordance with New Zealand and Australian masonry construction practice under particularly large magnitude earthquakes, which has never been studied in the past. Prior to this research, most of the published data has only focussed on brick veneer walls built on timber framing and on load bearing unreinforced masonry (URM) walls. In this research, an extensive seismic test program was designed to undertake a comprehensive series of shaking table tests on a typical brick veneer structure. The main aim was to assess the behaviour of the brick walls when subjected to out-of-plane loads and understand the interaction of the brick veneer walls with the structural frame via the brick ties. A three-dimensional steel-framed brick veneer test structure representative of domestic houses built in New Zealand was constructed on a bi-directional shaking table. The test structure measured approximately 2.6m x 2.8m x 2.4m high and designed such that its stiffness and dynamic characteristics are representative of a typical single-storey house. The out-of-plane behaviour of the brick veneer walls were assessed using destructive simulated earthquake excitations. The El-Centro earthquake record which is compliant with the New Zealand Earthquake loading standard (NZS 1170.5) was adopted to conduct the tests and scaled in accordance with performance levels in NZS 1170.5. Nine different high levels earthquake tests were conducted starting from the Serviceability Limit State (SLS) to well beyond the Maximum Considered Earthquake (MCE). The test structure was subjected to excitations in each direction up to the MCE level of earthquake intensity. As part of the experimental program, small-scale component tie-stud connections were tested to evaluate their in-service behaviour. In the analytical investigation, detailed two-dimensional Finite Element (FE) models were developed in ANSYS and validated against the experimental results. The models were adequate to capture the out-of-plane behaviour of the brick veneer walls while providing acceptable results of the distribution of forces in the wall ties. Detailed analyses were undertaken for both uncracked and cracked conditions of veneer walls. The FE models were used to conduct sensitivity analyses to examine the influence of varying certain critical parameters on the out-of-plane response of the brick veneer wall. Results of analyses indicated that the cracked wall behaviour is most critical to the ultimate performance behaviour of the wall. Experimental and analytical results have shown that the strength and stiffness requirements given in the joint tie standard AS/NZS 2699.1 are not representative of brick ties attached to steel studs. Laboratory and analytical investigations also revealed that less stiff earthquake duty rated ties are not detrimental to the out-of-plane performance of brick veneer walls if sufficient strength is achieved at both ends of the tie connection. Accordingly, it was proposed that brick veneer structures similar to those described in this research would be expected to exhibit acceptable performance in regions of moderate to high seismicity. The final phase of this research proposed a simplified approach for analysing the out-of-plane response behaviour of brick veneer walls. A nonlinear lumped mass model was developed and validated against time-history analyses. Results indicated that the simplified model adequately predicts the wall response behaviour with acceptable level of accuracy. The model provides a simple tool for use by practising engineers for analysing such wall systems. Based on findings from this research, design recommendations have been proposed for enhancing the understanding of out-of-plane seismic performance of brick veneer steel-framed structures