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

© 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

Out-of-plane performance of a brick veneer steel-framed house subjected to seismic loads

C1 - Journal Articles Referee

Shaking table tests on strength degradation behaviour

Structures such as unreinforced masonry walls, soft-storey buildings, gravity structures and components which include free-standing objects are well known to be non-ductile and yet they are commonly found in regions of low-moderate seismicity. Potential significant degradation in strength in these structural systems in projected earthquake scenarios has been a cause for concern. Shaking table experiments undertaken recently by the authors revealed very interesting phenomena with the behaviour of the (“non-ductile”) free-standing objects in an earthquake. Vulnerability to overturning is shown not to be sensitive to the height of the object nor its aspect ratio. The trends revealed earlier by the authors based on analytical modeling have been confirmed experimentally. Importantly, the displacement time histories predicted by program Rowmanry and Romain are shown to be very consistent with recordings from the shaking table experiments

Out-of-plane performance of a brick veneer steel-framed house subjected to seismic loads

This paper summarises results of an experimental shaking table test program conducted on a single room steel-framed brick veneer house. The Test House was constructed of full scale components and represents current building practices in New Zealand. The primary objective of the test program was to assess the performance of the brick veneer walls when subjected to out-of-plane earthquake loading, having been previously subjected to in-plane loading which has the potential to weaken the veneer/tie/stud system for subsequent out-of-plane loading. The veneer walls of the Test House incorporated typical geometric features in different directions. The Test House was subjected to varying levels of the El-Centro (ElC) earthquake ranging from moderate Serviceability Limit State (SLS) ground motion to excitation well beyond the design Maximum Considered Earthquake (MCE) for New Zealand. These levels of excitation were selected in order to ascertain the response for specific limit states and compare against minimum performance requirements specified in the New Zealand Earthquake Standard, NZS 1170.5 (2004). Results presented are based on comprehensive measurements including acceleration, drift and differential movements between the structural steel frame and veneer. The Test House performed very well, with no brick loss up to 2.6 times ElC earthquake which is well in excess of all performance requirements. The results from the Test House under the onerous testing program reveal that such form of construction would be expected to exhibit good performance under both serviceability and ultimate conditions in New Zealand

Seismic performance of a brick veneer steel-framed house

The use of high-strength, cold-formed steel frames in residential construction is steadily increasing in both Australia and New Zealand. One common form of this construction uses brick veneer as a cladding, where non-structural brick walls are attached to the structural frame via brick ties. Under earthquake loading there is a complex interaction between the frame and veneer walls. While there is a standard component test method for assessing the seismic capacity of brick ties, this method has been developed around brick veneer on timber studs and its application to the very different steel stud characteristics is inappropriate. In order to realistically assess the overall performance of brick veneer construction with steel framing, a full scale one-room test structure "Test House" was tested on a shaking table. The Test House incorporated veneer walls with different geometries. It was subjected to varying levels of the El Centro earthquake ranging from moderate serviceability limit state ground motion to well beyond the design maximum considered earthquake for New Zealand. These levels of shaking were selected in order to ascertain the response for specific limit states to the Australasian Loadings Standard and to compare against minimum performance requirements. Comprehensive measurements on the frame and veneer walls were taken including acceleration, drift and differential movements between the frame and veneer. The Test House performed very well, with no brick loss up to 2.6 times El Centro (ElC) earthquake which is well in excess of all performance requirements