In-plane seismic performance of glass facade systems

Glass façade systems in buildings are subject to racking action due to inter storey drift caused by earthquake and wind actions. The performance of façade systems is dependent on the amount of imposed drift and the interaction of the glass panels with the façade structural support frames. There are two major concerns related to the glass façade system performance during and immediately after a seismic event, hazards to people from falling glass and cost associated with building down time and repair. Glass façade systems can be classified into two types namely, framed glass façade system (FGFS) and point fixed glass façade system (PFGFS). It was observed that the damage to glass façade systems resulting from in-plane racking actions mainly earthquakes is increasingly common and yet there have been limited number of published research work available in this field. The research conducted to date mainly focused on traditional framed glass façade systems. However, the seismic performance of PFGFS is likely to be quite different from conventional framed systems. Therefore, the aim of the research presented in this thesis is to assess the inplane racking performance of PFGFS which is gaining popularity worldwide. Two unique full scale in-plane racking laboratory tests (Test #1 and Test #2) on typical PFGFS with different types of spider arms (brackets to connect the glass and the structural support frame) were conducted. Detailed 3-D finite element models were developed and validated against the experimental test results to interpret the racking behaviour of PFGFS. Specific racking mechanisms were attributed to the drift capacity in each test. Further detailed FE analyses were conducted to evaluate the individual drift contributions of each racking mechanism such as rigid body translation at the built-in standard gaps, spider arm rotation and spider arm deformation. It was found that most of the drift capacity is attributed to the rigid body translation at the built-in standard gaps. The FE models were then used to predict the racking performance of PFGFS with different configurations. The seismic assessment of glass façade systems requires an estimate of the likely drift demand from the building. Codified provisions for in-plane drift limits on glass façade systems can be used as a conservative option. Analysis results presented in this thesis indicated that the inter-storey drift demand is much less than the 1.5% limit specified in AS 1170.4 (2007) for most buildings in Australia for a 500 year return period seismic event except for soft storey structures. Standard seismic assessment procedures can be used to estimate the optimum in-plane seismic drift demands from the buildings. Based on that some rapid inter storey drift assessment methods were presented with example calculations. Conservatively, the in-plane racking capacity of PFGFS resulting from the rigid body translation of the glass panels at the built-in standard gaps can be used as the design in-plane drift capacity. If required, the drift capacity can be increased by introducing special articulation features at the bolted connections. Care should be taken at the boundary conditions of the perimeter glass panels to achieve the racking capacity of the PFGFS from the rigid body translation at the built-in gaps. In order to assist façade engineers, particularly at the conceptual design stage, a quick selection guide is presented to identify the structural components of PFGFS which can increase the racking performance of the façade system.