Keywords: façades, buildings, earthquake, time histories, inter-storey drift, connection, stiffness, damping, distortion, finite element.

Façades are popular in modern buildings and are made of different materials such as pre-cast concrete, glass, aluminium and steel. For a long time, the design of façades had undergone some questionable simplifications, whereby façades have become widely considered to be merely dead weights that do not possess any structural characteristics. Consequently, structural engineers have often allowed the choice of façade and its connections entirely to architects and precast concrete contractors. During recent times seismic activity in densely populated areas has resulted in damage to several buildings and a consequent loss of life. There were many types of building failure, which also included the failure of building façade systems. Façade systems are highly vulnerable and fail more frequently than the buildings themselves with significant devastating effects. During an earthquake building frames suffer large inter-storey drifts, causing racking of the building façade systems. The façade systems may not be able to cater for such large deformations and this can result in either the functional or total failure at the façade connections or damage by pounding (impact) with adjacent façade panels. The importance of a well designed façade system on a building needs to be emphasised as it must address the above mentioned important structural considerations as well as environmental and energy conservation aspects as they represent between 15 - 30% of the total building cost.

A research project has been carried out at the Queensland University of Technology to investigate the influence of connections and their energy absorption capability on the seismic performance of building façade systems. The objectives of the study are to determine and control façade distortions to avoid failure and to establish the required connection properties. This paper presents some of the results of that investigation and treats the effects of façade and connection properties on this response. Finite Element techniques have been used for modelling and analysis of the building frame, façade and connections. Beam and shell elements were used to model the frame and façade respectively, while link elements with stiffness and damping properties were used to model the connections. Time history analyses under earthquake loadings were carried out to determine the system response in terms of inter-storey drifts, façade distortions, differential displacement between façades and frames, the relative lateral displacement between façade panels and the axial force in horizontal connections. Connection properties with respect to stiffness and energy absorption capability (or damping) have been modelled and varied to obtain the desired response.

Results show that it is possible to reduce façade distortions and relative displacements by significant amounts by using connections with appropriate properties and that energy absorption at connections is by far the most important controlling parameter. Findings illustrate the influence of these connection properties on system response and show that it is possible to control façade distortions to be within acceptable limits. They also demonstrate that energy absorbing connections are able to reduce inter-storey drifts and mitigate the detrimental seismic effects on the entire building façade system. The result has also demonstrated that the introduction of façade to the building frame shown to have significant effect on the behaviour of structure. It is hoped that the results will be useful in designing suitable connections to obtain satisfactory seismic response of building façade systems.

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