Experimental and numerical study on seismic behaviour of aluminium alloy frames

Aluminum alloys have continued to attract growing attention in academia and construction industry. This can be attributed to their numerous advantage and remarkable properties, such as high strength-to-weight ratio and ease of fabrication. In fact, the application of aluminum alloys in engineering structures has dramatically increased in the past decades. More recently, their applications in frame structures have emerged as an effective alternative because they are durable, recyclable and easy to assemble and disassemble.

Numerous studies have been carried out to enhance the structural performance of aluminum alloy frames and their components and promote their applications. Nevertheless, despite the growing body of knowledge in this direction, there are limited studies on the structural behaviors of aluminum alloy frames under earthquakes. Due to the light weight of aluminium alloy frames, the seismic loads acting on them are relatively smaller than that acting on concrete and steel structures. Regardless, understanding the seismic performance of frame buildings constructed of aluminum alloys is critical in improving the safety integrity of such buildings.

On this account, Associate Professor Zhongxing Wang from Tianjin University together with Professor Yuanqing Wang from Tsinghua University, Professor Beibei Li from Hefei University of Technology and Dr. Ying Zhang from Tsinghua University conducted a comprehensive numerical and experimental investigation of the seismic behavior of aluminum alloy frame structures. In particular, they focused on the cyclic response of beam-to-column joints, which play a fundamental role in the seismic design of frames. Their research work is currently published in Journal of Building Engineering.

In their approach, four full-scale aluminium alloy beam-to-column joints connected with swage-locking pins were designed and tested under cyclic loads. During testing, two joint types (web angle cleats connection (TSWAC) and top-and-seat angle cleat connection (TSAC)) were studied, considering the influence of various material and geometric parameters. The specimen design, instrumentation, test setup and loading process were reported. Key structural performance data, including test observations, stiffness degradation behavior, energy dissipating capacities and hysteretic responses for all the joints, were obtained and evaluated.

The authors observed several failure modes. They included the block shear failure at the collar pull-out of the swage-locking pin and beam end and fracture at the angle cleats and web-to-flange junction of the beam. All studied specimens exhibited good ductility and hysteresis response characterized by pinching effect and stiffness degradation. Specifically, specimen TSWAC-S2-C recorded the best seismic performance regarding energy dissipating capacity, rotation and moment resistance. The seismic performance of the joint could be improved further by using stronger swage-locking pins and stainless-steel angle cleats and increasing the slip factor.

The seismic behavior of a typical full-scale 2-story aluminum alloy frame developed using OpenSees program was evaluated under various earthquake hazard levels using different performance indices. Its seismic performance was analyzed to validate the proposed numerical model. Results showed that the joint rotations and inter-story drift response of the aluminum alloy frame were relatively smaller than the preselected limit values under FOE, DBE, MCE and ERE levels. This suggested that the deformation performance of the structural frame could be predicted and controlled effectively using appropriate design. While economically feasible repairment was required for MCE level, FOE and DBE levels required no repairment.

In summary, a comprehensive study of the seismic behavior of aluminum alloy frames was reported. Except for columns under ERE and MCE levels, the column and beam members of the structural frame were in an elastic state. Beam-to-column joints dissipated seismic energy under earthquakes and served as the main fuse-type dissipater because they were in an inelastic state. The findings demonstrated the importance of adequate safety margins for alloy structural frames subjected to seismic loading. In a joint statement to Advances in Engineering, the authors said that their findings provide the basis for the earthquake-resistant design and rapid repair of aluminium alloy frames.