Load-slip behaviour of single-leg bolted angle steel connections at elevated temperatures

Steel lattice transmission towers and communication towers are vital infrastructure components of power grid and telecommunication systems, respectively. They are usually located in rural or urban wildland areas and can be prone to bushfires or wildland fires in the current climate of heatwaves and droughts. However, an understanding of the resilience of steel lattice towers in fire has not received due attention. Such lattice structures are commonly made from steel angle members with bolted connections in which slippage might occur inevitably due to relatively larger size of bolt holes for erection purpose. Therefore, this paper investigates the axial load-slip behaviour of the single-leg bolted angle steel connections at elevated temperatures for the steel lattice structures. A three-dimensional finite element model is developed for the investigation by using ABAQUS software. Temperature-dependent material nonlinearities and the interaction of structural components at elevated temperatures are taken into account in the model. An effective approach of generating bolt pretension and the quasistatic analysis method using the dynamic explicit procedure are adopted for the analysis. The reliability of the developed finite element model is validated by comparing its predictions with available experimental results reported in the open literature. By using the validated finite element model, extensive parametric studies are conducted to elucidate the effects of the change in the angle section dimension, the direction of applied loading, the grade, size and number of the bolts on the load-slip responses of the connections at elevated temperatures. A simplified theoretical model in component formulation form is proposed and verified for predicting the axial load-slip curves of the single-leg bolted angle steel connections at elevated temperatures and would be applicable to advanced analysis of steel lattice structures considering joint slip.