Spring-stiffness model for flexible end-plate bare-steel joints in fire

This paper describes a spring-stiffness model developed to predict the behaviour of flexible end-plate bare-steel joints at elevated temperature. The joint components are considered as springs with predefined mechanical properties (i.e. stiffness and strength). They are also assumed to follow a trilinear force-displacement relationship. The elevated temperature joint's response can be predicted by assembling the stiffnesses of the components which are assumed to degrade with increasing temperatures based on the recommendations presented in the design codes. Comparison of the results from the model with existing experimental data showed good agreement. Also, the predicted degradation of the joint's stiffness and capacity compares well with the experimental results. The proposed model can be easily modified to describe the elevated temperature behaviour of other types of joint as well as joints under large rotations.