Mechanical properties and creep behaviour of cheese head studs for arc stud welding at elevated temperatures

Cheese head studs for arc stud welding (CHS-ASW) are widely used as fasteners in steel-concrete composite structures. Under fire conditions, prolonged exposure to elevated temperatures and high stresses leads to the degradation of the mechanical properties of CHS-ASW, accompanied by an increase in creep deformation. These combined effects adversely impact the strength and stiffness of CHS-ASW within composite structural elements, ultimately reducing the load-bearing capacity and compromising the overall stability of the structural system. In this study, a comprehensive tensile coupon test programme was conducted on CHS-ASW specimens fabricated from the commonly used ML15 and ML15AL steels, under both ambient and elevated temperature conditions. Based on the tensile test results, a series of creep tests were subsequently performed at various elevated temperatures and stress ratios to investigate the creep behaviour of CHS-ASW. The experimental results demonstrate that temperature has a significant influence on the mechanical properties of CHS-ASW. It was observed that the current design standards tend to overestimate the yield and ultimate strengths of CHS-ASW made from ML15 and ML15AL steels at temperatures between 500 °C and 800 °C, leading to unconservative predictions. Notably, the creep effects for ML15 and ML15AL steel CHS-ASW become increasingly pronounced above 600 °C and must therefore be accounted for in structural fire analysis. Based on the experimental results, temperature-dependent reduction factors for the high-temperature mechanical properties of ML15 and ML15AL steel CHS-ASW are proposed, along with an improved creep model derived from the classic Fields & Fields creep model. The proposed model demonstrates high reliability in predicting the high-temperature mechanical performance of ML15 and ML15AL steel CHS-ASW while effectively accounting for their creep behaviour.