Behaviour and design of extended endplate hybrid steel beam-column connections at elevated temperatures

In this paper, the behaviour of semi-rigid beam-column connections, with a primary focus on extended endplate connections, at ambient and elevated temperatures is investigated. Both pure carbon steel (including normal- and high-strength steel) connections and hybrid connections, i.e. incorporating carbon steel and stainless steel components, are considered. Upon validation against physical experiments, finite element models are developed to conduct comprehensive parametric studies, considering various combinations of endplate thicknesses and material grades, bolt sizes and material grades, and temperature levels. The numerical analyses results indicate that hybrid steel beam-column connections exhibit greater resistance and deformation capacity compared with carbon steel counterparts, especially at elevated temperatures greater than 500℃. The component-based design method provided in EN 1993–1–8:2024 for semi-rigid steel beam-column connections at ambient temperature is extended to cover fire scenarios; however, it only predicts the initial stiffness and plastic strength of beam-column connections. Therefore, another function is developed for predicting their ultimate strength at elevated temperatures. The developed fire design methods are shown to be safe and accurate through comparisons with the benchmark numerical results for carbon steel and hybrid steel and stainless steel beam-column connections. • Numerical parametric studies are performed to investigate behaviour of hybrid steel connections at elevated temperatures. • Hybrid steel connections exhibit greater resistance and deformation capacity compared with carbon steel counterparts. • Component-based design method given in EN 1993–1–8 for room temperature design is extended to cover fire scenarios. • An alternative design approach for predicting the rotation limit and ultimate strength of connections is presented. • Developed design methods provide accurate and safe predictions of stiffness, plastic strength and ultimate strength.