Elevated temperature performance of hybrid semi-rigid steel joints: Analysis and design

This paper investigates the structural performance of carbon steel and hybrid stainless steel–carbon steel semi-rigid beam-to-column connections under both ambient and elevated temperature conditions. Stainless steel exhibits superior strength retention, stiffness and ductility at high temperatures, making it an attractive material for enhancing fire resilience in steel-framed structures. To leverage these benefits, a nonlinear finite element model of a semi-rigid flush endplate connection is developed in ABAQUS and validated against experimental tests at ambient and elevated temperatures. A comprehensive parametric study is then conducted to examine the influence of endplate thickness, material grade, bolt size and temperature. The results demonstrate that hybrid connections where stainless steel is selectively used in critical components offer improved moment resistance and rotational capacity, particularly under fire conditions. A component-based approach is subsequently proposed, extending the Eurocode framework to elevated temperatures. The method predicts initial stiffness, design moment resistance and ultimate moment resistance, and is shown to be both safe and accurate through comparison with numerical results for both carbon steel and hybrid stainless steel–carbon steel configurations. • Parametric analyses explore behaviour of hybrid steel joints at high temperatures. • Hybrid joints exhibit higher resistance and deformation capacity than carbon steel. • EN 1993-1-8 is extended to address joint behaviour at elevated temperatures. • New design approach estimates rotation limits and ultimate moment resistance. • The design methods provide safe, accurate stiffness and moment estimates.