Numerical Studies and Practical Design Suggestions on Fire Resistance of Unprotected High-Strength Steel Extended End-Plate Connections

The material properties of high-strength steels deteriorate under fire conditions and depends on the temperature and fire duration. As a time-dependent inelastic strain behavior, the thermal creep effect becomes significant at elevated temperatures and influences the fire resistance of connections. This paper presents numerical studies on the fire response of unprotected extended end-plate connections made of high-strength steels (Q460, Q690 and Q960), explicitly considering the creep effect. Transient state finite element models including or excluding creep were developed using ABAQUS and validated against the experimental results under the restrained sub-framework. The numerical analysis results exhibit a better agreement with the experimental results regarding the deformation ability and failure mode if the creep effect is considered. Thus, creep is a non-negligible effect in investigating the fire performance of end-plate joints. Parametric studies were carried out to quantitatively assess the influence of moment ratio of connection, axial pressure ratio of column, end-plate thickness and heating rates on rotation–time–temperature characteristics and stress distribution. The numerical results show that the magnitudes of bending moment applied on the connection and axial load on the column play crucial roles in evaluating the fire endurance and critical temperatures. However, the effect of end-plate thickness on the fire-structural behavior of extended end-plate connections is negligible. The heating rate has little effect on the critical temperatures of connections. The rotation capacity of high-strength steel extended end-plate connections depends on the failure mode to a large extent. Finally, fire resistance design suggestions for high-strength steel end-plate connections were put forward according to the observations on the parametric studies.