Modeling creep of steel under transient temperature conditions of fire

This paper presents a methodology for explicit modeling of the time-dependent behavior or creep of structural steel in the Abaqus finite element (FE) models under transient temperature conditions representative of building fires. In this methodology, available creep models based on conventional creep tests under constant or steady-state temperature conditions were used to predict the time-dependent or creep behavior of steel under variable or transient-state temperature conditions. Specifically, user-defined CREEP subroutines were created in Abaqus to define time-dependent or viscoplastic deformation of structural steel under changing temperatures. To demonstrate the robustness of the proposed methodology, the time-dependent behavior of structural steel at elevated temperatures was modeled under three distinct conditions. These were: steady-state temperature conditions, stepwise steady-state temperature conditions, and transient-state temperature conditions. This paper further presents and discusses the application of the methodology in studying the creep behavior of a shear tab connection assembly under the transient temperature conditions of a fire. Through this application, the importance of explicit consideration of creep in predicting the response of connection assemblies at different stages in the evolution of a structural-fire is also emphasized.