Thermal creep behavior of steel frames with shear tab connections under transient-state conditions of fire.

Abstract

This study aims to investigate the behavior of full-scale steel frames with shear tab connections subjected to fire. It is often stated that creep (time-dependent) material of the steel can significantly influence the overall response of steel structures when subjected to fire temperatures. To address this issue, the effect of thermal creep of steel on the behavior of steel frames with shear tab connections due to fire temperatures is investigated. First, the study presents a methodology for explicit modeling of creep of structural steel in the ABAQUS finite element (FE) models under transient temperature conditions representative of building fires. Starting from existing creep model, the equations describing the time-dependent strains are derived and used to develop a new user-defined subroutine as per ABAQUS documentations. The development of this subroutine is presented through different stages which reflect the transition from conducting a steady-state analysis to a transient-state analysis. FE models of full-scale steel frames with shear tab connections are first developed in ABAQUS. Then, the models are validated by comparing predictions from the FE analyses with experimental work available in literature. Afterwards, the time-dependent behavior of the validated FE models is investigated by explicitly including the thermal creep strains via the developed subroutine. Moreover, parametric studies are carried out to study the effect of key geometrical parameters and heating conditions on the overall response of steel frames in fire. These parameters are heating rate, column size, cooling duration, initial cooling temperature, beam geometry, and shear tab location. The outcome of this study clearly emphasizes the importance of accounting for the creep effect in the structural-fire analyses of steel structures and shows that ignoring its effect can impose a major threat on the safety and integrity of steel structures when subjected to fire.