Thermal creep effect on the behavior of shear tab steel connections due to fire temperatures -

Abstract

The objective of this study is to investigate the effect of thermal creep of steel on the behavior of shear tab beam-column connections due to fire temperatures. Creep is the time-dependent plastic deformation of steel material which occurs at elevated temperatures under applied load over a long time duration. To address this issue, finite element (FE) models are first developed under time-independent (fast) steady-state fire conditions and validated against experimental data available in the literature where the effect of thermal creep is not significant. Then, a series of time-dependent FE models are developed for the same connections to study the effect of thermal creep on the behavior of the shear tab connections at different fire temperatures and various load ratios. Parametric studies are also performed to investigate the impact of major geometric parameters (setback distance, load angle, shear tab location and thickness) on the behavior of shear tab connections during fire temperatures with and without creep effect. The thermal creep effect is explicitly included in the creep-free temperature-stress-strain curves under steady-state temperature conditions to study the time-dependent deformations of shear tab connections when applied forces and temperatures are kept constant. A proposed mechanical model is developed to predict the time-independent (fast) and time-dependent (due to thermal creep) force-rotation characteristics of shear tab connections subjected to fire. The time-independent behavior of the connection is modeled by using a group of springs that can predict the rotational stiffness and the strength of the connection when subjected to fire temperatures. A modified Burgers model is incorporated in the mechanical model to include the effect of thermal creep of steel material. The modified Burgers model is composed of linear springs and viscous dashpots that can predict the time-dependent behavior of the shear tab connection before and after contact of beam with column, and bolt shank with hole. T