Non-linear finite element analysis of the effects of fire protection on a top and seated angle bolted steel connection with double web angles.

Abstract

This study was aimed at investigating the performance of steel structures, towards improving fire design, by examining the effects of fire protection on a steel connection exposed to elevated temperatures. A literature review formed the keystone of the study, whereby relevant principles were contextualised. Two steel I-sections formed a cantilever beam-column connection that was selected as a relevant substructure to form the crux of the analyses. The modelling and numerical analysis of the steel connection was performed using Abaqus, Finite Element Analysis (FEA) computer software. In particular, a three-dimensional, non-linear, finite element model was developed for the simulation of the structural behaviour of the steel connection. The developed models accounted for the semi-rigid behaviour of the connection using contact mechanics laws between the interfaces of all the contacting parts. A proper plasticity model was used to depict damage of the structural steel. Two types of analyses were conducted: steady-state simulations with sequential thermal and thermomechanical analyses, as well as transient simulations with coupled temperature-displacement analyses. The former approach was adopted to gauge the effect of thermal protection and associated variables on the steel connection under fire. The latter approach considered the gradual delamination and deterioration of the protection due to elevated temperatures. A procedure for the numerical implementation of this idea was considered and presented. In both approaches, the steel connection was modelled separately with and without fire protection, in order to provide comparable results. The types of fire protection investigated were concrete and gypsum board. Variables of the fire protection under examination were the thicknesses and extent of coverage thereof, located initially on the top flange of the beam and progressing onto the overall structure. The steady-state analysis results indicated that fire protection offered an improved behaviour of the steel connection under fire. The role of the fire resistant materials became increasingly important for more severe fire phenomena, indicating a significant increase in strength of the fire-protected models. The transient analysis results deemed that progressive delamination has detrimental effects on the performance of the steel structure and fire protection mitigates these effects for a limited period of time.