Effect of thermal creep on the behavior of flush endplate 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 flush endplate beam-column connections subjected to elevated temperatures. Creep refers to the time-dependent inelastic deformation of structural steel at high temperatures. To address this issue, finite element (FE) models using ABAQUS are first developed to reproduce the experimental results available in the literature and specifically the total force-connection rotation characteristics of the connection under combined shear and tension forces during fire without creep effect. Then, a series of FE models for the same connection are developed to investigate the effect of creep on the behavior of flush end plate connections at different elevated temperatures with different load ratios. Different geometrical parameters are incorporated in this study such as load angle, plate thickness, and bolt diameter to investigate their effects on the overall thermal creep response of flush endplate connections in fire. In this methodology, time effects on the strength of flush endplate connections are explicitly considered in the form of isochronous force-rotation curves. This will help developing a holistic performance-based methodology to evaluate the performance of steel connections in fire. Using experimental results available in the literature and finite element (FE) models conducted in ABAQUS, a mechanical model is developed to predict the total force-connection rotation characteristics of flush endplate connections at elevated temperatures including creep effect. The proposed model consists of multi-linear springs that predict each component stiffness, strength, and rotation. The multi-linear springs temperature expressions are based on the ambient temperature formulations proposed in Eurocode3 Part 1.8 where material properties are considered temperature dependent. To include the effect of creep, modified Burgers creep model is used to predict the time-dependent connection rotation and temperature of the flush endpl