Investigating the response and the thermal axial force demand of shear tab connections with composite beams subjected to fire temperatures.

Abstract

This study aims at developing a rational model to predict the thermal axial forces in shear tab connections with composite beams subjected to transient-state fire temperatures. Shear tab connections are one of the most commonly used simple beam-end framing connections. Simple connections are designed to resist shear forces at ambient temperature. During a fire event, large axial forces are generated due to the thermal expansion of the materials. These forces, which are not considered in the design, could lead to connection failure. To achieve the aforementioned objective, finite element (FE) models are developed in ABAQUS and validated against experimental data available in the literature. Parametric FE simulations are then performed to investigate the effect of different parameters on the behavior of shear tab connections in composite beams during a fire. This includes: beam length, shear tab thickness, shear tab location, concrete slab thickness, setback distance, and degree of composite action. Based on the FE results obtained in this study, a design oriented model is developed to predict the thermal induced axial forces generated in the composite beams during the heating and cooling phases of a fire event. The proposed model consists of multi-linear springs that can predict the stiffness of each component of the connection and of the composite beam. The proposed model is capable of predicting the thermal axial forces in shear tab connections with composite beams under different geometrical properties. The FE results show that the main factors that impact the behavior of shear tab connections with composite beams at elevated temperatures are: load ratio, setback distance, and bolt diameter. In addition, the creep in the concrete and the partial composite action result in larger displacements, however, they do not change the failure mode of the composite beam. Significant thermal axial forces are generated in the composite beam in fire as found in the FE results. This is prominent when the beam bottom flange