Resistance of Axially Loaded T- and X-Joints of Elliptical Hollow Sections at Elevated Temperatures - A Finite Element Study

This study presents the results of a numerical study to develop a method to calculate the static strength of welded Elliptical Hollow Section (EHS) joints at elevated temperatures. Extensive numerical simulations using the non-linear finite element package, ABAQUS v6.14-1 on EHS T- and X-joints under brace axial compression or tension and pre-stress in chord member with different type of joint orientations at elevated temperatures over a wide range of diameter ratio have been conducted. The adjustments required to be made to the equations of joint resistance under ambient temperature conditions for estimating joint resistance at elevated temperature conditions are investigated in this study. The FE simulation results have been compared with the calculation results of a number of existing methods at ambient temperature. It has been found that the method proposed by Packer et al. gives the best agreement with the authors' simulation results at ambient temperature. At elevated temperatures, for T- and X- joints with braces in compression welded to the wide sides of chords, replacing the ambient temperature yield strength of steel by the elevated temperature value in the current design method overestimates the ultimate load carrying capacity of axially loaded EHS T- and X-joints due to inability of the ambient temperature calculation equations to take into consideration EHS flattening at high temperatures. For these cases, it is recommended to calculate the joint strength reduction factor at elevated temperatures according to the Young's modulus of steel.