Capacity of tubular X-joints reinforced with collar plates under tensile brace loading at elevated temperatures

Abstract

This paper investigates the effect of the collar plate size and the joint geometry on the static behavior of the collar plate reinforced X-joints under tensile load at elevated temperatures. At the first step, a finite element model was developed and validated by results of the experimental tests. At the next step, extensive numerical simulations were carried out on the collar plate strengthened X-joints considering a wide range of geometrical parameter. Using these numerical simulations, the structural behavior under different high temperatures (200 °C, 400 °C, 600 °C, and 800 °C) was investigated and compared to the behavior at ambient temperature (20 °C). Results showed that the ratio of joint strength at elevated temperature to that at ambient temperature increases with the decrease in the ratio of chord diameter to twice the chord wall thickness (γ). Also, for the joints at elevated temperatures, the increase of the collar plate length and thickness remarkably leads to the increase of both the initial stiffness and the ultimate strength. Moreover, the use of the collar plate with big sizes can significantly improve the failure mechanisms of the joints. Also, it was found that for the collar plate reinforced X-joints under tensile load, the joint strength reduction at increasing temperatures follows closely the reduction in the elastic modulus of steel at elevated temperatures. Hence, in the proposed design method for determining the ultimate strength of the collar plate reinforced X-joints under tensile load at elevated temperatures, the Young's modulus reduction factor is used as a modification factor.