Stability of equal-leg angle section braces with torsional restraints

Abstract

Cross bracing using the single leg angle sections are connected on both sides at the joints, affecting the stability capacity of the cross bracing because of the torque. The study on the stability capacity of equal-leg angle sections with the effects of torsional restraints at joints was insufficient. Additionally, there is no clear guidance from relevant design codes. In this study, an end constraint was designed to simulate the effect of torsional restraints for the angle sections. A total of 105 specimens of angle sections, divided into three kinds of pieces (A, B, C), were tested under three boundary conditions. Additionally, Finite Element Method modeling to study the effects of end constraint was parallelly conducted. Class B specimens had the worst stability. When the slenderness ratio is <120, the stability capacity of Class C specimens is larger. When the slenderness ratio is larger than 120, Class A specimens have better stability. The stability capacity of the equal-leg angle sections is positively related to the stiffness of the end constraint, when the stiffness is less than or equal to 200 kN•m/θ, the change of the stability capacity appears more dramatic, when the stiffness exceeds 200 kN•m/θ, the increase becomes slower. The effect of the slenderness ratio and the ratio of the torsional stiffness at nodes to the bending stiffness of columns were quantified through the stability capacities obtained from the experiment and FEMs to propose a modified method for effective length coefficients, which could optimize transmission tower design.