Study on seismic performance of built-up double angle X-braces

To study the seismic performance of double built-up angle x-brace, five 1/ 3 scale specimens were tested under horizontal cyclic reversed loading. The individual chord’ s slenderness ratio ranges from 34. 5 to 86. 2 and considered braces’ inclinations are 35°, 45° and 55°. The effects of these parameters on the hysteretic performances of built-up double angle X-brace were analyzed. The test results show that when the individual chord of the braces satisfied the requirements of GB 50011—2010 ‘Code for seismic design of buildings’, increasing the individual chord’ s slenderness ratio tends to compromise the composite action of the two angle members, but the individual chord’ s slenderness ratio has slight effect on the bearing capacity, stiffness and energy dissipation capacity; reducing the inclination of brace can improve the bearing capacity and lateral stiffness of brace, but the bearing capacity rapidly degrades and the fatigue fracture occurs earlier. Based on the finite element model verified by the test results, a parametric analysis considering the slenderness ratio of brace and the width thickness ratio of the angle was carried out. Based on the finite element and test results, it is found that the bearing capacity contribution of the compression members should not be ignored in design of built-up double angle X-braces, and the slenderness ratio of the brace has a great influence on the post buckling performance of the compression members. Calculation formulas for the bearing capacity and the unloading coefficient of the compression members in built-up double angle X-braces were proposed. The calculated results from the proposal formulas is 9. 2%-43. 0% higher than that of the results predicted by the GB 50017—2017‘Code for design of steel structures’, and are on the conservative side. Based on the proposal formulas for the unloading coefficient, the tensile bearing capacity calculate formula considering the influence of unloading of the compression members was obtained. The ratio of the calculate formula to test results is between 0. 83 to 0. 93, the formula is proved to be able to given accurate and safe tensile bearing capacity predictions of the built-up double angle X-braces. © 2023 Science Press. All rights reserved.