双片角钢X形支撑抗震性能研究

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

为研究双片角钢X形支撑的抗震性能,对5个1/3缩尺试件进行水平往复加载试验,分析单肢长细比(34.5~86.2)和支撑夹角(35°、45°及55°)对双片角钢X形支撑滞回性能的影响。试验结果表明:在满足GB 50011—2010《建筑抗震设计规范》设计要求的情况下,双片角钢X形支撑单肢长细比越大,双肢共同工作能力越差,而单肢长细比对其承载力、刚度和耗能能力影响较小;减小支撑夹角能提高支撑的承载力和抗侧刚度,但承载力退化更快,且疲劳断裂更早发生。采用经试验验证的有限元模型研究了支撑长细比、角钢宽厚比等参数对支撑抗震性能的影响。综合分析有限元和试验结果发现,设计双片角钢X形支撑时不应忽略压杆的承载力贡献,且支撑长细比对压杆屈曲后性能影响较大。提出了适用于双片角钢X形支撑的承载力和压杆卸载系数计算式,承载力计算结果较GB 50017—2017《钢结构设计标准》中计算结果提高了9.2%~43.0%,偏于安全。基于修正后压杆卸载系数,得到此类支撑考虑压杆卸载影响的抗拉承载力计算式,计算结果与试验结果比值介于0.83-0.90之间,可准确且安全地预测双片角钢X形支撑的抗拉承载力。

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.