双层柱间支撑框架在循环荷载下的破坏机理

为研究双层柱间支撑框架(steel two-tiered braced frames,简称STBF)的滞回性能及在罕遇地震作用下的破坏机理，对1个1/2缩尺STBF进行了往复加载试验。在试验基础上，又对31个经试验验证的STBF模型进行了数值模拟。分析了STBF在循环荷载作用下的破坏模式、变形和内力变化规律，研究了柱顶荷载、支撑长细比、支撑截面径厚比和层高比等参数对STBF破坏机理的影响。结果表明：STBF在循环荷载作用下，支撑破坏主要集中在某一层，该层支撑会出现较大支撑平面外屈曲变形，并可能发展为断裂破坏；由于上、下层支撑不同时破坏，导致柱产生支撑平面内弯矩；随着层高比的增大，STBF的耗能能力提高；当轴压比大于0.5或层高比小于0.5时，STBF可能由于柱失稳而过早破坏，建议柱轴压比不应大于0.5,且层高比不应小于0.5。

Collapse mechanism of steel two-tiered braced frames under cyclic load

The hysteretic behavior and collapse mechanism of steel two-tiered braced frames (STBF) under rare earthquake was studied. Quasi-static test was conducted on a 1/2-scale STBF, and numerical simulation was carried out for 31 validated models of STBF. The failure mode, deformation, and internal force of STBF under cyclic load were analyzed. The influences of parameters on the collapse mechanism of STBF were investigated, including the load on the top of the column, slenderness ratio, diameter-thickness ratio, and tier-height ratio of braced frames. Results show that the bracing failure of STBF under cyclic load was primarily in one tier. The tier underwent a larger buckling deformation outside the brace plane, which might develop to fracture failure. The column experienced in-plane bending moment due to the asynchronous failure of upper and lower braces. With the increase in the tier-height ratio, the energy dissipation capacity of STBF increased. When the axial compression ratio was larger than 0.5 or the tier-height ratio of the braced frame was less than 0.5, STBF was damaged prematurely due to the instability of columns. Therefore, it is recommended that the axial compression ratio of the column should not be larger than 0.5, and the tier-height ratio should not be less than 0.5.