焊接箱形截面梁抗震性能影响因素研究

为考察板件宽厚比对焊接箱形截面梁抗震性能的影响，对中国、美国、日本和欧洲的钢结构设计标准中的相关规定进行了比较，结果表明各国规范对于梁板件宽厚比限值的规定总体上具有较好的一致性。采用钢材循环加载本构，建立了多尺度非线性有限元计算模型。提出了刚性竖杆 箱形梁加载方式，模拟水平地震、重力荷载与轴向压力对箱形截面框架梁的作用。有限元分析结果表明，在设计常用的板件宽厚比范围内，箱形截面梁的弹性屈曲荷载均显著高于其屈服荷载。在水平往复荷载作用下，随着板件宽厚比减小，箱形截面梁极限变形角与延性系数随之增大，抗弯刚度降低速率变缓，塑性耗能能力显著增强。当满足一级抗震宽厚比要求时，焊接箱形截面梁的梁端截面转角约为1/30。承受轴压作用时梁刚度退化很快，变形能力减弱。当轴压比不大于0.2、满足一级抗震宽厚比要求时，梁端截面转角约为1/50。跨高比对梁承载力影响不大，但变形能力可以大幅度提高。横向荷载对梁抗震性能的影响显著，随着静载比（重力荷载代表值与屈服弯矩之比）增大，骨架曲线逐渐发生平移，抗弯刚度降低，耗能性能减弱。当地震弯矩与静力弯矩方向相同时，箱形截面梁承载力显著降低，静载比0.8时极限变形角可减小约50%；当地震弯矩与静力弯矩方向相反时，梁虽然承载力稍有提高，但极限变形角略有减小。

Study on influencing factors of seismic performance for welded box section beams

In order to investigate the influence of width-to-thickness ratio on the seismic performance of welded box beams, a comparison of the steel structure design standards among China, the United States, Japan and Europe was made in this paper. A multi-scaled nonlinear finite element analytical model was established by using structural steel constitutive relationship under cyclic loading. The rigid vertical rod-box beam loading mechanism which could simulate the effects of horizontal earthquake, gravity load and axial pressure on the box beam in a frame was proposed. The results of finite element analysis show that for commonly used width to thickness ratio, the buckling loads of box beams are significantly higher than the yield loads. Under horizontal cyclic loading, as the width-to-thickness ratio decreases, the ultimate rotation angle and ductility coefficient of box beam increase, the bending stiffness decreases slowly, and the plastic energy dissipation capacity increases significantly. When the width-to-thickness ratio for the first grade seismic measure is satisfied, the rotation angle of box beams is about 1/30. The stiffness of box beams degrades rapidly under axial compression, and the deformation capacity is weakened. When the axial compression ratio is not greater than 0.2, the deformation angle is about 1/50 when the width-to-thickness ratio limitation for the first grade seismic measure is met. The span to height ratio has little effect on the bearing capacity of box beams, but the deformation capacity can be greatly improved. The effect of lateral load on the seismic performance of box beams is significant. As the gravity load capacity ratio（the ratio of bending moment to yield bending moment caused by the representative value of gravity load） increases, a gradual translation occurs to the skeleton curve of box beams, and the bending stiffness and energy dissipation capacity decreases. When the seismic bending moment and the static bending moment are in the same direction, the bearing capacity of box beams is significantly reduced. When the gravity load capacity ratio is 0.8, the ultimate deformation angle can be reduced by about 50%. When the seismic bending moment and the static bending moment are in opposite directions, although the bearing capacity of box beams is increased, the ultimate deformation angle is slightly reduced.