考虑P-Δ效应的结构地震倒塌及影响因素分析

Research on collapse of structure under earthquakes with consideration of P-Δ effect and its influence factors

P-Δ效应是引起结构在地震作用下倒塌的主要原因之一。以钢框架结构为研究对象,采用增量动力分析法(IDA)和推覆法(Pushover)分析了结构在考虑P-Δ效应时的地震响应特征。结果显示:考虑P-Δ效应后,结构的整体刚度降低,结构下部较容易出现动力失稳,而上部经历卸载,层间位移较小;由于几何非线性与材料非线性的共同作用,骨架曲线会产生明显的负刚度;对具有负刚度的骨架曲线,用三段折线模型进行简化更为合适。基于完全弹塑性滞回模型,研究了不同骨架曲线参数对结构抗倒塌能力的影响。结果表明:二阶效应系数增大,结构发生倒塌的概率增加,而名义延性系数和屈服后刚度比增大则会使结构的抗倒塌能力增强。

P-Δ effect is one of the crucial reasons causing the collapse of the structure under earthquake excitations.The response characteristic of the steel frame with P-Δ effect under strong earthquakes is researched in this paper.The numerical example shows that the stiffness of the structure decreases when the P-Δ effect is considered,and the lower stories of the structure are prone to dynamic instability,while the upper stories experience unloading and the interstory drifts are small.Due to the combination of the geometric nonlinearity and the material nonlinearity,the backbone curve is easier to behave a conspicuous negative slope,and the simplified trilinear curve is more appropriate than the bilinear curve to fit the original backbone curve with a descending segment.On the basis of the full elasto-plastic hysteretic model,the influences of the parameters of the backbone curve on the collapse resistance capacity of the structure are analyzed.The results demonstrate that the probability of the collapse becomes large as the second-order effect coefficient increases,while the increase of the nominal ductility factor and the post-yield stiffness ratio leads to the improvement of the collapse resistance capacity of the structure.