考虑非线性剪切效应的RC桥墩抗震分析模型

剪跨比较小或配箍不足的钢筋混凝土桥墩易发生剪切破坏,而现有的纤维单元模型忽略了剪切变形,不能合理评估弯剪或剪切破坏桥墩的抗震能力。为有效模拟剪切作用影响下钢筋混凝土桥墩的抗震性能,以36个剪切及弯剪破坏圆形截面钢筋混凝土桥墩抗震拟静力试验结果为依据,建立了墩柱剪切破坏时墩底转角的计算公式。利用OpenSees分析平台,建立了基于非线性纤维梁柱单元和零长度剪切弹簧单元的数值分析模型,以此来考虑弯曲和剪切效应的耦合作用。以数值模型中墩底转角来监测试件剪切破坏的发生,剪切破坏发生前模型以纤维梁柱单元模拟的弯曲变形为主;此后,桥墩地震反应以剪切弹簧单元控制,以模拟试件由于剪切破坏导致的强度和刚度退化等行为。通过对12个剪切及弯剪破坏圆形截面桥墩抗震拟静力试验的模拟结果表明,模拟的滞回曲线与试验结果吻合较好,并且能很好地模拟钢筋混凝土结构由于剪切作用引起的刚度与强度的退化现象,验证了模型的合理性。

SEISMIC ANALYSIS MODEL CONSIDERING NONLINEAR SHEAR EFFECT FOR RC BRIDGE PIERS

Bridge piers with low aspect ratio or low transverse reinforcement are vulnerable to shear failure under seismic action. The existing fiber element model ignores the nonlinear shear deformation of piers and could not be used to model the seismic behavior of bridge piers failed in shear or flexure-shear modes. In order to simulate the seismic behavior of bridge piers, a rotation-based shear failure model was built based on 36 quasi-static test results of circular piers failed in shear or flexural-shear modes. A numerical analysis model comprising the nonlinear fiber beam column element and the zero-length shear spring element was built on OpenSees analysis platform to simulate flexural shear interaction of piers. The rotation of the end region of the pier in the analysis model was used to monitor shear failure initiation of the specimen. Before shear failure, the cyclic behavior of the pier was controlled by fiber beam column element. Then, seismic response of the pier was governed by the shear spring element to simulate the strength and stiffness degradation behavior as a result of the shear failure. The analysis model was verified through a comparison with the quasi-static test results of 12 nonlinear shear dominated circular bridge piers. The results indicate that the simulated hysteretic curves agree well with the test data, the stiffness and strength degradation of the piers as a result of shear failure could be well simulated and the rationality of the model is verified.