采用纤维梁单元分析钢-混凝土组合结构地震反应的原理

Theory of seismic response analysis of steel-concrete composite structures using fiber beam elements

通过大型通用有限元程序MSC.MARC(2005r2)二次开发将纤维截面模型和基于位移的无滑移分布塑性铰梁单元相结合,得到了一种用于钢-混凝土组合结构地震反应分析的纤维梁单元。该单元在兼顾模型的准确性、通用性以及高效性的同时,具有较优的求解效率、数值稳定性以及前后处理速度。根据工程中常用组合截面的特点提出了组合截面的定义方式及其纤维离散过程,并给出了截面本构关系的求解流程。分析了混凝土、钢材以及钢筋三种材料的单轴本构关系,混凝土材料模型能反映普通、高强以及约束混凝土的不同力学特性,并在已有的考虑单次加卸载强度退化模型的基础上发展了能够考虑多次加卸载强度退化行为的混凝土滞回准则,从而使模型更符合地震作用下组合构件中混凝土材料的实际复杂非线性行为,钢材和钢筋模型能较合理地考虑往复荷载作用下的包兴格效应。

For the consideration of accuracy,broad applicability,efficiency,rapid and stable numerical solution,as well as powerful and convenient pre-processing and post-processing,the customization of the large generic FE package MSC.MARC（2005r2） is proposed to combine the fiber section model and the displacement-based perfectly-bonded beam element with distributed plastic hinges,resulting in a fiber beam element for seismic response analysis of steel-concrete composite structures.Based on the characteristics of composite sections usually used in practice,the definition approach of composite sections and the discretization process of section fibers are proposed.The solution algorithm of the sectional constitutive law is also derived.The uniaxial constitutive laws of the concrete,steel and reinforcement materials are focused on.The proposed concrete constitutive model covers the ordinary,high-strength and confined concrete material.Based on some previous models which can only reflect the strength degradation phenomenon due to single unloading and reloading,the hysteretic law is improved to consider the strength degradation phenomenon due to repeated unloading and reloading so that the model can more reasonably and accurately trace the actual complex nonlinear behavior of the concrete material in composite members subjected to the real seismic action.The adopted steel and reinforcement material model can consider the Bauschinger effect rationally.