基于扩展有限元进行钢筋混凝土柱捏拢效应的机理分析

XFEM BASED SIMULATION ON THE MECHANISM OF PINCHING EFFECT OF RC COLUMNS

预测地震荷载下钢筋混凝土柱的力学性能,对评估震后混凝土结构的安全性和震害损失具有重要意义。由于混凝土材料在受力过程中的复杂性,目前对钢筋混凝土结构力学性能的模拟主要依靠数值方法。已有的数值模拟方法大都基于有限元法,将混凝土视为连续体,通过人为定义参数来指定混凝土的滞回本构,因此存在一定的主观性与局限性。该文结合扩展有限元法与断裂准则,直接模拟混凝土裂缝的开展与闭合,并考虑钢筋和混凝土的粘结滑移作用,通过数值计算,直接再现了钢筋混凝土结构在低周反复荷载下的力学行为。模拟方法得到了试验的验证,与结果吻合较好。该文进一步分析了钢筋混凝土柱的滞回行为中混凝土、钢筋的各自作用和相互抵消行为,从细观的角度,在机理上揭示了捏拢效应出现的三个主要原因。

It is of great significance to predict the behavior of a RC column under seismic loading and make assessments on the safety of a structure. The accurate calculation on the behavior of concrete members mainly relies on numerical simulation analysis at present due to complicity of material and mechanical response. However, the majorities of conventional methods are normally based on the finite element method, taking concrete as continuum and using simplified parameters to describe the hysteretic behavior of RC members. To exhibit the mechanism of seismic damage, a novel numerical method based on extended finite element method is proposed. The extended finite element method and fracture criterion is engaged to simulate the discontinuous behavior of concrete, namely crack initiating and propagating and closure. The bond-slip relationship between concrete and rebar are taken into account in the interval of cracks. Specific hysteretic performance is not specified by material property inputting, but by reflecting in mechanical response. Simulation result is verified by test, which shows good agreements in all aspects. Besides, the further analysis is conducted on the aseismic behavior of RC columns in a micro-level and three main causes are raised to explain the mechanism of pinching effect.