动态循环荷载下大坝混凝土拉压转换损伤本构模型构建及影响研究

Damage constitutive model including tension-compression conversion for dam concrete under dynamic cyclic loading

目前混凝土坝抗震安全评价中,对于动态循环荷载下大坝混凝土损伤本构模型中从受拉状态向受压状态转变过程(拉压转换)中的混凝土弹性模量变化,一般都基于商用软件ABAQUS的“单边效应”假设,认为混凝土弹性模量立即恢复为初始弹性模量。上述假设的合理性缺乏试验验证,直接影响混凝土坝抗震安全评价的可靠性。通过对全级配大坝混凝土拉压转换全过程试验成果的观察分析,发现混凝土从受拉状态进入受压状态后弹性模量并非立即恢复为初始弹性模量,而是由损伤后弹性模量连续渐进恢复至初始弹性模量,期间原有的受拉残余应变在压应力作用下迅速减小到较小数值,因此ABAQUS的“单边效应”假设并不符合实际情况。本文以全级配大坝混凝土拉压转换全过程试验成果为基础,提出受拉损伤发生后,拉压转换时受压应力应变关系采用双折线模型的思路,据此推导了相应的应力-应变关系解析表达式,构建了更接近混凝土拉压转换时真实状况的本构关系数值模型。通过实际工程的计算分析,发现常用的受压弹性模量立即恢复为初始弹性模量的损伤本构模型过高估计了坝体刚度,可能带来偏于不安全的评价结果。

In the seismic safety evaluation of concrete dams,the change of elastic modulus of concrete in the process of transition from tension state to compression state(tension compression transition)in the damage constitutive model of concrete dam under dynamic cyclic load is generally based on the so-called"unilateral effect"assumption of commercial software ABAQUS,which considers that the elastic modulus of concrete immediately returns to the initial elastic modulus.The rationality of the above assumptions is lack of experimental verification,which directly affects the reliability of seismic safety evaluation of concrete dams.Through the observation and analysis of the test results of the whole process of tension compression transformation of fully graded dam concrete,it is found that the elastic modulus of concrete does not immediately return to the initial elastic modulus when it enters the compression state from the tension state,but continuously and gradually returns to the initial elastic modulus from the damaged elastic modulus,during which the original tensile residual strain rapidly decreases to a smaller value under the action of the compressive stress,It is pointed out that the so-called"unilateral effect"hypothesis of ABAQUS is not in line with the actual situation.Based on the experimental results of the whole process of tension compression transformation of fully graded dam concrete,this paper proposes the idea of adopting the double broken line model for the stress-strain relationship during tension compression transformation after the occurrence of tension damage.According to this,the corresponding analytical expression of stress-strain relationship is derived,and a numerical constitutive model closer to the real situation of concrete tension compression transformation is constructed.Through the calculation and analysis of the actual project,it is pointed out that the damage constitutive model of the commonly used compression elastic modulus immediately restored to the initial elastic modulus overestimates the stiffness of the dam body,which may lead to unsafe evaluation results.