静动组合载荷下混凝土率效应机理及强度准则

混凝土结构在受到动载荷作用之前,通常已承受着初始静载荷的作用.大量关于混凝土应变率效应的研究均没有考虑初始静载荷对动强度的影响,会导致过高地估计混凝土的动强度,使混凝土结构设计偏于危险.本文通过分析混凝土材料在静动组合载荷下的率效应机理,给出了初始静载荷的定义.在此基础上,推导了混凝土材料参数与初始静载荷和应变率的表达式,提出了建立静动组合强度准则的一般方法.通过材料参数反映初始静载荷与应变率的联合影响,给出了由初始有效静载荷、动态黏聚强度和摩擦强度共同组成的混凝土动态强度,将广义非线性强度准则发展为静动组合多轴强度准则.建立的强度面在相同初始静载荷下随应变率的增大向外扩张,在相同应变率下随初始静载荷的增大向里收缩,即混凝土的强度在相同初始静载荷下随应变率的增大而增大,在相同应变率下随初始静载荷的增大而减小.此外,当初始静载荷和应变率不变时,加载路径对混凝土材料的应变率效应无影响,但会影响混凝土材料的静水压力效应,即当初始静载荷和应变率固定不变时,静动组合强度面的位置和大小即可确定,不同加载路径下强度的不同是由于静水压力效应导致的.最后利用多组混凝土材料静动组合强度试验对建立的静动组合强度准则进行了验证.

STUDY ON STRAIN RATE EFFECT AND STRENGTH CRITERION OF CONCRETE UNDER STATIC-DYNAMIC COUPLED LOADING

In practical engineering, the concrete structures are usually subjected to an initial static load before dynamic loading. Most previous studies on the strain rate effect of concrete do not consider the influence of initial static load on the dynamic strength, which leads to the computed results of dynamic strength larger than the actual value. Therefore the structural designed by these methods is unsafe. Based on the mechanism analysis of concrete rate effect under static-dynamic coupled loading, a clear definition of initial static load was given by authors. Then, the relationship of concrete material parameters with the initial static load and the strain rate was derived. And, a general method for static-dynamic coupled strength criterion was proposed. The combination influence of initial static load and strain rate on concrete strength is reflected by the strength parameter. The static-dynamic strength of concrete is consist of the initial static load, the dynamic cohesive strength and the frictional strength. Then a static-dynamic coupled multiaxial strength criterion of concrete was established by combining the obtained concrete material parameters with nonlinear dynamic multiaxial strength criterion. The strength surface of the present strength criterion expands outward with the increase of strain rate under the same initial static load, while contracts inward with the increase of initial static load under the same strain rate. In another word, the strength of concrete increases with the increase of strain rate at the same initial static load, and decreases with the increase of initial static load at the same strain rate. Moreover, when the initial static load and the strain rate are invariable, the strength surface of this criterion is determined, and the loading path has no influence on the strain rate effect of concrete, but the hydrostatic pressure effect is influenced by the loading path. Thus, the strength of concrete at different loading path is different due to the various hydrostatic pressure effect. Finally, the established criterion was verified based on the static and dynamic combined strength test results of concrete.