Dynamic Multiaxial Strength Of Concrete Under Static-dynamic Coupled Loading

Many investigations on the strain-rate-dependent properties of concrete have been performed,and a relatively complete theoretical framework was formed.However,most of the existing dynamic strength analysis method did not consider the effect of initial static load on the dynamic strength of concrete.Without considering the effect of the initial static load on the dynamic strength of the concrete,the dynamic strength of the concrete material is overestimated,which makes the structural design dangerous.Considering this problem,the strain-rate-dependent strength mechanisms of concrete are analyzed.A static-dynamic coupled strength criterion for concrete is established based on the mechanism analysis of concrete rete effect under static-dynamic coupled loading.The correctness of the proposed theory is verified by the regularity cognition obtained through simulation of mechanical response of concrete material and structure under static-dynamic combined load in ABAQUS software.The main work and analysis of the paper are as follows:(1)Based on the internal mechanism of the strain rate effect on strength of brittle material,systematic analysis has been carried out in the process of changing the strain rate from low to high.Through distinguishing the real strength from macroscopic bearing capacity of the material,the intrinsic physical mechanism of the strain rate effect of concrete in different strain rates is presented with considering the heterogeneity and anisotropism of concrete materials.It is concluded that the strength rate sensitivity of concrete material is the result of the interaction between thermal activation mechanism and viscous mechanism,that is,the real dynamic strength of concrete material is caused by strain rate effect.The part beyond the real dynamic strength of the material performance as further improving of bearing capacity,this part of the increase is the results of inertia effect which is not related with strain rate effect.(2)The definition of initial static load is given by analyzing the rate effect mechanism of concrete under static and dynamic load.The strength parameter of concrete is derived by the initial static load and strain rate based on the mechanism.The general method of establishing the criterion of static and dynamic combination strength is put forward.The dynamic strength of concrete composed of initial effective static load,dynamic cohesion strength and frictional strength is given by using strength parameter to consider the influence of initial static load and strain rate.The generalized nonlinear strength criterion is developed into static-dynamic coupled multiaxial strength criterion.The developed static-dynamic strength criterion is verified by several static-dynamic coupled strength test results of concrete materials.The comparisons show that the dynamic uniaxial and multiaxial strength of concrete materials varies with the change of the strain rate and the initial static load can be reasonably described by this criterion.(3)A series of dynamic mechanical response of concrete materials and structures under static-dynamic coupled load are simulated by numerical method.The influence of strain rate and initial static load on the strength of concrete materials is considered respectively.The change rule of the strength with the strain rate and the initial static load is analyzed.The results show that the strength of concrete(structure)increases with the increase of strain rate and decreases with the increase of initial static load.