NUMERICAL ANALYSIS OF CONCRETE MATERIAL PROPERTIES AT HIGH STRAIN RATE UNDER DIRECT TENSION

摘要

The tensile strength of concrete material increases with the strain rate. Dynamic tensile strength of concrete material is usually obtained by conducting laboratory tests such as direct tensile test, flexural test, spall test or splitting test (Brazilian test). Some codes of practice such as Comite Euro-International du Beton (CEB) give empirical relations of concrete material dynamic increase factor (DIF) based on testing data. However, the reliability of the dynamic testing and the derived DIF are under debating. It is commonly agreed now that the DIF obtained from dynamic impact test is affected by lateral inertia confinement effect. Therefore, those derived from testing data do not truly reflect the dynamic material properties. The influence of the lateral inertia confinement, however, is not quantified. Moreover, concrete is a heterogeneous material with different components, but is conventionally assumed to be homogeneous, i.e. cement mortar only, in most previous experimental or numerical studies. In the present study, a mesoscale concrete material model consisting of cement mortar, aggregates and interfacial transition zone (ITZ) is developed to simulate direct tensile tests and to study the influences of the lateral inertia confinement and heterogeneity on tensile strength increment of concrete materials with respect to strain rates. The commercial software AUTODYN is used to perform the numerical simulations. The influence of lateral inertia confinement on tensile DIF of concrete material is examined.