Numerical Investigation Of The Concrete Strength And Mechanical Impedance Under Composite Stress

Composed of many different materials, concrete is the mixture of two-phase (or three), with the fact of random distribution of aggregate (especially coarse aggregate) and the internal defects such as the initial defects on the interface of different phases, the accuracy to calculate strength by rebound method which is the representative of the concrete nondestructive detection technology is very low, far from being able to meet the needs of practical engineering. With the development of concrete strength nondestructive detection theory and technology, hammer blow method based on mechanical impedance theory has appeared and gained great attention, by greatly improving the detection accuracy and the convenient operation.The concrete strength obtained by utilizing the rebound method, hammer blow method as well as destructive detection method, are strength assumed to be in one-way force condition, while the concrete structure in service is in a complex stress state, the strength of which has the characteristics of changing with confining pressure. The hammer blow method has opened up a new space for the rapid and nondestructive testing of concrete considering that it is able to test the mechanical impedance of concrete througth the high precision acceleration sensor, and finally calculate the concrete strength. Therefore, it needs further consideration when using the hammer blow method to test the concrete structure in survice, that whether the mechanical impedance will be affected by the confining pressure, and then affecting the calculation of the concrete strength. The numerical simulation analysis method is carried out in this paper to study the relationship of mechanical impedance value and confining pressure, and to explore the possibility of detecting the compressive strength of concrete in complex stress condition.With the development of multi-axis mechanics of concrete and the concrete plasticity damage model in finite element software ABAQUS, the contents of this paper includes:1)Through simulating the concrete strength under multiaxial stress, prove that the ABAQUS concrete plasticity damage model is in good agreement with the characteristics of concrete strength under complex stress conditions;2)By building model of hammer knocking on the concrete specimen based on the mechanical impedance theory, and applying different confining pressure, it is found out that the relationship between mechanical impedance index and concrete strength with the confining pressure while it ranging irregularly. The result shows that the mechanical impedance value can not express the concrete strength changes with confining pressure;3) by sensitivity analysis of the initial speed, the elastic modulus of concrete, concrete density and the Poisson’s ratio, it explains the possible reasons that the mechanical impedance values fails to detect the changes of the confining pressure from the internal mechanism, and points out the influence of concrete parameters to the mechanical impedance value.