Finite Element Simulation Of Cracks In Concrete Structures

There are many small cracks in internal concrete before load act, and under the effect of external load, these tiny cracks will develop to macro-cracks, then concrete will be destroyed. Before instability expansion of macro-cracks in concrete, there is slow and stable growth stage of cracks, with a micro-crack zone exists in the vicinity of crack tip. When the cracks develop and plastic zone or micro-crack zone form, more external work will be consumed. Therefore, criterion of linear fracture mechanics is not available, and analysis method of non-linear fracture mechanics needs to be used as fracture criterion of concrete. A good fracture model must be used when the work of concrete with cracks is analyzed. In this paper the research situation and main features of several common crack models for analysis of concrete cracks are described, which can provide reference for choosing appropriate concrete crack model, furthermore, energy-based crack propagation criterion is established, an efficient mesh remeshing procedure called "insert-separate" is givened, a numerical algorithm with nonlinear equations is developed to solve the snap-through or snap-back phenomenon which always appears near the extreme points of the load-displacement curve of concrete. Accordingly, in this paper a local arc-length method suitable for tensile strain softening of concrete is presented, which is an improvement of the normal arc-length method. This method adopts constraint equation to combine the relative displacement parameter with the local fracture zone of structure. The mixed cracks of four-point sheared concrete beams are simulated by FEM, and the results are analyzed which shows the superiority of the local arc-length method, also the influence of notch depth and elastic modulus on sliding displacement of the crack mouth is given, and the load-deflection curve at loading points can be accurately and efficiently alculated. Using pre-crack element embedding algorithm, propagation path of pre-cracks at concrete gravity dam heel under deadweight and water pressure effect is simulated, and influence of rock materials of dam foundation on the pre-crack propagation path is researched.The results show that the effect of pre-crack element embedding algorithm is useful, which can be used in simulation of the crack propagation process of concrete gravity dam, and crack propagation path of the ShunXi arch dam is simulated by this algorithm, with the result well consistent with the maximum principal tensile stress obtained by the linear elastic analysis. The study shows that pre-crack element embedding algorithm is effective in simulation of crack propagation of concrete dams.