Numerical Simulation Study Of Multiple Cracks In Concrete Beams

With the continuous development of economy,concrete,which is an economical and durable material,is used more and more.However,due to the material properties of concrete itself,concrete structures in practical projects often work with joints.Cracks have also become an important potential safety hazard of concrete structures,so scholars at home and abroad have done a lot of research on concrete cracks.With the application of fracture mechanics in concrete fracture,people began to use finite element method to study the fracture of concrete.Up to now,more satisfactory results have been achieved,but most people only study single concrete crack.However,in practical engineering applications,most concrete structures themselves have multiple cracks,but at present.The main reason for the lack of research on multi-cracks is that the problem of multi-cracks is more complex than that of single crack,the expansion of cracks is more random,and the test of concrete multi-crack structure is more difficult.So in this paper,aiming at the problem of multi-cracks in concrete,numerical simulation is used to study it.The main work is as follows:(1)Based on the multi-crack equation and the minimum load criterion,the real "expansion" or "closure" of multi-cracks are analyzed.Based on the virtual crack model,the dual-node model of cracks and the migration of crack propagation path are studied.The numerical model of multiple cracks in this paper is determined.(2)Four-point bending tests of two groups of four-crack concrete beams are carried out in this paper.By changing the position of the main crack(i.e.the crack with the longest opening length)on the concrete specimens,different failure modes and load of the specimens are obtained.At the same time,concrete compressive strength test,splitting tensile strength test,axial compressive test,modulus of elasticity and wedge splitting tensile test were also included,which laid the foundation for subsequent numerical simulation.(3)In this paper,the Fortran finite element program is used to simulate the multi-crack model of concrete beams,and the failure modes,failure loads and cracking sequence of multi-crack beams are obtained.By changing the gridding accuracy of the numerical model,it is concluded that the sensitivity of the multi-fracture numerical model to the gridding accuracy is not strong when the gridding accuracy meets the calculation requirement.Based on the interaction coefficient of the multi-fracture,the interaction relationship between the multi-fracture is analyzed by establishing different fracture models.By analyzing and comparing the numerical simulation results with the experimental results,it is found that the failure load of concrete beams is basically the same,and the failure mode and crack propagation path are basically the same,which verifies the accuracy of the numerical simulation in this paper.