Microplane-crack Band Coupling Approach To Crack Analysis For Concrete Structures

As is known to all,concrete is one of the typical quasi-brittle materials which is sensitive to tensile stress due to the countless micro cracks inside it.During cracking,the material undergoes obvious strain softening.Among all the existing constitutive models describing the behavior of concrete,the Microplane model stands for its simple conception and unified parameters.However,it is difficult for Microplane model to achieve accurate simulation of strain localization of concrete structures in practical applications,what’s worse,the numerical settlement calculation results are greatly affected by element size.The fracture zone model defines fracture energy as a basic parameter of the material;the stress-strain softening curve needs to be adjusted depending on the element sizes to keep the fracture energy unique.Based on the ABAQUS secondary development platform,this paper combines Microplane model with crack band model to achieve the goal of simulating the actual cracking behavior of concrete more realistically.In this paper,the main works are as follows:(1)Based on the VUMAT secondary development interface provided by ABAQUS finite element analysis software,the fracture band subroutine was programmed in FORTRAN language to simulate the actual cracking behavior of concrete,using the numerical analysis of uniaxial tensile test,and bending test of notched beams and unnotched beams,to verify the rationality of the procedure.(2)Based on the equivalent localization theory,the VUMAT subroutine interface provided by ABAQUS is used to realize the coupling between the Microplane theory and the crack band model.The main coupling idea is that it is assumed that there is a localized element at each integration point of each finite element in the three-dimensional model,which is coupled by the strain softening zone and the elastic behavior zone of the concrete.The purpose of coupling is to achieve the equivalence between the Microplane theory and the crack band model,and to reduce the mesh sensitivity of the Microplane model in numerical simulation analysis so that the mechanical response in concrete nonlinear computation can be more reasonable.(3)The uniaxial tension,uniaxial compression and bending test of unnotched beam with different element sizes were simulated by the coupling procedure,and the results are compared with the results of the separate use of Microplane model.It shows that the coupling procedure can effectively reduce the mesh sensitivity problem caused by strain localization,and simulate the nonlinear mechanical response during concrete failure more realistically.(4)The subroutines developed in this paper have been applied in practical engineering,the results reveal a certain degree of credibility.However,the application of this subroutine in practical engineering is still restricted by the size of finite element.Meanwhile,the computational efficiency needs to be improved and further developed.The optimization for this program is still needed.