The Research On The Constitutive Model And Size Effect Law Of Masonry Mortar

At present,the existing fine numerical analysis model of masonry structure lacks accurate material constitutive relation.In the existing refinement models,block is generally regarded as elastic brittle material,mortar is regarded as elastic material or elastic-plastic material of concrete constitutive relationship,interface and mortar are combined to establish a simplified meso model,or simulating the block-interface normal and tangential mechanical properties by spring element to establish a refined numerical analysis model.The above refined model still has disadvantages.Compared with the refined model,the simplified model has faster calculation speed,but the calculation precision is between that of the integral model and the refined model.The interface performance of spring element simulation is not easy to be converged due to the excessive number of springs,and the calculation is cumbersome with poor applicability.The refined numerical analysis model lacks finite elements and material models with high computational accuracy and applicability,which restricts the application and development of refined finite element analysis of masonry structures.In view of the above situation,this paper carried out the basic mechanical properties research and finite element theoretical research on the materials with microscopic layers of masonry structure.The main work and results are as follows:(1)To establish the general mortar compression constitutive model,the mechanical properties and deformation properties of mortar compression were studied by means of test method and theoretical analysis method.Taking the types of mortar cementitious materials,the ratio of mortar to sand and water to cement as the research variables,the elastic modulus test and the stress-strain full curve test of mortar are designed by the orthogonal design method and the failure state,elastic modulus,Poisson's ratio,compressive strength and stress-strain full curve of mortar specimen are obtained,and the influence of component change on its mechanical properties and deformation performance is analyzed.Also,by introducing elastic-plastic mechanics and damage mechanics,the elastic-plastic constitutive model and damage constitutive model of mortar under compression were established,and damage variables were calculated.The results show that the mortar compression constitutive model presented in this paper is in good agreement with the test results,which can provide a basis for mortar engineering application and finite element analysis.(2)To study the mechanical properties difference between ash seam mortar and test block in laboratory,to predict and evaluate ash seam mortar's properties,this paper studies the behavior of mortar size effect by physical model test method and theoretical analysis method.Uniaxial compressive strength tests were carried out on 12 groups of geometrically similar mortar cube specimens and 12 groups of non-geometrically similar mortar plate specimens to study the behavior of mortar size effect and the influence of mortar strength grade on the size effect.Based on the theory of energy release of fracture mechanics,Bazant is introduced to analyze the size effect behavior of mortar geometrically similar specimens.Strength term is added to modified Bazant size effect law and the modified dimension effect law is used to analyze the dimension effect behavior of non-geometrically similar mortar specimens.The formulae for calculating the dimension effect law of mortar compressive strength are established respectively,and the mechanical properties of mortar are evaluated.The research results show that the calculation results of the size effect law of mortar proposed in this paper are in good agreement with the measured data.(3)To study the bond slip constitutive model of mortar block interface,a total of 17 groups of 102 three brick specimens of shale solid brick and shale porous brick were designed to carry out double shear bond slip test.The effects of mortar joint thickness,mortar strength and void ratio on the mechanical properties and deformation properties of brick mortar interface are analyzed.The bond failure mode,bond strength and bond strength slip curve of the three brick specimens are also obtained.Meanwhile,based on the experimental research and theoretical analysis,the bond strength formula of masonry and the bond slip constitutive model of block mortar interface are established.The results show that the calculation formula of bond strength of masonry presented in this paper is in good agreement with the engineering data,and the constitutive model of interfacial bond slip between block and mortar is in good agreement with the experimental results.(4)To establish the fine numerical analysis model of masonry with high computational accuracy,this paper statistics the mortar,block compression and tension test data to establish the mortar,block compression and tension constitutive model and failure criteria,so as to determine the elastic modulus,Poisson's ratio and fracture energy.According to the test results of mechanical properties and deformation properties of block mortar interface,the interface contact relationship is established by introducing the surface based adhesive behavior model.By comparing the results of calculation and test,the applicability of material constitutive model and the validity and rationality of masonry separated meso model are verified.This research will perfect the basic theory of masonry structure,provide theoretical support for the application of mortar engineering and afford important evidences for the numerical analysis theory of masonry refinement.