Study On Meso-mechanical Properties Of Lightweight Aggregate Concrete And Seismic Performance Of Lightweight Aggregate Concrete Frame Columns

Lightweight aggregate concrete(LWAC)is a kind of concrete prepared by natural or artificial lightweight aggregate(LWA),which has the advantages of light weight,heat insulation and shock absorption.Its mechanical and seismic performance are the focus of attention in the field of civil engineering structures.Most of the current research on LWAC has sought the relationship between material composition and mechanical properties from a macro-level perspective by means of experiments.However,the factors affecting the mechanical and seismic performance of LWAC are numerous and complex,and the macroscopic mechanical behavior of LWAC depends on its meso-structure.Therefore,it is important to study the mechanical and seismic properties of LWAC from a mesoscopic viewpoint.In this paper,based on experimental and test data,the mechanical and seismic properties of LWAC are discussed and investigated from a mesoscopic viewpoint by using numerical simulation method and theoretical analysis.The mechanical properties of LWAC with circular LWAs and LWAC with polygonal LWAs are tested,and the crack propagation characteristics,stress-strain behavior and mechanical properties of LWAC with circular LWAs and LWAC with polygonal LWAs are simulated by using the cohesive zone model(CZM).Based on the experimental data and simulation results,the parameters of CZM for LWAC with circular LWAs and LWAC with polygonal LWAs are modified to improve the accuracy of CZM for uniaxial tensile simulation of LWAC.Based on the concrete damage plasticity(CDP)model in ABAQUS,the relevant parameters of the concrete constitutive model of LWAC with circular LWAs and LWAC with polygonal LWAs are optimized based on the experimental and simulation data.Furthermore,three-dimensional models of LWAC with circular LWAs frame columns and LWAC with polygonal LWAs frame columns are established to simulate their seismic performances under horizontal low cyclic loading,and the seismic performances are analyzed from the mesoscopic perspective.The main research work and results are as follows:(1)Sintered circular fly ash ceramsite and polygonal shale ceramsite were used to design and prepare LWAC,and their mechanical properties were tested.The test results show that the failure morphology of LWAC is affected by the shape and strength of aggregate,and the shape and surface state of aggregate play a more important role in the tensile properties of LWAC than the aggregate strength itself.Although the barrel compression strength of polygonal LWA is only 46% of that of circular LWA,the tensile strength of LWAC with polygonal LWAs is higher than that of LWAC with circular LWAs,while the compressive strength of LWAC with polygonal LWAs is similar to LWAC with circular LWAs.Mortar has a better reinforcement effect on LWA,especially polygonal LWA with low strength.(2)Two-dimensional mesoscopic models of LWAC with circular LWAs and LWAC with polygonal LWAs were established in ABAQUS.The failure characteristics and mechanical properties of 60 groups of LWAC random samples with different aggregate shapes and volume fractions of 0.3～0.8 under uniaxial tension were simulated and analyzed.The results show that the crack of LWAC under uniaxial tension starts from the inside of LWA,and form penetrating cracks through interfacial transition zones(ITZs)and mortar.As the volume fraction of LWA increases,the slope of the rising section of LWAC stress-strain curve increases,and the tensile strength and strain decrease.Compared with LWAC with circular LWAs,crack initiation time of LWAC with polygonal LWAs is earlier and tensile strength is slightly lower,while the time and strain of penetrating crack are larger.LWAC with polygonal LWAs may have better damping effect.(3)By drawing on the orthogonal test method,64 sets of orthogonal test with 9factors and 4 levels of the CZM parameters were designed.Based on the orthogonal test,the mechanical behaviors of LWAC with circular LWAs and LWAC with polygonal LWAs under uniaxial tension were numerically simulated,and the degree of influence of CZM parameters were analyzed,respectively.The results show that for the same LWAC,the LWA bond strength has the greatest effect on the tensile strength of LWAC,and the mortar bond strength has the greatest effect on the tensile strain of LWAC.In order to make the simulation results more consistent with the actual situation,the CZM parameters for LWAC with circular LWAs and LWAC with polygonal LWAs are modified according to the orthogonal analysis and test results,and the results are verified to be more reliable by simulation.(4)Based on the parameters of the concrete constitutive model of LWAC with circular LWAs and LWAC with polygonal LWAs optimized in this study,threedimensional finite element models of LWAC frame columns were established,and the seismic performances of structure under horizontal low cyclic loading were investigated based on the meso-structure of LWAC.The results show that although the seismic performance of LWAC frame columns is slightly weaker than that of normal weight concrete(NWC)frame columns,it can meet the seismic code requirements.The peak load,displacement,ductility and deformation capacity of LWAC with polygonal LWAs frame column are larger,and the skeleton curve and energy consumption are higher,so it is more suitable for structural engineering with seismic requirements.