Study On The Seismic Performance And Mechanism Of Precast ECC/RC Composite Coupled Shear Walls

The precast shear wall structure is an important structural form of housing industrialization that conforms to "energy saving and land saving" and "building industrial system" in the development stage of our country.Whether the seismic performance can meet the requirements is an important factor that depends on if it will be popularized and applied smoothly.In this paper,ECC(engineered cementitious composites)materials,which have excellent shear deformation resistance,high ductility,high toughness and deformed compatibility with the steel bars,are applied into the weak parts and the main energy dissipation components or energy dissipation areas of the precast concrete shear wall,forming a kind of new structure system—precast ECC/RC composite coupled shear wall.Through the low reversed cyclic loading experiments,numerical simulation and mechanism analysis,seismic performance parameter analysis,based on Pushover’s capacity spectrum analysis,the seismic performance and mechanism of precast ECC/RC composite coupled shear walls are studied comprehensively.The main research contents and achievements include the following aspects:1.Uniaxial compression tests on ECC cube specimens and prism specimens are carried out,direct tensile tests on ECC dumbbell tensile specimens are carried out,and the failure modes,stressstrain curves and stress mechanism of ECC were analyzed.Accordingly,based on the principle of energy equivalence,an ECC plastic damage model for ABAQUS nonlinear analysis are derived and proposed.2.According to a high-rise precast coupled shear wall structure for the pilot project which is supported by the Twelve-Five Science and Technology Support Project,a precast ECC/RC composite coupled shear wall is designed and fabricated.The low reversed cyclic loading experiments are made and the failure characteristics,load-displacement hysteresis curves,load-displacement envelope relationship,stiffness degradation,ductility and energy dissipation capacity of the precast ECC/RC composite coupled shear wall and precast RC coupled shear wall are comparatively analyzed.The multiple failure mechanisms including plastic hinges appeared at the ends of the coupling beams,multi crack development in the middle part of the coupling beams,the longitudinal reinforcement in the coupling beams almost all yielded,the web wall piers appeared flexural shear failure,the flange wall piers appeared flexural failure,yield of longitudinal reinforcement at the bottom of the wall,crushing and breaking of concrete at the bottom of the web,shear failure between the web and the base joint and so on.Compared with the precast RC coupled shear wall,the hysteresis loop of the precast ECC/RC composite coupled shear wall is more full,the skeleton curve decreases more gently,the stiffness degrades more slowly,the ductility is better,the energy dissipation capacity is stronger,and the seismic energy dissipation capability is better.3.The general finite element analysis software ABAQUS is used to simulate the spatial structure model of the precast ECC/RC composite coupled shear wall and the precast RC coupled shear wall.The numerical simulation results are compared with the experimental results.The results of numerical simulation can effectively react the crack,damage and break law of the structure model,and the loaddisplacement hysteresis curve of finite element simulation is almost the same as that of the test,which is in a great agreement.On this basis,load-displacement hysteresis curves,load-displacement envelope relationship,stress distributions of concrete and ECC,compression damages of concrete and ECC,crack distributions of concrete and ECC,stress distributions of the steel bars,slips of the splicing regions,development of plastic hinges for the coupling beams and walls,failure mechanism of the coupling beams and walls are analyzed according the whole loading process.The internal force,deformation and damage distribution of the precast ECC/RC composite coupled shear wall are deeply revealed.4.Load-displacement curves,load-displacement hysteresis curves,energy dissipation capacity and the stiffness degradation under different parameters including the regions ECC used in the coupling beams and walls,the strength of the ECC,the stirrup ratio of the coupling beam and the strength of the longitudinal reinforcement are analyzed in detail.It is proposed that the best areas of where the ECC used is the laminated layer of the coupling beams and the bottom 400 mm of the walls.It is also suggested that the ECC strength is E40,the longitudinal reinforcement strength is HRB400,and the stirrup ratio of the coupling beams is 0.5%~1.13%.5.An ABAQUS finite element model of precast ECC/RC composite coupled shear wall structure with 32 stories is established and the “Pushover Analysis” is carried out.The capacity spectrum curve and the seismic demand spectrum curve are determined,and the performance points of the structure under various seismic fortification level are calculated and obtained.Based on the Pushover’s capacity spectrum method,the lateral displacement,storey drift,interstory drift,compression damage distribution of the walls and plastic hinge distribution of the 32 storey precast ECC/RC composite coupled shear wall structure are analyzed.Under the action of large earthquake,the lateral displacement,storey drift and interstory drift of the precast ECC/RC composite coupled shear wall structure are all less than those of cast-in-situ RC coupled shear wall structure and precast RC coupled shear wall structure.The ductility and energy dissipation capacity of the ECC materials play an important role in the plastic stage,which effectively improves the seismic performance of the precast ECC/RC composite coupled shear wall structure.