Study On The Seismic Behaviour Of Prefabricated ECC Encased CFST Piers

Engineered Cementitious Composites(ECC)have been widely studied and applied due to their high tensile ductility and crack control ability.This paper proposes that the cast-in-situ concrete in the prefabricated ECC outer steel tube forms a composite cross-section compression member,which not only solves the difficulty of casting and demoulding of ECC concrete piers,but also improves the durability and stability of the concrete filled steel tubes.In this paper,a qualitative and quantitative analysis of the parameters affecting the seismic performance of ECC concrete-filled steel tube columns is carried out through pseudo-static tests and numerical simulations based on Open Sees.The main results obtained are as follows:(1)The pseudo-static test of 3 precast ECC concrete-filled steel tube columns and one ordinary concrete-filled steel tube column was carried out.The test design parameters are the thickness of the steel pipe,the axial compression ratio and whether the ECC material is outsourced.The seismic performance of the specimens,such as failure form,hysteresis performance,ductility performance,cumulative energy consumption and stiffness degradation,are analyzed through experiments.The test results show that the precast ECC concrete-filled steel tube pier has a fuller hysteresis curve compared with ordinary concrete-filled steel tube piers,the accumulated hysteretic energy is significantly improved,the ductility and elastoplastic deformation capacity are enhanced,the local buckling of the steel tube is improved,and the strength of the specimen is attenuated Slower,better stability and less damage.The thicker the steel pipe,the greater the degree of improvement in seismic performance,and the peak load,ductility and energy consumption capacity will also increase.Compared with the ECC pipe concrete piers with similar steel consumption,the energy consumption capacity of the prefabricated ECC steel pipe concrete piers is increased by more than 3 times.(2)The fiber beam finite element model of each specimen in the test was established by Open Sees and compared with the test results.The results show that the numerical simulation results are in good agreement with the experimental results,that is,the modeling method and material constitutive used in this paper are reasonable and effective.(3)Based on the validated fiber beam model,a parameter analysis was carried out to clarify the influence of factors such as ECC strength,core concrete strength,and whether to wrap ECC pipes on the seismic performance of precast ECC concrete-filled steel tube columns.The results show that the ECC pipe can delay the local buckling of the steel pipe to a certain extent,improve the ductility of the component,and improve the load-bearing capacity of the component while also improving its energy consumption;for the same thickness of ECC,the thicker the steel pipe,the more significant the improvement ability of ECC;The greater the ECC strength,the higher the horizontal load-bearing capacity of the component,and the stronger the cumulative energy consumption capacity,but the lower the plastic deformation capacity;the higher the strength of the core concrete,the higher the horizontal load-bearing capacity of the component,but the degree of improvement is far less than the change in ECC strength The greater the axial compression ratio,The higher the steel grade of the precast ECC concrete-filled steel tube pier,the smaller the ultimate displacement,and the worse the plastic deformation capacity,but the energy consumption capacity increases.