Numerical Study On Seismic Performance Of A Novel Type Of High-strength Reinforced UHPC-NC Composite Column

Ultra-high performance concrete(UHPC)is a novel type of cement-based composite material with high strength,high toughness and excellent durability.It can be used in actual construction structures to effectively extend the life span of buildings.The strength of highstrength steel bars from HRB400 to higher has the properties of high ductility,high toughness and a high yield strength.The use of high-strength steel bars and UHPC materials can take full advantage of the two materials and improve the seismic performance of the components.To this end,this paper proposes to use UHPC as a replacement for normal concrete(NC)in the plastic hinge area of the reinforced concrete column and to combine high strength steel to form a new type of high strength reinforced UHPC-NC composite column member.In order to discuss the seismic performance of composite columns,based on the multifunctional finite element program ABAQUS,this paper establishes a high-strength reinforced seismic finite element model for UHPC-NC composite columns by selecting suitable materials and element types and verifies them with experiments.On this basis,the numerical analysis of the displacement ductility of the composite column was carried out and the formula for calculating the equivalent plastic hinge length of the composite column was created.The specific research content is as follows:(1)Based on the ABAQUS dynamic analysis theory,combined with the mechanical properties of high strength steel bar reinforced UHPC-NC composite column,the value criterion of the corresponding plastic parameters in the yield criterion,flow rule and hysteretic rules of the concrete damage plastic model are discussed.The damage factors,recovery stiffness coefficients,the selection of concrete and reinforcement elements,the contact between concrete and reinforcement and the precautions of boundary conditions when setting the analysis step are clarified.(2)Applying the multifunctional finite element program ABAQUS,combining appropriate material constitutive and element types of UHPC,NC and high-strength steel bars,concrete damage plasticity model is calibrated,and a high-strength steel bar reinforced UHPCNC composite column seismic finite element model is established.Compared with the test results of NC column and UHPC column under low cycle load,the validity of the established seismic finite element model is verified.(3)Relying on the established high-strength reinforced UHPC-NC composite column seismic finite element model,by analyzing the load-displacement curve and displacement ductility coefficient curve of the composite column under different axial compression ratios,longitudinal reinforcement diameters and UHPC length,the effects of the above parameters on the seismic ductility of composite column are discussed.(4)Based on the ductility analysis model of the high-strength steel bars reinforced UHPC-NC composite column and the method of determining the equivalent hinge length,the results between numerical and test are compared firstly.Next,on the basis of experimental verification,the numerical evaluation of the equivalent hinge length of the plastic column under different axial compression ratios,longitudinal bar diameters,longitudinal bar strength and specimen height is studied.Then,the applicability of the recommended formula used to calculate the equivalent plastic hinge length is discussed.Finally,the formula for calculating the equivalent hinge length of high-strength steel bars reinforced UHPC-NC composite columns is proposed by regression analysis.