Experimental Research On Compressive Strength Level Of T63E/E/G High-strength Steel In Eccentric Compression Member

The new heat-treatment high-strength ribbed 630MPa steel bar（T63E/E/G）has high strength and good ductility,which can reduce the reinforcement density and resource consumption,and has significant environmental and economic benefits.However,in China’s current implementation of the"Code for Design of Concrete Structures",the maximum strength of reinforcement material is 500MPa,In the Shaanxi Provincial Engineering Construction Standard"Technical Specification for Application of New Heat-treatment High-Strength Ribbed Bar in Concrete Structures"（DBJ 61/T157-2019）,the compressive strength design value of the eccentric compression member is determined by the plane-section assumption using the ultimate compressive strain of concrete,which limits the strength exertion level of T63E/E/G high-strength steel bar,and the different design value of the compressive strength and tensile strength will bring inconvenience to the engineering design.Therefore,to solve the quantitative problem of the compressive strength of T63E/E/G high-strength steel bar used in reinforced concrete member and difficult problem in engineering design,in order to promote T63E/E/G high-strength steel bar be used in reinforced concrete structure,and be included in the"Code for Design of Concrete Structures",11 eccentric compression concrete column reinforced with T63E/E/G high-strength steel were designed and fabricated in this paper.The mechanical properties of large eccentric compression concrete column reinforced with high-strength steel were studied in depth.The stress state and compressive strength exertion level of T63E/E/G high-strength steel in eccentric compression members are mainly researched.The main research contents and results of this paper are as follows:By the mechanical performance test of 11 eccentric compressive concrete members reinforced with T63E/E/G high-strength steel bar,the influence of factors such as the stirrup configuration（including two major factors such as intensity and spacing of stirrup）and eccentricity on the compressive strength level of high-strength steel bar and ultimate compressive strain of concrete is mainly considered.The results show that:T63E/E/G high-strength steel reinforced concrete column with large eccentricity presents a typical tensile failure mode,which is consistent with ordinary reinforced concrete column.The tensile and compressive longitudinal bars of the specimens with different stirrups in the large eccentric tensile failure exceed their yield strength,and the tensile and compressive strength of the rebar are fully exerted.The stirrup strength and the stirrup spacing have little effect on the bearing capacity of the column with large eccentricity,but have great effect on the deformation performance of the member.The ultimate compressive strain of concrete members reinforced with stirrups and longitudinal bars is greater than-3300×10^-6 as used in the current code,which is conducive to the compression yield of high-strength longitudinal bars and can ensure that the compressive strength of T63E/E/G high-strength steel bars reaches the same value as the tensile strength.By comparing the calculation values of bearing capacity in the Code for Design of Concrete Structures with the test values of T63E/E/G high-strength steel reinforced concrete columns with large eccentricity,the applicability and reliability of the calculation model in the current Code are analyzed.Considering the influence of stirrup and longitudinal reinforcement on the ultimate compressive strain of concrete,the deformation coordination conditions suitable for the calculation of the bearing capacity of T63E/E/G high-strength steel reinforced concrete columns under large eccentricity and the analysis of the stress state of high-strength longitudinal bars are put forward.The results show that it is still reasonable and feasible to design and calculate the bearing capacity of T63E/E/G high-strength steel reinforced concrete column under large eccentricity according to"Code for Design of Concrete Structures",and there is a large safety space.Therefore,it is suggested that the design values of the tensile and compressive strength of the T63E/E/G high-strength steel bar in the large eccentric compression column with stirrups are f_y=f_y’=545MPa.Mander model considering the complex details of the configuration of the stirrup parameter,and by introducing the effective constraint effect coefficient k_e for reliable correction of the lateral constraining arch effect,based on the Mander model to calculate the stress and strain of concrete model parameters for analysis of T63E/E/G high-strength steel reinforced concrete is of high precision.It can also be used as a deformation coordination condition to predict the stress state of compression longitudinal barsThe crack development process and distribution pattern of T63E/E/G high-strength steel reinforced concrete eccentric compression column is analyzed,and the relationship between the maximum crack width and the average crack spacing to the bearing capacity is studied.By researching the effects of various design parameters on the maximum crack width,and analyzing the crack pattern of T63E/E/G high-strength steel reinforced concrete eccentric compression column under normal use ultimate state according to the Code for Design of Concrete Structures.The results show that the crack control of T63E/E/G high-strength steel bar in eccentric compressive concrete member can satisfy the maximum crack width limitω_limin the first class environment grade.This study is based on group project"Enaction of Shaanxi province engineering construction standard of The Technical Specification for Application of New Heat-treatment High-strength Ribbed Bar in Concrete Structures".The research results provide the basis for revising the design value of T63E/E/G high-strength rebar’s compressive strength to 545MPa,which has been included in the latest revision of this code（DBJ 61/T157-2020）.The correlation analysis process of using concrete constitutive relation considering the constraint of stirrups as a condition of deformation coordination provide a new idea for analysis of mechanical properties of high-strength steel reinforced concrete member,also provide reference for the application of high-strength steel and incorporate the strength of more than 600MPa high-strength steel in the Code for Design of Concrete Structures.