Experimental Study On Influence Of Shape Change Of High Strength Reinforcing Steel On Performance Of Eccentric Compression Member

With the development of economy and the diversification of social needs,the structural form of buildings is developing towards the direction of high-rise buildings and large-span buildings.Reinforced concrete structure is widely used because of its many excellent characteristics.Reinforcing steel is one of the basic materials of the structure.Therefore,the requirements for reinforcing steel become higher.In recent years,different varieties of high-strength reinforcing steel continue to appear,but because of Chinese concrete design code for the use of reinforcing steel in reinforced concrete structure,the highest strength is only stipulated to 500MPa.Therefore,it is particularly important to carry out relevant research for the revision of concrete design code for 500MPa,especially 600MPa and above high strength reinforcing steel.But at present,Chinese concrete code only provides relevant provisions for steel bars with strength grades of 500Mpa and below.Therefore,it is particularly important to carry out the related research on the high strength rebar with the strength grade of 500MPa,especially 600MPa and above to provide conditions for the improvement of concrete specifications.In the relevant standards and codes of our country,there are clear provisions on the shape parameters of reinforcing steel,but the distance between the transverse ribs on the surface of reinforcing steel stipulated in Chinese code is much smaller than that stipulated in the international code and the British code.Increasing the space between transverse ribs can reduce the number of transverse ribs on the surface of reinforcing steel and improve the utilization rate of steel.Therefore,in this paper,T63E/E/G high strength reinforcing steel with the standard shape and T63E/E/G high strength steel bars with increasing transverse rib spacing are selected as the longitudinal reinforcement and stirrups of large-eccentric compression column members for experimental research to explore whether the various mechanical indexes of high-strength reinforced concrete large-eccentric compression specimens with different reinforcement shapes are consistent.In addition,different reinforcement ratios and different concrete strengths are set to explore whether the influence of various factors on the T63E/E/G high strength reinforced concrete column with large eccentric compression is consistent with the corresponding law of ordinary concrete column.The failure modes of the specimens were summarized and classified,and the lateral deflection curves and load-concrete strain curves which could reflect the mechanical properties of the specimens were drawn.Through comparative analysis,it is found that the failure mode,bearing capacity and deflection of the T63E/E/G high strength reinforcing steel with increased transverse rib spacing are not significantly different from those of the T63E/E/G high reinforcing steel bar with standard shape.The curves of the T63E/E/G high strength reinforced concrete columns with large eccentric compression are basically consistent with those of the typical specimens with large eccentric compression.When T63E/E/G high strength reinforcement is used as stirrups,the stirrups basically reach yield at the later stage of test loading,which improves the deformation performance of the specimens.The comprehensive analysis shows that when the T63E/E/G high strength reinforcing steel with the increase of transverse rib spacing is applied to the member with large eccentric compression,the mechanical indexes have no great difference due to the change of the shape of the reinforcing steel.Therefore,there is no need to do special treatment to apply T63E/E/G grade steel bar with increased transverse rib spacing in large eccentric compression member.On the basis of the test results in this paper,the relevant calculation methods in the current concrete codes of China and the United States were selected to calculate the bearing capacity of large eccentric compression members and the cross section bending bearing capacity,and the feasibility of using the two methods for T63E/E/G high strength reinforced concrete columns with large eccentric compression was verified.Suggestions on the design value of tensile and compressive strength of T63E/E/G high strength reinforcing steel used in eccentrically compressive concrete members are put forward.The comparative analysis shows that the calculation values of the large eccentric bearing capacity and the cross section bending bearing capacity of T63E/E/G high strength reinforced concrete by the American code method are all higher than those by the Chinese code method.From the perspective of safety,the relevant calculation methods in the current concrete design code of China are more suitable.When the member is equipped with stirrups,the design values of the tensile and compressive strength of T63E/E/G high strength rebar in the eccentrically compression member is f_y=f_y~,=545MPa.This paper is mainly based on The compilation of Shaanxi engineering construction standard—Technical specification for application of heat-treatment high-strength ribbed bar in concrete structures.The comparative analysis of the application of two kinds of high strength reinforcing steel in large eccentric compression members can provide reference for revising the current concrete design code in China.At the same time,it can also provide ideas for optimizing the manufacturing technology of the shape of reinforcing steel and improving the utilization rate of steel.