Experimental Study On Shear Capacity Of Reinforced Concrete Deep Beams With High-strength Bars Under Uniform Load

High-strength concrete and high-strength reinforcement can collaborate with each other to give full play to the material performance,which has the characteristics of high strength and good durability.As a typical reinforced concrete structure,it is widely used in various complex building structures such as factories,high-rise buildings and bridges because of its excellent load-bearing performance.For the shear bearing capacity of deep beams,the current European Code,American Code and Canadian Code all recommend the use of tie-compression bar model for design calculation,while the Chinese Code GB50010-2010 adopts the semi-theoretical and semi-empirical formula based on the tie-arch model.Meanwhile,compression field theory(CFT),modified pressure field theory(MCFT),softened tie-compression bar theory(SSTM),and neural network model(NN)are also widely used in the theoretical study of deep beams.Through a large number of shear performance tests and elasticity theory,St.Venant’s principle shows that reinforced concrete deep beam is a complex mechanical analysis and structural treatment problem,and there are still many differences on the influence parameters of deep beam,for this reason,scholars at home and abroad have conducted a lot of research and theoretical analysis for the shear bearing capacity,damage mechanism and shear calculation model of deep beam.For the shear test of deep beams,the main method used is two-point centralized loading,and in actual engineering,in addition to the action of moving load and centralized loading,the situation of deep beams under the action of uniform load is more common,at present,there is less research on the shear performance of deep beams under the action of uniform load,so this paper starts the research.This paper adopts eight points of concentrated loading to simulate the uniform loading,and completes the shear performance test of seven high-strength reinforced concrete deep beams,observes the damage process and damage morphology of deep beams,and focuses on analyzing the effects of longitudinal reinforcement rate(0.67%～1.27%),horizontal web reinforcement rate(0.33%～0.50%)and hoop reinforcement rate(0.25%～0.50%)on the shear bearing capacity of deep beams,mid-span deflection,The effects of reinforcement strain,concrete strain,maximum crack width,etc.On the basis of this test,ANSYS finite element model is established and the calculation formula in the Code for Design of Concrete Structures(GB50010-2010)is used to calculate the shear bearing capacity of deep beams,and the finite element calculation results and the code calculation results are compared and analyzed with the test values,and the research results are as follows.(1)The concrete deep beam under the action of uniform load mainly occurs in three typical damage forms of oblique compression damage,splitting damage and local compression damage,and the damage form is expressed as crushing of compression bars,splitting of compression bars,and local crushing of concrete.(2)With the increase of longitudinal reinforcement rate from 0.67% to 1.27%,the ultimate bearing capacity of the deep beam gradually increases,the mid-span deflection gradually increases,the load-deflection curve gradually smooths out,the longitudinal reinforcement,horizontal reinforcement and hoop tendons basically do not yield,the neutral axis moves upward with the load,and the assumption of flat section is not satisfied.(3)With the increase of horizontal reinforcement rate from 0.33% to 0.50%,the development of mid-span deflection and diagonal section crack width is effectively suppressed,but there is no obvious effect law on the positive section cracking load,diagonal section cracking load and ultimate load.(4)With the increase of hoop reinforcement ratio from 0.25% to 0.50%,the ultimate load carrying capacity of deep beams was significantly increased.The increase of the hoop allocation ratio reduces the average stress of each limb hoop reinforcement,which makes the cracking load of the positive section and the cracking load of the oblique section show a rising trend,and the maximum crack width decreases with the increase of the hoop allocation ratio,which effectively inhibits the development of oblique cracks.(5)The calculation results of ANSYS are close to the test values,in which the ultimate bearing capacity,mid-span deflection and reinforcement strain of the deep beam are in good agreement with the test values,and the cracking load is slightly different from the measured values,and the simulation results are satisfactory in general.(6)Adopting the specification GB50010-2010 for theoretical calculation of bearing capacity of deep beams,the mean value of the test value compared with the calculation result of the specification is 2.208,the result is on the conservative side,and the specification GB50010-2010 has sufficient safety reserve.Comparing the test value with the calculated value of the formula proposed by Prof.Wang Xinmin,the mean value is 2.322 and the variance is0.021,the formula is relatively conservative for the DBU series deep beams and the data dispersion is generally small.