Shear Behavior Of UHPC Beams Without Web Reinforcement

Ultra-high Performance Concrete(UHPC)has the advantages of ultra-high strength,super toughness and excellent durability,and has a broad application prospect in civil engineering.UHPC beams without web reinforcement,which use the shear strength of steel fiber in UHPC and are only fitted with longitudinal reinforcement,have an increasing number of application in bridge engineering in recent years because of convenient construction and shorter construction period.However,the shear mechanism of UHPC beams is complex and the influencing factors are various.There is still a lack of research on the shear performance and failure mechanism of UHPC beams without web reinforcement,and there is no unified regulation on the calculation of shear capacity.This paper focuses on the above issues,and the main contents are as follows:(1)Six UHPC beams were designed with reinforcement ratioρ_sas the parameter to conduct shear exploration test of UHPC beams without web reinforcement.Based on the results of the exploration test,the shear span ratioλand steel fiber contentρ_fwere taken into consideration,and the shear failure process of UHPC beams without web reinforcement under different parameters were simulated by finite element software ABAQUS.The influence of the two factors on shear capacity and load-displacement curve were analyzed,and the shear failure mechanism of UHPC beam without web reinforcement was preliminarily discussed,which provided a basis for the shear test design of UHPC beam without web reinforcement.(2)Taking shear span ratioλand steel fiber contentρ_fas variables,10 UHPC beams without web reinforcement were designed for four-point bending test.The shear failure patterns,load-displacement curves and strain data of the specimens were analyzed.The results show that the shear failure occurred in all the specimens,and the shear span ratioλis the main factor affecting the failure patterns of the UHPC beams without web reinforcement.Due to the"bridging"effect of steel fiber,the shear failure of UHPC beams has better ductility than that of ordinary reinforced concrete beams.With the increase of steel fiber content,the shear bearing capacity and ductility of UHPC beams have been significantly improved.(3)Parameter analysis of shear performance of UHPC beams without web reinforcement.ABAQUS was used to carry out finite element simulation analysis on UHPC beams without web reinforcement under test conditions,and the results were compared with the test results,which showed that the two were in good agreement,verifying the effectiveness of the finite element analysis method for UHPC beams without web reinforcement in this paper.On the basis,the parameters of UHPC beams without web reinforcement are analyzed with three variables,i.e.,shear span ratioλ,longitudinal reinforcement ratioρ_s,and section size b×h,and the influence rules of each variable on the shear performance of UHPC beams without web reinforcement are obtained.The results show that:with the shear span ratio increasing from1.0 to 1.9,2.8 and 3.6,the ultimate bearing capacity increases by 44.0%,57.2%and 63.3%,respectively.The effect of longitudinal reinforcement on the ultimate bearing capacity decreases with the increase of shear span ratio,and the increase of longitudinal reinforcement ratio on the ultimate bearing capacity becomes less and less.After analyzing the parameters of five different section sizes,it is found that the relationship between effective cross-sectional area and ultimate bearing capacity is linear.Finite element analysis of UHPC beam with stirrups is carried out.The calculation results show that the stirrups has little effect on the ultimate bearing capacity of UHPC beam.(4)The formula for calculating the shear capacity of UHPC beams without web reinforcement is proposed.Five relevant UHPC codes and four shear calculation methods of UHPC beams were used to calculate the shear capacity of the specimens in this paper.The calculated values were compared with the test values,and the reasons for the difference in results were analyzed.The shear capacity test data of 81 UHPC beams without web reinforcement from relevant literature were collected,and the key parameters in the shear capacity calculation formula of UHPC beams without web reinforcement were regression fitted.Based on the fiber-matrix separation theory,a formula for the bearing capacity of UHPC beams without web reinforcement was proposed.The formulas for calculating the bearing capacity presented in this paper are in good agreement with the experimental values,finite element values and experimental values in literatures,which can provide a reference for the shear design of UHPC beams without web reinforcement.