Experimental Research On Shear Behavior Of Ultra-High Performance Concrete Structure With Coarse Aggregate

Ultra High Performance Conrete(UHPC)is a new type of concrete-base material featuring in high stength,high durability,tesile strain-hardening as well as good durability.It can be categorised into Coarse Aggregate Ultra High Performance Conrete(UHPC-CA)and Reactive Powder Concrete(RPC)based on whether coarse aggregate is contained.Given limited researches on the shear behavior of UHPC diagonal section have been focused on RPC,while coarse aggregate enhances the economical efficiency of UHPC and lowers the intensity of it.Researches on the shear capacity of UHPC-CA beams are presented in this thesis.The main work and conclusion are as follows.Experimental research on UHPC’s mechanical properties was conducted to examine the impact of the volume ratio of steel fiber on UHPC’s mechanical properties,and provide data for the shear behavior analysis on of diagonal section of UHPC-CA beams.The result indicates the volume ratio of steel fiber has a distinct impact on splitting tensile strength and flexural strength of UHPC-CA,whereas has little impact on flexural first-crack strength and modulus of elasticity of it.Steel fiber can effectively increase concrete’s compression strength but the vloume ratio of it has little to do with compression strength.The diagonal section of nine T-type UHPC-CA beams was tested in shear.Failure mode of test beams was observed.And test phonomena and data were used in the analysis for shear behavior of UHPC-CA beams.The test shows with the shear span ratio ranging from 1~3.5,diagonal compression failure and shear compression failure can be observed.Comparing to conventional concrete beams,concrete beams without stirrups with high shear span ratio is not subjected to diagonal tensile failure.Steel fiber is able to remarkably increase the postcracking deformability of UHPC-CA beams but unable to transform brittle failure on its diagonal section.The diagonal section cracks multiple times and the average width is fine and small spacing.The volume ratio of steel fiber plays an essential role in affecting crack distribution and average crack spacing.Higher ratio leads to more intensive crack distribution.The initial crack width of UHPC-CA beams is less than 0.02 mm.The mix of two kinds of short and fine steel fiber provides a better confinement effect for crack width within 0.1mm.Stirrup can decelerate the increase of crack width over 0.2mm.The volume ratio of steel fiber has a significant impact on the strain value of test beam’s longitudinal reinforcement in ultimate failure.UHPC-CA beams with high ratio of longitudinal reinforcement should adapt high volume ratio of steel fiber so as to give full play to its shear behavior.Combining test and shear behavior test result,Shear capacity research on the diagonal section of UHPC-CA beams was carried out.According to existing codes and recommendations,the calculations of UHPC-CA beams were compared.The research shows the existing codes and recommendations lead to a conservative result in calculating the shear capacity of UHPC-CA beams.The deterioration of bond strength between steel fiber and matrix is the main cuase of low shear capacity of UHPC-CA beams.Shear span ratio,stirrup reinforcemant ratio and vloume ratio of steel fiber are the main factors impacting shear capacity of UHPC-CA beams.Based on theoretical deduction and test analysis,a statisitc formula of shear capacity of UHPC beams is brought up.It is found that the calculated values agree well with the test values,and can provide a reference for the design of UHPC beams.