Research On The Interfacial Bond Performance Between Steel Fiber And UHPC Under Static And Dynamic Load

Steel fibers can significantly enhance the compressive and tensile strengths of Ultra High Performance Concrete(UHPC),and can also improve the toughness of the material.The reinforcing effect of steel fibers on the UHPC matrix is mainly achieved by the stress transmission between the steel fibers and the matrix.Therefore,the interfacial bond performance of the steel fibers and UHPC matrix plays a vital role in the high strength and high toughness of UHPC.This paper explores the influence of different factors on the bonding properties of the steel fibers and UHPC matrix interface under static and dynamic loads through single steel fiber pullout tests.Based on the simplified bond-slip model between the steel fiber and the matrix,a nonlinear finite element model of steel fiber pulled out of the UHPC matrix is established.By comparing the finite element results with the test results,the bond-slip model between the steel fiber and the matrix has been effectively validated.The main contents and conclusions of this article are as follows:(1)Under static load,by changing the volume fraction of hybrid steel fibers in the matrix,the bonding properties of two kinds of steel fibers(straight and hooked-end steel fibers)in hybrid steel fibers reinforced UHPC were studied.Based on the measured load-displacement curves of the steel fibers,the effects of hybrid steel fibers and their volume fractions on the bonding properties between the hybrid steel fibers and UHPC were analyzed,as well as the correlation between the fiber-UHPC interfacial bonding properties and the compressive strength of UHPC.It was found that when the volume fractions of both straight and hooked-end steel fibers embedded in the UHPC matrix are 1.0%,the hybrid of steel fiers could achieve the best interfacial bond performance between the steel fiers ans UHPC.(2)Under dynamic load,by changing the diameter and embedding depth of the steel fiber,the bonding properties of steel fibers with different diameters and lengths in UHPC were studied.Based on the measured load-displacement curves of the steel fibers,the steel fiber peak pullout load,pullout energy,average bonding stress,tensile performance utilization rate and their dynamic influencing factors at various pullout rates were analyzed,and the influence of steel fiber diameter and embedding depth on the loading rate sensitivity of interfacial bonding performance was discussed.It was found that when the steel fiber diameter is 0.30 mm,the average bonding stress is the largest,and the bonding performance and material performance utilization rate are the most sensitive to the loading rate.When the steel fiber embedding depth is 6.5 mm,the average bonding stress is the largest,peak load and material performance utilization rate are the most sensitive to the loading rate,and when the steel fiber embedding depth is 15 mm,the pullout energy is the most sensitive to the loading rate.It was found that when the steel fiber diameter and embedding depth are 0.3 mm and6.5 mm,the interface bonding performance under the impact load is the strongest.(3)Simplify the straigtht and hooked-end steel fiber pullout load-displacement curve to linear model.By establishing a nonlinear finite element model for straight and hooked-end steel fibers pulled out from the UHPC matrix,the stress distribution of the steel fiber and the matrix at different pullout displacements is analyzed.The results show that the maximum stress of the matrix in the hooked-end steel fiber pullout simulation is about twice that of the straight steel fiber pullout simulation.The simulated load-displacement curves were compared with the test results,and the effectiveness of the bond-slip model was verified.