Beam Experimental Investigation And Finite Element Analysis On Bond Behavior Between Steel Bars And Steel Fiber Recycled Concrete

Steel fiber reinforced recycled coarse aggregate concrete is a new type of concrete material with excellent mechanical properties and durability.At the same time,it has the advantages of being green,low-carbon and environmentally friendly,and has broad application prospects in the process of new urbanization construction under the background of ecological priority and green development.The bond between steel bars and steel fiber reinforced recycled coarse aggregate concrete is the basis for the safety and performance of reinforced steel fiber recycled concrete coarse aggregate structure,and it is also the prerequisite for its application in engineering structures or components.In order to systematically study the bond performance between steel bars and steel fiber reinforced recycled coarse aggregate concrete,this paper considers the main influencing factors such as steel fiber volume ratio,recycled aggregate replacement rate,concrete strength grade,anchorage length and stirrup constraint,and analyzes the bond failure mode,load-deflection curve,bond-slip curve,bond strength and bond-slip constitutive relation of 13 groups of steel fiber reinforced recycled coarse aggregate concrete beam bond specimens through four-point bending test.On this basis,according to the proposed four-stage bond-slip constitutive model,the bond performance between steel bar and steel fiber reinforced recycled coarse aggregate concrete is numerically simulated by using nonlinear analysis software ABAQUS.The main research contents are as follows:(1)Thirteen groups of beam-type bond specimens were made,in which the influence factors such as different steel fiber volume ratio,recycled aggregate replacement rate,concrete strength grade,anchorage length and stirrup constraint were considered.Fourpoint bending loading tests were carried out to analyze the influence of various factors on the bond performance between steel bars and steel fiber reinforced recycled coarse aggregate concrete.The results show that the failure modes of beam bonded specimens can be classified into three categories: shear failure,bond failure and yield failure of steel bars.(2)The influence laws of various factors on the load-deflection curve,bond-slip curve and bond strength of beam bonded specimens are analyzed,and the loading process of specimens is divided into micro-slip stage,crack propagation stage,failure stage and residual stage,and the effect of steel fiber in recycled concrete is revealed.The results show that with the increase of steel fiber volume ratio,the bond strength of beam bonded specimens is obviously improved;For beam bond specimens without steel fiber,the replacement rate of recycled aggregate increases from 0% to 100%,and the bond strength of beam bond specimens decreases significantly.For beam bond specimens with steel fiber,with the increase of replacement rate of recycled aggregate,the initial bond strength of beam bond specimens is not affected,but the ultimate bond strength and residual bond strength are significantly affected.The increase of concrete strength grade can delay the appearance of cracks in the surrounding medium of steel bars in beam bonding specimens,increase the bonding force and mechanical bite force between interfaces,and improve the bonding strength;The bond strength of beam bonded specimens decreases with the increase of anchorage length,and the failure mode changes from bond failure to yield failure of steel bars.The ultimate and residual bond strength of beam bonded specimens increase with the increase of stirrup constraint.(3)The influences of steel fiber volume ratio,recycled aggregate replacement ratio,anchorage length and stirrup reinforcement ratio on the normalized bond strength are introduced.A four-stage bond-slip constitutive model is proposed by studying the test results,and the parameters of the bond-slip constitutive model proposed in this paper are given.Based on the knowledge of elastic mechanics and virtual crack theory,combined with the cracking and softening model of steel fiber reinforced recycled coarse aggregate concrete,the calculation formula of ultimate bond strength between steel bar and steel fiber reinforced recycled coarse aggregate concrete is derived.(4)Based on the proposed four-stage bond-slip constitutive model,the numerical model of steel bar and steel fiber reinforced recycled coarse aggregate concrete beam bond specimen established by finite element software ABAQUS is analyzed,and verified according to the corresponding experimental behavior,which shows that the proposed bond-slip constitutive model can accurately predict the failure mode and load-deflection relationship of beam bond specimen,and can be used to simulate the bond performance between steel bar and steel fiber reinforced recycled coarse aggregate concrete,providing a basis for structural design of steel fiber reinforced recycled coarse aggregate concrete.