Bond-slip Behavior And Numerical Simulation Of Ribbed Steel Bar And Lightweight Aggregate Concrete

The problem of bond-slip between deformed steel bars and concrete is always a difficult point in the basic theoretical research of concrete structures,and there are always disputes about the interaction mechanism and how to reasonably express it.The failure mechanism of lightweight aggregate concrete is different from that of ordinary concrete.Therefore,considering the difference between the two and the influence of incompatible deformation of adjacent layers of concrete members,the paper systematically studies the bond-slip behavior of deformed steel bars and lightweight aggregate concrete from the aspects of physical test,meso analysis and macro numerical simulation,and puts forward the applicable constitutive model.The research results can provide reference for the theoretical analysis of engineering structures or members.The main research contents are as follows:1.The pull-out tests of 19 groups of lightweight aggregate concrete and 4 groups of normal concrete were completed.The effects of the number of embedded steel bars,the clear distance and diameter of steel bars,the anchorage length and the type of concrete on the bond-slip behavior were studied.The results shown that the bond strength of LWAC specimen was higher than that of NWC specimen at lower water binder ratio.The existence of embedded reinforcement changes the distribution of bond stress,so the diameter,clear distance and quantity of reinforcement in the same direction should be considered comprehensively.2.A two-dimensional lightweight aggregate concrete model based on random aggregate model was established,and the compressive stress-strain curve of lightweight aggregate concrete was obtained,which was embedded in the bond slip constitutive model to reveal the bond failure mechanism of the interface between reinforcement and concrete,and a shear strut analysis model was proposed.The results shown that the proposed compressive stress-strain curve of lightweight aggregate concrete and the bond stress-slip curve of deformed reinforcement were in good agreement with the test curve,which can accurately simulate the cracking behavior of concrete and the failure mode of components.The interaction of the surrounding steel layers was considered reasonably in the shear strut model.3.Based on the thick walled cylinder theory and the analytical model of shear compression bar,the theoretical calculation formula of bond strength under local constraint was derived.The influence of bond failure mechanism on bond strength and the influence of rib spacing on slip were analyzed systematically.Combined with the theoretical formula of bond strength,the proposed constitutive model was proposed.The results shown that the bond strength formula was in good agreement with the experimental data,and the proposed constitutive model was more accurate in predicting the whole process of the test curve.4.A three-dimensional solid model directly reflecting the interaction between reinforcement and lightweight aggregate concrete was established at the macro scale,which verified the rationality of the proposed constitutive model and revealed the influence of various parameters on the bond slip behavior.The results shown that the model could accurately reflect the stress state of concrete,and the simulation curve was in good agreement with the experimental results.At the same time,when f_cu,k≥40MPa,the effect of cover thickness on the peak stress can be ignored.When there is embedded bar and the diameter of steel bar is more than 16mm,the peak stress increases,but the change is not significant.