Study on bond-slip behavior of ribbed steel bars in engineered cementitious composites concrete: Experimental analysis, constitutive model and refined finite element model

The good bonding performance of ribbed steel bars in engineered cementitious composites (ECC) concrete was the basis of their cooperative work, which is very important for the bearing capacity and safety of ECC concrete structures. To study the bond-slip performance between ribbed steel bars and ECC concrete, 30 groups of pull-out tests were conducted with key design parameters. Thereby the influence of key parameters on the failure process and bond performance was analyzed. Based on the experimental data, calculation formulas for bond strength and shape coefficients considering key parameters were calibrated, and a unified functional form of the ECC concrete bond-slip constitutive model was established. A three-dimensional (3D) scanning technology was used to obtain real rebar ribs, and a three-dimensional fine finite element model of ribbed steel ECC concrete was established to conduct in-depth analysis of bond slip behavior and damage failure process. The results show that fibers could delay the shear failure of concrete teeth by rebar ribs, making the bond performance of ECC concrete degrade more slowly compared to ordinary concrete. The strengthening of materials strength and the densification of stirrups had a significant impact on the bonding performance. Increasing the cover thickness could improve bond strength, but the influence on the bond strength was weak when it was too large. Reducing the diameter of steel bars could enhance bonding behavior. The established ECC concrete bond-slip constitutive model included material strength grade, cover thickness, stirrup constraint, longitudinal rebar diameter and other key parameters. The calculated bond strength and overall slip behavior both exhibited good accuracy and applicability. The 3D scanning method could more accurately reflect the ribs and surface defects of the rebar compared to traditional modeling methods (sweeping commands), and the established 3D fine finite element model was more accurate and reasonable.