Bond Behavior of Steel Bars in Concrete Confined with Stirrups under Freeze-Thaw Cycles.

In order to evaluate the influence of freeze-thaw action on the durability of concrete structures, this paper presented an experimental study to investigate the effects of freezing-thawing cycles and concrete strength on the bond behavior between steel bars and concrete confined with stirrups. Through freeze-thaw cycles and center pullout tests, the failure mode of pullout specimen, concrete strength, mass loss, dynamic elastic modulus, and bond-slip curves were analyzed. At last, the bond-slip constitutive model was proposed for specimens with stirrup confinement under freeze-thaw action. Main test results indicate that the failure mode and shape of bond-slip curves are affected by stirrups. The bond strength hasa certain increase after 100 freeze-thaw cycles owing to the constraining force from stirrups, whereas the splitting tensile strength significantly declines. After 100 freeze-thaw cycles, the splitting tensile strength of C20 and C40 decreased by 40.8% and 46.5%, respectively. The formula was provided to calculate the bond strength of constrained concrete after freeze-thaw cycles, and the damage coefficient and other related parameters in the formula were suggested. The predicted bond-slip curves are close to the experimental results, which could provide reference for the related research of bond performance after freeze-thaw action.