Experimental investigation on the bond of reinforcing bars in high performance concrete under cyclic loading

The bond performance between reinforcing bars and concrete under cyclic loads were experimentally investigated in this paper. In particular, the effects of steel fibers and hybrid fibers (including steel fibers and carbon fibers) on␣the bond performance were analyzed. Based on the experimental results, the deterioration laws of the peak bond stress, the stiffness of the unloading branch, frictional bond resistance and remnant ultimate bond stress under cyclic loads were summarized. Meanwhile, the increasing law of the remnant slip and the effect of the loading order on the deterioration of the bond performance were studied. Then, two damage factors d _u and D _u were introduced, where d _u is a factor that reflects the damage of the peak bond stress under constant controlling displacement and D _u is also a factor that reflects the damage of the remnant ultimate bond stress under changeable controlling displacement. Making use of the two damage factors and other key variables, the bond constitutive relationships between reinforcing bars and concrete under cyclic loads could be expressed by formulas. The computed τ–s relationships agreed well with those obtained by experiments.