Effect of active confinement on the local bond stress-slip behavior of steel bars embedded in plain concrete with variable covers : experimental investigation and analytical modeling -

Abstract

Reinforced concrete structures are mainly designed for the concrete to carry compressive stresses and the steel to resist tensile stresses. Therefore, a composite interaction between concrete and reinforcing steel bars is necessary to achieve a good performance. This interaction depends on the local bond and slip behavior between the two materials. In the past, various experiments investigated the composite action between the concrete and reinforcing bars to examine the performance of reinforced concrete structures. Under monotonic increasing load, the influence of numerous parameters on the bond behavior were studied and it mainly includes the concrete compressive strength f'c, addition of fibers to concrete, bar diameter and geometry of the ribs, concrete cover, confining reinforcements, and transverse pressure. This study summarizes the results of a series of experimental and analytical studies on the effect of active confinement on the local bond stress-slip characteristics of steel bars embedded in plain concrete. Twenty specimens representing the confined region of a beam-column connection were tested under monotonic increasing load in tension. Different types of confinement and their effect on the local bond stress-slip response of reinforcing bars were investigated and compared. These include concrete cover-steel bar diameter ratio, and transverse applied pressure or active confinement. Based on the parameters that influence the bond strength, splitting, pull-out, and mixed mode failures were identified. A comprehensive analytical model predicting the local bond stress-slip response for steel bars embedded in plain concrete subjected to active confinement (transverse pressure) was developed. The model accounts for most of the important parameters that influence the behavior as observed in the experiment. The proposed analytical model shows acceptable agreement when compared against experimental results conducted as a part of this research.