Behavior of reinforced concrete beams with loss of bond at longitudinal reinforcement

The effect of loss of bond for longitudinal reinforcement on the structural behavior of RC beams is investigated in a test series of six beams where nominal length without bond is varied. Loss of bond is created with plastic tubes surrounding the longitudinal reinforcement leaving short bonded lengths over support and at positions where stirrups are crossing the longitudinal reinforcement. Using a bond-stress slip relationship made it possible to see that the total bond force could be calculated as the sum of local bond forces. Maximum bond force occurs at maximum load and when the available bond force decreases the load carrying capacity is also reduced. Even for significant loss of bond, the reduction in shear capacity was moderate, implying that short bond lengths are sufficient to create high bond forces. Local areas with bond contributes efficiently to create anchorage for the longitudinal bars. It was also found that the loss of bond was compensated by increased utilization of stirrups, and that loss of bond does not lead to more brittle types of failure.