Title: Bond Failure in Reinforced Concrete Under Monotonic and Cyclic loading: A Fracture Mechanics Approach
Author(s): Kent Gylltoft, Krister Cederwall,
Lennart Elfgren, and larsgunnar Nilsson
Publication: Symposium Paper
Appears on pages(s): 269-288
Keywords: bond (concrete to reinforcement); bonding; cracking
(fracturing); crack propagation; cyclic loads; fatigue (material);
fatigue tests; loads (forces); pullout tests; reinforced concrete.
Bond-slip failure between a smooth steel bar and con-crete was studied in micro scale. Both theoretical and experimen-tal work are presented. The theoretical analysis was perfomed as a nonlinear fi-nite element analysis, based on fracture mechanics. Roth a virgin loading stageanda subsquentloadingstagewasmdelled. In the experimental part a total of ten pull-out tests were performed, both with monotonic loading and cyclic loading. As far as the load-slip relations are concerned, the specimens were much softer at virgin loading compared to subsequent repeated loading. This is suggested to be caused by the phencmenon that the concrete, when it was cast, did not completely grow into the irregularities of the steel. The gaps, which consequently arised, were determined to be of the same magnitude as the depth of the irregularities, and were causing a soft performance for shear movements at virgin loading. This softness also caused the shear stresses in the contact zone to be quite uniformly distributed along the anchorage length. At subsequent repeated loading, as far as shear movment in the same directionas the virgin loading is concerned, all gaps were filled up, which resulted in a much stiffer performance.