Hitoshi Furuuchi

Intermediate Crack Debonding of Polymer Cement Mortar Overlay-Strengthened RC Beam

The bond behavior at the polymer cement mortar (PCM)-concrete interface particularly affects the structural behavior of overlay-strengthened slabs or beams, and the debonding of the PCM overlay was one of the major failure modes. The design procedure of PCM overlay to strengthen an RC element should avoid these premature debonding failures. Because no reliable design method for retrofitting with the PCM overlay is currently available for the practitioner, a need exists to understand the mechanism of the PCM overlay debonding process to prevent failure. This paper presents an analytical approach for a PCM overlay-strengthened beam failed by intermediate crack (IC) debonding. The limit of transferred shear force along the PCM-concrete interface to avoid any occurrence of debonding is analytically provided. The reliability and accuracy of the proposed analytical procedure have been successfully verified by knowing the ratio of analytical and experimental strength of the PCM-strengthened beams compiled in a bending test database, which has a mean value of 1.10 and a standard deviation of 0.14.

Average Crack Spacing of Overlay-Strengthened RC Beams

This research evaluates the average crack spacing of overlay-strengthened RC beams. Current equations in different structural codes for predicting the average crack spacing of RC beams with multilayered reinforcing bars have proved inapplicable to overlay-strengthened RC beams, although both types of beams are reinforced with multiple layers. We have developed a simple, practical analytical model that can predict the average crack spacing of this type of beam. We analyzed an overlay-strengthened beam element using equilibrium and compatibility equations to formulate the average stresses of concrete, overlay, and tension reinforcement. Then we made a series of comparisons among various types of beam elements, using the experimental investigations to verify the model’s validity and reliability. The proposed model performs satisfactorily against measured responses from the experimental database.