Mechanical behavior of cracked beams strengthened with composites: application of a full-field measurement method

The mechanical behavior of pre-cracked Steel-Reinforced Concrete beams strengthened with Carbon Fiber Reinforced Polymer laminates bonded on the bottom surface is addressed. The displacement fields over the lateral face of beams loaded under four-point bending are measured with the grid method. The analysis of the results in the constant moment span is achieved at two different scales : local and global. At the global scale, the parameters of a classical beam of Bernoulli (curvature and neutral axis) are identified. It is proved that they can characterize the structural behavior both before and after repair. At the local scale, the cracks are localized and their width is measured. It shows that the stress distribution is modified between tensile cracks due to the bridging effect by the composite laminate, leading to the creation of new smaller cracks. The investigation of the bridging effect by the composite laminate is of major interest for the characterization of a possible enhancement of pre-cracked RC beam serviceability. It has already been addressed in the literature but some confusion still remained. The present experimental study clearly shows that it is mostly located in the cover concrete and that the composite slightly modifies the beam mechanical behavior.