Size and shape effect in the pull-out of FRP reinforcement from concrete

Scaling phenomena in the progressive debonding between fiber reinforced polymer (FRP) strips and concrete substrate are examined on the basis of single lap shear tests, considering different bond lengths and widths. To capture a stable post-peak response of the FRP-concrete joint, the slip between the concrete support and the reinforcement strip, measured at the reinforcement end using a clip gage, was selected as feedback control signal during the tests. This allowed a quasi-static stable fracture propagation in the descending branch until complete load relaxation and debonding. Experimental tests were simulated by means of 2D and 3D finite element analyses adopting two different approaches. At first, a numerical model based on linear elastic materials with all non-linearities concentrated at the interface was assumed. It clearly revealed the inability to recognize all the aspects of the debonding process. Then, a different numerical model, based on a non-linear constitutive model for concrete and perfect adhesion between all the materials, was adopted.