The effect of the shape of the cohesive material law on the stress transfer at the FRP-masonry interface

Debonding of the fiber-reinforced polymer (FRP) from the substrate that occurs before its tensile strength is reached typically controls the effectiveness of the stress transfer mechanism between FRP composites and a quasi-brittle substrate, such as masonry. The FRP-substrate interface is usually modelled as a zero-thickness interface whose fracture Mode-II cohesive material law (CML) is defined in terms of shear stress and slip at the interface. In this paper, the effect of the shape of the CMLs of the FRP-brick and FRP-mortar interfaces on the stress transfer process will be presented and discussed. Several multi-linear CMLs, obtained from experimental data for both mortar and brick interfaces, will be adopted to obtain the load response of the FRP-masonry interface. It will be shown that the shape of the CMLs adopted does not strongly affect the load response if the fracture parameters are the same or similar among the CMLs. Finally, certain geometric relationships of brick and mortar joints imply more pronounced differences in terms of load response between the CMLs adopted.