The inverse analysis technique is used to derive a non linear mode II interface law for Fiber Reinforced Polymer (FRP) – concrete bonding starting from experimental data. The proposed interface law is based on a fractional formula and includes the non linear compliance contributions of adhesive and concrete cover at high shear stresses. It depends on three parameters (the maximum shear stress, the corresponding slip and an exponent), which are calibrated from experimental results on debonding tests. The values of maximum loads and strain profiles along the FRP plates for different bonding lengths are used. The parameter identification is performed by the inverse analysis using a Direct Search algorithm. Some considerations on the well-posedness of the inverse problem adopting different cost functions to minimize the error between experimental and numerical data are given. After the parameter identification, the numerical results obtained with the proposed interface law are in very good agreement with the experimental results.
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