Mode II interface constitutive law for concrete substrates strengthened with steel reinforced polymers

A new, effective and economical method has been introduced in the literature for the external strengthening of existing reinforced concrete structures, consisting of an innovative composite material using steel wires, in lieu of traditional carbon or glass continuous fibers, embedded in a polymer matrix. The resulting composite is termed Steel Reinforced Polymer (SRP). The SRP can be externally bonded to a substrate via wet lay-up, using either epoxy or polyester resin. To accurately predict the debonding load and the interface mode of failure of SRP strengthened concrete interfaces, a robust local bond-slip model is required. For estimating debonding failure load, some design guidelines specify the mode II fracture energy (GII) as the key material property. For SRP-concrete interfaces the above quantity has not been established yet. Since GII is related to the area under the bond-slip curve of the SRP-concrete interface, knowledge of this curve is necessary. Consequently, here two interface laws are presented and calibrated using results of a previous extensive experimental program on SRP-concrete bonded joints. Specifically, detailed measured axial strain values of the bonded SRP strips are utilized for calibration. The first model entails a bilinear bond-slip relationship and is analogous to the model originally proposed by others for bonded FRP-to-concrete system. The second model, proposed here, comprises a fully nonlinear bond-slip relationship. The results show that the proposed nonlinear bond-slip model provides a more accurate prediction of the maximum shear stress and corresponding slip than the companion bilinear model.