Modeling SRP-concrete interfacial bond behavior and strength

Relatively recently a steel fabric/laminate has been proposed for externally strengthening concrete structures, using a polymeric resin. The steel fiber-polymer composite system is termed Steel Reinforced Polymer (SRP). To determine the ultimate load capacity of an SRP retrofitted concrete structure, one must accurately predict the SRP-concrete interface debonding load, which requires a robust local bond-slip model. Many design guidelines recommend mode II interfacial fracture energy limit as the failure criterion for FRP-concrete interface. For SRP strengthened members, a suitable constitutive law and failure criterion have not been established yet. Consequently, in this study the applicability of five existing bond-slip interface models for FRP-concrete interface to SRP-concrete interface is examined. The models' parameters are calibrated for SRP-concrete interface using an experimental database by the present authors and compared with the values suggested by the original authors for FRP-concrete interface. The database involves results of tests on concrete prisms bonded to SRP strips. The experimental interfacial bond-slip relationship for the former interface is observed to have a more precipitous descent after the peak stress than predicted by the existing models; consequently, a new model is proposed here to capture this phenomenon. All the models are calibrated using a classical technique which minimizes the difference between the measured and computed interfacial shear stress values at different slip levels. The results indicate that all the models predict relatively well the slope of the ascending branch of the shear stress-slip curve, but they give substantially different values for the maximum shear stress attainable and noticeably different descending branch profiles. Among these, overall, the proposed model is in relatively better agreement with the experimental results.