Bond-slip models for the interface between steel fabric reinforced cementitious matrix and concrete substrate

Abstract

Composite materials for strengthening existing structural members represent a valid alternative to the traditional strengthening techniques. In particular, Fabric Reinforced Cementitious Matrix (FRCM) composites have been successfully employed to strengthen existing reinforced concrete and masonry structures.Among the different FRCM composites available on the market, the attention of the authors was recently focalized on systems composed of high tensile strength steel cords embedded in a cementitious matrix (systems also well known as Steel Reinforced Grout, SRG).The main failure mechanism of FRCM is represented by the debonding at the matrix-fiber interface. Therefore, the study of the bond behavior of FRCM composites is a key topic to develop reliable design procedures. In this paper, the applicability of different existing bond-slip interface models for FRP-concrete interface to SRG system is studied. The different parameters characterizing the models are calibrated by using an experimental database available by the authors and including results of direct single-lap shear tests on concrete prisms bonded to SRG strips. 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 descending branch profiles.The calibrated models are, then, compared with some other laws proposed in the literature for PBO and basalt FRCM systems; some of them are also implemented within a numerical procedure developed by the authors for the estimation of both the maximum axial stress at debonding and the corresponding effective bonded length of the SRG strip. The comparison with the experimental data has allowed for verifying the accuracy of the calibrated bond-slip models.