Modelling and verification of response of RC slabs strengthened in flexure with mechanically fastened FRP laminates

Mechanically fastened fibre-reinforced polymer laminate systems are emerging as a promising means for the repair and strengthening of reinforced concrete members. This technology entails the use of pultruded carbon-and glass-vinyl ester fibre-reinforced polymer laminates with enhanced longitudinal bearing strength that are connected to the concrete substrate by means of steel anchors. Attractive applications are those for emergency repairs where constructability and speed of installation are critical requirements. In this paper, an experimental investigation is first presented that included laboratory testing of scaled reinforced concrete slabs strengthened with four different combinations of laminate lengths and fastener layouts to study optimised strengthening configurations. Compelling evidence was gained on the influence of the partial interaction between reinforced concrete slabs and mechanically fastened fibre-reinforced polymer laminates on the flexural response arising predominantly from bearing of the fasteners on to the fibre-reinforced polymer laminate. A numerical study is presented where the proposed finite-element procedure incorporates non-linear constitutive models for materials and the concrete-fibre-reinforced polymer interface. For the latter, an accurate and simplified, conservative bilinear stress-slip model is successfully implemented and verified to evaluate applicability for analysis and design purposes.