Simulation of RC beams with mechanically fastened FRP strips

A common approach to the strengthening of RC beams is by attaching fibre reinforced polymer (FRP) strips to the beams’ soffit by either externally bonding (EB), or rapid attachment with mechanical fasteners (MF). Simulating an RC beam with an MF-FRP strip is complex as a full member analysis is required to determine the developed strains in the FRP strip between fasteners. Moreover, as no direct interaction between the concrete and strip exists, strain compatibility does not apply and thus a conventional full-interaction (FI) approach becomes reliant on an empirically derived member behaviour. This paper presents a member analysis in which a segmental M/θ approach is used to determine beam deformations and forces in beams with prestressed and unprestressed MF-FRP strips. Being mechanics based the approach incorporates residual strain partial-interaction (PI) theory to directly simulate the effects of tension-stiffening and a size-dependent stress–strain model to simulate the concrete wedge formation associated with concrete softening. Furthermore PI theory allows directly for the influence of concrete creep and shrinkage. The approach can be used in the design of members to quantifying the number and spacing of fasteners resulting in strengths exceeding conventional EB systems, and thus can be used to develop design guidelines.