Computational modelling and experimental investigation of the bond behaviour between concrete and braided fibre ropes

Abstract

Achieving a good bond between fibre and concrete is vitally important. This paper describes an initial investigation of the bond behaviour between concrete and braided fibre ropes as a substitute for steel reinforcing bars. Experiments were performed to determine the bond behaviour at ambient conditions. An equivalent 7mm diameter Siltex c pre-stressed carbon fibre ropes embedded in 6 samples of 150mm by 200mm C40 concrete cylinders were used for pull-out tests according to ACI 440.3R-04. Due to the lack of rope surface deformation, an average bond stress of 4.17MPa was achieved, approximately 36% of bond strength of 7mm steel reinforced bar (as defined by CEB-FIP Model Code and BS EN 1992-1-1). The response can be approximately described as a linear load-displacement behaviour, followed by a rapid de-bonding. A further bond enhancement was developed, by inserting oval beads in the rope’s core, forming ribbing effect similar to that of reinforcing bars using 10mm diameter Marlow c T12 Technora pre-stressed rope. A 5.5 times enhancement in bond strength was achieved compared to bonded plain fibre. The use of hierarchical higher-order (HO) approximations (based on the Legendre’s polynomials) is an feasible way of implementing p- or hp-refinement to a Finite Element (FE) Model. HO approximations for finite elements are only implemented by adding additional degrees of freedom to the system of equations rather than to the mesh database, resulting in a better computational performance while the order of approximation required is easily modified while keeping linear elements. A simple FEM is presented to explain how HO approximations within interface elements (in such case representing the bond between concrete and ropes) could be used to achieve a better rate of convergence. Consequently, such implementation would be used to derive a cohesive constitutive relation representing the benchmark achieved in the experiments.