Numerical study on flexural behaviour of FRP reinforced concrete beams with compression yielding blocks

Fibre-reinforced polymer (FRP) bars are used in concrete structural members to tackle the corrosion problem of steel bars. However, the brittle rupture of FRP bars results in relatively low ductility of such concrete members. This paper numerically investigates the feasibility of using compression yielding (CY) block to enhance the ductility of FRP bar reinforced concrete beams. A finite element model is developed to study the behaviour of beam adopting the CY block, followed by a parametric analysis on the effects of material properties and geometry of the CY block. The results indicate that the adoption of CY block changes the failure mode of the beam from brittle concrete crushing to ductile compression yielding, increasing both the loading capacity and ductility of the beam. Increasing the compressive yield strength of the CY block can effectively increase the loading capacity but decrease the ductility of beams. A higher compressive ultimate strength of the CY block also increases the loading capacity but has limited effect on the beam ductility. In addition, the beam ductility can be increased by reducing the yielding and ultimate strains of the CY block, while the loading capacity can be enhanced by higher yielding strain or lower ultimate strain. It is revealed that sufficient height of the CY block is required to prevent concrete crushing in the compression zone, and an increase in CY block height improves the beam ductility. The CY block length should cover at least the pure bending zone when the section with the block has higher flexural capacity than that without the block, otherwise the length can be controlled as the theoretical plastic hinge length.