Numerical investigation of flexural behaviours of precast segmental concrete beams internally post-tensioned with unbonded FRP tendons under monotonic loading

•A verified 3D FE model of PSCBs prestressed with unbonded FRP tendons was successfully built.•Segments' interface imperfection effect on the beam initial stiffness was successfully captured.•The distinguished working mechanism between segmental vs monolithic beams.•Using FRP vs steel tendons in tension- and compression-governed PSCBs was thoroughly discussed.•An intensive parametric study was conducted to examine the flexural response of PSCBs.•A model was proposed for better prediction of the ultimate stress of unbonded FRP tendons. This study numerically examines the prospects of replacing steel tendons with fibre reinforced polymer (FRP) tendons in precast segmental concrete girders/beams (PSCBs) for mitigating the corrosion damage to precast structures using finite element (FE) software Abaqus. This is the first study in the published literature that successfully builds an experimentally-verified 3D FE model of dry-joined PSCBs internally prestressed with unbonded FRP tendons to thoroughly investigate the beam’s flexural behaviour. The effect of segments’ interface imperfection on the initial stiffness of PSCBs was successfully captured in this study. The distinguished working mechanisms between monolithic and segmental beams, and between FRP and steel tendons in both tension- and compression-governed cases were comprehensively discussed. An intensive parametric study was also conducted to examine the effect of primary parameters (effective prestressing stress, prestressing reinforcement amount, span-to-depth ratio and different types of FRP tendons) on the flexural response of PSCBs. The results have proven that commonly available CFRP tendons (Young’s modulus Ep = 145 GPa) can well replace steel tendons in PSCBs while high-modulus CFRP tendons (Ep = 200 GPa) should be used with caution to ensure the PSCBs can achieve sufficient deformability. Moreover, among some existing models, ACI 440.4R-04′s model gave the most accurate predictions of the ultimate stress of unbonded FRP tendons (fpu) in PSCBs compared to the numerical results but its estimation was slightly unconservative and scattered. A new bond reduction factor was, hence, proposed for better prediction of fpu of FRP tendons in PSCBs. The ultimate stress of unbonded FRP tendons in PSCBs should be limited to 75% of the tensile strength of the tendon in design to account for the deformation concentration at the joints and the brittle failure characteristics of FRP tendons.