Proposals for Flexural Capacity Prediction of Precast Segmental Concrete Beam Prestressed with Internal Un-Bonded CFRP Tendons

Abstract

The application of CFRP tendons in precast segmental concrete beams (PSCB) as internal un-bonded prestressing reinforcement is a newly developed scheme to improve structural flexural performance. The stress increment of the un-bonded tendon, depending on the whole structural deformation, is a crucial value to be predicted for flexural capacity design. Due to the discontinuity of the opening joints, the deformation modes of segmental beams differ from the monolithic ones. The existing prediction methods built for monolithic beams can not be directly used for segmental beams. In this paper, the new prediction equations of the tendon stress increment and flexural capacity were put forward for PSCB with internal un-bonded CFRP tendons (PSCB-IUCFRP). Firstly, the differences between the deformation modes of monolithic and segmental beams were compared and clarified based on the numerical model analysis. Then, a parametric analysis was conducted on 162 numerical models, and the results were employed to evaluate the applicability of existing methods for PSCB-IUCFRP. The predictions of the ACI 318-14 model and the AASHTO LRFD model were both conservative and scattering compared with numerical results. The ACI 440.4R model underestimated the tendon stress increments of beams under one-point loading but overestimated it for those under two-point loading. According to the failure mode of PSCB-IUCFRP, a simplified curvature distribution mode was assumed, and the relation between tendon elongation and structural deflection was derived. The prediction equations for PSCB-IUCFRP were proposed using the back-calculated plastic hinge length. Compared with existing methods, the proposed equations considered the deformation characteristic of segmental beams and had clear physical significance. The predictions of the proposed method were in good agreement with the numerical and experimental results. Furthermore, a balanced prestressing reinforcement ratio equation is proposed for PSCB-IUCFRP to avoid tendon rupture-controlled failure. The proposed equations provide suggestions for the flexural design of PSCB-IUCFRP and will help to popularize this new structure.