An FE study on the behavior of CFRP shear strengthened and anchored post-tensioned beams

Strengthening of post-tensioned concrete bridge girder is on the rise as a result of heavier vehicles and higher traffic volumes. In order to strengthen existing bridges, the use of carbon fiber reinforced polymers (CFRP) have become the preferred material to increase the strength of existing bridge girders in flexure, shear and torsion. However, when applied as externally bonded reinforcement, such materials suffer from premature debonding. In order to mitigate premature failure, modes the use of innovative anchorage systems have been a subject on ongoing research in recent years and these have been proven to increase the level of CFRP utilizations prior to failure. Patch anchors were chosen to be applied on large-scale post-tensioned beams deficient in shear; in order to study their influence on them and to investigate the effects of other factors. Bidirectional fiber patch anchors have been proven to counteract the end peeling and interfacial shear stresses that occur at fiber ends, resulting in much higher material utilization prior to debond. Patch anchors involve using two layers of bidirectional carbon fiber sheets with +/- 45 degrees fabrics to sandwich both ends of the CFRP laminates and are ideal for shear strengthening applications. This paper presents both an experimental and finite element study on large-scale post-tensioned (PT) beams, which were strengthened in shear with CFRP laminates and anchored using patch anchors. For the sake of increasing the theoretical knowledge on the performance of CFRP laminates and patch anchors on strengthening of PT beams, a nonlinear finite element (FE) model was constructed and calibrated based on the experimental results. Therefore, in this paper the outcome of conducting a nonlinear finite element analysis (using the program ATENA 2D and 3D) on three large-scale post-tensioned beams, which were strengthened in shear with CFRP and anchored with patch anchors, will be presented.