Strengthening of metallic beams with different types of pre-stressed un-bonded retrofit systems

Unlike bonded retrofit systems, un-bonded systems do not need any surface preparation prior to bond application, which reduces the overall time and cost of a retrofit plan. Because the carbon fiber reinforced polymer (CFRP) plate in the un-bonded (tendon) systems is not bonded to a metallic substrate, different variants of the retrofit systems can be developed to ease application in the field. This paper presents four different variants of the prestressed un-bonded retrofit (PUR) systems: trapezoidal PUR (TPUR), triangular PUR (TriPUR), Flat PUR (FPUR), and Contact PUR (CPUR) systems. Analytical solutions based on the flexibility approach are developed to predict the behavior of the metallic beams retrofitted with the PUR systems. A finite element (FE) model is created to simulate the behavior of the retrofitted beams. The results of the analytical solutions are compared with those obtained from the FE model. The results from the analytical and numerical models have been compared with the results of an experimental study on steel and aluminum beams retrofitted with the PUR systems. A series of parametric studies are performed to investigate the influence of different parameters such as the type of the PUR system and the CFRP pre-stress level on the behavior of the retrofitted beams. The results show that for a specific CFRP pre-stress level, all four different PUR systems result in approximately the same stress reduction in the steel beam bottom flanges. Therefore, it is possible to use any of the four pre-stressing technique depending on the requirements of the structure to be pre-stressed.