The prediction of Fiber Reinforced Polymer (FRP) plate and sheet detachment failure in externally strengthened beams is still a subject of interestto develop admissible design models. The majority of studies attribute this failure mode of initiation and sudden propagation of the horizontal plane of separation to the shear stress concentration at the plate tip. Accordingly, several investigators have developed and used anchorage U-wraps todelay or control such separation. While this is one viable failure mode, it is shown in this study to be the less likely immediate cause of separation in a significant number of experiments. A numerical nonlinear analysisprocedure is developed for this purpose. The main hypothesis of the design model, established in conjunction with the analysis procedure, is the arresting of plate tip shear crack by internal shear reinforcement followed later by the initiation of a horizontal shear crack branching off of any shear, flexure or shear-flexure crack along the shear span including the tip crack. Depending on the shear stress concentration at the FRP cut off point, the separation failure is classified into two categories. The experimental results of 101 specimens with long plates and 31 specimens with short plates were analyzed using the present procedure. The results, obtained from a plate tip crack initiation model and a maximum plate strain limit model, are evaluated using the experimental data of the 132 tests yielding inconsistent findings. Cracking at the shear stress concentration point is shown to initiate at an early loading stage causing no instantaneous separation failure. The parameters controlling the critical modes of failureare identified. The design model proposed is based on an interface shearstress limit. The design model developed is applicable to test data of long and short plates or sheets.
Samenvatting