Analytical and experimental studies of fiber-reinforced polymer-strengthened concrete beams under impact loading

A series of 27 concrete beams were tested to investigate the behavior of beams strengthened with fiber-reinforced polymer (FRP) laminates wider impact loading. Two out of the 27 beams were not retrofitted and were used as control specimens. The impact force was delivered with a steel cylinder drop weight. The test results revealed that bonding composite laminates to concrete beams could significantly improve the performance of this type of structure to resist impact loading. In addition, bonding laminates increased cracking and flexaral strength, as well as residual stiffness of the beams. Furthermore, it reduced the number of cracks, crack widths, and the maximum deflection. The residual stiffness of the strengthened beam. after first impact was two to three times that of an unretrofitted beam, and the maximum deflection decreased by 30 to 40%. The improvement depends or the type and weight of composite laminate. compared with the static test results, the ultimate deflection, number of cracks, and crack width were smaller but the maximum reaction force was three to four times larger than those of the beam under static loading. The residual stiffness of the strengthened beam after first impact can be calculated using a regression equation. The impact force can be obtained with a send-empirical equation, which is derived from Spring-Mass models and modified by the test results. From flexural wave theory, an equation has been developed for predicting the deflection of a beam caused by impact loading.