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CFRP Strengthened RC Beams under Impact Loadings Kazunori Fujikake*, Sam Soeum*, Takahiro Matsui** and Kenji Suzukawa** * National Defense Academy, Department of Civil and Environmental Engineering ** Toray Industries Inc. Abstract Carbon fiber reinforced polymer (CFRP) materials are being increasingly used to repair bridges and buildings for main advantages of CFRP including high strength, high fatigue strength, high stiffness, high resistant to corrosion, light in weight, ease of application and high durability. However, little is known about the effect of impact loads on reinforced concrete (RC) structures strengthened with the CFRP materials. Therefore, the aim of this study was to experimentally examine the impact behaviors of RC beams strengthened with CFRP materials and to present a developed analytical model which predicts an important index (maximum midspan deflection) to evaluate the damage levels of CFRP strengthened RC beams subjected to impact loadings. Twenty RC beams with a cross-section of 160×170 mm and a length of 1,700 mm were prepared, of which sixteen RC beams were strengthened with CFRP materials in flexure; and four RC beams were unstrengthened as a control. Two types of impact loading tests were performed with a drop hammer impact machine; one was single impact test; the other was repeated impact test. In the test, the RC beam was simply supported over a span of 1,400 mm. In the single impact test, the drop hammer with a mass of 300 kg was freely dropped only once onto the RC beam at midspan from the specified heights ranging from 100 to 400mm. In the repeated impact test, the drop hammer with a mass of 300 kg was repeatedly dropped onto the RC beam at midspan until failure. The initial drop height was 0.05m, and then the drop height was doubled after every two hundred drops. The experimental results clearly showed that strengthening RC beams with CFRP materials can reduce their maximum deflections than those of unstrengthened RC beams under the single impact loading. In the repeated impact loading test, the CFRP strengthened RC beam could withstand more than 400 drops, while the unstrengthened RC beam failed at the 7th drop. Therefore, it can be said that the RC beams strengthened with CFRP are significantly improved in the resistance to both the single and repeated impact loadings. In the analytical model, a perfectly plastic collision was assumed between the drop hammer and the RC beam. The maximum midspan deflection was calculated from the load-midspan deflection relationship evaluated by the nonlinear analysis based on a finite-element layered method, in which the loading rate effects were duly considered, following the law of conservation of energy after impact. The analytical result is in good agreement with the experimental midspan deflection.