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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.
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.