Impact response characterization of shear CFRP strengthened RC beams by Fourier and wavelet methods: tests and analyses

Abstract The current experimental study investigates impact response features of reinforced concrete (RC) beams with dominant shear failure mode. Six built nonstrengthened and strengthened RC beams with a shear span-to-depth ratio of 2.5 were subject to repeated low-velocity impacts. Projectile energy is equal to the amount required for collapse. Retrofit consists of carbon fiber-reinforced polymer (CFRP) sheets attached to the exterior surface in vertical-unidirectional and cross-ply orientation. Laser linear variable differential transformer (LVDT) and micro-electro-mechanical systems (MEMS) accelerometers record the resultant deflection and acceleration to inspect the relationship between retrofit and damage. Fast Fourier transform (FFT) and continuous wavelet transform (CWT) extract the response content specimens to monitor the frequency change for each case. According to extracted results, CFRP skin provides notable stiffness on the upward shift of active frequency range and peak spectrum amplitude maintained for impact repeats. The active domain in FFT spectrum is sensitive to failure type (shear or flexural). CWT analysis ridges show a clear difference between failure type samples. CFRP retrofit controls cracking and deflection, which is shown as increased acceleration in records, especially for the cross-ply wrap. Effective stiffness recovers during initial impacts and then starts degrading because of the rupture of horizontal fibers in cross-ply retrofit, but the stiffness is stable for unidirectional retrofit during all impacts.