Erfan Shafei - PhD Candidate
Mohammad Zaman Kabir - Professor, Structural Engineering Branch, Civil and Environmental Engineering Department, Amirkabir University of Technology (Tehran Polytechnic), Tehran, ۱۵۸۷۵-۴۴۱۳, Tehran, Iran,

Dynamic response features of reinforced concrete beams with dominant shear failure mode are investigated within experimental approach. Regarding natural frequencies as indicative factors of structure condition, oscillation content of built intact and carbon fiber reinforced polymer (CFRP) strengthened specimens is extracted using Fast Fourier Transform (FFT) and continuous wavelet transform (CWT). Free-falling steel weight impacts six simply supported beams, three pairs, repeatedly at mid-span location. Resultant deflection and absorbed acceleration time histories are recorded precisely to inspect the relationship between stacking effect and effective frequency domain change. Composite skin attachment provides notable stiffness on active vibration frequency range shift-up and peak spectrum amplitude maintain for impact repeats. Natural frequencies found by FFT are sensitive to failure type either shear or flexural. Results from the CWT analysis show a clear difference between the intact and retrofitted samples. Carbon fibers control shear-flexural cracking and deflection which is also revealed as enhanced acceleration values especially for cross-ply wrap. Acceleration frequency contents of unidirectional and cross-ply retrofits are retained around 1st and 3rd fundamental modes respectively with little deviations for impact repeats, beside excessive frequency range aberration occurred in intact samples. Effective stiffness is recovered initially during preliminary impacts and then starts degrading due to rupture of horizontal fibers in cross-ply retrofit, but provided stiffness is stable for unidirectional retrofit during all impacts.

Reinforced Concrete; Impact; CFRP Retrofit; Damage Assessment; Frequency Content