Effect of cracking, corrosion and repair on the frequency response of RC beams

This paper presents a laboratory investigation to study the effect of cracking, corrosion and repair on the frequency response of simply-supported reinforced concrete beams. The beams were subjected to four-point bending at 70% of their theoretical ultimate loads. Corrosion was then induced using an electro-chemical acceleration technique. The beams were then repaired to restore their load-carrying and deflection capacities. Based on response time histories, the fundamental frequency characteristics of the beams were deduced using Fourier transform (FT) and Hilbert-Huang transform (HHT). Experimental results revealed significant changes in the normalized frequency, Rf, with decrease in Rf associated with load-induced cracking, an increase in Rf associated with moderate reinforcement corrosion and a subsequent decrease in Rf associated with repair. The results of this study support the use of frequency response, obtained with an appropriate signal processing technique such as HHT, to infer the health of monitored structures, taking into account environmental conditions, likelihood of corrosion occurrence, properties of repair material and interfacial bonding.