ASA 126th Meeting Denver 1993 October 4-8

4pEA4. Decay of resonances of reinforced concrete beams with cracks.

Zhijing Wang Shail Pandya Robert D. Finch

Dept. of Mech. Eng., Univ. of Houston, 4800 Calhoun Rd., Houston, TX 77204-4792

Ben H. Jansen

Univ. of Houston, Houston, TX 77204-4793

Reinforced concrete beams in practical use always contain cracks. This paper reports a study of the changes in decay rates of resonance frequencies when cracks occur in a vibrating concrete beam. The experiments were performed using model reinforced concrete beams with general end conditions as well as ideal pinned--pinned end conditions. The power spectrum and its time variation were studied. The short time Fourier transform (STFT) technique was used. Theoretical studies were made to establish the effects of damping on the vibration of the beam. A complication exists in that the reinforced concrete beam is in effect a composite material. The results will be compared with the data obtained from a steel beam of homogeneous material [J. Robin, Acoust. Soc. Am. 92, 2441 (A) (1992)]. The changed behavior of decay rates of resonance frequencies could be a feature in the vibration monitoring of reinforced concrete structures such as highway bridges. [Work supported by NSF Grant No. MSS-9024224.]