科研之友
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摘要
The random decrement (RD) technique is a time-domain procedure in which the random structural response under service loads is transformed into the free decay response. The RD technique is used for monitoring and determining structural performance, being able to predict damage and handle the occurrence of sudden failures during operation of the structure. The technique is considered a unique method for nondestructive testing. The RD signature can be utilized as a damage indicator. The technique is based on output measurements, whereas both input and output measurements are required for other, traditional methods commonly used in aerospace and mechanical engineering, including frequency- and time-domain methods such as the frequency response function and state equation. In civil engineering, input excitation forces such as wind, earthquake, and traffic loads are often hard to determine. The RD technique determines the changes of the structure's dynamic parameters according to external forces without knowledge of the magnitude of the excitation forces. The method is already considered efficient for detecting damage to steel structural members, so the current study focuses on use of the RD technique to determine dynamic parameters for reinforced-concrete (RC) members and explores the possibility of determining the presence of damage and its location. The main focus of this research work is assessment of the suitability of RD for monitoring RC beams. Two laboratory investigations were performed to determine the applicability of the RD technique for RC members and compare the indication of damage using a random signature for RC and steel beams. The beams were excited randomly, then the response signals were detected and the dynamic response signature was calculated at each stage. The RC beam was subjected to damage by applying a concentrated load at its midpoint, while the steel beam was subjected to different structural damage ratios by cutting the cross section to 25, 50, and 75 % damage ratio using a mechanical saw. The natural frequencies and damping ratios were calculated for different applied loads on the RC beam and the steel beam for different damage ratios. The changes in the dynamic parameters of the structure were determined for both undamaged and damaged beams. The investigation indicates the role of the change in the random signature due to damage, which was detected for different damage ratios for steel and RC beams, also revealing the particular significance of this technique for small damage and cracks. The results indicate meaningful changes in damping values that enable detection of the level of damage for the RC beam. The RD technique provides a promising, efficient approach for determination of dynamic parameters for important structures.
- 出版日期2016-11
