Damage assessment in reinforced concrete beams using eigenfrequencies and mode shape derivatives

The use of changes in dynamic system characteristics to detect damage has received considerable attention during the last years. This paper presents experimental results obtained within the framework of the development of a health monitoring system for civil engineering structures, based on the changes of dynamic characteristics. As a part of this research, reinforced concrete beams of 6 meters length are subjected to progressing cracking introduced in different steps. The damaged sections are located in symmetrical or asymmetrical positions according to the beam tested. The damage assessment consists in relating the changes observed in the dynamic characteristics and the level of the crack damage introduced in the beams. It appears from this analysis that eigenfrequencies are affected by accumulation of cracks in the beams and that their evolutions are not influenced by the crack damage locations; they decrease with the crack damage accumulation. The MAC factors are less sensitive to crack damage compared to eigenfrequencies, but give an indication of the symmetrical or asymmetrical nature of the induced crack damage. Next to this, the COMAC factors, the strain energy evolution and the changes in flexibility matrices are also examined as to their capability for detection and location of damage in the RC beams, the strain energy method appears to be more precise than the others. (C) 2002 Elsevier Science Ltd. All rights reserved.