A reflection on the application of vibration tests for the assessment of cracking in PRC/RC beams

Occurrence of cracking damage in a structural, reinforced, concrete element leads to changes in its dynamic response. Nevertheless, the typical non-linear behavior of prestressed reinforced concrete (PRC) and reinforced concrete (RC) beams is characterized by cracking, due to the low tensile strength of concrete. It is necessary to take adequate account of cracking effects, in vibration-based monitoring of PRC/RC beams' structural health, by distinguishing cracking of tensile concrete due to bending moment under service loads; which does not reduce the structural availability of beams although it modifies their dynamic response, from real damage deriving from defects, loss of integrity and cracking due to overloading during service life. This paper deals with cracking effects through an investigation of PRC/RC beam models in real scale, subjected to increasing static loading and natural vibration tests. Degradation of stiffness and development of cracking were related to frequency values measured in a frequency range through vibration tests on free end beams. The results are compared with theoretical values and discussed. (C) 2012 Elsevier Ltd. All rights reserved.