Experimental damage identification in a post tensioned concrete beam

The paper deals with the results of an experimental campaign carried out on a post tensioned concrete beam with the aim of investigating the possibility to detect early warning signs of deterioration based on static and/or dynamic tests. The beam was tested in several configurations aimed to reproduce 5 different phases of the ‘life‘ of the beam: the original undamaged state, under increasing loss of tension in the post tensioning cables, during and after the formation of cracks at mid span, after a strengthening intervention carried out by means of a second tension cable, during and after the formation of further cracks on the strengthened beam. Responses of the beam were measured by an extensive set of instruments consisting of accelerometers, inclinometers, displacement transducers, strain gauges and optical fibers. The paper presents the test program and the dynamic characterization of the beam in the different damage scenarios in terms of the first modal frequency identified from dynamic tests. The evolution of the bending stiffness monitored during static tests is also reported and a simplified mechanical model of the cracked beam was proposed to interpret the correlation between the two parameters.