ABSTRACT
Due to aging, to aggressive environment and/or to increasing service loads, a large part of the existing bridges all over the world have been deteriorating and require inspections to assess their health state. Static and dynamic non destructive methods can be used for this purpose and extensive experimental and numerical studies have been carried out on the subject (see e.g. Saiidi et al., 1994). Despite the above interest, very few studies deal with the correlation between the results of static and dynamic tests in different health conditions of the structure.
In this paper are reported the results of an experimental campaign carried out on a post tensioned concrete beam (see Figure 1) with the aim of investigating the possibility to detect early warning signs of deterioration based on static and/or dynamic tests. Location of sensors. D = displacement transducers; P = strain gauges; A = accelerometers, I = inclinometers. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig73_1.tif"/>
The beam was tested in several configurations aimed to reproduce 5 different phases of the ‘life’of the beam: phase 0: tests on the original undamaged beam;
– phase 1: de-tensioning of the bottom cables (L1 in Figure 2); Variation of the bending stiffness from static tests. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig73_2.tif"/>
– phase 2: cracking at the mid-span and loading in three points bending;
– phase 3: tensioning of the second cable (parabolic cable L2 in Figure 2) and loading of the ‘repaired’ beam;
– phase 4: cracking at 1/3 of the span length with a point load and loading at different sections to simulate the effect of a moving load.
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.
