ABSTRACT
This paper presents the results of the dynamic monitoring of a bridge’s scale model and how they are used to calibrate a numerical structural model by modal parameters analysis. The experimental structure model (Figure 1) was monitored using capacitive accelerometers and acquisition systems able to read and save the vibration information through time, which made possible to determine specific dynamic parameters, such as natural frequencies, damping and mode shapes. Experimental model. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig322_1.jpg"/>
The geometric characteristics of the experimental model were based on a small-scale model of a bridge (reinforced concrete frame), extracted from the dissertation TICONA MELO 2011 [1].
The modal parameters were extracted from the collected signals using frequency domain decomposition techniques and ARTeMIS Modal software [2]. The initial finite element model was developed using SAP2000 software [3] and was calibrated by changing the elastic modulus of concrete and mass, assuring that the natural frequencies and mode shapes used in model are similar to those obtained in the monitoring.
The experimental model that was used was cracked, providing a challenge to calibrate the numerical model. However, with the dynamic test and the acceleration transducers positioned at key points, it was possible to obtain the modal deformed with the help of ARTeMIS Modal software [2], in addition to the natural frequencies. Modal deformed allowed different comparisons of the experimental numerical models (Table 1), in which the structural behavior of the numerical model was observed, not only due the similarity of the natural frequencies, but also due the similarity of the modal deformed, giving more certainty to the calibration parameters. Comparison between experimental and numerical natural frequencies.
Mode
Natural frequencies (Hz)
Mass Participation Ratios (%)*
Experimental
Numerical
X
Y
Z
1-Trans.
10.9
12.0
0
91
0
2-Trans.
50.0
45.1
0
1
0
3-Long.
46.4
48.2
91
0
0
4-Vert.
101.7
116.9
0
0
33
5-Trans.
162.9
164.8
0
1
0
6-Vert.
341.8
346.5
1
0
1
7-Trans.
451.5
453.4
0
1
1
The mass contribution factors of the vibration modes refer to the numerical model.
