Abstract
The natural frequencies and mode shapes are unique characteristics of each mechanical structure. Their prediction is a crucial part of each dynamic experimental measurement. However, the proper identification of higher natural frequencies and mode shapes can be a problem, especially for big structures such as bridges. The reason is the need to excite the bridge in such a way that it responds in a free-vibrations mode shape. This paper describes three various sources of excitations, which are used to identify the modal characteristics of the pre-stressed concrete bridge. The impulse excitation, traffic load and ambient vibration are used and analyzed. In the case of the loading by a force impulse, modal shapes are also obtained. The study shows that the intensity and kind of the excitation has a noticeable impact on identification of modal frequencies. Finally, the results of the experimental measurements are used to calibrate the numerical model.
Highlights
There is a long tradition in the Czech and Slovak Republic to investigate the effect of moving load on the bridge structures [1], [2]
The results show that all the calculated modal frequencies of the structure are recognized by the experimental measurements
The third natural frequency was not possible to be identified if the bridge was excited by the vertical loading
Summary
There is a long tradition in the Czech and Slovak Republic to investigate the effect of moving load on the bridge structures [1], [2]. From a practical point of view, diagnostic methods, like operational modal analysis (OMA), are preferred because no excitation devices are used and the traffic on the bridge is not limited [6]. Even though that these techniques are useful, it is not clear if they are useful for all conditions. The first source of excitation is the impact device, which loads the bridge with an impact impulse (impulse load) in the selected points In this case, the intensity of impulse is measured so the techniques of experimental modal analysis (EMA) are used to obtain the modal shapes and frequencies. The shapes of the girders and the layers of pavement are showed in the Figure 1b
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