A Simplified Dynamic Analysis of Existing Pedestrian Bridges, a Possibility to get new Experience for Designing

Technology gives us new instruments that can help us in our daily work. There is a rapid development of different kinds of sensors used in buildings, bridges, towers and other structures. These sensors can help us gather much information from our existing structures, which gives us the possibility to use a large amount of data obtained from real structures to evaluate our theoretical models used in the design and refine them.

In the topic of pedestrian bridges, it is interesting to evaluate their dynamic properties since they are sensible to the dynamic vertical and horizontal loads from people. The fundamental data for the dynamic behaviour of a pedestrian bridge are the eigenfrequencies, which can be obtained easily using an accelerometer. Today there is almost always one available since the mobile phones are equipped with them. With an application, it is easy to obtain the fundamental vibration frequency for a bridge and it is also possible to analyse the higher vibration modes in a frequency spectrum. Furthermore, it is easy to obtain a measurement of acceleration in the time domain from walking or running. Also the damping has a very important effect on the vibration level, and it can also be evaluated with measurements.

This tool can be used for evaluating a similar structure as the one to be designed and it could provide us with valuable insight in the dynamic behaviour of the structure. This paper presents some examples, where the theoretical results from models are compared with measurements of the finished bridges. The results from measurements are validated with a simple, well known structure.

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