Serviceability assessment of three lively footbridges in Reykjavík

This paper presents results from experimental study on human-induced vibrations of three lively footbridges in Reykjavik. The project was funded by the Icelandic Public Roads Administration with three main focus areas; validating the FE-models used at the design stage in terms of dynamic characteristics, measure the response of the bridges to human induced excitation such as walking, running and jumping and define a set of design guidelines for future implementation regarding vibration serviceability of footbridges in Iceland. The first bridge is a continuous 86 m long post-tensioned concrete bridge in five spans (max. 23.5m), the second bridge is 169 m continuous post-tensioned concrete bridge in eight spans (max. span 27.1m). The third bridge is a 54 m long steel bridge with two equal spans crossing the same highway in 2000. The measured vertical acceleration induced by single pedestrians was compared against the predictions and it was found that all the bridges satisfy the criteria set in this standard, i.e. both the calculated and the measured response from single pedestrians were within the acceleration limits. For a single runner and small groups of people the response exceeds the comfort criteria threshold on all the bridges. Regardless of that, the local authorities have not knowingly received any complaints regarding the serviceability of the bridges so far. The aim is to define suitable design criteria regarding the vibration serviceability for footbridges in Iceland by using the knowledge of existing structures with a known dynamic behaviour to set reasonable acceleration limits where the function and the proposed use of the bridge define the desired performance.