Evaluation of human induced vibrations in Kjærra Bridge

Abstract

The users of the 132-meter-long Kjærra Bridge in Larvik, Norway, noticed severe lateral vibrations due to pedestrian loading on the opening day in 2001. During the period that the bridge was designed, there were no clear guidelines to minimize pedestrian induced vibrations in footbridges. This article aims to explain severe vibrations induced by pedestrians on the Kjærra Bridge, and to highlight the importance of clear guidelines to prevent similar cases in the future. To this end, a series of vibration measurements, both free and forced, are conducted on the Kjærra Bridge. The free- and forced-vibration tests are supplemented by numerical analysis for several different loading scenarios. Field measurements and numerical analysis results are compared with the current guidelines to evaluate the design of the bridge. The analyses results show vibration levels in the unacceptable range put forth by current design guidelines for several loading scenarios indicating that these guidelines can successfully predict human-induced vibrations on footbridges.