Gotaalvbron, the bridge over Gota river, was built in the thirties and is now more than sixty years old. The bridge is more than 900 meters long and consists of a concrete slab supported on nine steel continuous girders, supported on nearly 40 columns. During the last maintenance, a number of cracks were found in the steel girders, notable in zones above columns where the important negative bending moments are present. Two issues are in cause of steel cracking: fatigue and mediocre quality of the steel. The bridge authorities decided to keep the bridge in service for the next fifteen years, but in order to increase the safety and reduce uncertainties related to the bridge performance an integrity monitoring system has been mandatory. The aim of the monitoring system has been to detect and localize new cracks that may occur due to fatigue and to automatically send warning messages to responsible engineers. The main issue related to the selection of the monitoring system has been the total length of the girders which is for all the nine girders more than 8 km. It therefore was decided to monitor the most loaded five girders (total length of 4.5 km approximately) and logically a fiber optic distributed sensing system was selected. For the first time a truly distributed fiber optic sensing system was employed on such large scale to monitor bridge integrity. The monitoring system itself, the monitoring strategy, installation issues, and the data flow are presented.
