The mystery of the noise of some old prestressed concrete bridges now cleared up

Pierre TROUILLET 
MEDD / DGITM   

John DUMOULIN, Pierre BARRAS, Dominique COCHET, Angel BARREU, Laurent FRITZ, Pierre ROENELLE, Michel DAUVILLIERS   
CEREMA

Abstract

During the inspection of different prestressed concrete motorway bridges, some cracks near the anchorage of prestressed units could be heard. An internet site gives samples of those rare noises which could be heard on a viaduct. Those bridges are all equipped with the same type of prestressed units. Various tests in laboratory but also on site, such as radioscopy, measurement of displacement, strains and accelerations, had been undertaken to understand the reasons and causes for such noises. Some of those tests have been undertaken 35 years after the first test. The source of the noises had now been localised and their causes are known. We noticed that as the strands could be submitted to fatigue, it has to be taking into consideration. The reinforcement of the viaducts by external cables (needed for other reasons too) leads to the long-term ending of the issue.