THE ROLE OF MODULAR BRIDGE EXPANSION JOINT VIBRATION IN ENVIRONMENTAL NOISE EMISSIONS AND JOINT FATIGUE FAILURE

Modular bridge expansion joints (MBEJ’s) are widely used throughout the world for the provision of controlled pavement continuity during seismic, thermal expansion, contraction and long-term creep and shrinkage movements of bridge superstructures. Modular Bridge Joint Systems (MBJS) are considered to be the most modern design of waterproof bridge expansion joint currently available. It was generally known that an environmental noise nuisance occurred as motor vehicle wheels passed over the joint but the mechanism for the generation of the noise nuisance has only recently been described [1]. Observation suggested that the noise generation mechanism involved possibly both parts of the bridge structure and the joint itself as it was unlikely that there was sufficient acoustic power in the simple tyre impact to explain the persistence of the noise in the surrounding environment. Engineering measurements were undertaken at Anzac and Georges River (Tom Ugly’s ) Bridges and the analysis of these measurements indicated that an environmental noise nuisance resulted from modal vibration frequencies of the MBEJ coupling with acoustic resonances in the chamber cast into the bridge abutment below the MBEJ. This initial acoustic investigation was soon overtaken by observations of fatigue induced cracking in structural beams transverse to the direction of traffic. A literature search revealed little to describe the structura l dynamics behaviour of MBEJ’s but showed that there was an accepted belief amongst academic researchers dating from around 1973 that a significant part of the load history was dynamic. In spite of this knowledge it would appear that almost all designers use a static or quasi-static design with little consideration of the dynamic behaviour, either in the analysis or the detailing. Principally, this paper identifies the role of vibration in the generation of environmental noise complaints and links this vibration to the now endemic occurrence of structural fatigue failures of MBEJ’s throughout the world.