The fatigue enhancement of Gade Valley Viaduct box girders due to distortional effects

This paper examines a case study in which a bridge structure with fatigue critical details was successfully managed and remediated without extensive traffic closures. Severe theoretical fatigue life shortfalls have been identified at the transverse stiffener frames of the box girder due to distortional effects in the steel box. Gade Valley Viaduct was the final link in the M25 London orbital motorway, constructed in 1986 at Kings Langley, UK. It is a composite box girder viaduct 440m long with typical spans of 42m and carries 180,000 vehicles daily. A series of cracks and original sub-standard weld quality issues were discovered in the transverse stiffener frames of the box girder. The fatigue shortfall that was a significant contributor to the identified fatigue cracking, was confirmed by assessment and strain-gauge monitoring. A fatigue enhancement bracing system was deployed at all spans and boxes to provide a full 120-year fatigue life. The use of off-structure testing in a mock-up girder before the application on the live structure was a key feature of this project, where several lessons were learnt from weld trials. This case study illustrates how heavily used structures with theoretical fatigue life shortfalls can be successfully rehabilitated to ensure safety.