4A6-1 Disaster Case Study Group 9 Milford Haven: Steel Box Girder Collapse Alan Hunt Danielle Pickett Ed Lawlor Michael Cirillo

Milford Haven Bridge Spans 820m across River Cleddau between Neyland & Pembroke Dock, Wales. Joint Consulting Engineers: Sir Alexander Gibb & Partners and Freeman Cox & Partners Contractor: A.E. Farr Ltd. Construction began beginning During 1970, steel box girder failed during placement of final girder piece of 4th span. 4 workers were killed and 5 others were seriously injured. Redesign carried out and was completed in 1975.

Bridge Design Primary structural members are steel box section girders. Greater 2 nd Moment of Area than standard I-Beam ⇒ better resistance to bending. Particularly important near a costal span (such as Milford Haven) with wind loadings. Girder of choice for large spans.

Bridge Construction Consists of 48 box girder sections welded and bolted together. These box girders form a continuous section that behaves like a beam. During construction the welded box girders behave as a cantilever until the pier opposite is reached. Huge bending moments exist in termination of box section at pier.

Collapse & Failure Collapse occurred due to buckling of the support diaphragm. Consequently, the distance between flanges decreased ⇒ buckling of lower flange Design Load = 5kN, Load at Failure = 9.7kN

Results and Effects BS153 were inadequate for construction of Steel Box Girders at that time. IDWR were created by the Merrison Committee, creating new rules for Steel Box Girder Design and Analysis. Foundation for the New British Standards, BS5400