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 1969. • 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 2nd 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