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