1. Milford Haven Bridge Disaster
Pembrokeshire
Wales
Group 7:
Stephen Cantrell
Chris Hodge
Chris McKeown
Peter Weldon

2. Cleddau River
Pembroke Dock and Neyland separated by 1 mile of water, but a journey of 28 miles was required by road
Ferries operated up until 1975

3. Conception 1960s: Decision to replace Ferry with a Bridge
Sir Alexander Gibb and Partners and Freeman Fox and Partners appointed as joint consulting engineers
Contract awarded to A.E. Farr Limited in September 1968.
Initial Value: £2.1 million

4. Bridge 820 meter span Daily traffic: 10905 vehicles
Original opening time:
March 1971
Box Girder Design

5. Origins of the Box Girder
Aftermath of WWII
Bailey Bridge insufficient
Follow on from I-beams

6. Box Girder Design
Main beams comprise girders in the shape of a hollow box
Comprises of pre-stressed concrete, structural steel or a composite of steel and reinforced concrete
Either rectangular or trapezoidal cross-section
Very good in torsion.

7. Failure June 2nd, 1970 Constructed by cantilevering.
Occurred as one of the final sections was being moved out.
70 metre cantilever putting 135 tonne section into place collapsed.
The extra loading from the cantilevering caused the collapse.

8. Failure
The diaphragm of the box girder was not designed to carry the extra load and buckled.
Diaphragm torn away from web.
Lever arm reduced.
Bottom flange then buckled.

9. Failure 4 workers killed, 5 injured. Could have been much worse.
Bridge passed virtually over a village
Debris and girder sections missed houses by feet.
Construction halted until October 1972

10. Merrison Committee
Committee of Inquiry into the Design and Erection of Steel Box Girder Bridges
Findings:
BS153 was inadequate for applications like Cleddau
Inadequacy of the design of a pier support diaphragm
“the failure of site organisation between the parties [was] of more general significance”
Interim Design and Workmanship Rules, which formed basis of BS5400, Parts 3, 6 and 10

11. Completion
Final Cost: £11.7 million (more than 5 times initial estimate)
£7 million due to design changes
Opened to traffic March 1975
885,900 crossings in first year of operation

12. References
- Department of the Environment (Merrison Committee of Inquiry) (1973) - Inquiry into the Basis of Design and Method of Erection of Steel Box Girder Bridges.
- Bridle, Ron; Porter, John (2002) - The Motorway Achievement: Frontiers of Knowledge and Practice. Thomas Telford Ltd. pp. 346–348. ISBN
- referencing: Merrison Committee of Inquiry (1973) - Inquiry into the Basis of Design and Method of Erection of Steel Box Girder Bridges.

13. Any Questions?
Thanks for listening!