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

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

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

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

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

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.

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.

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.

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

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

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

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 978-0727731975. - http://www.istructe.org/knowledge/topic_areas/learning-from-structural-failure/Pages/steel-box-girder-bridges.aspx, referencing: Merrison Committee of Inquiry (1973) - Inquiry into the Basis of Design and Method of Erection of Steel Box Girder Bridges. http://www.geograph.org.uk/photo/845071 http://www.newcrossing.gov.bm/photo-library/pages/engineering-options-2.html http://www.istructe.org/knowledge/topic_areas/learning-from-structural-failure/Pages/steel-box-girder-bridges.aspx http://theconstructor.org/structures/box-girder-specifications-advantages-disadvantages/2166/

Any Questions? Thanks for listening!