Gary Donohoe
Joseph Gill
Aisling Kearney
James Thompson

 History
 Construction
 Collapse
 Reasons for Collapse
 Actions Taken
 Conclusions

 The Milford Haven Bridge is now known as The Cleddau Bridge since its collapse during construction in 1970
 It spans the River Cleddau between Neyland and Pembroke Dock in Wales
 Milford Haven in the mid 1960’s had grown to become a major oil port capable of handling some of the worlds largest tankers
 The bridge was built because only a ferry service existed to travel across the river at the time
 Construction began in September 1968
 The bridge collapsed in 1970 resulting in the loss of four lives
 Construction recommenced in 1972
 The bridge opened to traffic in 1975 and approximately 885,900 vehicles used it in its first year
 This figure has grown to almost 4 million in 2006
 It is still in use as a toll bridge

 The bridge has 7 spans and rests on 6 piers
 It is a box girder design
 The shape of the girder makes its inherently strong
 The box girders can be bolted or welded together to form a section which behaves like a single beam
 This presents solutions to designers as when used appropriately it can created a very strong and stiff beam

 The collapse of the partially completed bridge happened on Tuesday 2nd June 1970
 A 70m cantilever collapsed on the south bank
 The collapse happened as one of the 150ton sections was being cantilevered into position to connect the road span of the bridge to the second of the 100-feet-high reinforced concrete pillars, on the Pembroke
Dock side
 During construction the stresses are quite different of what might be expected on completion of the bridge
 The structure just appeared to fold

 Improved steel producing techniques meant that designers could be more confident of the strengths of steel being consistent and so section sizes could be reduced
 At the time the stresses which arise during construction were not fully appreciated
 There was no substantial stiffening of the box sections other than at the pier support’s of the bridge
 This meant that during construction the box section developed very large moments causing it to buckle about the pier it was being constructed from

 This and two other box girder bridge disasters led to the formation of the
Merrison Commission
 They looked at the adequacy of existing codes in relation to box girders
 They set down guidelines for stress analysis and the way in which box girders were to be connected
 These were formalised in BS 5400 and led to the creation of specialised sections dealing with box girders
 Other recommendations included clarifying the roles of the engineer and contractor, such as vetting of design and construction methods
 It was recommended that the design rules should be used only by suitably experienced designers

 This failure occurred due to the fact that the engineers were pushing the boundaries of their knowledge at the time of this incident
 The disaster led to a better understanding of the complexities of steel box girder design
 Armed with this knowledge, more powerful computers, and the updated codes, we are hopeful that a disaster like this will not happen again