1. Milford Haven Bridge Collapse Group 9 Gary Donohoe Joseph Gill Aisling Kearney James Thompson

2. Contents  History  Construction  Collapse  Reasons for Collapse  Actions Taken  Conclusions

3. History  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

4. Construction  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

5. Collapse  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 150- ton 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

6. Reasons for Collapse  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

7. Actions Taken as a Result of The Milford Haven Collapse  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

8. Conclusion  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