Milford Haven Bridge Milford Haven Bridge CollapseCollapseCathal KennedyCathal KennedyTerence MeadeTerence MeadeSara FarivarzSara Farivarz

Padraig O’RourkePadraig O’Rourke

ContentsContents

IntroductionIntroduction Milford Haven Milford Haven

BridgeBridge The CollapseThe Collapse ResultsResults ConclusionConclusion

IntroductionIntroduction

Box Girders:Box Girders:

used for large 2used for large 2ndnd moment of area & moment of area & torsional resistancetorsional resistance

Hard to analyse, Hard to analyse, howeverhowever

One of 4 similar One of 4 similar bridges that failed bridges that failed from 1969 - 1971 from 1969 - 1971

Milford Haven BridgeMilford Haven Bridge

Box Girder designBox Girder design Consisted of 7 separate spans from Consisted of 7 separate spans from

77m to 312m in length77m to 312m in length Built by being cantilevered out from Built by being cantilevered out from

pierspiers Sections then welded or bolted to Sections then welded or bolted to

endend

The CollapseThe Collapse

Occurred when Occurred when launching deck launching deck section acrosssection across

Stresses during Stresses during construction are construction are very different and very different and often larger than often larger than when the bridge is when the bridge is completedcompleted

ContinuedContinued occurred during occurred during

launching a pre-launching a pre-assembled deck assembled deck section towards the section towards the second pier.second pier.

subjected tosubjected to bending bending moments and vertical moments and vertical shear forces.shear forces.

buckling of diaphragm buckling of diaphragm lead to buckling of lead to buckling of lower flange.lower flange.

Load before failure Load before failure 9700kN9700kN

ResultsResults

Committee of Inquiry concluded that Committee of Inquiry concluded that BS153 was inadequateBS153 was inadequate

Merrison committee sets rules which Merrison committee sets rules which become the basis for BS5400become the basis for BS5400

West Gate Bridge strengthened but West Gate Bridge strengthened but collapsed 2 months after killing 32.collapsed 2 months after killing 32.

ConclusionConclusion

Ultimately caused Ultimately caused by human error – by human error – failure to anticipate failure to anticipate effects during effects during constructionconstruction

Highlights need for Highlights need for engineers to fully engineers to fully understand understand principles behind principles behind constructionconstruction