The results of a special girder test carried out by TWI at Abington have improved our understanding of steel bridge behaviour at the ultimate strength or buckling limit state.
Steel girders are increasingly competitive with other forms of construction for highway bridges. Efficient use of material is the prime objective of BS 5400 Part 3, the section of the steel bridge design code which deals with the ultimate strength limit state.
While TWI has been responsible for much of the research used by BS 5400 for the fatigue and fracture limit states, the buckling limit state has hitherto received less attention. However, in an important test on the buckling strength of unbraced compression flanges ("U frame action"), a tenth scale model bridge 5.6m long was fabricated and tested to failure by TWI. Scaling down the welds and controlling distortion required particular care. The results of this research will be used to improve current theory on U frame action in BS 5400.
The work was carried out as part of a study into U frame action by Travers Morgan, Leeds University and TWI for the Transport and Road Research Laboratory and the Department of Transport.
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