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Motorway Bridge Design

The link between bridge design and traffic jams may not be immediately apparent, but by designing structures that can he more speedlily erected across motorways, the time taken sitting in lane closures caused by construction projects can be considerably reduced.

A joint project between G Manusell and Partners (Civil Engineers) and Cambridge University is currently under way to evaluate the performance of composite space truss bridges. The word 'composite' is used in the normal civil engineering context and refers to the combination of a concrete slab and exposed steelwork which act together to form an effective beam section.

Using a space truss in construction means that the steel part can be pre-fabricated and erected in one piece; for example a section can be made long enough to span a 3-4 lane carriageway. Reduced lateral span of the concrete span also results from this design which means the concrete thickness can be reduced by tip to a half (down to 150mm) which is a great weight saving.

Test programme

The actual research programme involves the construction and testing of a 12m span of an almost full-scale section of bridge (see photo) which will be tested under various combinations of bridge loading, including torsion. Although the overall behaviour of the girder is expected to be reasonably predictable, the behaviour of the profiled steel decking and slab in the lateral direction is rather more complex. The test programme will provide new information on this aspect of the behaviour of the proposed bridge.

The model bridge in our Structures Laboratory.

Design advantages

The project is aimed specifically at replacing the bridges that cross motorways as they are widened to accommodate more lanes. The advantages of this design are: savings in weight, fast erection times and subsequent knock-on effects such as shorter motorway closing times, etc. Thoughts are also being directed towards using this type of structure in suspension bridge applications, primarily because of the lightness.

As they drive along the nation's motorways, alumni from the Engineering Department may reflect on their days spent designing, building and testing trusses in the first-year Structures and Design course, and realise that all was not in vain...

For further information please contact Dr Dick McConnel on (01223) 332759.

number 2, spring '94 back | contents | previous | next