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In research, and in analysis for design, the global and local behaviours of bridge deck slabs are normally considered separately. Research has shown that bridge deck slabs are able to resist very much greater local wheel loads than is implied by conventional design methods and, as a result, new empirical design methods have been proposed. Bridges with the very lightly reinforced slabs designed to these rules have
not previously been tested under full NB load. Non-linear analysis suggests that global transverse moments could significantly reduce the local strength of bridge deck slabs, and tests on two half-scale model bridge decks confirm this. Thus both the tests and the analysis show that global and local behaviour are not independent. Several other aspects of the behaviour of the bridges which conflict with the suggestions of previous research are also predicted by the analysis and confirmed by the tests. Despite this, both the analysis and the test results show that the behaviour of bridges with deck slab reinforcement designed to the empirical design rules proposed for Britain will be satisfactory. It even suggests that some of the requirements previously imposed for the rules, notably the requirement for support diaphragms, are unnecessary.
Two major bridges on the A46 Newark Relief Road (Nether Lock Viaduct and Windmill Bridge) are presently being completed using steel construction for the bridge decks. This follows preparation of dual designs in both steel and concrete and comparison of tender prices. Factors leading to the selection of the bridges for dual design are considered. The design requirements and features of the bridges are outlined.
E. Jeffers and S.J. Wood
Potential for catastrophe in building alterations - a question of responsibility Peter Mawer of Bude in Corn wall has written about a most interesting case where sequential building alterations could have led to the development of a potentially disastrous situation:
A most extraordinary circumstance has come to light during a survey of a large shop. The implications are so devastating, I feel compelled to pass on the information. It is simply this: -If a terrace of shops is developed over a number of years from a row of domestic dwellings and takes the form of extended walls and raised roofs and if the landlord sees fit to use party walls to support the floors and roof and if he removes all the cross-walls except the rear wall-the buildings become like houses on stilts with little or no lateral stability. (See Fig 1.)