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Bridge Design & Assessment


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The three most common types of reinforced concrete bridge decks are :

Solid Slab

Voided Slab

Beam and Slab

Solid slab bridge decks are most useful for small, single or multi-span bridges and are easily adaptable for high skew.
Voided slab and beam and slab bridges are used for larger, single or multi-span bridges. In circular voided decks the ratio of [depth of void] / [depth of slab] should be less than 0.79; and the maximum area of void should be less than 49% of the deck sectional area.

Analysis of Deck

For decks with skew less than 25° a simple unit strip method of analysis is generally satisfactory. For skews greater than 25° then a grillage or finite element method of analysis will be required. Skew decks develop twisting moments in the slab which become more significant with higher skew angles. Computer analysis will produce values for Mx, My and Mxy where Mxy represents the twisting moment in the slab. Due to the influence of this twisting moment, the most economical way of reinforcing the slab would be to place the reinforcing steel in the direction of the principal moments. However these directions vary over the slab and two directions have to be chosen in which the reinforcing bars should lie. Wood and Armer have developed equations for the moment of resistance to be provided in two predetermined directions in order to resist the applied moments Mx, My and Mxy.
Extensive tests on various steel arrangements have shown the best positions as follows




Bridge Components | Choice of Deck