Construction in bridge decks usually refers to the interaction between
insitu reinforced concrete and structural steel.
Three main economic advantages of composite construction are :
Typical Composite Deck
It is possible to influence the load carried by a composite
deck section in a number of ways during the erection of a bridge.
By propping the steel beams while the deck slab is cast and until it has gained strength, then the composite section can be considered to take the whole of the dead load. This method appears attractive but is seldom used since propping can be difficult and usually costly.
With continuous spans the concrete slab will crack in the hogging regions and only the steel reinforcement will be effective in the flexural resistance, unless the concrete is prestressed.
Generally the concrete deck is 220mm to 250mm thick with beams or plate girders between 2.5m and 3.5m spacing and depths between span/20 and span/30.
Composite action is developed by the transfer of horizontal shear forces between the concrete deck and steel via shear studs which are welded to the steel girder.