Different types of bridge decks include prefabricated flat-bridge, box girder, girder, truss, and arch designs. Each has its own advantages and limitations, but all aim to provide an open roadway with minimal visible support structures.
A bridge deck is a design in which a bridge’s road or walkway, called a deck, sits cleanly atop any supporting structure, which is usually made of concrete, steel, or wood. Different support designs are used, but the advantage of a bridge bridge is the absence of a visible support above the roadway. This design offers an open roadway with no steelwork to obstruct views or create hazards to nearby helicopters or aircraft.
Prefabricated flat-bridge bridges are perhaps the simplest design, but they have limitations. These bridges are constructed of reinforced concrete rectangles connected end to end and placed on vertical supports called piers. Less steel is used in precast deck designs, and the pillars must be placed relatively close together to provide support. They are best suited for footbridges or short connecting sections where there is space underneath for multiple pillars.
A different type of precast bridge is a box girder design. This bridge is constructed using a reinforced concrete box with a flat road section on top. Concrete box girder designs can span greater distances than a flat concrete deck, because the box will support greater loads without sagging or sagging.
Another type of deck deck is a girder design. The horizontal beams, typically made of steel, are connected end-to-end along the length of the bridge and supported by pillars placed under each connection point. A steel and concrete roadway can then be placed on top of the girder supports. The steel girders can sag up and down if the span is too long, which will weaken the bridge. Girder bridges are useful for foot or road bridges where multiple pillars will not create any space or clearance issues underneath them.
A truss bridge uses a series of steel beams in a square or triangular design to create a box that rests on pillars at each end. The steel supports of a truss system can be more difficult to construct than a girder bridge, but they can be built on the ground and then lifted into place with a crane. They can span a greater distance than a beam bridge, making them useful where free space underneath is needed. A truss bridge requires more height than a girder deck for the space needed beneath it, because the truss system has a height of approximately 12% of the bridge’s length.
Arches can be used in a bridge bridge design, if the arch is placed under the road deck. In this project, a steel arch is constructed supported by foundations at both ends of the arch. The roadway is built above the arch, with the highest point of the arch at the center of the street light. Arc designs are useful where more clearance is needed underneath, such as above a river, harbor stream, or another roadway.
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