What is "girder bridge"

Girder \Gird"er\, n. [From Gird to encircle.]

1. One who, or that which, girds.

2. (Arch. & Engin.) A main beam; a stright, horizontal beam to span an opening or carry weight, such as ends of floor beams, etc.; hence, a framed or built-up member discharging the same office, technically called a compound girder. See Illusts. of Frame, and Doubleframed floor, under Double.

   Bowstring girder, Box girder, etc. See under Bowstring, Box, etc.

   Girder bridge. See under Bridge.

   Lattice girder, a girder consisting of longitudinal bars united by diagonal crossing bars.

   Half-lattice girder, a girder consisting of horizontal upper and lower bars connected by a series of diagonal bars sloping alternately in opposite directions so as to divide the space between the bars into a series of triangles.
   --Knight.

   Sandwich girder, a girder consisting of two parallel wooden beams, between which is an iron plate, the whole clamped together by iron bolts.

Bridge \Bridge\ (br[i^]j), n. [OE. brig, brigge, brug, brugge, AS. brycg, bricg; akin to Fries. bregge, D. brug, OHG. brucca, G. br["u]cke, Icel. bryggja pier, bridge, Sw. brygga, Dan. brygge, and prob. Icel. br[=u] bridge, Sw. & Dan. bro bridge, pavement, and possibly to E. brow.]

1. A structure, usually of wood, stone, brick, or iron, erected over a river or other water course, or over a chasm, railroad, etc., to make a passageway from one bank to the other.

2. Anything supported at the ends, which serves to keep some other thing from resting upon the object spanned, as in engraving, watchmaking, etc., or which forms a platform or staging over which something passes or is conveyed.

3. (Mus.) The small arch or bar at right angles to the strings of a violin, guitar, etc., serving of raise them and transmit their vibrations to the body of the instrument.

4. (Elec.) A device to measure the resistance of a wire or other conductor forming part of an electric circuit.

5. A low wall or vertical partition in the fire chamber of a furnace, for deflecting flame, etc.; -- usually called a bridge wall.

   Aqueduct bridge. See Aqueduct.

   Asses' bridge, Bascule bridge, Bateau bridge. See under Ass, Bascule, Bateau.

   Bridge of a steamer (Naut.), a narrow platform across the deck, above the rail, for the convenience of the officer in charge of the ship; in paddlewheel vessels it connects the paddle boxes.

   Bridge of the nose, the upper, bony part of the nose.

   Cantalever bridge. See under Cantalever.

   Draw bridge. See Drawbridge.

   Flying bridge, a temporary bridge suspended or floating, as for the passage of armies; also, a floating structure connected by a cable with an anchor or pier up stream, and made to pass from bank to bank by the action of the current or other means.

   Girder bridge or Truss bridge, a bridge formed by girders, or by trusses resting upon abutments or piers.

   Lattice bridge, a bridge formed by lattice girders.

   Pontoon bridge, Ponton bridge. See under Pontoon.

   Skew bridge, a bridge built obliquely from bank to bank, as sometimes required in railway engineering.

   Suspension bridge. See under Suspension.

   Trestle bridge, a bridge formed of a series of short, simple girders resting on trestles.

   Tubular bridge, a bridge in the form of a hollow trunk or rectangular tube, with cellular walls made of iron plates riveted together, as the Britannia bridge over the Menai Strait, and the Victoria bridge at Montreal.

   Wheatstone's bridge (Elec.), a device for the measurement of resistances, so called because the balance between the resistances to be measured is indicated by the absence of a current in a certain wire forming a bridge or connection between two points of the apparatus; -- invented by Sir Charles Wheatstone.

A girder bridge, in general, is a bridge that uses girders as the means of supporting the deck. A bridge consists of three parts: the foundation ( abutments and piers), the superstructure ( girder, truss, or arch), and the deck. A girder bridge is very likely the most commonly built and utilized bridge in the world. Its basic design, in the most simplified form, can be compared to a log ranging from one side to the other across a river or creek. In modern girder steel bridges, the two most common shapes are plate girders and box-girders.

The term "girder" is often used interchangeably with "beam" in reference to bridge design. However, some authors define beam bridges slightly differently from girder bridges.

A beam may be made of concrete or steel - many shorter bridges, especially in rural areas where they may be exposed to overtopping and corrosion, will utilize concrete box beams. The term "girder" is typically used to refer to a steel beam. In a beam or girder bridge, the beams themselves are the primary support for the deck, and are responsible for transferring the load down to the foundation. Material type, shape, and weight all affect how much weight a beam can hold. Due to the properties of inertia, the height of a girder is the most significant factor to affect its load capacity. Longer spans, more traffic, or wider spacing of the beams will all directly result in a deeper beam. In truss and arch-style bridges, the girders are still the main support for the deck, but the load is transferred through the truss or arch to the foundation. These designs allow bridges to span larger distances without requiring the depth of the beam to increase beyond what is practical - however, with the inclusion of a truss or arch the bridge is no longer a true girder bridge.