الفهرس 
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Abstract
The common type of a girder bridge generally consists of the following main parts
The main girders supporting the floor system, which consists of the cross girders, stringers and the bridge floor. The stringers are optional and the bridge floor may be designed as steel plates or as a reinforced concrete slab.
The bracing system, that is necessary to stiffen the structure against the lateral lorces, such as wind pressure and to reduce vibrations. It consists of tipper and lower bracing and a number of cross frames or U-Frames. The upper bracing is optional.
The bearing of the bridge, which spreads the reaction of the main girder over the required area of abutment.
These bridges can be classified according to the position of the floor as deck bridge, semi-deck bridge, and through bridge.
They are also structurally classified according to the type of the main girder as one wall or double wall plate girder bridge.
The theory of bridge design is based oil the assumption, that the bridge is built up of a group of vertical and horizontal plane structures, acting independently upon each other. The vertical loads acting on the floor system, are supposed to be transmitted by the main girders to the bearings of the bridge, while the horizontal loads are assumed to be resisted by the horizontal bracing, then transmitted through the end vertical bracing’ or frame to the bearings of the bridge.
In reality, the whole bridge acts as one space structure. The vertical loads develop axial forces, not only in the main girders, but in the horizontal bracing and transverse bracing or bracket as well. The horizontal loads affect the main girder as well as the bracing system.