Steel box girder, also known as steel plate box girder, is a commonly used structural form for long-span bridges. Generally used in bridges with large span.
In long-span cable-supported bridges, the span of steel box girders is several hundred meters and up to kilometers. Generally, they are divided into several sections to be manufactured and installed. The cross-section of steel box girders has the characteristics of wide and flat shape, and the aspect ratio reaches about 1:10
Steel box girders are generally made up of roof, bottom, web, diaphragm, mediastinal diaphragm and additions.
Ribs are joined by full welding. The roof is an orthotropic bridge deck composed of a cover plate and a longitudinal stiffening rib.
Typical thickness of steel box girder plates can be: cover thickness 14 mm, longitudinal U-rib thickness 6 mm, upper width 320 mm, lower width 170 mm, high 260 mm, spacing 620 mm; bottom thickness 10 mm, longitudinal U-shaped stiffener; inclined web thickness 14 mm, middle web thickness 9 mm; diaphragm spacing 4.0 m, thickness 12 mm; beam height 2-3.5 mm.
In order to study the effect of diaphragm spacing on the distortion of simply supported steel box girders under concentrated loads, the distortion effect and rigid torsion effect of simply supported steel box girders with different numbers of diaphragms under concentrated loads are compared, and the curve of maximum distortion effect with the number of diaphragms is obtained. Load is calculated by load decomposition method under four working conditions: distortion, rigid torsion, symmetrical bending and eccentric load.