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.