30m box girder is generally marked with concrete, 30m box girder is a long-span box girder, and concrete is generally C50 or C60.
In box girder analysis, the main loads acting on the box girder are dead load and live load. The dead load is symmetrical, and the box girder section is basically symmetrical, so the dead load generally does not produce eccentricity; Live load can be symmetrical or asymmetrical and eccentric, which must be considered separately. Under eccentric load, box girder will produce four basic deformation states: longitudinal bending, torsion, distortion and lateral deflection.
Box girder structure:
The box girder span is generally 40~60m (80m in foreign countries), with simple structure and quick construction.
The vertical layout of box girder should be equal span or unequal span, the ratio of side span to middle span should not be less than 0.6, and the height-span ratio is generally115 ~1/25. (3) Suitable for support construction, span-by-span erection construction, movable formwork construction and jack-up construction.
Box girder variable cross-section box girder variable cross-section box girder is mainly suitable for long-span prestressed concrete continuous beam bridge, and the vertical curve of beam bottom can adopt arc, quadratic parabola and broken line. In order to meet the stress requirements of each section in the beam, the thickness of the bottom plate, top plate and web plate of the section can be changed.