The section shape of box beam is same with that of common boxes, which usually consists of cover plate, web plate, bottom plate and clapboard. It's mainly made of steel or pre-stressed reinforced concrete. The basic concept of box beam structure is that all upper structure changes into a whole hollow beam, and when the main load passes any position on the hollow beam, the entire hollow beam (including the beam rib, top plate and bottom plate) will bear the stress as a whole.
The box-type section has good bending and torsion resistance property. Its top and bottom plates are two main parts that providing the bending resistance capacity. The box girder web mainly bears the principal tensile stress caused by the bending shear stress and torsional shear stress of the structure. Compared with the solid web girder of same section, the box girder web has lighter weight, less material consumption and good bending resistance, and is applicable to the construction, machinery manufacturing, housing construction, steel construction and other projects.