Box Girders (Railways)

For railways, construction depth is usually very tightly constrained and half through construction must be employed. One option is then the Network Rail ‘Standard Box Girder’.

The Network Rail Standard Box Girder type bridge that covers a span range from 21m to 39m uses trapezoidal box girders with a transverse ribbed steel deck spanning between notionally pin-jointed shear plate connections: the box girders are stabilized by linear rocker bearings. This design is particularly suited to piecemeal crane erection during track possession. With half through construction, the deck can be either in situ concrete, partially encasing close centredcross girders, or a normal slab above more widely spaced cross girders. Stiffened steel plate construction can also be used, depending on the proposed erection method and available construction depth.

For railways on new alignments, where construction depth may not be so tightly constrained, the track can be carried on a slab-on-beam composite bridge, in the same way as used for highways. The use of box girders is then particularly advantageous as their greater torsional stiffness reduces susceptibility to track twist.