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 stabilised by linear rocker bearings.
One option is then the Network Rail ‘Standard Box Girder’. Network Rail standard box girder (shown for three-box, twin track option)įor railways, construction depth is usually very tightly constrained and half through construction must be employed. With those longer spans the girders are very often variable depth. This allows two girders to support wide decks (dual carriageway roads). The slab is deeper over the webs of the girder, allowing the transverse span of the slab to be up to 7m.įor longer spans, twin girders (usually rectangular cross section) with cross girders and cantilever girders are often used. This limits the transverse spacing of webs to about 4m.Īn alternative form used in continental Europe is a single cell trapezoidal cell steel girder with a transversely prestressed deck slab. The deck slab is of nominally uniform thickness, about 250 mm thick. With ‘trapezoidal’ sections, this results in a variation of the width of the bottom flange, as shown below. With both forms, the girder depth is usually uniform at the lower end of the span range, but variable depth girders are used for longer spans. With this configuration, material access during construction can be minimised by the use of permanent formwork (or precast slabs) and for maintenance the cells are larger than those for rectangular steel boxes, thus reducing the difficulties of access. The closed cell is formed by the reinforced concrete deck slab. These girders have a steel bottom flange, inclined steel webs and a narrow steel flange on top of each web. Composite box girder bridge with open-topped trapezoidal steel sectionsĪn alternative configuration that is now more commonly used employs ‘open topped’ trapezoidal girders.
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