Strood High Street bridge, photographed on 10th April 2009. photograph by Gregory Beecroft

Strood High Street bridge. photograph by Gregory Beecroft

Strood High Street bridge, on the Medway Valley line, clearly illustrates the difference between riveted plate and welded steel structures. The main girders of the newer northern span have been welded and have a smooth finish. Those of the southern span (to the left) are riveted. The many rivet heads and the overlapping plates give an uneven surface, which is particularly obvious on the underside of the girder. The deck of the southern span comprises corrugated steel plate. The northern span has steel plate on welded cross-beams.

Larger bridges often follow the same construction principles as earlier plate structures, with cross beams supported off main beams that also form the parapet. The cross beams are bolted or riveted to the main beams.

M25 bridges, Merstham, photographed on 25th August 2007. photograph by Gregory Beecroft

These bridges carry the Redhill line (nearest) and the Quarry line over the M25 motorway at Merstham. All steel spans are favoured for railway underbridges because of the speed with which they can be erected. Like many welded steel railway bridges, these are of the half-through type. The vertical flanges on the outside of the girders are for added stiffness.

Leatherhead Bypass bridge, photographed on 26th April 2009. photograph by Gregory Beecroft

This bridge carries the Leatherhead to Dorking line over the Leatherhead bypass. Cross beams support a concrete deck. The bridge has been built long enough to allow the road to be widened to a dual carriageway.

A24 bridge, Dorking Deepdene, photographed on 25th July 2009. photograph by Gregory Beecroft

A24 bridge, Dorking Deepdene. photograph by Gregory Beecroft

The bridge carrying the Redhill to Guildford line over the A24 at Dorking has welded steel main beams. The deck was welded together in sections that could be transported and lifted relatively easily and bolted together on site.

Penge High Street bridge, Penge West, º236, photographed on 11th August 2007. photograph by Gregory Beecroft

Penge High Street bridge, Penge West. photograph by Gregory Beecroft

The bridge that carries the London Bridge to Croydon line over Penge High Street has five main beams that directly support a concrete deck.