Engineering and Construction

Steels to BS EN 10025 of grade S355 are usual for bridges as they offer a better cost-to-strength ratio than grade S275.All parts subject to tensile stress are required to achieve a specified notch toughness, depending upon design minimum temperature, stress level and material thickness.

Special consideration may be needed if tensile stresses occur only during erection, for example arising from lateral bending in girders due to wind loading, or during lifting of components. Judgement is necessary but it is often accepted that modest values of tensile stress can be permitted in such cases without the need for specific notch toughness provided that the work is not carried out during very low temperatures. In all other cases appropriate grades having specified notch toughness are necessary.

Weathering steel
To eliminate the need for painting, weathering grades in BS EN 10155 should be considered. Although it can be shown that the commuted cost of repainting steel bridges is not of great significance compared with the initial bridge cost, weathering steel is particularly useful in eliminating maintenance where access is difficult – over a railway and increasingly so over highways.Weathering steel is not suitable at or near the coast (i.e. within about 2km of the sea). The Highways Agency requires sacrificial thickness to be added to all exposed surfaces for possible  long-term corrosion of 1.5mm per face in a severe industrial environment, 1mm otherwise.