This lecture is intended to give detailed information on the corrosion protection of steel components in bridges for the design engineer.
SUMMARY
Bridges are normally built for a very long service life. They are subject to an unfriendly environment. For economic reasons, high quality corrosion protection is required. For the main structure, painting or weathering steel is the normal choice. Hot dip galvanising or stainless steel are also used. The possibility of unpainted steel in closed sections is discussed.
Bridges are generally built for a long service life - of over 100 years - and they are subjected to attack arising from their use and from the environment: loads, wind, accidental damage, rain, de-icing salts, sun, etc.
To ensure a sufficient life, the right degree of protection against corrosion is required.
There are numerous means for preventing corrosion of steel structures, but for bridges the usual method is to use coating systems - paint or metallic coatings. Another way to ensure long durability and avoid the need for protective systems is the use of alloyed steels - weathering steels and, from time to time, stainless steels (e.g. for pedestrian bridges).
Several parameters influence the choice of a protective method: the required lifetime, the environment, design, and economic considerations.
The required lifetime of the coating protection system is not the same as the lifetime of the steel structure it protects. The protective system usually required has a life in the order of 20 to 40 years between two periods of maintenance, depending on the severity of environment and on the age of the structure (e.g. 15 to 20 years for old bridges, 25 years and beyond for new ones).
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