Coating of Long Span Bridges

Abstract

Seto Ohashi Bridge was opened to traffic as one of the national constructing projects in April 10, 1988. The construction of the bridge was the epoch-making project in terms of construction period and its lifetime. It was spent over 10 years to build and is expected to be over 100 years of usage. The coating system of the bridge, which is a combination of zinc rich primer, epoxy resin primer and polyurethane top-coat, was established through long term durability tests of various Heavy Duty Coating (HDC) systems under civil institute. The concept of the coating system became a good guideline for steel constructions under severe environmental conditions. Kansai International Airport Bridge, Tokyo Bay Crossing Bridge and other steel constructions such as, sea-front objects, oil tanks and plants followed the same system. Akashi Kaikyo Ohashi Bridge, which is the world largest cable stayed bridge took also the same anti-corrosion system.
The key technology of providing ultimate anti-corrosive property onto steel constructions is named as composite anti-corrosion method, which is a combination of sacrifical cathode effect of zinc power and interception effect of epoxy based film. The environmental condition is strictly severe in Japan, where long span bridges are put over the sea, therefore the concept of coating method is to protect steels firmly under such conditions. It has an advantage of extending maintenance cycle leading to long-term economy and environmetal friendly in term of number of coatings.
The following is the report of coating system of Honshu Shikoku Bridges, which is the most important work among long span bridges in Japan.