14. High-strength bolted friction joints for existing weathering steel bridges

Weathering steel bridges are a special type of bare-steel bridge where corrosion is prevented by the protective rust that forms on the steel surface (Fig.1).
Bridges of this type began being built 40 years ago and today the first signs of fatigue cracking and other damage are beginning to appear, calling for increasingly urgent repair and reinforcement.
However, in order to apply repair or reinforcement members, rust has to first be completely removed from the steel surface with large-scale blasting equipment, which is extremely time consuming and expensive.

A method of high-strength bolted friction joints with protective rust was developed for the repair/reinforcement of existing weathering steel bridges.
In this method, only the surface grained layer of protective rust is removed with a hand-held electric brush (Fig. 2), and the friction between the contact surface of the inner layer of protective rust and repair/reinforcement member ensures the joint strength (Fig.3). The slip coefficient used for the design of the friction joint strength is determined according to the surface properties of the repair/reinforcement member and the protective rust and depending on the bridge’s surrounding environment (Table 1).
Furthermore, the surface condition of the protective rust can be classified using a visual inspection index (Table 1).
Using the proposed joint method, means that large scale blasting equipment to remove rust in reinforcement/repair work is no longer required, shortening work time and reducing work cost by approximately 2/3.