The cost of initial painting and periodic repainting of structural steel bridges can often be eliminated by the use of bare weathering steel. From an economic standpoint, the use of multicoat high-technology paint systems should be reserved to those bridges that are not suitable candidates for weathering steel.
To ensure successful long-term performance, the Federal Highway Administration
(FHWA) has published “Guidelines for the Use of Unpainted Weathering Steel.”
Principal considerations are as follows:
• Consider with caution use in marine coastal areas; in areas of frequent high rainfall, high humidity, or persistent fog or condensing conditions; at grade separations in “tunnel-like” conditions; and at low-level water crossings. (Some states such as New Jersey require painting of weathering steel girders if within 15 ft (4.6 m) of salt water.)
• Eliminate expansion joints where possible.
• Use a trough under open expansion joints.
• Paint all steel within a distance of US times the depth of girders from bridge joints.
• Seal box members where possible or provide weep holes to allow proper drainage and circulation of air.
• Seal overlapping surfaces exposed to water to prevent capillary penetration action.
• Implement maintenance and inspection procedures designed to detect and minimize corrosion.
• Divert roadway drainage away from the bridge.
• Clean troughs, reseal deck joints, and periodically clean and—when needed— repaint all steel in the vicinity of joints.
• Regularly remove all dirt, debris, and other deposits that trap moisture.
• Regularly remove all vegetation that can prevent natural drying of wet steel surfaces.
