Weathering Steel Structures Will Perform Best

Weathering steel structures will perform best

Once the early research that evaluated weathering steel performance was complete, recommendations

were developed for the proper design and use of weathering steel structures. Most notably, these

guidelines are presented in the 1989 FHWA Technical advisory and NCHRP Report 314, also issued in

1989. Considerations for utilizing weathering steel often include economics (lower cost due to

maintenance of paint coatings), safety (eliminating painting over traffic), and aesthetics. However, in all

cases a weathering steel structure is only cost effective if it is used in the proper environment. The reports

listed above, and many others, typically group the different environments into four categories: rural,

urban, industrial, and marine (in approximate order of least aggressive to most aggressive). Due to

increasing Environmental Protection Agency (EPA) restrictions, levels of atmospheric pollutants have

been decreasing since the research of the early 1980’s. As a result, it is expected that nearly all bridge

structures in Iowa are located environments that may be categorized as rural or urban.

Microclimates present within each environment also affect the performance of weathering steel bridges.

For example, a weathering steel structure in a marine environment could perform very well or a structure

in rural environment could perform poorly due to varying microclimatic conditions. Conditions can also

vary from location to location on the same bridge superstructure. Some factors commonly affecting

microclimates include:

 Shelter

 Orientation

 Angle of exposure

 Time of wetness

 Chloride exposure

 Atmospheric pollutants

 Debris

 Continuous moisture and thermal effects

 Structural details and geometries