PERFORMANCE OF WEATHERING STEEL IN HIGHWAY
BRIDGES
A Third Phase Report
VII. FREQUENT HIGH RAINFALL, HIGH HUMIDITY OR PERSISTENT FOG
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Figure 11 - PR Route 52; Bridge#2039 Built 1972
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Several bridges included in this study have been exposed to these
moisture conditions for more than 20 years and display no apparent
effect from the high rainfall and ever-present high humidity. In this
report, Figure 11 shows the conditions of a steel girder of a typical
bridge in Puerto Rico exposed to levels of rainfall that approach 70
inches per year as indicated by the U.S. Geological Survey Annual
Rainfall map. In addition, two of the Puerto Rico bridges are in a
location where there is a warning sign advising drivers of frequent
dense fog conditions.
The FHWA TA recommends caution in employing weathering steels in
areas where the material could remain wet for extended periods of time
due to high levels of rainfall, humidity or fog. The FHWA TA recommends
evaluating these conditions using ASTM Test G 84 "Time of Wetness
Determination (On Surfaces Exposed to Cyclic Atmospheric Conditions)."
If the average time of wetness exceeds 60 percent, use of weathering
steel is not recommended. No measurements of the time of wetness were
taken at any of the bridge sites visited, so an assessment of the
adequacy of the FJWA TA recommendation cannot be made. It has been
reported by others that weathering steel in bridges located in the
Northwest portion of the United States, west of the Cascade Mountain
range, and southeastern Alaska, has not performed satisfactorily and
required painting. However, the White Chick River bridge built in 1982
in the Mount Baker-Snoqualmie National Forest located in the northwest
corner of Washington State is performing extremely well.
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