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Cracking is common in Oregon's Interstate-era reinforced concrete deck girder (RCDG) bridges. In 2001, of the 555 RCDG bridges owned by Oregon, 487 had structural cracks. By 2003, 140 bridges had load restrictions. At the time it was thought that billions of dollars would be needed to repair and replace bridges to maintain freight mobility and highway safety. However, in 2002, the Oregon Department of Transportation (DOT) contracted with Oregon State University to investigate the load capacity and fatigue damage of cracked RCDG bridges.
The research results conclusively indicated
that the steel reinforcement in cracked RCDG bridges was
not undergoing fatigue damage. Furthermore, cracks did not
necessarily indicate that a girder had lost load capacity;
in short, the crack density and the crack size were not
good indicators of damage level.
Research revealed that the calculations
for the load and resistance factor rating (LRFR)-the newest
code for rating bridge capacity-accurately accommodate the
effects of cracks. Oregon DOT has adopted the LRFR with
Oregon-specific live-load factors, confident that the method
provides a high degree of reliability and safety in rating
the many cracked RCDG bridges in the state.
The shift to LRFR has improved the load
rating values for many of the cracked RCDG bridges rated
as insufficient under the previous method. As a result,
120 bridges were removed from the list of those to be replaced,
and 80 bridges were shifted from the list of those to be
repaired or replaced to the list of those that require no
work.
From 2001 to 2003, the Oregon legislature
allocated nearly $1.8 billion for bridge repair and replacement.
After reevaluating the bridge work, Oregon DOT estimates
that approximately half a billion dollars could be reallocated
from the initial set of bridges designated for repair or
replacement to other needed bridge improvements.
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