For decades, Ayres Associates has
partnered with Federal Highway
Administration (FHWA) hydraulic engineers
to develop guidance documents related
to scour policy that state departments of
transportation rely on and adhere to when
evaluating the scour risk of bridges in their
inventory.
Divers placing a filter on a pier in swift water as part of
an NCHRP research project at Colorado State University
“It’s not an exaggeration to say that we helped to
write the books on scour and the FHWA guidelines
related to scour, scour prediction, and mitigation
of scour,” said John Hunt, manager of Ayres’ river
engineering group.
Pete Lagasse, a senior hydraulic engineer at Ayres, and
the late Everett Richardson have been on the bridge scour
front lines, beginning with the catastrophic failure of the
New York State Thruway bridge over Schoharie Creek in
1987. Scour attacked the bridge’s foundation and sent the
540-foot-long bridge plunging into the floodwaters. Ten people
died in the collapse. Lagasse and Richardson’s efforts in the
ensuing investigation with the National Transportation Safety
Board led to the first version of Hydraulic Engineering Circular
No. 18, also known as “HEC-18,” a federal document detailing best
practices for scour evaluation of bridges.
“That helped FHWA to set its course on what they were going to
require of the state highway departments moving forward,” Hunt
said, noting that Ayres has created scour plans of action on bridges
throughout the county, including in Nevada, Florida, and several New
England states.
A laboratory study at CSU showed scour at
an unprotected pier
Clopper emphasized that all their efforts are directed at improving safety.
“We don’t protect bridges for the bridges’ sake. We protect bridges for the
safety of the traveling public,” he said.
‘Reverse engineering’
In addition to the company’s scour work on the theoretical side, Ayres is also
deeply entrenched in the topic on a practical, hands-on level.
With properly designed
riprap, the piers don’t
experience scour
Engineers can design new bridges to resist failure from scour, but what do you do
if the bridge in question was built half a century ago when records of its original
design just aren’t there? Hisham Sunna, Ayres’ manager of southeast operations for
structural design and inspection, is part of a research team that’s analyzed more than
1,500 bridges with unknown foundations throughout Florida. The work was designed
to help the Florida Department of Transportation (FDOT) determine which bridges were
candidates for repair, replacement, or protection from scour.
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