Trends Summer 2017 | Page 15

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. │15