New bridge goes up in a hurry
When Tropical Storm Irene wreaked havoc along the Vermont and New Hampshire border last August, between 7 and 10 inches of rain dropped on the border in 12 hours. The extreme weather washed out hundreds of bridges and culverts in the central Green Mountain region. In the town of Roxbury, Vt., an 11-foot-round pipe on Bull Run Road was clogged by debris, causing the road embankment above to fail. A quick-turnaround design and installation were needed for the replacement structure.
The solution chosen was a 24-by-12-foot aluminum structural plate (ALSP) structure from West Chester, Ohio-based Contech Engineered Solutions. The plate structure was chosen for its short manufacturing and lead-time, rapid assembly and long service life. The new arch was designed to accommodate 12 feet of earth cover. One cast-in-place foundation was poured on ledge and the other was a conventional spread footing with pedestal walls buried 6 feet below the stream to protect against scouring.
“When evaluating the alternatives for the replacement structure, the ALSP open bottom arch culvert provided the town with the best combination of cost, durability, fabrication and installation speed, and geometry to meet the hydraulic demands under high flow events,” said Jon A. Olin, senior structural engineer with Burlington, Vt.-basedHoyle, Tanner & Associates. The company does consulting engineering. “In addition, the open bottom provides a natural setting for aquatic organisms to thrive in as they reestablish themselves in this mountain stream,” Olin said.
ALSP weighs 1/50 as much as a reinforced concrete pipe, reducing assembly and equipment costs and allowing for easy handling of long, preassembled structures. This structure was assembled in the field directly onto the foundation, contributing to the quick installation.
Overall, the project required a little over four weeks to complete: one to complete shop drawings, three to manufacture, and two days to assemble and install the 150-foot-long structure onsite.