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Bottomless structural plate arch bends with creek to save time and money

Oct. 16, 2009

By: Judd Murphy

When traditional concrete bridge or box culvert options were too costly for a meandering stream crossing because of substantial environmental fees and mitigation associated with altering the watercourse, the best solution was a custom-angled bottomless arch structure that followed the stream’s path. Designed and fabricated by Big R Bridge , the 420-ft, zig-zagging structure incorporates seven prefabricated elbows as it runs under Commerce Boulevard, a new four-lane artery serving a busy commercial area, a hospital and a future residential area in Canton, Ga.

Project engineer Mike Ross with Ross Consulting Engineers discussed several options with Bob Crossk of Big R Bridge to solve the challenge.

“As the civil engineer, we were challenged with a variety of competing factors—environmental restrictions, a compressed construction schedule and cost,” Ross said. “We quickly determined that a traditional bridge was not feasible from a time and cost perspective. While a traditional box culvert could do the job, the environmental permitting and mitigation costs would have stretched the project beyond the desired schedule and budget.”

Ross Consulting Engineers has successfully used open-bottom culverts on numerous projects and chose to include this structure as a design option. Faced with 40 ft of fill and six bends during design, the Bolt-A-Plate was the right choice.

Contractor North Georgia Concrete, based in Dahlonega, Ga., specializes in challenging bridges and large drainage structures. Safe design, environmental impact, financial impact and time of construction completion were the leading factors in North Georgia’s decision.

The project was completed in six and a half weeks, with four weeks for rock excavation and forming/pouring of approximately 500 cubic yards of concrete.

Big R Bridge prefabricated the elbow sections one of its manufacturing facilities to allow for a faster, more-controlled installation in the field. North Georgia assembled the entire structure in only one and a half weeks. The final week was for the engineered backfill zone. With sidewalks, the parkway width called for a 40-ft cover depth, which added to the culvert length requirements. The structure had a span of 20 ft and a rise of 10 ft with 2:1 beveled-ends.