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CTL|Thompson Designs Helical Anchor Foundation System for Outdoor Tension Fabric Structure in Fort Collins, CO
by Wayne Thompson
Colorado-based engineering firm CTL | Thompson is not new to helical piles and anchors. The expert team manages the only testing lab in the world that can perform every aspect of ICC-ES’ AC358 standards. But CTL is new to rock and roll – or at least applying helical piles and anchors to the sector.
This past summer, organizers of The New West Fest by Bohemian Nights, a free, 3-day music festival held annually in historic downtown Fort Collins, Colorado, contacted Wayne Thompson, head of CTL’s Fort Collins branch, with a question. They needed a new way to anchor large shade structures that shelter concert goers from the formidable Colorado sun at each of the festival’s three stages.
These tension fabric structures are rising in popularity for outdoor festival venues, but they require a temporary anchoring system. In the past, the shade architects, Portland, Oregon-based firm Guildworks, used “Jersey barriers” to anchor guy wires that held the shade structures. It worked, but the barriers were a hindrance to pedestrian and car traffic in the busy Old Town area that houses the festival.
CTL proposed a solution. Install helical anchors that could be hidden with a manhole cover or sprinkler valve box when not being used. The process was new to city officials and concert organizers, but CTL’s knowledge of helical anchors and its expertise in local soil conditions instilled the confidence needed to try the unique approach.
CTL’s engineers designed a system that included (10) helical anchors to anchor rope “guys” that stabilize six main truss columns. The anchors were 1-1/2 inch square shaft piles ranging from six to 15 feet deep, depending on soil conditions. High capacity ropes were then suspended between the trusses to support the shade structures.
“Because of the small diameter of the helical anchors, we were able to work with existing utilities and keep things out of the way of water lines and tree roots,” said Thompson. “Working closely with city utilities engineers and arborists, we determined where to place the anchors, which included both street and landscaped areas, creating minimal disruption to the pavement, soil and existing tree roots.”
The anchoring system was used for this year’s festival and will remain in place for years to come. Not only did CTL solve the problem created by the Jersey walls, but they simplified the set up and take down process for Guildworks and the city. Moreover, helical piles and anchors are easier to use than drilled concrete piers so the overall impact on the streets, sidewalks and landscaped areas was minimized.
“We didn’t have to be concerned with drilling, extracting dirt or disposing dirt because with a small center shaft, no dirt comes out,” said Thompson.
About CTL |Thompson
CTL | Thompson is a full-service geotechnical, structural, environmental and materials engineering firm. Established in 1971, the firm currently employs 230 technical and non-technical employees and provides expertise in small and large-scale projects in all areas of construction. CTL|Thompson is headquartered in Denver and has offices in Fort Collins, Pueblo, Colorado Springs, Glenwood Springs and Summit County, Colorado, and Cheyenne, Wyoming. For more information, please visit www.ctlthompson.com.