LaPlatte River Bridge

PERCH was designer for the LaPlatte River Bridge, a footbridge located in LaPlatte Nature Park in Shelburne. This suspension bridge crosses the LaPlatte River with a clear span of 68 feet. It opened to the public last weekend in a festive ceremony with refreshments and a band.

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Swedish band Kolonien leads a parade across the newly completed LaPlatte Crossing.

The bridge owes its existence to a Shelburne resident who would walk to work every day through LaPlatte Nature Park. Joplin built about a dozen bridges over a seven-year period to cross the LaPlatte River, some as simple as a single log with a handrail. Most of these primitive bridges washed away; one was condemned because it was built on town land without a permit. So Joplin set about to build a permanent bridge, with full permission from the town.

Joplin also wanted a landmark, something that would be fun to cross and look at home in an Indiana Jones movie. A girder bridge seemed far too pedestrian (no pun intended), and he decided early on that a suspension bridge was the way to go. But designing a suspension bridge is complicated: the load path goes from the deck to the hangers to the main cables to the towers, and the load distribution changes as people walk across and deform the deck. That’s where PERCH came in.

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Using a handheld driver to install the ground anchors.

The foundations for the towers (compression) and the main cables (tension) went through many iterations based on constructability and environmental impact. With no vehicle access to the site, all materials were designed to be transported and installed by human power. And the permits prohibited excavation, eliminating the possibility of metal piles or concrete anchorages. An initial plan to wrap the cable ends around sturdy trees was scrapped when the strength and longevity of the trees could not be confirmed. We ended up renting a generator-powered handheld driver to install screw-like ground anchors for both the towers and the cables.

Almost every detail of the bridge was revised or refined as construction challenges cropped up. The girders supporting the deck kept falling off the needle beams as the bridge moved, so a splice was devised to enable full bearing on the needle beams without changing the deck’s overall flexibility. The 3/16” diameter hangers, spaced 4 feet apart, connect to the 5/8” diameter main cables via wire rope clips that can’t slide along the main cables. Turnbuckles were added to the main cable ends so builders could easily adjust the cable tension post-installation.

The towers are 20 feet tall and made from 8×8 timbers; fabricated steel base plates that connect to the ground anchors and fabricated steel saddles that hold the cables in place were designed late in the game. Rubber thresholds were added at both towers to provide an unbroken surface between the moving bridge deck and the stationary access ramps. Even the tower locations were moved 5 feet east from the initial plan due to erosion concerns, requiring a revision to the site survey.

Attending the chilly opening ceremony, I didn’t need to tell the crowd they should test the bridge to its limits. They recorded the first piggyback crossing, the first to skip across, the first parade (led by the band) and many other variations of their own volition. There may never be another day when 50 people try to cross this bridge all at once, so I’m confident it will last many years. Endless thanks to Joplin, the Town of Shelburne, and the hundreds of volunteers who made this bridge possible – it has been a wonderful opportunity.

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Donors and volunteers carved their names in the deck boards.

Tiny Tuesday: Carpentry Workshops With a Shot of Tiny

Peter King owns Vermont Tiny Houses, a company that builds custom homes and runs workshops to teach carpentry. King is a lifelong Vermonter and a longtime carpenter and teacher.

In a recent Burlington Free Press article, King admits he anticipated his workshops would draw a community of extreme environmentalists. He has since relaxed that vision, and aims primarily to teach carpentry skills and systems integration (plumbing, septic, electrical) that one could apply to any house. As King says, “A tiny house has all the foibles of a real house, just less of it.” He then imparts his philosophy to his classes, seeing small living as the answer to many of America’s problems including fossil-fuel reliance, severe debt, and lost interpersonal relations.

I applaud King’s business model: he finds landowners looking to build a tiny house, then plans his workshops around the construction of those houses, saving substantial labor costs to the owner. He is currently seeking projects for 2018. Check out his website to learn more.

Thrifty Thursday: The New Shop Class

More and more schools are discovering the value of hands-on education as part of their technical curriculum. Whether students see physical trades as a useful life skill or just want a break from academic subjects, building classes are in high demand wherever they’re offered. I’ve discussed organized building projects for students on this blog before (for example); here are a couple more.

In Alaska, the most popular class at Tri-Valley High School is “Building Trades.” The class learns carpentry skills by building a small cabin each semester. The insulated 2×6 cabins then become employee housing at nearby Denali National Park, replacing a variety of seasonal structures. Since student labor is free, it’s a great deal for the park to provide materials and tools for each year’s projects. It also amounts to free outreach as community residents can see the cabins in progress on school grounds. (They’re trailered to the park upon completion.) Now in its 17th year, the partnership earned Tri-Valley High School the George and Helen Hartzog Youth Volunteer Group Award in 2016.

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Student-built employee housing in Denali National Park.

In Wisconsin, a class at Sun Prairie High School builds a complete residential house every year. Technology Education teacher Justin Zander instructs the class and plans each year’s project, including buying land and permitting. This course is for students who seek a career in carpentry and other trades to replace an aging skilled workforce; nevertheless, it’s over-enrolled every year. Each house is sold when finished, and the proceeds fund the program for the following year.