05 November 2017

Canadian Bridges: 6. Treetop Walkway, Capilano, Vancouver

The third attraction I visited at Capilano Suspension Bridge Park, of relevance here, is the "Treetops Adventure", an elevated walkway formed of seven suspension bridges slung between eight 250-year old Douglas Fir trees.

It was opened in 2004, and allows visitors to experience the forest from up to 33m above ground level.

The structures were designed by McElhanney Consulting Services to have as little permanent impact on the trees as possible. Platforms around the tree trunks, and the bridge spans themselves, are supported from collars, connected without any nails or bolts. These act only in compression, tightened so that friction is sufficient to hold them in place. Out of balance forces on trees carried by braided polyester guy ropes.

The collars are adjustable and moveable, so that they can accommodate continuous growth of the trees, and are regularly inspected by the engineers to see whether adjustments are necessary. The pressure on the tree bark is reported to be about 20 psi, which in metric is a piffling 0.14 N/mm2.

Unlike the neighbouring Capilano Suspension Bridge, the support cables are below the deck, rather than being at handrail level. This is necessary to allow visitors to exit each span and walk around the tree trunks without having to climb above bridge handrail level. It also offers the benefit of giving unimpeded views from each span, although these are marred by chunky brown-painted handrail posts.

As you'd expect, there's a fair degree of movement on each span as you walk across it, but not to an extent which will un-nerve many visitors.

I can't say I entirely admire the appearance of this walkway, which is clunky, with way too much of that brown-painted metalwork. However, I think the way it has been engineered is highly admirable.

There can't be many sites blessed with such mighty trees that they can support a structure in this way, but that's just one reason why this one is worth visiting.

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