14 June 2011

Plans issued for bridge across Millennium Dome

Yes, the abbreviated description of this project gave me pause for thought when I first saw it at BDOnline. I think my precise reaction was something like: "Huh?"

The 365m wide, 52m tall Millennium Dome, I'm sure, needs little introduction. It's hardly an obstacle - you can just walk round it (or through it, when in its current guise as The O2 it is unoccupied by some event or other).

Planning consent is being sought for the construction of a skywalk right across the Dome, from one side to another, a skywalk which would therefore also be 365m long and 52m high. It will be open only to supervised access, with visitors being escorted across in groups. Apart from the obvious concerns about people wandering off-piste and trailing muddy footprints over the pristine teflon-coated Dome, this is more of an adventure experience than a stroll across a simple footbridge.

The maximum gradient of the skywalk will be some 28.5° (some 1 in 3), and it will support only a single handrail down its centreline, with visitors passing either side, secured by tethers. Access for the disabled will be arranged by specially-trained escorts (probably drawing on techniques that climbing instructors use with disabled people), including a purpose-built wheelchair if required.

Structurally, a rigid-frame solution has been rejected in favour of another tensile membrane, sitting a little way above the Dome's roofing material, and anchored down at its ends. In between, the tension is provided by guys attached to the Dome's existing support masts at intervals.

This slender band of fabric in turn supports a secondary walkway layer made from a non-slip combination of PVC and stainless steel mesh. I imagine that only the sheer height of the Dome allows this to work - a bridge deck at a shallower curve simply couldn't be drawn tight enough against the guy cables to retain sufficient stiffness.

If you have time, you can see the proposals yourself at Greenwich Council's planning website.

The developers hope to establish a tourist attraction to rival the experience of climbing the Sydney Harbour Bridge, and it's certainly something I'd fancy a go at.

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