The Suspension Bridge
This suspension bridge relies on the handrail being tensioned – the footway is merely fixed at either end then suspended beneath the handrails using a continuous, thin cord. The most difficult part of this bridge is ensuring that the strings between the handrail and footway are exactly equal.
Equipment
- 4 x 4m (13ft) spars
- 8 x 2m (6ft) spars
- 8 x 2m (6ft) spars
- 2 x 20mm ropes 8m longer than the width of the stream/ravine
- 2 x 15mm ropes 3m longer than the width of the stream/ravine
- 2 x 10mm ropes 3 x the width of the stream/ravine
- 16 lashing lengths
- pegs and ropes for temporary guys
- handy billy (ref July 1997)
- 10 pickets
Method
Prepare two identical frames. Each frame consists of a rectangle of 2 x 4m spars and 2 x 2m spars. Position the lower cross pieces at least 0.5m from the butt ends of the long spars. Diagonal bracing is positioned at the top of the frame and consists of 2 x 2m spars. (diagram a)
A rope ladder that is long enough to span the ravine/cross the stream plus 2m is prepared. The struts must be no more than 0.5m apart.
Dig two small holes at the base of each frame approx 1.0m back from the edge of the stream, then raise the frames, one on each side of the ravine/stream, to the vertical, dropping the butt ends into the holes. Hold them upright (may be using temporary guys).
Tie the rope ladder to the base of the frames, under the cross bars, using a round turn and two half hitches. Once this is in place you can drive in pickets next to the uprights and lash the frame to them.
Two pickets are driven in behind each frame. The distance between each pair should be slightly more than the width of the frames. These pickets are used to anchor the ends of the top ropes. Two more pickets are driven in about a metre behind those on one side of the bridge. A handy billy can be attached to them, to tension the top ropes.
The top ropes are laid across the uprights and tied off to the pickets, using a round turn and two half hitches. They should then be carefully tensioned.
Finally, tie off one end of the long cords to the bottom cross bar on one side of the bridge. Carefully thread the cord over the top rope and round the struts in the bridge, inside the ropes. It must be threaded symmetrically – you do not need to go round each rung of the ladder but it will be worth working out which ones you will use before you start. Once the footway is attached to the handrails, pull the thin cords tighten the thin cords until the bridge is stable and tie off to the uprights on the other frame.
Note: Since the design of the project the principles of Health and Safety have changed dramatically.
Caution should be exercised to assess the risks associated with this build and especially regarding possible falls from height, so handrails or belays and harnesses may be required.
To download the complete plan and design document please Click Here
