The technique we used to achieve such spans relied on a stressed cable made up of several strands running through the bottom chords of the trusses. These strands were stressed using hydraulic jacks and then the whole lot was locked into place by filling the chords with high strength grout. The result was an incredibly stiff but very light weight truss. See the picture below of a roof for cattle sale yards by s-squared. 70m clear span.
The strands used in these projects is the same as is used in post-tensioned concrete floors in large commercial building projects.
These strands are made of very tough steel, and this instructable is for just one way of reusing the off cuts.
- All you need is about 200mm of stressing strand.
- Twist the strand with pliers against the lay to break it apart.
- You will notice the centre wire is straight. It is known as the king wire.
- Carefully sharpen the king wire with a grinder. Don't let it get too hot.