I am thinking of making some reinforced concrete posts for use as fencing , but also frame elements for a geodesic dome , the faces will be mosquito net .
Since I have a lot of 4 mm high tensile steel already, I plan to use this. Although only 4 mm dia it is spring like , sold in a 1 meter diameter coil , when released it springs out strait , and is much stronger than normal re bar ... thin walled low quality rigid plastic water pipe is very cheap so I plan to use this ... "2 inch" (in reality it has a 55mm internal diameter ) ...
I will have 16 lengths of the 4mm steel wire in each drainpipe tight to the circumference on the inside of the pipe and arranged symmetrically all around the circumference , the plastic pipe will not be removed after concrete sets and this will protect from frost /water damage , this allows me to keep the reinforcement tight to the surface for maximum strength in finished posts .. I will vibrate well , and apply vacuum to the top of pipe after concrete is poured , to get air bubbles out.
I have two questions ...
1 ... I understand it is customary to have hoops of wire going around the 16 lengths of steel and tied to them , I think this maybe mainly to hold these in the correct alignment, but will also give a strength component preventing failure of the finished post ... Do I really need these for strength ? I can secure the steel wire by other means , if I do need them , how many , how frequently ...
2... It maybe possible to pre stress the 16 wires , what is the approximate % increase in strength of finished product from doing this ???
Thanks in advance ...oz