Length of spiral reinforcement 1

[vincentpa]

I am doing a take-off for concrete columns with spiral reinforcement. I have never designed with spiral reinforcement but I now how to calculate the reinforcemtne ration. However, I do not know how to calculate the actual length of the rebar for a quantity. I have looked in the ACI detailing manual, CRSI, and all of my text books. None of these references have the formula to calculate the length of spirals. I even called a local fabricator. Because nobody uses them in my area, they do not know how to calculate the length. Does anyone know how to calculate the length of spiral reinforcement? And what does ACI mean by 1.5 turns extra at the top of the column? Does that mean the pitch must tighten up to achieve 1.5 turns extra?

 

[shin25]

If you are asking how to calculate length- then it should be = pi*diameter*(no. of turns). I believe that the ratio for spiral reinforcement is the ratio between volume of steel and volume of concrete.

 

[vincentpa]

What about the pitch? Wouldn't you have to divide the diameter by the cos (pitch angle)?

 

[shin25]

Pitch is not relevant. Spirals are like springs. Even though they may have certain pitch, yet you can close them completely.