Effective length in anchor bolts embedded in concrete. 2

[buski]

I am dealing with a bolt-ring consisting of 24 bolts. The bolts are D=30mm and about 1 meter long and embedded in concrete and are welded fast at the bottom end (the concrete is clamped between two bolt-rings). I need to pretension the bolts and I am wondering what the effective length of the bolts would be. The reason I need the effective length is because I am thinking of pretensioning the bolts by measuring the elongation when the nut is tightened.
The bolts have no threads on the part that is embedded in concrete.

If anyone have been in a similar problem and can give me some advise it would be greatly appreciated.

I picture of the bolts embedded in concrete can be seen here

http://img59.imageshack.us/img59/7892/picturezb5.jpg

 

[civilperson]

The length of the bolts surrounded by sleeves and above the top surface,(not adhered to concrete), is the length to use in the elongation formula for pre-tensioning. I suggest hollow pipe sleeves full length welded to a plate or washers that bolts can pass through. After tensioning, the pipe sleeves can be filled with high strength grout.

 

[buski]

Is it not necessary to account for some elongation of some part of the bolts that are embedded in concrete?

 

[dimjim]

Is it still common to add one bolt length to the effective length to account for 1/2 penetrations in nut and head?
I have seen this is some standards. If so it would be
as civilperson suggests except one bolt length would be
added to the length.

 

[buski]

I not sure what you mean "dimjim" by 'one bolt length'. Total length of the bolt is about 1 meter and most of that is embedded in concrete. Could you explain to me what you mean by 'one bolt lenght'?

 

[dimjim]

I really meant one bolt diameter length.
or plus 30mm in your case. This assumes the
effective length penetrates into the head 15mm
and into the concrete 15mm.