FRICTION and TENSION, what is the link

[jossaad]

Hello gents,

Sorry for my poor English, I will do my best to describe my case I have to resolve.

I have a steel bracket devided by 4 pieces I need to tighten them around a concrete column (diameter 2.5m).
The 4 parts are bolted to one another by 6 bolts.
The height of the bracket is 0.6m
Each 1/4 bracket supports a vertical force 40 Ton.

My problem is I need to know how much torque I need to apply to tighten the bolts to be sure that the bracket is tighten enough to transfer the vertical force by friction to the column. Besides, The vertical forces are offset (1m), which means I have Vertical forces plus a moment.

I will appreciate your help

Many many thanks

 

[DWHA]

I have done this calc before. What I did was determine the normal force that I need based on coeff of friction between steel and concrete. Then I solved for the tension in the steel ring based on the theory of hoop stress. The tension in the steel ring is equal to the tension in the bolts. Of course, apply a F.S. that you are comfortable with.

Now you know the tension required in the bolts. I have never heard of a direct correlation between torque in a bolt and the tension in a bolt. So I just call out the required tension in the bolts. This leaves it up to the contractor to determine the correct torque. On my project the contractor was a bridge contractor that had access to a rotational capacity calibrator, they used this with a torque wrench to determine the torque to tension correlation.

 

[jossaad]

Dear DWHA.

I appreciate ur answer and I start having an idea how to deal with my case.

By the way, may be I will ask u a favor is to give me this example with refrences then i can be sur I m not making mistakes. But please feel free to do it or not. no pb.

Many many thanks

 

[ishvaaag]

By lack of a sketch I do not visualize how the moment is passed to the outfit; is in the end passed to a cylindrical steel shell divided in 4 parts? If such is the case I would try to free the cylindrical shell of such tension coming from the cantilever action by direct anchor to the concrete or equilibrating the loads one against another.

 

[csd72]

As DWHA has said above, there is no direct relationship between torque and tension as the variances in bolt thread tolerances change this greatly.

There are minimum torques though to achieve the required tension for a friction grip bolt. I suggest you use these standard values where possible.

 

[DWHA]

jossaad

I am sorry, but I do not have access to my calc file for this project. Hoop stress calculations can be found in just about any mechanics of material text book. Typically under pressure vessel section. Then all you need is the coefficint of friction between concrete and steel.