how can i calculate the required torque for the pre-tension joints 6

Long Answer: If you are working under AISC Specifications, you will need to be very familiar w/ this document:

Short Answer: The relationship btw torque and proper bolt pretension has many variable and they can be dependent on proper manufacturing, storage, and installation techniques. For instance, bolt lubrication is very important in the torque/bolt-tension relationship. Even w/ pre-installation verification (Skidmore), it's not guaranteed that ironworkers w/ calibrated wrenches will follow all necessary procedures. The most reliable methods of verifying pretension of high-strength bolts are not dependent on torque. Instead they use DTI's, turn-of-nut, tension control bolts, or other verification method.

I don't know where you are but in Australia the answer is, you don't. It's too unreliable. The permitted options are;
Part-turn method of tensioning
Tensioning by use of direct-tension indication device (load indicator washer)

Pre tensioned joints in Canada, by definition, are slip critical as opposed to snug tight.

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So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik