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RE: Bolt Torques

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Installation of bolts requiring pretensioning should not be done with a torque wrench.  There are 3 approved methods of high strength bolt installation, but I would lean hard toward using a direct tension indicating washer.  Even then I would verify the installation with a calibrated Skidmore at the project site.

A torque wrench is only to be used for arbitration.  Even then it should be calibrated with a Skidmore.

High strength bolt installation required tensions are given in the "Specification for Structural Joints Using ASTM A325 or A490 Bolts".  The intent is to provide an initial bolt tension of 70% of the minimum bolt tensile strength.  I am not aware of any requirement for pretension requirements for A354 bolts, but you could use the same 70%.

To preload an A354 2" bolt to 70% would require some serious iron workers with some heavy duty cheater bar or use a direct tensioning hydraulic device such as a Biach bolt tensioner.  Biach bolt tensioners have been used on very large high strength bolts in the nuclear industry.

The question you may want to ask is - Do you really need to tension the bolts in the first place?

By the way, the approximate torque required for the 1 1/2" A490 is about 3500 ft lbs.  That's two 175 pound steroid crazed iron workers with a 10 ft cheater. 

Harold Sprague
Krawinkler, Luth & Assoc.
4412 W. Eisenhower Blvd.
Loveland, CO 80537
Voice: 970 667-2426
Fax: 970 667-2493
Email: hsprague(--nospam--at)

-----Original Message-----
From:	Bruce Hopper [SMTP:Bruce(--nospam--at)]
Sent:	Wednesday, February 18, 1998 9:24 PM
To:	internet:seaoc(--nospam--at)
Subject:	Bolt Torques

Does anyone have information on required bolt torques an/or
tension indicating devices for 1-1/2 inch diameter A490 and
2 inch diameter A354 Grade BD bolts?

I have two immediate problems:

1) The contractor needs to order a wrench large enough to
fully tension the bolts.

2) I must have some method to test the bolted connection.

Bruce Hopper