RE: Bolt Tightening[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
- Subject: RE: Bolt Tightening
- From: Charlie Carter <carter(--nospam--at)aiscmail.com>
- Date: Fri, 19 Jan 2001 13:17:27 -0600
>... from AISC edition 7 ... the preferred method of tightening
>structural bolts for bearing connections was the turn-of-nut method.
>Looking at current editions, the method for bearing connections
>is called snug tight. I prefer the turn-of-nut method and wonder if this
>requirement is an undue expense for the erector.
>Does anyone have a feel for the cost difference????
A lot has changed since the early 70s when the 7th Edition was current, especially in the area of bolted design and construction.
When high-strength bolts were first introduced in the 1950s, it was required that they be pretensioned regardless of the application in which they were used. this had more to do with protectionism than science. Rivet manufacturers were afraid bolts would eliminate the use of rivets. The concession that got bolts in the code at the time wa sthat they always be pretensioned. Apparently rivet manufacturers had reason to worry. Anybody still know where to find a rivet installation procedure today?
Slowly and steadily, we've backed away from the unilateral requirement of pretension. Snug-tightened installation is now allowed for the majority of bolted joints. In very specific applications, pretension is required. This is all explained very well (I think, anyway) in the 2000 RCSC Specification for Structural Joints Using ASTM A325 or A490 Bolts. That Specification will be posted in the near future for free download on the RCSC web site:
If you go there now, you can enter your email address to receive a notice when it does become available.
As far as cost, there is definitely a cost advantage to specify snug-tightened joints when you can. It makes design easier. It makes installation easier. And it makes inspection easier. It eliminates the need for costly arbitration entirely. And snug-tightened joints have withstood the test of time. Heck, ASTM A307 bolts were/are always installed the way a snug-tightened ASTM A325 or A490 bolts would be today. I don't have a dollar figure to quote you on the cost difference, but it is worth it to use snug-tightened joints whenever you can.
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