×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

AISC bolt pretension

AISC bolt pretension

AISC bolt pretension

(OP)
I have noticed something that seems odd regarding bolt required pretension and bolt strength. I'm looking in 2005 AISC manual, ASD.

In Table J3.1 of the AISC manual, a table of minimum bolt pretension values is given, for joints that require pretensioning. For a 1 inch A325 bolt, the minimum pretension is 51 kips.

However, in table 7-2, for a one inch bolt, the available tensile strength is only 35.3 kips.

It looks like the minimum pretension is higher than the allowed bolt load. How is this possible?

RE: AISC bolt pretension

Table J3.1 does not depend on load factors, strength reductions or the like.  It is simply the minimum tensile strength times 0.70.  Now, there appears to be a typo in Table J3.1 because 0.70 * 0.79in^2 * 90ksi = 50k, not 51.

The bolt pre-tension is not considered a load, per se, because the purpose of the pre-tension is to create friction that does actually carry the load.  This is why load factors and phi or omegas don't show up here.  The tensile "load" on the bolt is controlled and doesn't have the ability to change much over the life of the structure.

The phi and omega DO show up in Table 7-2 because you are actually loading the bolt in tension there.  For the ASD case it is 0.79in^2 * 90ksi / 2 = 35.6k and for LRFD it is 0.79in^2 * 90ksi * 0.75(phi) = 53.3k.  Yes, it's a little off of what Table 7-2 says, so I guess they round somewhere that I don't or vice versa.  But hey, they made a typo in this table as well by calling the factors omega-v and phi-v; they should be omega-t and phi-t.  The v is for shear from Table 7-1...



If you "heard" it on the internet, it's guilty until proven innocent. - DCS

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources