×
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

Temporary Rock Anchors

Temporary Rock Anchors

Temporary Rock Anchors

(OP)
The PTI Manual recommends a design load of 0.6 times the specified minimum tensile strength of the steel bar.  Has anyone ever designed TEMPORARY anchors using a higher factor, and if so, what was your basis for the higher factor?

RE: Temporary Rock Anchors

You want to avoid a zipper failure.  If one anchor should fail, the ones on either side would need to hold 1.5 times their design load or all anchors could fail.  0.6 x 1.5 = 0.9.

RE: Temporary Rock Anchors

No.  Temporary anchors are designed for a maximum working (service) load of 0.6 x GUTS (guaranteed ultimate stress of Grade 150 KSI and Grade 270 KSI tendons.  Grade 60 & 75 KSI bars are designed for a maximum working load of 0.6 x Fy (yield stress of bar). On highway jobs, the 0.6 is often lowered to 0.55 for permanent applications.

RE: Temporary Rock Anchors

Right.  This also works neatly since anchor test loads are usually 133% of the design load.  Designing for 0.6 x GUTS and testing to 133% DL gets you to just about 0.8 x GUTS, which is just under where the bar wants to yield.  Some bar manufacturers will say in their literature that it's okay to design temporary anchors around 0.7 x GUTS, but I would not do that.

Also - if your specs need you to test to more than 133%, like say 150% DL, then you have to design around even lower than 0.6.  This often happens on DOT jobs as PEinc mentioned.

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