×
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

High moment on base PL, anchor bolts

High moment on base PL, anchor bolts

High moment on base PL, anchor bolts

(OP)
I have a base plate on a 54" sq pedestal with (2) 2-1/4 diameter x 27" anchor bolts on each of the four sides. There is a HUGE moment which puts the M/P eccentricity about 7 feet away from the center of the base plate. Assuming the base plate is thick enough that the failure is pullout or yield of anchor bolts, how do I calculate the compression stress block in the concrete pedestal? Thanks.

RE: High moment on base PL, anchor bolts

The procedure is pretty long to explain.  Go to AISC's website and download Design Guide 1 (Column Base Plates).  It will have the required procedure you are looking for.  Also, Blodgett's Design of Welded Structures has some discussion on it in section 3.3.

RE: High moment on base PL, anchor bolts

Blodgett's Design of Welded Structures has a solution for "Base Plate for Column Loaded with Moment" under Column Related Design.  Try the Basic Method (If Uplift).

RE: High moment on base PL, anchor bolts

Blodgett's long solution involves the solution of a cubic equation which is ok if you have Mathcad or Mathematica (or trial and error.)  The basic method is good if you have a W shape with moment about the x-axis but for y-axis I would probably solve the general equation.

From what I remember the AISC is very comprehensive too.

Regards,
-Mike

RE: High moment on base PL, anchor bolts

A few years ago, I incidentally encountered some calculation inconsistency using this AISC design guide. The test is very simple, but the output is quite surprising.

Repeat Example 16 on page 23 (base plate with large eccentricity), simply change the Mu  from 700 kip.in to 480 kip.in. The bending moment is reduced, but the base plate should be still part in tension, part in compression (large eccentricity) because: e = Mu/Pu = 5.45in > N/6 (=2.33in)

Then we have A = 4.04in and T = - 0.16 kip (compression)!

This is contradictory since T must be in tension with the loading.

Where, A = depth of compression zone; T = tension of bolts on the “tension” side.

Some one told me that they found the calculation “falling apart” as well. This phenomenon was verified with different inputs. The question is still outstanding up to now.

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