×
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

EFFECT OF P-DELTA

EFFECT OF P-DELTA

EFFECT OF P-DELTA

(OP)
HI

i made high rise buidling in etab programm with high 100 meter but i found this massage in the analysis file


 CURRENT P-DELTA ANALYSIS ITERATION        =           1
 MAXIMUM NUMBER OF ITERATIONS ALLOWED      =           2

 CURRENT  DISPLACEMENT MAGNITUDE           =    0.044349
 RELATIVE DISPLACEMENT CHANGE              =    0.001288
 RELATIVE DISPLACEMENT TOLERANCE           =    0.001000

 ITERATION DID NOT CONVERGE


so i want to ask if that nesscssary to change the relative displacement tolerance or want can i do?


thanks for all comments

RE: EFFECT OF P-DELTA

What have you tried so far to figure this out yourself?

RE: EFFECT OF P-DELTA

The first thing you should do is approximate the P-Delta effects using manual methods.  If your building is mostly translating (not twisting a great deal), then you should be able to get reasonable close using the standard approximate methods.  Otherwise something's wrong.

RE: EFFECT OF P-DELTA

Usually when Pdelta analyses don't converge, it's due to the structure not being stiff enough.

RE: EFFECT OF P-DELTA

What did the second iteration give? You only posted the first iteration data. Increase iterations allowed and post result.

RE: EFFECT OF P-DELTA

usually, at least 3 iterations are required for convergence.  I use STAAD for P-Delta analyses.

RE: EFFECT OF P-DELTA

(OP)
i used 3 iterations but i found that massage again
( ITERATION DID NOT CONVERGE) because the relative displacement more than the tolerance displacement


so i increase the tolerance but i do not know if that right way or i should to calcuale the tolerance before i start calcualtion.

RE: EFFECT OF P-DELTA

swelm,

have you checked if your relative displacement value is within the code prescribed maximum?

RE: EFFECT OF P-DELTA

Try increasing the stiffness of the structure.  Perhaps what you have does not work.

RE: EFFECT OF P-DELTA

I'll re-iterate: It should take very little time (30 min. max) to manually estimate the P-Delta effects.  I think you owe it to yourself to do this.  Modifying the structure until "it works" is insufficient IMO--just like kluging a computer program.

RE: EFFECT OF P-DELTA

Swelm,
Do an Integrity Check if the program does it. And Do a linear static analysis first to see if the deflection is exceeding under say wind. Then check the specification you did for the P-Dalta analysis type (I don't kow ETAB well).

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