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!

*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.

Jobs

Differences between ACI318-08 and ACI318-11 Section 10.10.6, Cm factor lower bound limit

Differences between ACI318-08 and ACI318-11 Section 10.10.6, Cm factor lower bound limit

(OP)
I am going over the Moment Magnification Procedure for non-sway columns as described in ACI318-11 Section 10.01.6 and I noticed a difference in the code relative to ACI318-08 that I cannot find discussion or documentation of anywhere on the internet.

Equation 10-16 in ACI318-08 limits the value of Cm to a minimum of 0.4. However, this limitation is gone in ACI318-11. This can lead to a *significant* difference in the final magnification factor which, in turn, can lead to a *significant* difference in the final (magnified) design moment of the column. Further, this difference is in the unconservative direction, the design moment is allowed to be smaller relative to the 2008 version of the code. For example, in the problem I am currently working though (in preparation for the SE exam in the fall), this single change in the code reduced my design moment by a factor of 2 (Cm = 0.2 instead of 0.4).

Can anyone speak to this? Is this an intentional change? Am I misreading the code / overlooking the discussion about a lower-bound limit on Cm?

Thank you for your time.

Will Godfrey

RE: Differences between ACI318-08 and ACI318-11 Section 10.10.6, Cm factor lower bound limit

i don't see any limitation of Cm in this item except "For members with transverse loads between supports, Cm shall be taken as 1.0" and also i don't see any Differences between ACI318-08 and ACI318-11 in this item

RE: Differences between ACI318-08 and ACI318-11 Section 10.10.6, Cm factor lower bound limit

(OP)
Thanks for the reply.

You are correct! The lower bound limit on Cm doesn't exist in 318-08, it is last seen in 318-05. That is my mistake. This may explain why I couldn't find documentation of it being removed for the 2011 version of the code.

Regardless, any insight someone might have would be appreciated. I guess I can rule out it being a typo though since it's been this way through 2 revisions of the code. Maybe I'm being too pedantic.

wsg

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


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close