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

COLUMN TOP RESTRAIN - CsI SAFE

COLUMN TOP RESTRAIN - CsI SAFE

(OP)
Dear All,
I have a concern that I would like to address.

While exporting slab to SAFE for design. SAFE only account for column below with restrains but not column on the top. Though, it consider joint stiffness with col_stiff. I have went through few discussion that favor modeling column on top also as half or full length with fixed or pin support.

I would like to have input from respected engineers regarding their preferable method of practice and its effect. Thanks in advance.

RE: COLUMN TOP RESTRAIN - CsI SAFE

I believe that the stiffness of the upper column should be represented in your model. Otherwise, you're bound to underestimate negative flexural and punching shear demands which can cause problems. Some options for doing that:

1) Add the upper columns and model the columns above and below to their true heights and fixed at the far ends. The code procedures would seem to suggest that this is appropriate.

2) Add the upper columns and model the columns above and below to half of their true heights but pinned at the far ends. Some prefer this as, in a tall repetitive structure, your column inflection points are likely to be at approximately half of the story heights.

3) Don't add the upper columns but fiddle with the stiffness of the lower columns so that the effective stiffness is the same as option one or option two. I prefer to just model the upper columns. It takes no time at all to add them and makes things much more transparent for the next person who opens up the model. Another problem with this strategy is that your unbalanced column moments, as reported by the software, will not be accurate as they will not be divided between the upper and lower columns.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: COLUMN TOP RESTRAIN - CsI SAFE

(OP)
Dear KootK,

Col_stiff which SAFE add in the model as slab account for the joint stiffness, wouldn't it be sufficient for negative flexure and punching shear?

Second, I read your previous post too. Can you please dictate any code clause that direct towards modeling of Top column ?

Lastly, If I model column with fixed support, should the translation along Z axis be released ?

Awaiting your response. Thanks

RE: COLUMN TOP RESTRAIN - CsI SAFE

Quote (OP)

Col_stiff which SAFE add in the model as slab account for the joint stiffness, wouldn't it be sufficient for negative flexure and punching shear?

I've no idea what "col_stiff" is. At the end of the day, you need a) know how column stiffness is accounted for in the software and b) ensure that you've accurately modeled the stiffness of both the columns below and the columns above.

Quote (OP)

Can you please dictate any code clause that direct towards modeling of Top column ?

I know of no such code clause. But, then, do you really need a code clause to tell you that your structural model should accurately reflect structural reality? I think not.

Quote (OP)

Lastly, If I model column with fixed support, should the translation along Z axis be released ?

I don't think that it matters for slab design. Given the choice, I'd fix Z translation at the bottom and leave Z translation free at the top.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: COLUMN TOP RESTRAIN - CsI SAFE

(OP)
Dear KootK,

Quote:

I know of no such code clause. But, then, do you really need a code clause to tell you that your structural model should accurately reflect structural reality? I think not.

This is the problem I just faced when i was designing slab on grade separately and I modeled column above with fixed support. The doctor in the peer panel insisted me to remove it as it doesn't make sense to him.

As you also quoted in your second last reply point-1 that code also point towards it. Sometime when engineering though differ, a line from Code always seems to be reasonable thing to mention. I hope you understand why I asked you for it.

RE: COLUMN TOP RESTRAIN - CsI SAFE

Quote (rummaan17)

This is the problem I just faced when i was designing slab on grade separately and I modeled column above with fixed support. The doctor in the peer panel insisted me to remove it as it doesn't make sense to him.

That makes sense as a slab on grade is not normally constructed so as to have flexural continuity with the columns above.

Quote (OP)

As you also quoted in your second last reply point-1 that code also point towards it. Sometime when engineering though differ, a line from Code always seems to be reasonable thing to mention.

The section of ACI that describes the equivalent frame method mentions the columns being fixed at their far ends. That's all that I know of.

Quote (OP)

. I hope you understand why I asked you for it.

I understand but do not agree. If a reviewer asked me why I modeled an upper level column in the design of a suspended slab, I would simply respond "because there is a flexurally continuous upper level column attached to the slab". I don't need a code clause to tell me that my dog is a dog and not a cat.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: COLUMN TOP RESTRAIN - CsI SAFE

(OP)
Thanks alot @kootK

RE: COLUMN TOP RESTRAIN - CsI SAFE

You're welcome rummaan. Despite the reviewer hassles, it sounds as though it's quite an interesting project.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: COLUMN TOP RESTRAIN - CsI SAFE

(OP)
Mr. Kootk Indeed I am learning alot from this PeerReview. Also, I am very obliged to all professional like you who spare time to help new learner like me. I owe alot to our engineering community and that what I have started realizing now. Thanks again for everything.

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