Out of Plumb Column

[bouk715]

A 3-story steel framed building that I designed is currently in construction. Lateral resistance for the structure are braced frames.

We were called out to the site because at one location, a column is out-of-plumb 3" within the first story. The column does not appear deflected over this length, just leaning to one side. The building is already framed and floor slabs are in place. The movement was noticed when a stud wall was being framed in front of the column. Architectural pilasters have been built around the columns on the second and third floors, so I can't tell if the column is deflected or out of plumb over those lengths. Since the pilasters were built, I'm assuming that the column is reasonably (within AISC tolerances) plumb on the upper stories. I've requested the steel survey to see if this is the case. We have the foundation survey, and the footing is in the correct location.

I've analyzed the column for the P-delta effect caused by the movement, and it still works. I just have additional lateral forces I need to transmit into the rest of the structure. However, I believe I need to determine possible residual stresses in the column caused by bending. My assumption is that the movement occurred during erection and before the floor deck/slabs were in place. I'm hoping that the survey will confirm that. What is the best way to determine these stresses? I've modeled the column with imposed deflections - is this an acceptable approach? Or should I specify some form of testing? Just wondering what the typical approach is to this problem (if there is one).

 

[BAretired]

It is defective because it does not satisfy the code in respect to permissible tolerance from plumb.

BA

 

[kslee1000]

It (strong enough) is from engineering point of view, usually applied to older/existing structures. For new construction, the client paid for what was shown on the plans. Unless it is within industrial-wide tollerances specified by code, or testing agency, it is called a defective product. Would you accept a custom made cloth does not agree with the style on the catalog presented to you? How about a little burn hole you found after home? "What is the big deal, you still can wear it", claimed your talor.

 

[271828]

BARetired, that's a good point, of course.

Is there an "out" in the Code of Standard Practice for this? I don't have mine nearby, so can't look it up. Perhaps it says that the OOP is OK if the EOR signs off on it.

 

[BAretired]

271828,

Article 29.7.2 of CSA S16 "Plumbness of Columns" requires exterior columns in multi-storey buildings and elevator columns to be plumb within 1/1000 of their height (plus some other factors). For other columns, which would include the one under consideration the tolerance is 1/500. For a 15' height of column, the tolerance is 0.36" so 3" is more than 8 times the permissible.

I am not familiar with the AISC tolerances, but I imagine they would be similar.

If the OOP is okayed by the EOR, I expect it would be accepted by the authority. Whether or not it would be acceptable to the owner is another question. It could be considered an "oops".

BA

 

[kslee1000]

For anybody interested in AISC standing on "errection tollerance", please review LRFD 1st ed (blue book) section 7.11. Pay attention to Fig 3.