Column embedded in concrete design 4

[EDRV]

My company makes and installs free standing aluminum walkway covers and wall attached canopies with front columns. We provide the GC's with a foam block slightly larger than our column (1-1.5"on each side) which they use when the piers are poured. When we are ready to install, we remove the foam and embed our hollow columns 15"-24" with non-shrink grout (min 8000psi) inside and outside the column. Our engineer has always designed this connection as fixed. In a recent project, the EOR (who is responsible for the footing design) is requiring that we design this connection as pinned. I would like to hear feedback on this situation, and if anyone has any reference articles regarding this connection type it would be appreciated if you could share with me.

There is a brief discussion about a similar situation in the thread below:
thread507-127667
However, it does not fully address my question. Also, I was unable to find the article referenced in the thread.
Thanks.

 

[KootK]

It sounds pretty fixed to me. What's the EOR's justification for their position on this?

I don't know of a specific reference but there are spaces where things are definitely embedded with the intent to provide base fixities:

1) Commercial sign structures.

2) Pole barns.

3) Flag poles.

... probably a ton of other stuff.

IBC has a method for embedding cantilevered posts in soil. If soil can do the job, surely concrete can too if designed properly.

 

[Settingsun]

The EOR may be saying that the footing, that they are designing, won't restrain your column. What was the exact wording of their advice? And can you provide details of the column and footing sizes, and the base moment?

 

[OldDawgNewTricks]

I agree with steveh49. I don't think the EOR is saying that your detail will behave as pinned rather than fixed. The EOR is probably saying that they have already designed the footing assuming that a pinned connection would be provided. Perhaps there are constraints that won't allow them to design the foundation to support a fixed base reaction or maybe they just don't want to change the foundation because the client won't pay them to redesign it. So they might be asking you to provide a pinned base detail that is consistent with the assumption they used for the footing design.

 

[struct_eeyore]

I'm more concerned that you're embedding aluminum in concrete - if I understood that correctly.

 

[EDRV]

Thanks everyone for your timely responses.

I think that Steveh49 and olddawgnewtricks are correct in that they may have planned for a different footing design and do not want to address the moment at the column base.

The interesting part is that the EOR said in the meeting that he did not care if we embedded the column but that he wanted the reaction based on a pinned connection !! In my opinion, this would put my company at risk since the footing may be underdesigned and the reactions shown in the calculations and drawings would not match the proposed column embedment. My engineer is obviously reluctant to agree with the EOR.


Regarding Structee's comment, we have been doing this very successfully for years without any issues. Our columns are anodized and we also coat the base of the column with a bituminous coating or zinc chromate. Sometimes we use a two-part marine epoxy. We always make sure that there is no contact with any rebar or steel elements. We have pulled columns after 10 years and they are intact.

Thanks,
Ed

 

[Aesur]

I'm honestly not sure how your system would work without cantilever columns, 10+ years ago when I worked for an aluminum canopy manufacturer out east they were essentially all cantilever columns as the loss of strength due to welding rarely if ever provided a real moment frame in one direction and the along the length of the canopy you would need to rely on the gutter G shape, which again is not easy to use. If they are not allowing for fixed bases then your engineer would need to design a moment frame or braced frame system, which would most likely increase your costs. Another option is for your engineer to design the foundations and provide the foundation design needed for your structure, which is how it used to be done when I was working with such canopies.