Brick Veneer at Exterior Canopy 1

[WAstruc10]

I'm designing a cantilevered (steel HSS) column freestanding canopy. The architect now wants the steel columns surrounded by a wrap of brick veneer, with air gap. We're in seismic SDC=D here. First thought would be to provide veneer anchors to the sides of the HSS column. However, it would be a very heavy column to limit the column deflection to meet an acceptable limit for the veneer. Plus, kind of counterintuitive to support what is essentially a stiff box of brick with a steel noodle. Three questions: 1) If the veneer wrapping the column is only say 24" out-out per side, is there any need to use veneer anchors to the steel column? Or could we leave it unattached and assume it is self-braced by the returns at the corners? Assuming the steel column deflection with Cd included isn't so much as breach the air gap. Seems kind of reasonable except relies on the in-plane stiffness of the perpendicular (URM) brick wall returns. 2) If you think no anchors would be required and we could simply isolate the brick box from the column, seem reasonable to put square wire ties in the bed joints at spacing similar to what would be required of typ veneer ties, to prevent a face of the brick box from peeling away at the corner? 3) Would it make more sense, constructability-wise, to just omit the steel column and reinforce/grout the whole central void into a masonry cantilevered column? Thanks-

 

[TLHS]

If you don't tie the veneer back, what's going to stop it from falling on people in an earthquake?

 

[mike20793]

Can you run members over the top of the HSS members to get frame action out of them and help with deflection? I definitely think you need/want brick ties for any lateral loads on the brick, plus I think ACI 530 requires them regardless unless it is designed to be free standing under lateral loads.

 

[KootK]

Omitting the steel column and solid grouting the brick is attractive structurally and would surely work. However, when I've pitched it in the past, it usually dies on the vine as a result of construction sequencing issues. Contractors seem to want to be able to erect the superstructure first and come back for the brick later.

Plus, kind of counterintuitive to support what is essentially a stiff box of brick with a steel noodle.

I feel this way too. I like the concept of designing the brick to be free supporting and, as you've said, that's surely a better reflection of reality anyhow. Arranging things so that the brick and column are not laterally tied at the top may be a detailing challenge, however.

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.

 

[JAE]

For seismic demand on a column system like that - aren't you are dealing with an extreme ultimate event in which the engineer is designing for life safety vs. brick veneer serviceability?
I say this to at least suggest that an L/600 limit isn't perhaps required - you didn't state that was the limit you were using, though.

So with an earthquake - you'd want the structure to remain standing (possibly damaged to a degree) and the brick veneer to avoid falling away from the columns, but possibly damaged and cracked.

ACI 530-11, section 6.2.2.10 suggests isolating "veneer" away from a structural frame so that lateral loads are not imparted to the veneer - this is intended, I think, for more typical building veneer surfaces where sections of veneer falling down in an earthquake is a safety issue.

In your case, it seems that you would want to design the veneer separately from the interior column as a stand alone structural element - tied together with ties - or perhaps a separate stud wall backing perhaps - but not connected to the swaying column, which would possibly lead to collapse of chunks of the brick wrap.




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[Ron]

Agree with JAE....isolate the brick but tie back to the column as you would with any brick veneer. It is a veneer and does not support any load other than itself and load transfer through brick ties. Waterproofing the veneer cavity trumps the seismic for the long term!