Storefront beam design

[kushal2944]

I am new to commercial building design and have a quick (but several )questions on how you design the storefront beams.

Say my building is one story 20 ft tall (roof diaphragm at 20 ft.) and storefront at 10 ft level. I have series of HSS columns available every 22 ft.
What is the design consideration for my storefront beam? Is it the out of plane wind? It would be on the weaker axis too, so what is the general practice, use rotated (90 degree) C or I sections?
If I am correct about the beam, then would you again design your column for out of plane point load reaction at 10 ft.?
Also, what deflection criteria would you use? Since the fronts would be glass I feel like my beam should be very resistant to deflection.

Any help would be truly appreciated. Also if somebody has a reference design example or something, please upload it.

Thanks,
K

 

[jayrod12]

The last single storey strip mall I did was hss columns and I needed to portal frame the front entrances so I had hss wind beams at the top of doors and top of columns with cross bracing in between those two levels. .

7x7 and 8x8 columns mostly.

 

[kushal2944]

@jayrod12
Thanks.
What were the beams like?
and you provided cross bracing for in-plane load right? I have enough solid walls to take care of in-plane wind so I wont need the xbrace.

 

[KootK]

Masonry or CFM stud above? Canopy feature in front?

As you've suggested, your beams and columns will both be wind resisting members. Glazing systems are usually able to tolerate a fair bit of movement 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.

 

[jayrod12]

The wind beams were around 4x6 hss. If you don't need the cross bracing for lateral then why not orient your columns for the out of plane wind load and use w columns. It's cheaper.

 

[kushal2944]

@jayrod12
Yes, might do that or may be a rectangular HSS.

@kootk
What is a fair bit? Can I design based on L/360 deflection?
I have a 2'6" parapet above the roof level. I guess I will have to design a wind beam at that level too.

 

[jayrod12]

2'-6" isn't very tall. In that case we just cantilever angles @ 4' o/c or so that are fully welded to the beam at the roof level.

The steel stud guys then come in and fill in the gaps.

I've been told to attempt to design for 3/4" max vertical deflection for curtain walls. In terms of out of plane I don't think I've ever seen a real tolerance besides L/360 for brittle finishes. The glass windows and doors never seem to care about out of plane deflection.

 

[KootK]

L/360 would be fine. I would expect a 30" parapet to be cantilevered or braced back to the roof somehow. Again, much depends on what your wall is contructed from.

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.

 

[kushal2944]

Yes, I am cantilevering the parapet. If I don't put beam (a C channel) on top I will use cantilevered angles @ 4 ft O.C.

Thanks guys.

 

[DaveAtkins]

If you are anticipating vertical deflection above the storefront, put a note on the drawings to that effect. In my experience, the window supplier won't put a deflecting head at the top of his window unless you tell him to.

DaveAtkins

 

[kushal2944]

@daveatkins
I am designing for out of plane load (wind), meaning my deflections are horizontal. Do you take horizontal deflection differently?
Thanks.

 

[KootK]

@Kushal: you'll still have a vertical deflection to contend with as well. That's what Dave's recommendation pertained to.

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.