Balcony guardrail wind 2

[PMR06]

Trying to settle a debate here in the office... How would you guys calculate wind load on a typical balcony guardrail. The guardrail consists of stainless steel posts 3'+/- oc with horizontal stainless steel rail at top and tempered glass panels between. A typical balcony is 20' wide, 7' deep and the building is 15 stories tall.

Is the wind load calculated as:

1. Component & cladding?
2. Parapet?
3. Solid freestanding wall?

Thanks in advance.

 

[csd72]

PMR06,

I have never needed to as the horizontal live load is usually critical. If I felt the need to I would use the worst case of 2 and 3.

 

[Ron]

By definition it is a "component and cladding". It transfers wind and live load to the structure. I would treat it as I would a free standing sign structure.

 

[tmlim]

I agree with csd72. The live load at the top of the rail would most likely govern.

But for wind, I would not consider 1. Component & Cladding. Unless the guardrail is really close to the building, there would still be some leeward wind forces on it.

I would design it as a 3. Solid Freestanding wall

 

[racookpe1978]

The top of the balcony rail must withstand a 200 lb horizontal force (at the center of the 20 ft long balcony, 42" above the balcony floor. (Standard ADA/OSHA/building code railing rules.)

Gravity loads of a sufficient guard rail, plus the panels below the guard rail, are so high that the material needed to avoid "drooping and sagging" of even ornamental iron (open steel and castings) railing means that posts have be very close together: again, regardless of wind loads sideways. For example, a twenty foot long 2x2x14 gauge tube steel top rail will sag about 1/2 to 3/4 inch if supported only by its ends: and that is just under its own weight, with no glass or wood or fiberglass or metal panels attached.

Real wind loads will be much less than either gravity or sideways building Code loads, and will be centered on the face of the panel (only halfway up a typical 42 high balcony panels.) Also, wind loads (during a storm obviously) will be present only when "people and crowd" loads are absent, so the two aren't logically additive.

 

[jberg]

The IBC requires 50plf on handrails (not for one and two-family dwellings). Granted, it does not govern for your specific situation, but it something to keep in mind.

Joel Berg

 

[MaddEngineer]

This is a good one...

I agree with Ron I would treat it as a component or cladding or a sign.

I don't have ASCE 7 or and IBC code in front of me (i'm at the DMV) but I believe it imposes an increase in loads since they are typically light weight and can easily become projectiles. the panels also will be exposed to leeward and windward loading. I also think the wind loads will be larger than the railing loads and will be sustained for a longer period of time during a storm (railings are typically designed to higher allowables due to the transient nature of the loading)

 

[PMR06]

I agree, the 50#/ft and 200# loads need to be checked also, but at 140ft above grade exterior, wind load will govern.

Component & cladding and solid sign actually give about the same load (just under 40psf), so that is what I am using for now. I do not think the parapet wind loading applies because I just don't think the high roof suction loads can develop in the "pocket" of a balcony.

Thanks for the replies. If anyone else has any thoughts, please keep discussing.

 

[jdshiv]

Going a little beyond the original question - what is the general consensus about Code Section 2407.1.1 about "A safety factor of four shall be used." (similar for IBC 2006 and CBC 2007) This seems to apply when glass is used as the structural material, i.e. glass balustrade railings.

If this sentence is to be interpreted as 4 times the design loads of 50 plf / 200 lb, then these extreme loads of 200 plf and 800 lb point loads could still trump the wind loads at high elevations.

However, it could also be interpreted as simply a safety factor of 4 over the material strength of the glass and other fastening components.

Couldn't find much discussion of these loads online; one article from "Glass Magazine" implied that you do indeed have to use 4 times the 1607 loads; and California DSA IR 24-1 also seems to support this interpretation.

Eager to hear what others think about this.

 

[PMR06]

jdshic,

That safety factor is on the material strength, actually the modulus of rupture. In my case the guardrails were fully tempered glass with Fr=24000psi. The max stress from 50plf, 200# or wind was calculated, then checked it was not greater than Fr/4 = 6000psi.

For the project we just finished, wind governed from the 10th floor up. My original post was trying to make sure we were calculating wind correctly. Depending upon the interpretation, wind governed at the 3rd (using parapet wind), 10th, or 11th floor. We didn't think parapet loading was appropriate though.

 

[apsix]

The attached article discusses the results of testing done to determine wind loads (in an Australian context).
It suggests that wind loading will be critical in many cases.