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# [NZS1170.2] Deriving wind load on glass barrier on top of wall?

## [NZS1170.2] Deriving wind load on glass barrier on top of wall?

(OP)
I've got a glass barrier for a hillside home in NZ, and in a an extremely high wind area, and the building faces downhill.
Since it's right on top of a wall I figure it's like a parapet so then NZS1170.2 section B.2.1 applies, right?

As for the site, design wind pressures = 1.95KPAxCshp
Cshp = Cp,n x Kp = 1.63 x 1.0 = 1.63
so therefore Wind Pressure = 1.95KPA x 1.63 = 3.2 kpa !
But wait, there's more...where this barrier does a 90 degree turn, Cp,n = 3.0, cranking wind pressure up to a 5.9kpa!

Surely, there's another way to derive wind loads on this barrier? The issue is that there will be testing for this glass system because wind force is like the weight of 230mm concrete slab!

### RE: [NZS1170.2] Deriving wind load on glass barrier on top of wall?

I suspect your options will not include hiring a wind engineer to give advice.

First the good news, I don't think you get Cp,n = 3.0 unless it is a free end. If your barrier makes a 90 deg corner that doesn't apply.

Now the bad news. It might act more like a wall on the edge of a cliff. This means you could have a "topographic multiplier". A similar situation applies for roof mounted equipment and the ASCE code specifies that calculated loads be increased by a factor of 1.9 to allow for this effect.

Let's say b/c>5 and c/h=1; then Cp,n=1.2. Now if you include a "topographic multiplier" of 1.9; 1.2x1.9=2.28. With qz=1.95, pz=4.45kPa.

Well at least that is better than 5.9kPa. At least there will be nobody up there when you get that really big wind and parapet failure will not result in building failure.

Ooo eee ooo ah ah ting tang walla walla bing bang
Ooo eee ooo ah ah ting tang walla walla bing bang

### RE: [NZS1170.2] Deriving wind load on glass barrier on top of wall?

I don't see the jump from parapet to section B.

### RE: [NZS1170.2] Deriving wind load on glass barrier on top of wall?

I did the same design a few years ago. As I recall, I found specific information for wind pressures on parapets/balustrades on the top storey of a building and this was lower than the coefficients given in section B2. I don't remember if it was in the Holmes wind loading book or in a journal article. I would recommend looking in the Holmes book.

Edit: I can't find it in the Holmes book but I have reference to this article that you might want to look at:
"Wind Pressures on Parapets of Flat Roofs" Ted Stathopoulos.

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