Wind Load on Balcony Balustrade 1

[ajk1]

Any suggestions on the most appropriate way to determine the wind load on 42" high solid (glass) balcony balustrades of a 40 storey building with balconies surrounding the buildign at every floor? Would the Cf coefficients for "Walls above Grade" be appropriate (my feeling is that it may be overly conservative since there is only a limited distance between the balustrade and the building wall)or would soemthing else be more appropriate or is this one for a wind tunnel test?

 

[Ron]

I treat these as "solid signs". Even though you only have a limited space behind the solid portion, the turbulent character of the wind is at least as bad, if not worse than open space.

 

[ajk1]

Thanks Ron.

 

[apsix]

Report on wind tunnel testing of balcony balustrades attached

 

[ajk1]

Thanks apsix - the attached paper is very interesting. Can you tell me if it is a paper that was published in a journal, and if so, the journal name?

The National Building Code of Canada formula for wind loading is:

p = I Cp Cg Ce q

where
I= importance factor (generally 1.0)
Cp = pressure coefficient
Cg = gust factor (generally 2.5 for cladding)
Ce = exposure factor to account for surrounding terain roughness and height above grade to location where you are calculating the wind
q = basic wind pressure at 10 m above grade (in Toronto this is 0.53 kilonewtons per square metre)

Can you tell me what the formula in the Australian Code is, so that I know how to apply the results of the paper that you sent me?

I realize that I may have to convert the 3 s wind speed to the mean hourly wind speed on which the Canadian pressure values are based, but I have somewhere a formula for that.

Thannks

 

[apsix]

ajk1

It would only complicate things to use the 'Australian formula'.

Pressure coefficients are the response of the structure or shape to the acting wind pressure, and therefore can be used directly with any code.
To do otherwise would mean that the results are not compatible with the rest of your wind calculations.
Your I, Ce & Cg are all modifiers to the basic wind pressure to obtain a site and element specific wind pressure.

The paper was found on 'Windtech Consultants' website, they appear to specialise in determining wind loads on buildings.

 

[ajk1]

To Apsix - thanks for your comment. My problem is that I do not know what gust factor to use in conjunction with this Cp. In the National Building Code of Canada (NBCC), the gust factor for buildings > 60 feet high is 2.5 for cladding; for buildings < 60 feet the gust factor is combined with the shape factor and only a single value is given. However the NBCC is based on mean hourly wind speed, but the Australian Code seems to be based on the 3 second gust speed, so I expect their gust factor < 2.5. Perhaps I would have to see what the ASCE code (which is also based on 3 second wind) uses for gust factor for cladding in buildings < 60 feet high and use that in conjunction with the Cp determined by the wind tunnel test...after converting the mean hourly wind sped to 3 second wind speed.

 

[apsix]

You are correct, AS1170.2 uses 3 second gust speed, but typically doesn't use a gust factor.

A gust factor is defined (but not used directly)in relation to the dynamic response factor for dynamically wind sensitive structures, which is probably different to the NBCC definition.

AS1170.2 does use a local pressure factor for cladding and the like. This varies from 1 to 3, depending on location. However this would not be used with results from wind tunnel testing, as local effects have already been accounted for.

 

[ajk1]

I suppose that if I consder my case to be height > 60 feet, then I can use the Cp from the wind tunnel test together with the NBCC gust factor for cladding (Cg=2.5) and use the NBCC calculation throughout. That means that the balustrade wind tunnel test Cp=1.8 is greater than the NBCC Cp=1.3 for stand-alone solid walls above grade (for my case of width-to-length). I was thinking that the wind tunnel test would give me a lesser value but apparently not. This gives wind pressures very high .. several times 20 psf..but I will have to go into the ofice to see excatly what the calcualtion gives. I am at home now on vacation.