Wind loading

[NIO85]

I am looking at a building 45m above the ground in Kampala,Uganda. Since Ugandan Standards are not yet developed, British standards are used for structural design here but applying BS 6399-2 and using Indian Ocean as the sea level with basic wind speed of 32m/s yields lateral pressures in the region of (9-10)kN/m2, which appear unreasonable!
However, when I use Lake Victoria (major water body nearest to Kampala)as my sea level, the lateral pressure values fall to (2-3)kN/m2 which I believe are reasonable. Does everyone out there think this is a valid assumption?

 

[patswfc]

A value of 9-10kN/m2 doesnt look right if you have a vb wind speed of 32m/s. Can you post your calcs for comment.
Also are you satisfied that using 6399-2 is appropriate for your location?

 

[RME1]

What value are you getting for the factor which takes into account height above sea level?

 

[msquared48]

You appear to be dealing with a little over a 70 mph wind here, and depending on the exposure, probably should yield anywhere between 10 to 20 psf in lateral pressure, dedpending on local topo.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[NIO85]

The site altitude is 1160m. This results in to an altitude factor of 2.16 thus site wind speed of 69.12m/s.
If I assume mean sea level to be lake victoria which is at an altitude of 1133m, the altitude factor falls to 1.03 thus site wind speed of 33m/s.
The major issue here is altitude factor. Please see the attached map of East Africa showing location of Kampala relative to the Indian ocean and Lake Victoria and advice if L.Victoria can be a reasonable "mean sea level".
The challenge in this part of the world is that local standards have not been developed so we have to use either British Standards or Eurocode.

 

[hokie66]

Using British Standards for wind loading makes no sense to me. Britain is a little place, while Africa is huge. The main variables in wind loading should be topography and distance from the sea. High plains are not necessarily more susceptible to high winds than low plains.

 

[NIO85]

hokie66, If you were working in Africa particularly in a country without its own design standards, which design standards would you recommend?

 

[hokie66]

I would use the Australian Standard AS1170 for loading, mostly because that is the one with which I am most familiar.

I would also use the Australian Standards for structural design, for the same reason. I think you are best advised to use standards familiar to you, with adjustments to suit the locale based on engineering judgment.

 

[tempeng]

What hokie66 said.

Find a country with similar topography and weather conditions and make an informed amendment based on your knowledge of the area.

With Britain being a small island; the higher you go above sea level, the more isolated you become. Using our standards for that altitude would be the equivalent here of building a house on top of Ben Nevis.

 

[patswfc]

NIO85

Extract from the Foreword at the start of the code below

This Part of BS 6399 is only applicable to sites in the UK. The climate dependent
factors (for altitude, direction, season and probability) have been calibrated
specifically for the UK. While the general methodology and pressure coefficients
given in this standard may be used in other wind climates, it is essential to ensure
that the reference wind data are consistent with the assumptions in this
standard. The value of the site wind speed Vs should be obtained from the
relevant meteorological authority.

 

[asixth]

The height you use should be height above ground level. Using an elevation of 1160m would probably yield the free-flowing wind that you would get at the top of the burj khalifa.

32m/s which sounds like a working wind speed or 50yr wind speed should result in about 2kPa or (2kN/m^2) at the top of a 45m building and 1kPa (1kN/m^2) at the base of the building.

 

[homostructural]

Why don't you use Eurocodes (Eurocode 1 part 1-4 - EN1991 1-4)? They are easy to use, there are a lot of worked examples through internet and they are the official design standard of many European and non-European countries!

All about Eurocodes:

http://www.DesignToEurocodes.com

 

[fcu45]

I believe that the altitude from sea level is not that significant, but the terrain, almost full lands of Some countries such as in Latin america are thousands of meters above sea level and their wind speeds are not that huge.

For example the design wind speed for our friend here is 32 m/s while he is 1160 meters above sea level, while where I live it is 35 m/s although most of our land is few meters above sea level.

Regards

 

[NIO85]

Thank you all for your advise. I am gonna try it out using Eurocode and see what result I get.