topic Re: Wind speed factor meaning in Robot Structural Analysis Forum

Wind speed factor meaning

Anonymous — Wed, 25 Nov 2015 14:31:38 GMT

Hello there, first time poster, long time reader.

My problem concerns the wind profile dialog in the simulation tool and what is the exact meaning of the wind speed factor and how RSA actually use it.
In the Italian code the wind profile is given as the exposure factor Ce(z), calculated as follows:

And the wind pressure load is then given as:

where Ce is the exposure factor (really ), Cp is the areodynamic factor and Cd is the dynamic factor (Cd and Cp are not relevant in this discussion). Qb is the basic cinetic pressure, as function of the reference wind's speed:

I checked it against the eurocode and it results that it derives from two other factors, the roughness factor Cr(z), and the turbulence intensity lv(z), calculated as follows:

The wind pressure load, according to EC is then given as:

where Vm is the wind velocity in fucntion of the altitude z, as follows:

As you can see, even if the final wind pressure load is equivalent in both codes, the wind profiles differes of a factor of roughly (Ce(z))^0.5, because in the Italian code the variation,functions of z, is applied at the exposure factor level Ce, otherwise in the EC it is applied at the wind velocity Vm, and therefore is squared.

My question is, what is the wind speed factor we introduce in the dialog and where it is applied?

If it is applied at the wind velocity level, so that I have to square Vm(z), it is only the roughness factor Cr(z), or is it the combination of the roughness factor Cr(z) and the turbulence intensity lv(z), i.e. (Ce(z))^0.5?

Hope to have been clear. Thank for your help.

Stefano Follador

(PS:would be nice to have a simple LaTeX editor to enter math formula in the forum!)

Re: Wind speed factor meaning

Rafal.Gaweda — Wed, 25 Nov 2015 14:50:34 GMT

http://forums.autodesk.com/t5/robot-structural-analysis/terrain-type-wind-simulation/m-p/5313201#M27004

Re: Wind speed factor meaning

Anonymous — Wed, 25 Nov 2015 15:53:51 GMT

I read that post before posting and I didn't find a definite answer to my question.

I think you are reffering to the post of StefanoPasquinotti that list a procedure how to build a wind speed curve, but I got lost at point 3 of that list

"3) define from this pressure curve the velocity one, using the relationship between them;"

the relationship between them he is referrering could be this?

Re: Wind speed factor meaning

StefanoPasquini6790 — Thu, 26 Nov 2015 14:19:15 GMT

Hi,

IMHO your calculations are right, also if I use another way to create the wind load cases. Personally I use to input in Robot not he wind speed, but the maximum pressure for the main surface, calculated in an apposite excel spreadsheet, as shown in the following pic:

Hope I help you, cheers

Re: Wind speed factor meaning

alfredmx — Thu, 03 Dec 2015 16:30:27 GMT

Hello,

Here is a small example showing comparison between pressures manually calculated according to code vs wind simulation tool. As expected, code tends to be more conservative, however good agreement is seen, especially for Y+ direction. I hope this can be of any help.

Regards,

Re: Wind speed factor meaning

HoshangMustafa — Fri, 01 Jun 2018 14:31:17 GMT

@Anonymous wrote:
Hello there, first time poster, long time reader.
My problem concerns the wind profile dialog in the simulation tool and what is the exact meaning of the wind speed factor and how RSA actually use it.
Please find the attached pic.

Re: Wind speed factor meaning

morten4MDUW — Sat, 21 Aug 2021 16:12:35 GMT

Is this EN 1991.1.4 graph same as robot wind profile ?
Or is robot wind profile something else`?

Re: Wind speed factor meaning

lanh_streng — Sat, 18 Apr 2026 03:03:17 GMT

Is wind simulation in robot software dependable for design purposes?

Re: Wind speed factor meaning

StefanoPasquini6790 — Mon, 20 Apr 2026 07:00:28 GMT

Yes it is, but you need to know exactly your parameters and compare the load results with the design code values