RSA 2015 Wind simulation and Eurocode

[AF-thyman]

Hello community!

I've been toying around with the wind load simuation feature in RSA while modelling the top of a tower. The tower has a cylindrical shape with a steel superstructure holding it all together. And in the best of worlds I've had all the time in I want to continue toying and experimenting, although that is not the case, so I turn to you hoping there is someone who got experience using said feature.

I've had from our client that the survival wind speed is 47.22 m/s, and as I'm only modelling the top which is located +50m above ground,  I'm assuiming that the wind profile is constant over the structure. I've taken snaps of the wind setup as well as a picture showing the current model.

What I'm wondering is how well this correlates to Eurocode? Is it sufficient to just enter the survival wind speed into the wind velocity dialog box or do I need to take some other parameters into consideration? Doing hand calculations for a cylindrical shape seems rather cumbersome, when I in the end will just put those values into the model.

Can it more accurate to calculate the wind pressure by hand and then enter it as a manual wind pressure instead? Do I need to account for safety factors or is this included? (I'm thinking this can easily be accounted for using the wind profile to increase/decrease the load).

I'm gonna try some simple calculations using this feature, to see if I can find some correlations. I will come back if I find anything useful, however any help would be much appreciated.

Regards, Thyman

[Rafal.Gaweda · Accepted solution]

See this:
http://forums.autodesk.com/t5/robot-structural-analysis/terrain-type-wind-simulation/m-p/5313201#M27...

[AF-thyman]

Hello!

Thank you for a very rapid reply.

It was very good to see and compare values like this.z Altough I have some questions.

I took a peak at his models (in the post which you referred to) and I see that his wind velocity seems to be 42.04 m/s in the x-direction. This wind velocity gives a pressure gradient with a maximum of 1.5 kN/m^2 (see his attached picture). But when I look in to his verification model he applies the wind load as linear load with values spanning from -4.36 to -5.66, i.e. with an avarage of- 5.01 kN/m^2. Span between columns is 7 m, which means that the load area for each column is 7m^2 per meter column. This will give a wind pressure of 0.715 kN/m^2. I would had liked to see how he set up is wind simulation parameters including the wind profile to understand how everything hangs together.

On the other hand, in my model, I use 47.22 m/s as wind velocity, which induces a pressure gradient with a maximum of 1.35 kN/m^2. This is obviously lower than his, despite my height. I conclude that my wind profile is different from his. Which is not unreasonable since I haven't changed it from 1.0. I can't say why my client specified it as he did and not according to EC, but it correlates fairly well with a wind speed of 23-24m/s at a height of 100m according to Eurocode and trarain class 0 or I ( if I use exposure factor (c_e(z)) set to 1 for my clients value, which then becomes 1.4kN/m^2). The value also correlates well with the maximum value from my pressure gradient (1.35kN/m^2)

I'm afraid things might have become a bit messy, but if anything is unclear, please say so and I'll do my best to explain again.

What i still wonder about is why his modelled gradient pressure and wind pressure don't match while mine does.

Do I need to account for safety factors and similiar into the wind simulation to be in accordance with EC1?

Regards // Thyman

[StefanoPasquini6790]

HI AF-thyman,

keep in mind that the pressure value is the average one (integral) of the whole cladding.

Take 10 minutes to do an example:

1) make a 10x10 (meters) cladding and apply over it a wind simulation,

2) make on it side another cladding, composed by 100 claddings (1x1 meters).

As you can see, the values of the pressure are very different, but the reaction is very similar.

In my testing model, I have 1 cladding for building side so you can understand that the precision is not on top!!!!

Important note: in the selection of element exposed to wind, please insert only the claddings and not all the elements!!!

[394-98256677]

hello,

I leave as an example checked with the Spanish standard. The results differ from those achieved with the program but are of the same order.

I hope you find it useful.

[AF-thyman]

Hi Stefano! 

I'm sorry for a rather late reply, but I was quite busy yesterday! However I took the time and did the example you recommended. I did not know that  the size of the cladding would really matter as I beleived it used the actual load from the simulation. Thank you for the that clarification. Much appreciated. I tried to make a finer element mesh as well, but I couldn't see any improvement in the results from this. So I wonder how small should I make each panel for an accurate result, as I clearly get a higher load when increasing the number of panels. This might be troublesome as more elements seems to mean more load, I would have prefer it to be the other way around. Se attached screencaps.

One other thing that raised my concern was how to use the wind profile, and as I toyed around with it, I got even more confused. I have attached the two files that I have been using for this comparison (one with 1 100m^2 cladding and one with 100 1m^2 claddings). In each file I have performed 2 wind simlation with a wind speed of 24m/s and terrain height of 0m. The only changed factor for each wind case is the wind profile. For the first case (1) I used a constant wind profile of 1.2, while in the second (2) I also used a constant wind profile but with 1.0 as a value.

My initial though was that at the specified height, the wind speed would be increased with a factor of 1.2 and 1.0 respectively. this however doesn't seem to be the case. I took a screen cap of the values, see attached, and as you can see, the reaction force in the same node is almost increased by 50%. This can be seen in earlier mentioned screen caps.

What I need to know is how to use the wind profile to set up an accurate wind situation according to eurocode.

And as I said previously, I'm also curious how RSA accounts for safety factors in this calculations? Is this something that I manually need to add?

@394-98256677 Thanks for your file, I will take a look at it as soon as I have some time over, as my spanish is very limited and I need to do some googling. I'll return if I have any concerns regarding the document in the future.

[AF-thyman]

I was not able to upload more than 3 attachments. I've added the last one here.