60m span warehouse - check for vibration due to wind?

[clarke1973]

Hello,
I have a large span storage warehouse to design - 60m span, height to eaves is 9m. It is lightweight construction - sandwich panel sheeting on purlins with minimal services. The roof is only accessed for maintenance (0.6 Kn/m[sup]2[/sup] live load).
A colleague has suggested that checking the roof for vibration due to wind should be done. I was only intending to check for static loads (with a second order analysis). A preliminary run I have done on a 2D frame is showing deflections within the code limits.
Does anyone know of a code requirement that states vibration checks should be done over a certain span? I'm struggling to find anything on it.

Thanks in advance for any feedback

 

[WARose]

If the roof is completely covered (with some kind of cladding or whatever).....I'd be surprised if there was a wind vibration issue. You'd likely have some sort of dead+live deflection issue first.

 

[klaus.]

No snow Load....or wind pressure load on the roof ?

You should calculate the frequency of the roof to see if there is danger of wind dynamics

 

[SAIL3]

good luck on trying to find an estimate of the wind vibration driving force...I personally would not know where to start on that....

 

[Agent666]

The way most codes approach the issue is by way of assessing the natural frequency against some limit, and then if appropriate factoring the forces by a further dynamic multiplier. This is an estimate for the maximum design actions when subject to dynamic effects like wind induced vibration.

 

[civeng80]

60m is a huge span. As a matter of interest what sort of framing members are you adopting in the design ?

 

[clarke1973]

Thanks for the responses.

civeng, I'm using a haunched UB1016x305x222 rafter, and UB1016x305x437 columns (British sections). It is a double span roof, i.e 120m wide with central columns. It seemed a more economical system than using a truss.

 

[klaus.]

a (Mero Type) space frame system would be a good an economical option for such structures

 

[civeng80]

If vibration applied to such a large warehouse structure then it would also apply the smaller structures depending on their stiffness.

If this were the case then there would be provision for this in the steel codes.

Therefore I do not believe that you should be concerened with vibration of the structure or dynamic resonance.

Another question is this warehouse in Australia and what sort of frame spacings are you adopting ? I have designed some large fertiliser sheds with centre props every second frame, just wondering if this could be applied in your warehouse.

 

[klaus.]

@ civeng80
correct...this depends on stiffness and mass and not on span
but there are provisions in codes for wind induced vibrations...at least in europe
It is not a big deal to check frequency of the structure and to decide if there might be a (wind)problem or not
I would say if lowest eigenfrequeny is more than say 2 Hz there should be no problem
But depends on codes and/or project documents...

 

[ThomasH]

Hi
Check what the lowest natural frequency is. If it is below 1 Hz there is a definite risk for dynamic effects due to wind. If it's above 3 Hz, there is often no problem. Between 1 Hz and2 Hz it is more structure dependent. Since you structure is lightweight it is more sensitive to wind vibrations.

What is your concern? Is it strength you are worried about or is it comfort for people?

Thomas