Serviceability wind speed and ultimate wind speed

[tngv752]

Based on the Australian code, ultimate wind speed is V500 = 45m/s (Region A) and the serviceability wind speed is V25 = 37m/s (Region A).

I wonder if a roof structure is only allow to operate when the wind speed is 30m/s. So what is the serviceability wind speed to be used for serviceability check ? Still 37m/s or 37x(30/45) or 37x(30/45)^2 and why ?



Thanks.

 

[Settingsun]

Could you explain what you mean by the roof operating. Is it retractable? Do you mean wind speed to combine with live load?

 

[tngv752]

yes, it's retractable roof for deflection check.

 

[Settingsun]

In that case, you should come up with your own criteria unless maybe there's a mechanical code which covers it. I still don't know whether your roof is a bit of shade cloth out front of a café, or over a 50,000 seat stadium. How did you come up with 30m/s maximum operating speed?

There's a significant difference between fixed structures like AS1170 deals with and a retractable roof: the fixed structure gets built then has to withstand whatever nature throws at it; while the retractable roof is packed away when the going gets tough.

 

[tngv752]

Steve,
Thanks for your comment.
It's a small roof to cover a front cafe. The rafter length is varied from 3m to 10m long.
The rafter can take a maximum wind speed depending on the span support based on the strength capacity.
However, using AS1170 for deflection check under serviceability wind speed (for longer spans of 5m to 10m), it is not satisfied the deflection limit of Span/250.
As your comment, I can consider the deflection limit of Span/120 or Span/100 if the retractable can operate under that limit deflection of Span/120 or Span/100 ?

 

[Agent666]

The code serviceability limit is the 37m/s, you need to comply with this generally. But nothing stops you having a lower criteria for the roof operation. Remember when the roof is open that you'll have a dominant opening (depending on whether it seals up the space) and different internal coefficients. So to satisfy code design for 37m/s when closed, and 30m/s when open, these are the two bounds of interest. Hard to say which will govern without looking at the resultant internal and external pressure coefficients.

In reality 30m/s is still a fair old wind and you need some means of detecting this and closing the roof if its going to to be designed for lower than the SLS limit when closed/deployed. If its powered what occurs when the power goes out (often occurs in storms when wind is most likely to hit SLS limits)?

 

[tngv752]

Agent,

Thanks for your comments. The wind speed of 30m/s is just an example number. It can be 25m/s or 35m/s depending on how much is the loading area.
We already have a member size of roof rafter, roof dimensions and spans. So we need to check the maximum wind speed applying to the roof structure.
I believe that if the roof rafter can take the wind speed of 25m/s (of course, the roof must retract at 25m/s or less) then the serviceability wind speed is only 25m/s or less.