Relationship/ formula between safety factor/reliable index and return period of nominal windload

[hoangvhuy]

Hi everyone,
i am studying how to calculate wind load in ASCE 17,
For each risk category, we have MRI( mean recurrence interval/return period ) accordingly. and for each life building in year, we have the probability of exceeding wind load.
My question is: how to determine of safety factor/reliability index for buildings if we choose MRI to design? i see the relationship chart but don't know how to/formula to get a safety factor

THanks all so much

 

[hoangvhuy]

No one can answer?

 

[phamENG]

I typed up half an answer but got distracted the other day. Sorry. For one thing, I'm assuming you mean ASCE 7 and not ASCE 17. If you mean 17, I can't help you. I've never designed an air supported structure.

The simple answer: you don't have to. These are meant to be used with the load combinations in chapter 2 and the various material specifications referenced in the international building code. When all used together, you get a combination of loading and resistance that balance at a reliability index deemed sufficient by the code writers. I think it's something like a 1:300,000 chance of failure? I don't remember exactly. I'd have to dig for those references. But you don't set the reliability index or pick safety factors - they're set by the code.

 

[Lomarandil]

My understanding is that there is a statistical relationship as shown in your chart, but that the actual formulation is very statistics heavy. Anything less than that would only be curve-fitting.

 

[hoangvhuy]

@phamEng
i have mistake. ASCE 7 not ASCE 17.
Thank for your support
Any paper/document you can advice for my study for this issue. thanks