Converting Basic Wind Speed 50-year Return Period to 2-year Ret Period

[cwmullion]

Can anybody help me how to convert 3s gust basic wind speed at 50 year return period to 2year return period. I am considering 2 year return period since the structure is temporary to be removed after 2 years (max).

 

[WillisV]

If you are absolutely certain it will only be in service 2 years you might want to look into ASCE 37-02 (design loads on structures during construction) which gives a reduction in velocity of 0.85 for a construction period of 1 to 2 years, and 0.9 for 2 to 5 years. This translates into a reduction in force of 0.72 for 1-2 years and 0.81 2-5 years.

 

[cwmullion]

Thanks for your reply.
This is a structure which will only be in service for 2 years maximum. However, I am also concerned with what proper reference to use since I am using BS6399 for the wind load calculation. Do you think using ASCE reference to a BS-based calculation will be acceptable? I cannot find any reference in BS Standards for this basic wind speed conversion in respect to return period.

 

[sdz]

I believe the conversion will be region specific so you shouldn't use foreign conversions. Are you using working strength or ultimate limit state design? If ULS then you probably should be using a 20+ year return period.

 

[cwmullion]

Hi sdz,

I am using ULS. But if I am going to use 20+ year return period, is this practical, because in 2-years time the structure will no longer be in service.

Do you have any reference for this conversion in Middle East Area using British Standards. I am using BS6399 for the Wind Load Computation.

Thanks.

 

[sdz]

When using ULS the wind speed should be the speed that has a ~10% probability (depending on your design code) of occuring during the design life of the structure. So for a 2 year life this is approximately a 1 in 20 year event. You need to check the relevant standards to check what you should use in your case.

Sorry I don't have any references for that area. Can you ask a senior engineer in your company?