huangyhg

loads for temporary aircraft hangars
pals
temporary aircraft hangars of the type that use tensile fabric, has a typical life span of 20-25 years, simply put the design life is less than 50years.
doesnt this mean they should be designed for reduced wind and snow?
but asce7 has no importance factor less than 1.00, and using asce7 means designing for life of 50years as a minimum.
any other code you can suggest that mentions reduction?
respects
ijr
check out our whitepaper library.
i would still design for the 50 year loads. there is a 2% chance of the 50 year event happening in any given year. during a life span of 20 to 25 years, that is approaching 50% chance of the event occurring.
i would not want to tell the owner after something happened, 'well, it did have a 50% chance of collapsing sometime during its life time...'. don't thing they would be very happy. though their laywer might be!
also, keep in mind that some 'temporary buildings' last a lot longer than planned. last year i did some inspections/evaulations on some 'temporary buildings' on an air force base that were built in 1943. they are still referred to as 'temporary' 65 years later.
jmho.
ijr,
asce7 are for a 1 in 50 year return period, not a 50 year design life. this means that this wind speed/snow loading will occur on average once every 50 years, but as this is only an average return it is entirely possible for this speed to occur several times in a 25 year period.
25 years is not a temporary structure, 25 years is a normal design life for many residential structures.
temporary structures are normally considered those with lives less than one year.
as soon as you start going beyond the realm of the loading and life-safety requirements of the building code then you are putting a lot more responsibility on your own shoulders.
that's fine as long as a) you're willing to accept that responsibility, b) you do enough extra work to truly justify the reduction in loading that you are talking about, c) the owners and building officials are fully aware of the reduced design criteria and that reduced design criteria is clearly spelled out as a part of your contract.
to me this is almost like doint "performance based design". design fees for that sort of work are tremendous. if you're not going to go through that type of work (or you are not going to get paid for it) then i would say that you should just stick with the regular building code criteria and call it conservative.
and the wind and/or snow loads could happen next week!!

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