life of structure

huangyhg

" life of structure"
when we design a steel/concrete building, how can we predict the life of that structure? do all the newly designed buildings have same life?
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we do not assign a life to the structure. we can just say that there is a 95% probability of structure standing for 100 years provided we have taken corresponding values of wind, earthquake, loadinds etc. in design. but again there is 5% risk that such events(e.g. earthquake) may happen very next year.
in is a probabilistic age, like life expectancy but we can not guarantee any life period.
hth
dont forget maintenance and upkeep are a major factor in the life of a structure.
follow-up question:
does designing a structure to the 100 year wind load or the 100 year flood or the 100 year earthquake, mean its' intended useful life is 100 years (taking into consideration flame's proviso of 95% probability and maintence).
i don't recall seeing anything in any code discussions regarding relating the design load return period to the useful life of the structure.  a pre-engineered metal building with a useful life of 25 years is designed to the same loading conditions (say snow load for example) as a bank that may have a useful life of 75 years.  the same question arises with bridges.
i do realize that the code authorities use a statistical analysis when setting design live loads, but i've never seen this related to useful life of the structure.  
just wondering.
so if we are following latest codes, then we can say that the designed structure will stand for another 50 years at least, taking into account the maintenance and other unseen factors?
what about the life of structure if after 20 years new code revisions suggests that the building is no longer safe to carry the loading?
in other words if we analyse a structure today(which was designed 30 years ago) based on current code provisions and finds that the building is not safe then what happened to the life of structure predicted 30years ago?
building life expentancy
       does not equal
            statistical period of variable loading.
a 100 year wind load is a statistical maneuver where there is a 90% chance that this 100 year wind speed will be exceeded within any random 100 year period.  
even if it is exceeded, you won't necessarily have a collapse or loss of the structure.  
building's life is based more upon the maintenance and usefullness of the building to the owner, not the loading.
the life of a dynamically loaded structure will be influenced by the load cycles to which it is subjected, regardless of its age.
cage
guys, we have all contributed immensely to this topic and i must commend you all but, why don't we consider the behaviour pattern of the materials involved i.e. concrete of steel and we can draw conclusive inferences from the behaviour under stess in service.
the maajor area i will want for us to look at is the behaviour of the materials under creep load and the plastic state to breakpoint in the stress strain relationship in the lifrcycle of a material
i hope this will throow some more light, thanks.
aileme
who is asking the question?  an investor?
it's impossible to guarantee a building's life.
unless you can guarantee the viability of a society.
if you have societal breakdown all bets are off.
aluminum siding has an outstanding lifespan, but not if a homeless person has a shopping cart, a crowbar, and opportunity to pry that siding off the building.
good question.
i would like to see some answers from the life cycle experts out there.
smwpe
how long is a piece of string!?
the anticipated life may influence the design actions in accordance with the probabilistic approach mentioned above however the actual life will depend mainly upon the inspection and maintenance regime.
that said, one can design structures for greater durability, i.e.: corrosion allowance on steel elements; quality of concrete constituents; curing of concrete; concrete cover to reinforcement; protective coatings; etc.