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1/3 increase

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The reason for the 1/3 increase that I was taught (and found it logical then  
and still find it logical) is that *all* materials can sustain higher loads 
when loaded quickly and for a short period of time than they can sustain if 
loaded slowly and for a long period of time.  Wind and seismic loads are 
short-term loads applied quickly and then released, giving the material the 
appearance of higher strength.  Peak loads for these forces are even of much 
shorter duration.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Jim Harris wrote:

. > I realize that I may be denounced as insane or one of those damn code 
. > writing people (I am not, well not a code writing person anyway), but it 
. > has always been my understanding that the 1/3 increase was to take into 
. > account that full design live loads would not be present during a design 
. > wind or seismic event. Thus the 1/3 increase is not allowed for items that
. > only receive these transient loads. I realize that this is not what the 
. > code says but it is my understanding on the origination of the 1/3 
. > increase

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