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Re:Alternative Load Combination in UBC97

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Hur Soojin wrote:

>>On the contrary, UBC section 1612.3.1 might be based on 'Load Reduction
Concept' as specified in ASCE7-95, where 0.75 of load reduction factor
is adopted when more than one variable load (like live, wind or
earthquake load) is considered in load combination without allowance of
stress increase.<<

I don't know if I understand you correctly, but I will try to add 

0.75 * Loads is the same as increasing the allowable stress 33 percent.

1/1.33 = .75

In allowable stress design, you could either use 133 percent of the allowable 
stress, or, as I preferred to do, take 75 percent of the load combinations.

In strength design, rather than increase the capacity (ultimate strength) of 
the member, 75 percent of the factored loads is used to compare with the 
ultimate strength of the member.

Hope this helps.

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