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Re:Alternative Load Combination in UBC97 (1612.3)

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Thank Mr.Phil for your advice.

Based on my brief study, UBC section 1612.3.2 is based on traditional
practice which allows a one-third allowable stress increase for load
combination with one transient load like wind or earthquake load.

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 can't assess which concept is more reliable. However, two methods make
big difference in selected member size. Especially in may case, where
pipe rack design is governed by D+E/1.4, since live load (or operating
load) is negligible, two methods result in roughly 33% (not exact)
difference in material quantity.

Shall I apply new concept? If then, so far, have we done wrong design
based on wrong concept?

Look forward to any good advise from any body.

Soojin, Hur