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Re: Story Drift: 1994 UBC vs. 1997 UBC

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bill 

1- I stand corrected. I should not have included the term omega in the 
comparison, as Ron clarified in his posting. 

2- in your OMF comparison if you drop the 2.8 for omega you will essentially 
get the same number as the 94 UBC
=> 0.025/4.5 = 0.0055

3- the 1.4 factor is already included in the calculations for base shear in 
the 97 UBC so you need not consider it in the drift calculations. The only 
reason I included it, was to make the compariosn more transparent.

4- In regard to the cantileverd column, with the revised comparion calc:

delta97= (0.7)(1.4)(2.2)D94= 2.2 D94

0.025/2.2 = 0.011 

now this is almost double the allowable drift in the 94 UBC. However, if you 
note in the 94 UBC the limit was smaller of  0.04/Rw or 0.005. for Rw of 3 

0.04/3= 0.013 ~ 0.011 (essentially the same)

So, it appears that the lower arbitrary limit 0f 0.05 in the 94 UBC was left 
out of the 97 UBC and that is the reason for the discrepancy.

Ben Yousefi, SE
san Jose, CA