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Knee Braced Frame-Effective Column Length

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Consider a 5 story bldg. where all levels above the first elevated floor are 
X braced, but the first elevated floor level has knee braces from the girders 
to the columns below.  All the girders are simply connected to the columns.  
Therefore, the frame up to the first level has sidesway, which incidentally 
makes up most of the lateral deflection of the levels above under lateral 
load. I consider the frame up to the first level to be an "unbraced frame" 
because of the sidesway, even though it has knee braces, and K=1 does not 
apply here. How does one determine the "K" value and corresponding effective 
length of these first level columns ? The "sidesway uninhibited" curves in 
the ASD (9th) or LRFD (2nd) are based on *rigid* connections between the 
girders and columns such that the girders provide rotational restraint to the 
columns. But in my case the girders are pin connected to the columns, so in 
theory rotational restraint is absent. I would appreciate any insight to this 
problem. Thanks.