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Re: Knee Braced Frame-Effective Column Length

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Could you not look at the knee brace as a moment couple just as you have in
a moment connection?  Wouldn't that act as an effective moment connection
(albiet a deep one) for the column?


-----Original Message-----
From: James F Fulton <James_F_Fulton(--nospam--at)RohmHaas.Com>
To: seaint(--nospam--at) <seaint(--nospam--at)>
Date: Tuesday, March 09, 1999 4:52 PM
Subject: Knee Braced Frame-Effective Column Length

>Consider a 5 story bldg. where all levels above the first elevated floor
>X braced, but the first elevated floor level has knee braces from the
>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
>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
>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
>problem. Thanks.