From: Charles Greenlaw <cgreenlaw(--nospam--at)speedlink.com>
Date: Mon, 05 Apr 1999 23:00:35 -0700
I've been waiting for an expert to answer, but none have yet.
Your problem with the senior VA engineer reminds me of that famous trial,
Pope vs. Galileo. The issue then was how the solar system worked. Did the
sun go around the earth, or the other way around? The Pope had more clout
than Galileo, so the solar system worked his way.
The way I read this AISC Table (in the 1963 edition my grandfather used)
col.(f) is for "rotation fixed and translation free" (repeat,"free") at the
top, as you have said. I guess your man reads it that way too.
Now, is your building's lateral force resisting system so flimsy and "free"
that "translation" prevention at the roof and column tops depends on the
stiffness of the columns as downward cantilevers? If not, the condition
looks more like that in table col.(b), but upside down. K then would be 0.8,
not 2.0 This would be a relative rigidity matter to resolve, if doubt remains.
This is a pretty old and simple AISC table. I guess there's no way to make
the code simple enough for some people. Pity. Makes the simplification
effort a harder sell.
Charles O. Greenlaw SE Sacramento CA
another simple guy
At 10:42 PM 4/5/99 EDT, you wrote:
>We designed a tilt-up building with metal deck for roof (no zonolite or
>structural concrete fill). The building is approximately 200'x200'. Framing
>consists of OWSJ supported on WF steel girders.. The girders cantilever about
>4 ' over columns with drop-in beams at alternate bays.Connection is with
>shear plates. Girders have full height stiffners on both side of web at
>column supports and bolted with 4 bolts to the cap plate. OWSJ have slip
>connection at bot. chord to allow for free deflection of the joists. The
>columns are spaced at 40' on center, both direction, and are HSS 6x6x0.5 X
>22' tall. The framing, including columns were designed using RAMSTEEL
>programme (over kill) with eccentricites included in in both axis.This is a
>VA non-essential facility in West LA. Building and is all complete and ready
>for TI improvements.
>SO FAR SO GOOD. We now have a Very Senior VA engineer from Washington (shall
>remain name less for now) telling us that the columns should be designed per
>AISC Table C-2.1 column (f) (Page 5-135) with K=2. i.e with pin at ground -
>Rotation fixed and translation free at top.
>We have designed the columns as pin-pin with K=1. We, very strongly, do not
>agree with his assesment but because of his high position we cannot convince
>VA that our design is adequate.
>We thought this would make an intresting topic for discussion.
>Thanks to all, in advance.