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Re: Large Bay 'X' Bracing

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> From: "Rich Lewis" <seaint04(--nospam--at)lewisengineering.com>

> I have a warehouse condition of a 'X' braced bay that is 31 feet high and 42
> feet wide.  The diagonal length is over 51 feet.   I'm wondering if I should
> try to use the bracing as one large bay, or add a wind column in the middle
> and have two smaller bays.  The bracing is tension only for wind loads.  The
> load in the diagonal is about 21 kips.  What makes me most uneasy is the
> slenderness ratio of the brace.  If I try to limit the L/r ratio of the out
> of plane axis to 300 then I get extremely large angles.  If I ad a column I
> add almost 50% more bracing length, plus column and footing.

I sat and considered a couple responses to this. Bottom line is that, in
either case, the brace weight is going to be small relative to the
structure.

The larger problem that I see is handling 51' of spaghetti.

Two bays of full X-bracing will cut the brace force/bay but increases
flexibility at the same strength level and, probably, higher steel wt.

Other brace forms will add weight, as well. I usually find that I have very
similar wt options regardless of the form that I choose.

My suggestion: Add the post, to split the current bracing and keep the X as
31x42. Don't worry about the L/r unless you are trying to meet seismic
detailing requirements. Watch the lateral stiffness for attachments (e.g.
tilt-up, strorefront, etc.) sensitive to differential movement. Extra cost
is the post and detailing.

Regards
Paul
-- 
Paul Ransom, P.Eng.
ph 905 639-9628
cell 905 802-3707
fax 905 639-3866
ad026(--nospam--at)hwcn.org

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