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RE: Truss Connection

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I have run into this exact problem before - where
l/r constraints govern member size which in turn
murder the connections.

I typically justify a smaller connection force by
investigating the limit states of the truss. For
instance, take the force in the bottom chord when the
critical member fails, say top chord buckling, and
increase it some percentage (I use 30% to 50%) to
account for material (in the critical member) overstrength.

In your case, I don't know if I'd bother with this effort.
Your only talking a handful of bolts added per connection
over what you'll likely have if you try reducing the
connection force.


> -----Original Message-----
> From:	David Carpenter [SMTP:dca(--nospam--at)mcn.org]
> Sent:	Monday, February 09, 1998 11:57 AM
> To:	seaoc(--nospam--at)seaoc.org
> Subject:	Truss Connection
> 
> I am designing a 45' span steel truss for a middle school multipurpose
> 
> room.  The roof pitch is 7/12 and the spacing is 7' O.C.  The
> architect 
> desires a very simple truss in which the span of the bottom cord is
> 1/2 
> the truss span.  Code requirement for tension members in this
> application 
> is for an l/r of 300.  This results in a large bottom cord.
> 
> AISC states that " The connections at the ends of tension or
> compression 
> members in trusses shall develop the force due to the design load, but
> 
> not less than 50% of the effective strength of the member, based upon
> the 
> kind of stress that governs the selection of the member."
> 
> The design force in the bottom cord is 12 kips.  The capacity of the 
> bottom cord in tension is 292 kips.  Designing the bottom cord
> connection 
> for 146 kips seems absurd. Does anyone have any incite on this code 
> requirement or suggestions about how to proceed?
> 
>