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RE: Components & Cladding for Wood Roof Trusses

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Steel bar joist manufacturers will do what the EOR tells them to do.  I
provide a joist net wind uplift diagram on the structural drawings.  It is
like a key plan and shows the net wind uplift loads and boundaries.  Joist
manufacturers are directed to the uplift diagram in the general note section
regarding steel bar joists.  

As a rule of thumb, joists that are properly designed for wind uplift are
braced at the first bottom chord panel point.  The joists that are parallel
to and at the perimeter of a roof will often have larger bottom chords than
top chords.  An old Factory Mutual field representative taught me that
trick.  

Regards,
Harold O. Sprague

-----Original Message-----
From: Kestner, James W. [mailto:jkestner(--nospam--at)somervilleinc.com] 
Sent: Wednesday, April 14, 2004 11:59 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: Components & Cladding for Wood Roof Trusses

Wouldn't the same type of analysis be required of the steel joist
manufacturers? Granted, most of the joist roofs are flat, but they still
must comply with Figures 6-5c, 6-7a or 6-8. Does anyone know how they handle
C&C loads?

We should expect no less engineering from the wood truss and light gage
metal truss designers.

Jim K.

-----Original Message-----
From: Scott Maxwell [mailto:smaxwell(--nospam--at)engin.umich.edu]
Sent: Wednesday, April 14, 2004 10:35 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: Components & Cladding for Wood Roof Trusses


John,

But keep in mind the section 6.5.12.1.3 of ASCE 7-98 states that
components and cladding elements (for enclosed and partially enclosed
buildings) "...with tributary areas greater than 700 sq. ft. shall be
permitted to be designed using the provisions for main wind force
resisting systems."

Now, I will be the first to admit that typical wood trusses will _NOT_
trip the 700 sq. ft. limit, but I have encountered some structural members
that certain would (i.e. your typical steel truss in an industrial
building).

Regards,

Scott
Adrian, MI


On Wed, 14 Apr 2004, John C. Jones wrote:

> Wow, I had to do a double take because I typed a message with almost this
exact title and then didn't send it to the group.
>
> That's how I specify.
>
> Here was what I started to post...I came across some shop drawings that
said the trusses were designed as MWFRS.  I questioned the supplier and he
said that he could get a bunch of PE's to say that MWFRS is the way they
should be designed.  I asked if these people work for the truss industry.
The answer was yes.  This is nuts, evidently all trusses designed using
software and plates made by Robbins Engineering are designed as MWFRS.  Be
on the lookout for this.
>
> John C. Jones, PE
> Barnett Associates
> Pell City, AL
> 205-884-5334
> 205-884-0099 (fax)
>
>
> -----Original Message-----
> From: Kestner, James W. [mailto:jkestner(--nospam--at)somervilleinc.com]
> Sent: Wednesday, April 14, 2004 9:33 AM
> To: SEAINT
> Subject: Components & Cladding for Wood Roof Trusses
>
>
> ASCE 7-98 requires that wood roof trusses be designed for C&C loading with
Zones 1, 2 and 3 and overhangs. It seems impractical for the EOR to list all
the loads for the truss designers because of the various effective areas for
different trusses. About the best that we can do is to reference that the
truss designer needs to comply with the C&C requirements of ASCE 7-98.
Additionally, our drawings must list: Basic Wind Speed, Importance Factor,
Exposure Factor and Internal Pressure Coefficient and minimum dead load (to
determine net uplift).
>
> Does anyone else specify C&C loads differently?
>
> Does the typical truss designer know how to handle this loading or is it
done automatically for him? Does the typical truss program take these C&C
loads into account?
>
> Jim K.
>
>
>
>
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