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RE: trusses

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Sorry that I am late on this topic - I've been busy trying to get caught up.
I've read Scott and Andrew's responses and would like to add a couple of
notes. 
First, Most of us can design a heavy timber truss because we are dealing
with conventional materials including bolts and plates using the standards
established in the AITC manual.
Metal Side Plate Wood Trusses are a different animal. The problem is not
really the software as Andrew indicated. Yes, the software differs whether
you are dealing with a company that uses the MiiTek written software or
another popular truss package generally written by Keymark Industries. The
software is not the key to these trusses, it is the plate manufacture's
specifications based on the press plate connection. This includes the number
of teeth and the capacity of the plate at the connection. This information
is held in strict privacy to maintain competition between truss companies. 
Trus-Joist is a slightly different issue. Weyerhauser Trus-Joist has a
policy to verify all product design prior to shipping. They license the
software to architects and engineers, but they confirm the design and the
limit the software to cantilevers approximately 1/3 of the span.
Occasionally you may need more cantilever and this is were TJ intervenes and
provides the approval and design within house for your specific needs.
Commercial products are another issue that requires TJ's review and
submittal. This may seem redundant, but in my opinion it is a very good
practice for ensuring your companies reputation.
On the issue of heavy timber, Weyerhauser also produces a commercial grade
of their PSL lumber products. Similar in design to a GLB, the PSL beams can
be special ordered with a camber - something not commonly done with their
residential grade products unless you specifically request it. I ran into
this problem a few years ago where I had an very large cantilever occurring
above a corner to corner glass window and I used the deflection on the back
span to design a threaded tension rod and turnbuckle so that I could adjust
the cantilever deflection after all dead loads were in place and settled in.
TrusJoist was able to circumvent this by supplying a commercial grade lumber
with the calculated camber in it to insure that the glass did not crack from
deflection of the cantilevered end.

The Truss Plate Institute along with the Wood Truss Council of America has
done a lot of work recently to create standards that attempt to clearly
spell out the responsibilities of each member of the design team. The
quality of the materials and trusses are improving but this is not enough.
My general problem in the field is that the GC will not submit the plans
that show where I want trusses laid out or provide the truss company with
specific drag loads for drag and girder trusses that I clearly indicate on
the plan. If there is a time crunch, the GC will generally provide the
architectural plan to the truss company and leave it up to them as to how
the trusses are placed on the house. This creates a discontinuity in the
shear transfers that are so important in my designs.
I strongly suggest that you visit the Truss Plate Institute website and
review the documents especially the WTCA Responsibilities document at
http://www.tpinst.org/ or you can find it at the WTCA site at
http://www.sbcindustry.com/ and by the way the SBC or Structural Building
Components web site offers a free monthly magazine to those of us in the
trade who simply sign up for it. The site is very impressive and contains
almost everything you need. There are more documents and online training for
a reasonable fee and I highly recommend this since the EOR of a project must
take responsibility for the shear transfer from the roof and floors to the
foundation of the building. Working close with the Truss designer is the
best way to accomplish this goal.
Thanks
Dennis S. Wish, PE
California Professional Engineer
Structural Engineering Consultant
C-41250 (Exp. 3/31/07)
dennis.wish(--nospam--at)verizon.net
lqengineer(--nospam--at)structuralist.net

http://structuralist.spaces.live.com


-----Original Message-----
From: Scott Maxwell [mailto:smaxwell(--nospam--at)engin.umich.edu] 
Sent: Monday, January 29, 2007 9:23 PM
To: seaint(--nospam--at)seaint.org
Subject: re: trusses

Heavy timber trusses (either solid wood or glulam or other engineered
lumber) can be done either way...the EOR can do it or the manufacturer can
hire an engineer to do the design of the trusses.

Regards,

Scott
Adrian, MI


On Sun, 28 Jan 2007, Andrew Kester, PE wrote:

> Mark,
> For both wood and light-gage trusses, they are always pre-engineered and
signed and sealed by the truss mfr's engineer. This includes wood floor
joists. I am noticing that even when we specify TJI or some other engineered
wood product, the contractor may have the floor re-engineered by the floor
truss/joist supplier, and sometimes this causes some coordination issues
when nobody tells the EOR this happened.
>
> But for what you are talking about, I have never heard of the EOR
designing anything but the connections, as the truss engineering is part of
the price of the truss package. We specify on our drawings that all
truss-to-truss connections be specified by the truss engineer, as well as
any required bracing whether temporary or permanent.
>
> They have specialty software and it would probably be very difficult for
any "regular" engineer to sit down and design a bunch of trusses. Usually
the layout and design of the trusses are done by a truss "designer", then
supposedly reviewed and sealed by an engineer. Now if you have heavy timber
trusses or some other very unique specialty item, that is different. But I
think even that can be pre-engineered, I think Scott in Michigan for example
does that type of work.
>
> Andrew Kester, PE
> ADK Structural Engineering, PLLC
> Lake Mary, FL

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