Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Re: Glulam Roof Girders in a Tilt-Up

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Gerard,

An important thing to consider when using steel channels on wood members
is that they have MUCH different coefficients of expansion.  The
temperature of the roof area can vary significantly over the course of a
day in this type of structure, especially during the summer.  The
problem that arises is that the bolts or other fasteners will be worked
back and forth in the GLB as the steel channel expands and contracts
each day.  After some time the result will be that the steel channel
will be simply "hanging" from fasteners in horizontally slotted holes
from your "overstressed" GLB.  In other words you have simply added dead
load to an overstressed structure.  This is one reason that the
post-tensioning method is preferred.

David Pomerleau, S.E.
Irvine, CA 
dpomerleau(--nospam--at)fwcse.com




From: "Gerard Madden, SE" <gmadden(--nospam--at)maddengine.com>
To: <seaint(--nospam--at)seaint.org>
Subject: RE: Glulam Roof Girders in a Tilt-Up

This is a multi-part message in MIME format.

------=_NextPart_000_000A_01C39DFF.E6B79C80
Content-Type: text/plain;
	charset="us-ascii"
Content-Transfer-Encoding: 7bit

I am leaning toward creating a composite section with steel channels to
reduce both the stresses in glulam at the top and the bottom by shifting
the neutral axis and increasing distance to the extreme fiber.
 
I guess the problem I have with post-tensioning the beam is the
compressive stress at the top lams. But if I have enough Eccentricity, I
suppose this would offset the uniform compressive stress increase from
P/A.
 
I would think something like a ZONE 4 CT Anchor Ea. Side with rods or
cables and some kind of take up device to minimize losses in the tension
rod.
 
The main problem with this structure is the potential domino failure due
to the way the original engineer designed it. The series of cantilevered
beams are dependant on one another for support. Mixing in a simple span
or a double cantilevered glulam would have been nice.
 
Also, in my internet searches, I came across a lot of Fiber Reinforced
Glulam Hits.. anyone tried that???
 
Thanks to everyone for their great words of wisdom
-gm 

******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
*
*   This email was sent to you via Structural Engineers
*   Association of Southern California (SEAOSC) server. To
*   subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
*   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you
*   send to the list is public domain and may be re-posted
*   without your permission. Make sure you visit our web
*   site at: http://www.seaint.org
******* ****** ****** ****** ******* ****** ****** ********