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Re: GL beam strengthening

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The load sharing is all designed per deflection compatibility. I don't have the calcs in front of me here at home, but I think the difference is that the new beam is a 5 1/8" thick member not 6 3/4" and that 60% figure I gave is only "close" as my concern is at the support if the 12" beam is the only one being supported. Note, that I am not done yet (I am working through some iterations of different sizes for the new beam) and I also have to go back through to check for errors (I don't have anyone in the office to do that for me) so the figures I've given are not "on the nuts". The bolting is designed to transfer that load across the joint (the correct percentage of loads were used for the bolting). As of yet there is no dead load on the beam as the joists have not yet been installed so no shoring or jacking will be required at this time.

My main concern is more of a general question in nature. I'm asking (or trying to but not well) if I can bolt the new beam to "back to the existing" near the support with adequate bolting (or whatever) to transfer that 60% or 75%, or whatever it may be in the end that the new beam is carrying, with the 12" beam being the only beam supported. I haven't worked out the connection yet, but I don't want to detail additional support for the new beam if the existing beam is adequate in shear. Lets say the portion of the total load that the new beam carries is 8000 pounds. I would have to transfer 4000 pounds back to the existing beam, at or very near the support, if the existing beam is the only one supported (in this case a masonry wall). That 4000 pound transfer would be made with 4 or 5 bolts, whatever required, in a tight pattern near the support for the 12" beam. The 12" beam then transfers the entire reaction for the composite section to the support. Hope this all makes sense. I'll try to explain again later, if not.

But for now it is Friday evening and I am headed for the martini shaker.

thanks for the replies,

Joe


----- Original Message ----- From: "Scott Maxwell" <smaxwell(--nospam--at)engin.umich.edu>
To: "'seaint'" <seaint(--nospam--at)seaint.org>
Sent: Friday, June 02, 2006 6:00 PM
Subject: Re: GL beam strengthening


Joe:

As someone else hinted at, you need to make sure that your load sharing
percentages are determined by deformation/deflection compatibility.  It is
not clear from your post if the 60% to the new beam was determined from
relative strength or deflection compatibility, but by doing a quick
deflection capatibility calc I get that the new beam would take roughly
75% of the load.  My calc assumed that both beams were of the same glulam
grade (i.e. in theory the modulus of elasticity, E, would be the same).

Regards,

Scott
Adrian, MI


On Fri, 2 Jun 2006, Joe Grill wrote:

A client has installed a glue-lam beam of the incorrect size (too small).
The beam installed is a 6 ¾" x 12" GL. It is early enough in the project to
do a fix, but they don't want to remove and replace.  I have sized an
additional GL to be installed next to and bolted to the existing bm.  The
new beam is 16 ½" deep.  The original beam is bearing on top of a masonry
wall, therefore the new beam can't bear on top of the wall due to the deeper
section.  The original beam can take all the shear by itself, but just
barely. The new beam takes about 60% of the load. Bolting along the beam is
designed to transfer that 60% across the joint.  If I cut the new beam off
at the face of the wall can I provide bolting at the end of the new beam to
transfer its 60% back into the 12" deep beam?  Or, am I missing something?



This would be the easiest installation, then I don't have to design any
hangers at the wall.



Thanks,

Joe



Joseph R. Grill, P.E. (Structural)

Shephard - Wesnitzer, Inc.

Civil Engineering and Surveying







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