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Re: GL beam strengthening

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Bill,
 
So, "Shoot Me" you say.  Please hand me your gun - you're way too conservative.  Just kidding.
 
Bob Powell offers post-tensioned beam designs.  This is a beam-truss solution that must be modeled and analyzed correctly to work.  I've done lots of these and I will be happy to consult with anyone who needs help with an existing beam problem.
 
Basic good structural mechanics and an understanding of beam stiffness must be applied to any of these solutions.  If it passes good sound engineering judgment and you can demonstrate this with justified calculations, then existing published articles on your solution are not necessary.
 
There are many considerations to this beam problem.  Stiffness of the steel and wood is one of them.  Shrinkage of the glu lam beam is a big factor that should dictate all of the bolting and end connection detailing.  My earlier idea for placing a 2nd beam below the 1st beam requires that the both beams bear on the bottom of the lower beam because the two beams will shrink over time and the bearing points will shift if they are both supported separately.
 
Dave Gaines
Pasadena, CA
gainesengr at earth link dot net
----- Original Message -----
From: Bill Allen
Sent: Saturday, June 03, 2006 9:59 AM
Subject: RE: GL beam strengthening

To all offering solutions to this problem:

 

  1. Does the method you provide have a documented (published) reference?
  2. Has your method passed the ultimate test, the test of time?
  3. Have there been any known failures using your method?
  4. Are there any other defensible references (tests, etc.) justifying your approach?

 

My goal in raising these questions is not to be critical, but to ensure readers are not encouraged to use a method that doesn?t have a well founded (and legally defensible) methodology. I guess I?m ?tainted? by my experience with Bob Powell who has been reinforcing Glu-Lam Beams for a kajillion years and has served as an expert witness on projects where the four points above weren?t applied. Sure, Bob has a proprietary reinforcement system, but that shouldn?t discount his experience. There are other systems which I am sure are as well founded and would satisfy the four points above, so I?m not trying to sell Bob Powell, if he?s even working anymore. He may be retired by now.

 

All I know is that steel and wood don?t work very well together (certainly not as well as a cover plate welded to the flange of a steel beam) and I?m particularly concerned about ?flitch beams? which do not span to a support and are mechanically connected to the existing beam by bolts installed in holes drilled in wood. Personally, whenever I?ve had a situation like this, I?ve either used a ?Bob Powell Solution? (or equal) or designed the new ?system? such that the existing beam merely acts as a delivery mechanism to transfer the load from the roof or floor to the new beams. At that point the new beams take the load to the support and have to be connected accordingly. If the existing beam and new beam(s) are all supported, then distributing the load based on stiffness (including the existing beam) makes sense.

 

This topic has come up before and the general consensus has been that I?m conservative in addressing this problem. So shoot me.

 

My two cents.

 

T. William (Bill) Allen, S.E.

ALLEN DESIGNS

Consulting Structural Engineers
 
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