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RE: Glulam Roof Girders in a Tilt-Up

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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

 

-----Original Message-----
From: Nels Roselund, SE [mailto:njineer(--nospam--at)att.net]
Sent: Wednesday, October 29, 2003 8:48 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: Glulam Roof Girders in a Tilt-Up

 

Gerard,

 

Buy a Simpson strap and some nails and compare the hole sizes with the sizes of the recommended nails -- the nails will be loose in the holes.  The strap will carry no load until the nails are bearing tightly against the edges of the holes.  It is probable that initially, very few nails will be effectively located to transfer load from the wood beam to the strap.  Next compare AE of the straps with AE of the portion of the beam you want to reinforce.  Even if the tension load could be effectively shared with the strap, the strap's share would be minimal.

 

Bill's approach using post-tensioning, with or without Bob Powell, seems to be the right way to go.

 

Nels Roselund
Structural Engineer
South San Gabriel, CA
njineer(--nospam--at)att.net