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RE: Transfer force of large tie beam

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A slab on grade should be allowed to shrink independently of the contraints of a bond beam.  The old Butler foundation manual written by Fisher showed the detail of the SOG free of the bond beam.  I feel that it is a good detail.  But it is a servicability issue.  I just don't like cracks in the slab if I can avoid them. 

Harold Sprague

From: jvhannah(--nospam--at)
To: seaint(--nospam--at)
Subject: Re: Transfer force of large tie beam
Date: Mon, 12 Nov 2007 22:52:40 -0600

To: Harold Sprague or anybody else that has information to add,
In your response and in Butler's foundation manual, you suggest a space between the slab on grafe and the tie beam and you mention not allowing the bond beam to be bond ed to the slab on grade.  In a word why?  I am looking for additional info on why they should not be done in one placement of concrete.  The people who design our slab and bond beams usually just show them as one placement of concrete.
Thanks for your assistance.
Jim Hannah
----- Original Message -----
Sent: Monday, November 12, 2007 9:43 PM
Subject: RE: Transfer force of large tie beam

Tie beams are very common and the most cost effective choice once you have exceeded the limit of a hair pin in PEMB's.  It is fairly common to use 4 bars in the tie beam.  Provide a space between the slab on grade and the tie beam itself.  The tie beam is best not to be bonded to the slab on grade.  I would suggest that you use mechanical couplers in lieu of lap splices.  You can place ties at about 18" o.c. just to hold the tie beam bars in place.

I would not worry too much about the stretch of the bar.  Getting 40 grade bars would be more problematic than just using 60 grade bars.  Keep in mind that this is an industry that commonly uses H/40 for a lateral drift limit of the frame. 

Harold Sprague

From: seaint04(--nospam--at)
To: seaint(--nospam--at)
Subject: Transfer force of large tie beam
Date: Sun, 11 Nov 2007 22:00:04 -0600

I have a pre-engineered metal building with some large tie beam forces.  They are around 60 kips.  The reason they are so high is a 40 psf roof snow load with a 13 feet eave height.  The clear span of the rigid frame is 80 feet.  For smaller loads I typically wrap the anchor bolts with a ‘U’ shaped rebar and use mechanical ties for the rebar of the tie beam.  With loads this high I was wondering if I should be using a better mechanism for transferring the forces.  What other options might I consider to transfer the thrust force from the rigid frame to the tie beam?  I’m also wondering about stretching the tie bar itself.  This is a metal frame with metal siding.  What kind of limit should I use as a maximum stretch of the bars?  Should I consider using lower strength steel and a larger area in order to reduce the delta from the PL/AE stretch?






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