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RE: PT bm to Shearwall

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Will,
Your are smart to be afraid of restraint cracks in PT. Creep and shrinkage will impart an incredible force, and break almost any connection. It may be too late to effect major changes, but all lateral forces should be resisted with shear walls or other lateral force resisting system located near the center of the structure. This allows the floor to creep and shrink toward the center, and your imposed lateral forces are resisted by shear walls that remain in tact. Keep in mind that creep shortening may be greater than shrinkage.

Specifically to address your questions:
1. I don't know what your exact layout is, but you could cast columns integrally into the wall to maintain the integrity of the shear wall, and you could design your column to beam connection as simple and allow for differential movement.

2. You can design a beam pocket with the beam on a bearing pad, and allow sufficient space around the beam to accommodate differential lateral movement.

If you have not discussed this with an experienced PT contractor, you should. Tell him your concerns and he will probably have a more effective solution.

Regards,
Harold Sprague


From: "Will H" <haynewp(--nospam--at)hotmail.com>
Reply-To: <seaint(--nospam--at)seaint.org>
To: seaint(--nospam--at)seaint.org
Subject: PT bm to Shearwall
Date: Fri, 30 Jul 2004 13:53:17 -0400

I have a 7 story parking garage with a shearwall along the ramp. The ramp has a 60 degree bend about mid way up. My shearwall is along this ramp at the interior.

I was planning on making the connection from the PT beams with a corbel (perpendicular to wall) and along the slab parallel to the shearwall with corbels due my fear of restraint cracks in the slab. For a long thick wall like this, I have been told this is the best way to avoid restraint cracks. I am going to require a welded angle from the slab to the wall (about 4' o.c.) at the last stages of the project to transfer the lateral shear, in hopes that most of the shrinkage will be gone by then.

Anyway, along the first part of this ramp before it bends, there is hardly any opposing moment from the opposite side of the wall to counteract the moment from the ramp beams resting on the corbel.

1) I thought about not using the corbels in this area and putting columns in the wall with a movement joint on either side of the column, but then my shearwall is broken up into a couple of smaller segments instead of one 53' long piece. I really need this strip of shear wall for it's lateral component in one direction.

2) I considered placing the beams on the wall itself to get the eccentricity to a minimum. This way my wall stays intact and the moment is manageable. However, I am worried about restraint from the beam pocket not allowing the beam to shrink.

Any suggestions please?


Will


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