Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

RE: PT bm to Shearwall

[Subject Prev][Subject Next][Thread Prev][Thread Next]
I would strongly advise you not to lock in the stariwells at the corners of the structure. The worst rehab that I have ever done used the corner stair wells as shear walls.

Before you commit to this, calculate the shrinkage and creep slab deformations at the corners. If that is not enough, calculate the shrinkage and growth in the slab at the corners just due to thermal cycling. You can not design the shear walls and slabs to resist that much restraint force, and the shear walls can not deflect that much without significant cracking. That will allow moisture to penetrate, and you will be fighting corrosion and spalling forever.

On the structure I was tasked with repairing, we had to cut the stair towers free, add new gravity support for the slabs at the stair walls, add new shear walls near the center of the structure, and repair all of the damage in the walls. It was not a pretty picture. Gravity only columns should also be assessed to see if they can accommodate the creep, shrinkage, and thermal cycling due to the slab. Columns can generally accommodate the movement unless they are very short or cast monolythically into a wall.

I have just done way to many repairs where this was the culprit of an otherwise good design.

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: RE: PT bm to Shearwall
Date: Sat, 31 Jul 2004 09:39:44 -0400

Thank you Harold, I will call a contractor to discuss.

I am leaning towards the beam pocket if it is not too much of a hassle. I am thinking about using a 1/2" gap around the top and sides of the beam with bond breaker and felt paper at the bottom of the beam.

I think I still want to use the corbel to support the slab on the shearwall at each side of the beam, though I am somewhat concerned my shear transfer angles will not get put in at the last stages of the project and I will get a call about cracking. Other than adding add'l rebar at the slab next to the wall, I'm not sure what better I can do to limit any future cracking, from creep etc.

The other lateral elements I have are the stairwells and unfortunately, they want to have them in each corner of the structure.



From: "Harold Sprague" <spraguehope(--nospam--at)hotmail.com>
Reply-To: <seaint(--nospam--at)seaint.org>
To: seaint(--nospam--at)seaint.org
Subject: RE: PT bm to Shearwall
Date: Fri, 30 Jul 2004 19:14:06 +0000

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


_________________________________________________________________
Don?t just search. Find. Check out the new MSN Search! http://search.msn.click-url.com/go/onm00200636ave/direct/01/


******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
* * This email was sent to you via Structural Engineers * Association of Southern California (SEAOSC) server. To * subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
* Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you * send to the list is public domain and may be re-posted * without your permission. Make sure you visit our web * site at: http://www.seaint.org ******* ****** ****** ****** ******* ****** ****** ********

_________________________________________________________________
Express yourself instantly with MSN Messenger! Download today - it's FREE! http://messenger.msn.click-url.com/go/onm00200471ave/direct/01/


******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
* * This email was sent to you via Structural Engineers * Association of Southern California (SEAOSC) server. To * subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
* Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you * send to the list is public domain and may be re-posted * without your permission. Make sure you visit our web * site at: http://www.seaint.org ******* ****** ****** ****** ******* ****** ****** ********

_________________________________________________________________
Express yourself instantly with MSN Messenger! Download today - it's FREE! http://messenger.msn.click-url.com/go/onm00200471ave/direct/01/


******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
* * This email was sent to you via Structural Engineers * Association of Southern California (SEAOSC) server. To * subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
* Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you * send to the list is public domain and may be re-posted * without your permission. Make sure you visit our web * site at: http://www.seaint.org ******* ****** ****** ****** ******* ****** ****** ********