Wide Opening in Existing CMU Wall

[enigma2]

I have a new structure abutting a non-loadbearing 12" CMU wall in an existing structure. The existing wall is 50'-0 wide and 24'-0 tall and the tenants want to put an opening that is 36'-0 wide and 18'-0 tall in the wall to allow pass thru from the existing structure to the new structure.

I plan to use a W24 to span the opening. I will consider it laterally unbraced and also maintain a L/600 defelction criteria.

The existing wall was unreinforced, except at piers at the jambs of an overhead door that will be removed to make way for the new wider opening.

What are my options for the masonry "piers" to transfer the shear load from the lintel and the moment due to a 5 psf lateral load? I bar or two in the cell adjacent to the opening won't cut it. Do I need to anchor a channel or tube to the jamb to be able to transfer the load? I don't see conditions like this often and don't know what is common.

 

[archeng59]

Is it possible to just remove the CMU wall since it is not load bearing anyway? Seems like alot of work to save what little of the wall remains. Replace the CMU wall with cold-formed metal wall?

 

[enigma2]

Removing the wall was the original thought but with an odd high/low condition, an expansion joint between the two structures and some other issues, this was deemed the lesser of two evils.

 

[msquared48]

Possibly a fire wall too...

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[dhengr]

Put the W24 header as high as you can to lessen the conc. blk. loading on it, and to support the exp. jnt. and roof elev. differences, and just use light furring below it to whatever opening height you want. As part of the wall removal, you could carefully open up the cores of the adjacent blk. wall and fill them along with new reinforced jambs/piers which the header is tied into. You really have to show a detail of all that’s going on up there to make more sense of it.

 

[JAE]

I would suggest the following:

1. Definitely use some type of steel framing at the opening jambs - such as steel channels bolted through the wall on either side of the opening - or a tube column directly under the beam. Don't rely on the masonry to support so much load.

2. Check the newly concentrated load on the bottoms of each jamb area as the existing footings may not be adequate (probably won't be adequate).

3. Despite L/600 - which is almost 3/4" - you might want to limit the deflection even more as 3/4" is quite a lot and cracking will most likely occur.

4. There is still a code requirement for 5 psf laterally on interior walls - don't forget that.

5. Based on the new steel jambs of item 1 above, and any lateral load and lateral stability of the whole assembly, consider running the vertical jamb steel all the way to the roof to provide a lateral load path to the floor and roof diaphragms.

 

[DST148]

@enigma2: If you are stuck with masonry, then the deflection of the lintel will have to be lesser of L/600 or 0.3 inches. If possible, this new lintel may be supported laterally at ends and along the span, say @ 4feet to 6feet, by providing knee-braces(kickers) tied to the existing roof.

 

[JAE]

DST148 - the 0.3" limit was (I think) removed from the latest MSJC code. I would still keep the total deflection in mind though so your reference to it is good.

 

[DST148]

@JAE - Thank you for correction. I have ACI 530-05 and that is what I was referring to.