New openings in a CMU wall

[RVSWA]

I have a client with a 2 story commercial building constructed of CMU walls with wood floor and wood roof trusses. The overall dimensions are roughly 40' by 60'. Currently the windows along the front are very narrow and tall and spaced out nicely. It works great for a night club but they would like to turn it into retail space and open up the windows. I am seismic design category D.

I am comfortable with addressing the vertical loads as well as determining the viability of the lateral resistance (it will either work or it won't).

What I am trying to get my mind around is the reinforcement around the new openings. I don't necessarily like the idea of plates and angles because I'm not sure that bolts are the best way to transfer loads intended to produce ductility. Has anyone used the high strength metal weave that is epoxy applied to the wall? Would both sides be necessary?
Any ideas or advice is welcome.

 

[abusementpark]

We always call for them to put pinch beams (usually a channel with thru-bolts for temporary shoring) at the top of the new opening before removing any block to secure the block above the opening when they are removing. Then, they remove the block as required up to the opening and remove block above the pinch beam at a 45 degree angle until the two line of removal intersection.

So essentially the initial removal looks like this.

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We feel that if the block is removed in this fashion, then all the block load from above can be transmitted to the sides and the pinch beam can be removed.

Then we make them put a bond beam at the top the opening of the opening and replace the removed block above once the bond beam is secure.

Clear as mud???

 

[Lion06]

abusementpark-
Is that the entire length of the opening? That wouldn't work well with a 25' opening, would it? You would need 12.5' of wall above the opening, right?

Why not try needle beam shoring.

As far the end product, why not have a WF lintel above the opening and grout and reinforce the end cells of the wall jambs as required.

 

[abusementpark]

StructuralEIT,

Yes, it the entire length of the opening. I see your point, but we have never had an architect who wanted an opening that large on a load-bearing wall.

Can you explain this needle beam shoring?

 

[Lion06]

Here is my best pass at a description. Say you have a masonry wall that you need to add a 15' opening to. The top of the opening is 4' below the bottom of the second floor framing. You would knock out individual blocks at roughly 4' o.c. You would then place the "needle beams" through the knocked out blocks (typically W8's)- one end of the beam inside the building and one end outside. Then you would shore these needle beams to ground. I picked the 4' dimension, but it is really dependent on what it needs to be to allow the masonry above to arch to the needle beams. I got 4' assuming a W16 lintel and the W8 needle beams. This leave 24" of masonry between the top of the needle beam and the underside of the second floor framing which means the needle beams can be spaced at 48" o.c. to allow arching of the masonry to the needle beams.

 

[msquared48]

If these "needle beams" were placed just under the first horizontal bond beam above the new opening, then the existing bond beam can serve as a lintel beam during construction. A new lintel of either CMU or a steel channel or tube frame can be inserted in the opening and then the CMU replaced between the new beam and the existing bond beam. No worries...

Mike McCann
MMC Engineering

 

[RVSWA]

I will have a testing agency investigate the wall and if there is a viable bond beam between my floor bearing and top of opening then I am going to utilize it as a temporary lintel during construction if the span and loads would allow. If not, I will suggest a pinch beam because the loads aren't extreme. I think that StructuralEIT's needle beams are a great application if my loads are too big for the pinch beam or an absence of a good bond beam.

The architect has yet to send me plans, and for now, my mind is set for the worst, it may not be that bad. During the initial site visit I made it abundantly clear that modification of the CMU walls was going to be a challenge. I always tell them that it is like a scratch lottery ticket and I have the quarter. Their proposal will either work or it won't.

The greatest problem I still see is the vertical reinforcement that may not be present at the edge of their proposed opening and what can I put in there to provide the necessary ductility. I appreciate your thoughts on this...

 

[hokie66]

You can install missing vertical bars in block walls in cores that are empty by sawing out the face shell, inserting the bars, forming the face, and grouting. Of course, if the wall is grouted solid, this is not an option, and bond beams would also make it difficult.

 

[Lion06]

there may or may not be a bong beam in your wall. These needle beams work especially well for old rubble stone walls that you know for certain doesn't have a bond beam located anywhere in it.

 

[Lion06]

lol, sorry, I meant "bond beam" not "bong beam"!!

 

[RVSWA]

StrucutralEIT,
You should be careful, I've noticed how well thought out your posts are and I'd have to say that when you speak people listen... If you go off suggesting "bong" beams, then who knows were we'll find ourselves. All in good fun, thanks everyone for your thoughts.