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New opening in cmu wall

New opening in cmu wall

New opening in cmu wall

(OP)
Hello all,

If they are planning to make an opening in a cmu wall what is the retrofit design approach for this? Can anyone give me an idea on how I should approach this design? I am quite lost.

JO

RE: New opening in cmu wall

How big is the opening?

How tall is the wall?

Need a little more information here.

Just finished a retrofit today.

Mike McCann, PE, SE (WA)


RE: New opening in cmu wall

If the numbers work and the aesthetics are palatable, most gravitate towards horizontal channels fastened above the opening prior to cutting the opening. Some form of wind column may also need to be developed at the sides of the opening as well.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: New opening in cmu wall

If the opening is small, as in a mandoor, you may not need any special reinforcing at all. It depends on what condition you have as to what you do.

Mike McCann, PE, SE (WA)


RE: New opening in cmu wall

(OP)
2 story building, each story is 12' high, the opening at second floor are 9' and 3', 8 ft high. The total length will of the wall is about 30'.

The channel above the opening is to take care of the gravity loads correct, essentially a lintel? is that all i need? how about to analyze this wall as a shear wall?

Thank You

JO

RE: New opening in cmu wall

(OP)
It is a door and a window opening 9' by 8' or so high

RE: New opening in cmu wall

Your 30' shear wall probably turns into some shorter shear wall segments. It's pretty tough to retain the full 30' length as some kind of portal frame.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: New opening in cmu wall

Yep. You will probably need internal steel tube wind columns and a steel header.

Mike McCann, PE, SE (WA)


RE: New opening in cmu wall

(OP)
Excuse my lack of knowledge, but what is a steel tube wind column?

JO

RE: New opening in cmu wall

I just completed a project like this, this past week. Added 4-18' wide openings to an existing wall. Single story building 17'-4" tall. Luckily the owner wanted to shore the roof and demo a majority of the wall. I rand wind and seismic calculations and designed the wall for out of plain bending and in plain shear. I was also lucky to have 12" cmu because the openings were so large.

Basically you need to make sure the wall works for all the loads it will see.... Dead, live, snow, wind and seismic.... If something doesn't work you need to reinforce it so it does.

RE: New opening in cmu wall

(OP)
Does any one have any details?

JO

RE: New opening in cmu wall

@Kootk;

What are you fastening the channels with?

Thanks

RE: New opening in cmu wall

Usually through bolts if I plan to have channels on both faces. Hilti HIT-HY20 if it's a one sided application and I'm not confident of hitting grouted cells. I reviewed details by another consultant where they asked for the channels to be pre-deflected downwards prior to fastening. It's clever and I get the spirit of it but onsite quality control of that seems like it would be a nightmare. In my experience, mason's pay about as much attention to the nuances of my drawings as wood framers do.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: New opening in cmu wall

@Kootk;
Where are you getting design values for thru bolts?
Pre-deflected channels - yea, that's gonna happen.

RE: New opening in cmu wall

Essentially just masonry compressive bearing stress over the bolt bearing area. Occasionally, I'll have the affected cells grouted prior to installing the channels to improve matters.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: New opening in cmu wall

(OP)
So for lateral, I have to check that the wall opening doesnt affect the capacity of the wall, I have read something about that it cannot affect the DCR for more than 10%.

Also check gravity and out of plane? This will be taken by the steel frame?

Also, what are wind columns mentioned above?

JO

RE: New opening in cmu wall

For lateral, you simply have to find some way to demonstrate sufficiency. One strategy is to estimate demand and capacity. Another is to demonstrate that your modification won't reduce the lateral capacity appreciably (10% business).

Definitely check gravity loads and out of plane lateral loads. If those loads can be handled by the existing masonry, then utilizing the existing masonry will be your cheapest alternative. If the masonry can't handle it, then the steel frame will need to do the job.

Wind columns are simply columns that support the girts / horizontally spanning walls that collect the wind/seismic load and deliver it to those columns. Again, they can be the masonry if the masonry works. Otherwise, they might be steel columns installed behind or within the masonry walls.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: New opening in cmu wall

(OP)
If the columns are anchored to the wall, they will act composite correct? how do i approach that ?

RE: New opening in cmu wall

There's potential for composite action but I don't normally attempt to take advantage of it.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: New opening in cmu wall

Kootk said, "Essentially just masonry compressive bearing stress over the bolt bearing area. Occasionally, I'll have the affected cells grouted prior to installing the channels to improve matters."

Where did you get this information? I recently did a project where I wanted to use thru bolts but could not find any source anywhere that provided any information for thru bolt capacities in hollow CMU.
I ended up using HY70 epoxy. The contractor was not happy.

FWIW, if you are going to do it this way, you need to specify that they use rotation only mode if they use a hammerdrill. Otherwise, the back of the face shell gets blown out and reduces the bearing area.

RE: New opening in cmu wall

I've never seen anything specific in print XR250. It's a hand me down scheme developed well before my time. In the finished state, stitch plates are welded between the bottom flanges of the channels making the bolts essentially just LTB control.

The rotation only mode stuff is a fine suggestion. I'll roll it into my next spec.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: New opening in cmu wall

Another thing to add to this thread is that your channel/tube (lintel) will experience bi-axle bending (i.e. not just gravity). I'm in LA so I usually check out-of-plane seismic load from the wall that the channel is supporting which is why I eventually use steel tubes, depending on the width of opening. As for a detail, my framing around the opening is in the shape of an "H". My steel jambs go up passed the opening to about a foot below the roof. Then my lintel will be welded to both jambs and anchored in epoxy to the masonry a certain spacing. As for lateral, the DCR changing 10% is in the California Building Code. I don't know if its the same everywhere else. For retrofitting masonry shear walls, I specify Fiber Reinforced Polymers (FRP). If anyone has another way, I am open to learning about it.

RE: New opening in cmu wall

(OP)
How do you calc the capacity of something like the FRP with the URM, or is it something you just call out?

RE: New opening in cmu wall

For FRP we just call out either an equivalent reinforcement ("FRP equivalent to #4 @ 16"O.C."); so we can just design the new layout of walls with conventional reinforcement. Or you can do the change in capacity and call out the difference that the FRP will have to make up (e.g. your existing wall has a capacity of 5 klf and the new wall has a capacity of 2 klf, you would call out the FRP strength to be 3 klf). The latter is probably the most difficult and time consuming. I spoke to the FRP designers/manufacturers and they said I can just call out equivalent reinforcement. After I found that out, I started to do it that way, because it's easier (probably more conservative). However, I spoke to an old professor and he mentioned that FRP may be as strong as the steel reinforcement, but it is not as ductile, which led me to question using it for masonry shear walls and the reason I am looking for alternative ways to retrofit masonry.

RE: New opening in cmu wall

(OP)
Ah okay, I am not so familiar with FRP. This is actually a URM wall, my thinking was to have a brace frame. Collect the seismic load with a steel ledger, but like you said maybe the URM fails if I do not do this correctly. I do not know if should have some steel X bracing anchors to the URM to give it more strength.

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