New opening in cmu wall 1

[joengineering]

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

 

[msquared48]

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)

 

[KootK]

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.

 

[msquared48]

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)

 

[joengineering]

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

 

[joengineering]

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

 

[KootK]

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.

 

[msquared48]

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

Mike McCann, PE, SE (WA)

 

[joengineering]

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

JO

 

[SteelPE]

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.

 

[joengineering]

Does any one have any details?

JO

 

[XR250]

@Kootk;

What are you fastening the channels with?

Thanks

 

[KootK]

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.

 

[XR250]

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

 

[KootK]

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.

 

[joengineering]

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

 

[KootK]

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.

 

[joengineering]

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

 

[KootK]

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.

 

[XR250]

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.