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

 

[KootK]

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.

 

[chamokinawan]

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.

 

[joengineering]

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

 

[chamokinawan]

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.

 

[joengineering]

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.