URM Wall

[joengineering]

Hello,

We are creating an opening on a wall. Alterations no the wall are greater than 10%. What are some retrofit options. This building is URM with wood framing. Two story building, the alterations (openings) are going to be done at the first floor. it is about a 60'x80' building.

JO

 

[KootK]

I'll assume that we're talking lateral here. Some options:

1) Estimate the lateral demand in the remaining structure to see if it works without modification.

2) Reinforce the remaining masonry with steel/FRP reinforcing etc.

3) Introduce and strategically locate new bracing, moment frames, or shear walls such that the strength and stiffness lost is[pre][/pre] effectively replaced.

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.

 

[SteelPE]

KootK has outlined pretty much everything that I would do as an engineer.

I usually make them add reinforcing in the cells as my jurisdiction does not allow URM. I am not familiar with how to design FRP but I am interested in learning more.

 

[joengineering]

I checked the existing wall using the California existing building code section A112, it did not work. If i would introduce a brace frame, this would have to be a special brace frame because it is seismic category D, or since its an existing building, can I use an ordinary brace frame?

Also, I would have a continuous ledger on the wall to drag my lateral loads into the frame correct? How would I anchor the ledger to the URM, any idas? I have never done URM walls, any Hilti fastner?

Thank you

JO

 

[KootK]

Rationally, a special braced frame wouldn't make any sense in this application. Special braced frames are designed to yield early in the seismic load history. In your situation, you need the brace to not yield ever. As soon as the brace yields, all subsequent load will transfer to the un-special masonry that you're trying to shield. How you work this to meet CA building requirements, I'm not exactly sure.

You would need a ledger collector. You could fasten it to the masonry with something like Hilti HIT-HY20 anchors which are intended for hollow block.

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]

Moment frame would be the same thing right? Any recommendations?

 

[KootK]

I would think that the same would be true of a moment frame. Moment frames are also difficult to make stiff enough to do the job next to block walls. The attached sketch shows a creative solution that a colleague of mine used for a new opening in a retail structure. Obviously, not every occupancy could tolerate something like this.

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.

 

[SAIL3]

besides the deflection of the moment frame/special frame @ the opening......I would suspect that the remaining URM wall itself would not survive a seismic event in CAT D.....

 

[joengineering]

I agree, but then again what would you try to use?