cracked cmu walls

[seny]

I am working on renovation of 11 stories building – purely reinforced cmu walls & rc plank. Condition of walls is bad – on the some locations cracks are 1”.
Mainly occurred at shear walls around stairs cores (stepped shear cracks) and on the outside corners (vertical cracks between adjacent perpendicular walls).
I use Sika products, including fabric, to repair wall (sealing of cracks, low pressure grouting & reinforcing by two sides surface fabric). For corners I am going to provide corner L-shaped bars every (every other) course along w/ procedure explained above.
For some reason I can not work from outside the building.
I’ll appreciate any inputs (opinions, objections, advises…) on this matter.

Thanks in advance

 

[msquared48]

Were these cracks due to a seismic event, settlement of the foundation, or both?

Or...Is the 1" gap due to mortar degeneration? As it is inside, I can't see how this would happen though.

With the cracks that large, I would be seriously concerned about the lateral slippage of the horizontal reinforcing and subsequent lack of bonsd strength, particularly at the bond beams.

How old is this building? Is it old enough to have used K-Web for the bond beam reinforcing instead of actual mortar filled bond beams?

Mike McCann
MMC Engineering

 

[seny]

Building is about 50 years old.
The reasons of cracks are wind & settlement & poor performance during construction.
No bond beams, no regular vertical reinforcement...
Thanks for respond.

 

[csd72]

Could you bypass the shear walls entirely and provide metal straps (say 3" by 3/8" or whatever is required) as cross bracing connected to the frame and placed along the inside of the wall? This can then be finished over with a drywall.

 

[seny]

If you meant strengthening of walls by connected diagonal steel straps – I’m getting similar, if not better result, using surfaces coverage by Sika fabric.
Thank you

 

[msquared48]

If you can't work on two sides of the building, how are you going to install the fabric on both sides?

This does not seem like a workable solution structurally unless the fabric can serve as a tension element on both sides if the wall to resist the wind/seismic forces normal to the wall.

If the walls are ungrouted with no bond beams, why not install vertical rebar into the ungrouted cells through the parapet and/or roof structure, then grout the vertical cells?

Mike McCann
MMC Engineering

 

[seny]

Stepped shear cracks are on the interior walls only.
That is where I’m using Sika fabric on the both sides.
Fabric is perfectly working for tension support.
Condition w/ solidly grouted cmu and fabric gives enough good capacity for shear resistance – no need to provide vertical reinforcement in addition.
The main concern is how in good way repair outside corners to restore integrity of connection between adjacent walls.
Thanks