Cut Opening in Existing Concrete Shear Wall 1

[1SEngineer]

I have to determine if a double man door opening (6'-0" x 6'-8") can be cut into an existing, 19 story concrete shear wall. The opening would be at the 2nd floor level.

I plan to use a FE analysis to obtain the stresses around the opening.

Can anyone offer any suggestions about doing this. Specifically, what to install to replace the removed concrete. A Steel Frame?

Thanks

 

[csd72]

Is it in a high seismic zone, This will ahve a llarge bearing on what you have to do.

csd

 

[1SEngineer]

No. Wind Loads Only.

 

[csd72]

You may find that it is still adequate without additional reinforcing.

Check bending, shear, and compression on the wall. You can use finite element, but I would do it by hand as it is quicker.

The bending stresses have two components, one is the stress calculated when you treat the whole thing as a beam, and the other is the bending stress at the top and bottom of the opening due to the shear.

The second stress is easy to calculate. First divide the total shear in proportion to the stiffness of each section of wall. Then apply as two opposing loads at the top and bottom of the section. Taking the two sections on either side as fixed bottom and roller fixed top then you get moments top and bottom from the shear force.

Then if 0.6*Axial DL + tension from the 2 moments results in a compressive force then the two sides will not crack under the wind load.

You also need to check the capacity to arch over the opening under service loads.

csd

 

[1SEngineer]

What if the jambs are in tension? How would one handle this? I would consider installing a steel "box" frame around the new opening to replace the removed portion of concrete.

Any comments/suggestions?

Thanks for your help thus far.

 

[1SEngineer]

Another issue is the decrease in rigidity of the shear wall. The removal of a section would lessen the rigidity in that wall, and force that loss in rigidity to be transfered into the other shear walls. This would then place new, higher loads onto those walls.

 

[haynewp]

Yes you could put in HSS members, plates, etc. bolted to the face of the inside of the wall to reinforce the area as needed for gravity and tension/compression from lateral. And develop the new steel framing into the above unmodified wall area with the fastening. I have done this several times with tilt panels.

It may be a little more complicated figuring the reinforcing if you need it for add'l shear capacity, but normally I expect you wouldn't. And yes you would technically have a less rigid wall now because of the new opening.