Opening in Concrete Shear Wall

[Archie264]

Colleagues,

I have a situation where a sizable portion of an existing concrete shear wall was removed. It seems that someone wanted a doorway and simply removed the pesky concrete that was in the way. I suppose the most direct fix would be to dowel in rebar and replace the concrete but I just thought I'd check if any of you esteemed folks might have any creative ideas for remediation other than that? Thanks.

 

[xyyy]

Is it a new structure or existing one? Is the door or the opening still needed?

 

[JedClampett]

Yeah, and why repair it at all? Is the wall everstressed with the opening? My experience with concrete shear walls is that they're ususally (not always) overdesigned and usually (not always) dimensioned due to building size, not shear considerations.
I know it's easier to just repair the wall and claim "No harm, no foul", but if you can make it work, that should be your first approach.

 

[Archie264]

It's an existing structure. The tenant *wants* the door, whether he gets to keep it remains to be seen.

 

[xyyy]

My first approach will be check if it is working or not if there is that opening. If that does not work, then will try to retrofit it. maybe increase wall thickness or attach FRP or.... What kind of retrofit method will be depends on what will be inadequate.

 

[TDIengineer]

I would look at the the shear walls along that same line as your added opening. Study if adding this opening has much effect on the stifness of that line and whether it could have effected the lateral distribution of your rigid diaphragm (assuming you have one).

If in-plane shear is not an issue because there is plenty of solid wall along that line, then your only retrofit is to check out-of-plane.

Depending on the vertical bar spacing, you may still be able to justify the out-of-plane. If not, I like to add some C8 channels across the header and at the jambs, assuming the architect can deal with it.

If the doorway added is narrow, you normally can get the out-of-plane to figure by taking a "4t" tributary of wall thickness as your new jamb.
Last check, how is the lintel? How deep is it? 18" horizontal bar spacing? If the doorway is just a single door opening, and the lintel has any reasonable depth, it normally all figures ok.

Most building codes have provisions for when you have to upgrade the building depending on how much it was modified.

I believe there may be a 5% rule for a single element, 10% for the total change in mass...I would have to look it up.

And last, normally in-plane shear is not a problem for a concrete shear wall building and I doubt the opening caused problems with that unless the wall in question already has several narrow piers and not many long walls along that line. Not sure if you're in a high seismic zone or not.. If the wall is exterior, then wind may govern seismic for low seismic zone.

 

[Archie264]

Thanks folks. This will take closer examination. I appreciate the insight.

 

[msquared48]

The shear wall is everstressed, but perhaps not overstressed.

Mike McCann
MMC Engineering