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3" DIAMETER HOLES IN CMU SHEAR WALLS

3" DIAMETER HOLES IN CMU SHEAR WALLS

(OP)
Our client wants to be able to drill 3" diameter holes @12" o.c 12" down from the rigid roof diaphragm. What's the best way to analyze this problem?  It's a single story building in a high seismic category E?
 
 

RE: 3" DIAMETER HOLES IN CMU SHEAR WALLS

(OP)
I apologize if my question seems vague.  Let me add to this.  I'm looking to check the effect on the in plane shear on the walls due to these added holes.  Normally for a window or door opening, one would create wall regions, distribute the seismic shear based upon wall stiffness, because its a rigid rood diaphragm, etc..

Can someone tell me how to look at this problem?  Do I need to make regions around each hole opening or should I take the out-to-out dimensions of all the openings and model a single opening to represent them?

thanks

vvs

RE: 3" DIAMETER HOLES IN CMU SHEAR WALLS

Can you fill the block below the holes (or use a 'U' block), fill the cores of the block that you are drilling the holes through, and use a masonry 'U' block for the course above the holes?  With suitable spacing, it shouldn't matter where you drill the holes...

Dik

RE: 3" DIAMETER HOLES IN CMU SHEAR WALLS

Depending on how often you grout the walls, you could be lowering the capacity of the walls by as much as 25%, creating a line of shear failure - similar to instlling one line of bolts in a wood beam instad of two or more.  Staggering the holes vertically could be an option to minimize this.

Also, at 12" down, I trust that you are not putting the holes through the bond beam at the edge of the roof diaphragm with the risk of cutting any chord steel.

Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
 

RE: 3" DIAMETER HOLES IN CMU SHEAR WALLS

(OP)
Dik,  i like your suggestion.  thanks. because the 3" diameter holes are continuously spaced at 12" o.c. and because this is designed as a special reinforced cmu shear wall, we have to provide a continuous bond beam below the holes. (see SK-1)

Mike, at 12" down was exactly to prevent what you've mentioned (not putting holes through the bond beam).  One other concern I have is to prevent the dowels reinforcement from being cut.  (see dowel detail -  SK-2).  What can I do to prevent this from happening?

thank you both for your input and confirmation.


vvs

RE: 3" DIAMETER HOLES IN CMU SHEAR WALLS

vvs9770 -

Nothing wrong with an additional bond beam below the small cored holes if you can make is effective considering the amount of grout and rebar that was intentionally placed or just dumped into the unreinforced cores. - A common problem that occurs without initial regard to the masonry units used/specified and the construction inspection.

If it was "belt and suspenders" project it will work. The wall is the structural element for the building itself and you can go crazy trying to micro analyze what is in place and how to redesign it. The arbitrary excessive grouting could be a problem regarding placement and application if a second bond beam was actually required.

Poke a few holes in the wall to see what is there before going too far.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

RE: 3" DIAMETER HOLES IN CMU SHEAR WALLS

SK-2 does not mention the spacing of the wall vertical steel that I can see.  If you do not know it, you may have to sound test for grouted vertical cells, locate the rebar (rather than assume it is in the middle of the cell, and steer clear of the vertical steel.  This may mean a 3" variation in placement in a few places.

Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
 

RE: 3" DIAMETER HOLES IN CMU SHEAR WALLS

vvs9770 -

Also, check on the amount of excess grout that can affect your remediation process, since that can affect the methods and placement. You never know whether you are dealing with 2,3 or 1 core block or if they are eccentric for ideal vertical steel/grout alignment.

Without knowing the project location and age, it is difficult to give good recommendations on grouting.

If you are in the Eastern U.S, the block are probably the 2 core "clunkers" with flush ends and reasonable core alignment and minimal web alignment that do not allow good grouting. Elsewhere, there are many of variations that are made for good initial construction.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

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