openings in CMU wall ... a lot

[cmrdata]

I have an interior non-load bearing CMU wall with just enough reiforcings to satisfy the minimum code requirement.
MEP trades came in and put a bunch of openings through it without checking with us first. Some of them are clustered together with only about 3 to 4 inches of masonry wall left in between.
How does one evaluate such situation to say if it is acceptable or not? based on what guidelines/codes/etc.?
What is the appropriate remedy method?
Thanks in advance.

 

[KootK]

Mostly judgement. You might just have one big hole now. If you post a sketch of your situation, I'll be happy to give you my thoughts.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[cmrdata]

That's what I'm afraid of, KootK, I suspect this is more of a judgement call thing instead of hard science.
Attached is a rough sketches with the blue circles representing penetrations.
Again, to what degree do we say it is acceptable? And if not, what can we do about it?
Thank you.

 

[EngineeringEric]

Love those mechanical guys and blowing holes in everything. Perfect example of trades that need a sawzall (or invented)

I would be concerned with the lack of a head over some of those. you may want to add an angle (leg up) on both sides into a grout joint to span that. know that the cmu arches, assuming your drawings is to scale. Since it isn't load bearing, i am going to guess it isn't lateral either?? I second kootk that it is judgement and i am always curious what others have to say.

I just had a job where i had vert. bars at 48" o.c. and guess who added crawlspace vents at 48" o.c. and happened to cut nearly every rebar possible!! a little worse than yours but similar, Mine had to be repaired.

 

[KootK]

I think you'll be okay here. Your wall is actually pretty robust. I would have expected rebar at 48" in this kind of situation. Got horizontal bond beams at some regular spacing?

Some options:

1) maybe you can verify that there's one solid grouted core between the two primary groups. If so, at 5 PSF interior wind, you may well retain enough wall flexural capacity.

2) If you've got bond beams above and below, you could treat it like a ribbon window. That might also be your steel reinforcement strategy if you have to go that way.

3) if you turn the wall horizontally in your mind and think of it as a shitty, weightless slab loaded with 5psf, it doesn't seem so bad. If your comfortable with FEM and have the tools to do it efficiently, that might be an option. I know, this sounds a little ridiculous. I've got a masonry / FEM goddess in my office that could do this in 30 min.

Thanks for the sketch.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[SteelPE]

Interior non-load bearing wall with grout at 24" o.c. Seems like a lot to me..... But then against, I don't know your project requirements.

 

[CELinOttawa]

Never acceptable. I would send a bill for retainer for services to the Mech sub, and demand payment before I put pen to paper to check anything. Otherwise you're simply inheriting someone else's problem and the people responsible will never learn.

Failing payment by the responsible party or the owner, this is simply a "make good existing structure" moment, or a complete write off of any responsibility in writing.

Do not guess; Analyse. This is a simple question of strength and tolerances. What is the strength of the wall, and what does your code require? Treat this as new work, period.

As a profession we are quickly becoming a joke because trades and other professionals see us as push over. Be the exception and do the right thing: Stand your ground. Not your fault, but you're happy to help for the fair price of the work.

 

[hokie66]

I agree with CEL, but in new work, this is a failure of coordination. The architect or construction manager have a duty to inform the consultants of this type of thing. It may not be the Mechanical Contractor's fault. It could even be the structural engineer's fault if he did not review plans given to him.

 

[concretemasonry]

It is a little more than strength since the code has requirements for minimum reinforcement.

Any desired openings after the fact, must be located to avoid the grouted space where the rebar is, irregardless of the calculated "stress" in the non-bearing wall. This would require a location that does not cut any rebar. If the holes are as nice, pretty and neat as the drawing, the must be relocated to allow a continuity of the wall structure.

This is based on the fact that masonry walls are considered as a unit and the essential continuity. If the small openings are neat cores without cutting rebars, the essential continuity can be preserved because of the stiffness of the wall. Grouting in steel sleeves might help with the location of the penetrations and allow some flexibility for the mechanical contractor.

Dick

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

 

[haynewp]

That's an interesting perspective. I feel like structural has become an afterthought at the multi-discipline company I work at and I get the same attitude from architects and contractors that they can do whatever they want, and push structural to make it work anyway. As if we are always conservative to begin with and if we refuse to give in to their pressure, they bring up finding another structural who will let them do whatever they want and get us off the job.

 

[CELinOttawa]

Hokie66 is, of course, correct... I did presume that this wasn't YOUR fault, OP.

Barring it being your fault (be honest with yourself here) my advice stands. If it is your fault, calling your insurer and then openly admitting this is much easier in the long run, and EVERYONE respects the few people who actually stand up these days and say mea culpa. I haven't had to do this myself, but I sincerely hope I will have the integrity and class to do so should circumstances ever demand.

 

[cmrdata]

Looks like this question touches a nerve, especially those of my fellow structural engineers who have too often called to solve the problem created by other careless trades... situation normal.

I'd like to particularly thank KootK and EngineeringEric, for your practical advices.

Thank you.

 

[CELinOttawa]

You can point me out by name; I seem to be the most heated here... But my advice is very practical, if we all want to still make a living doing this in ten years.

Just had a friend show me the drawings to a structural job that was done for less than 0.2% of the project value, or about $0.20/ft^2. *sigh* How much of that place was actually checked? Black box anyone?

Back to the subject at hand, and for a little practical advice: Be very careful about the space available for the mech passing through, as well as the supports, particularly if you are in a seismic zone. Many codes (including here in Ontario as of 1 Jan 2014) require specific seismic checks and restraints. Only become responsible for what you're paid for, but what's more: Make sure that if you pass this, be very careful with your language about exactly what you are saying yes to.

 

[RFreund]

if you turn the wall horizontally in your mind and think of it as a shitty, weightless slab loaded with 5psf, it doesn't seem so bad

haha, nice. I like it.
Also I'm curious to know more about what you the

masonry / FEM goddess in my office that could do this in 30 min

What do you use?

EIT

http://www.HowToEngineer.com