Out of Plumb CMU Wall
Out of Plumb CMU Wall
(OP)
I have a project with multiple quality issues caused by the masonry subcontractor. The latest is that several load-bearing CMU walls have been built out of plumb. The walls in question are exterior walls of a hardened room area (elementary school in the midwest) that is designed for 250 mph wind speeds (tornado, FEMA 361) and support a 10" solid precast plank roof. Bearing height is 12'-8". Per FEMA 361, the walls are 8" CMU reinforced w/ #5 verts @ 8" o.c.
The worst case is actually a "wave" shape; it goes one way out of plumb and then back the other way. Overall, the top is only ~1/2" out of plumb from the bottom of the wall. However, the bulge in the wall results in closer to 1" in the last five feet.
Can anyone provide some guidance on how to analyse a curved wall section like this? besides FEA? If it was just leaning one way, I would just account for the eccentricity and reduce my capacity. I'm not sure how to account for the wave shape in my analysis of the wall section.
Note: the precast roof is already in place and the topping has been poured. So, if I tell them it's no good, there will be a huge confrontation. I have to have some solid evidence if I say it's not adequate. Thanks.
The worst case is actually a "wave" shape; it goes one way out of plumb and then back the other way. Overall, the top is only ~1/2" out of plumb from the bottom of the wall. However, the bulge in the wall results in closer to 1" in the last five feet.
Can anyone provide some guidance on how to analyse a curved wall section like this? besides FEA? If it was just leaning one way, I would just account for the eccentricity and reduce my capacity. I'm not sure how to account for the wave shape in my analysis of the wall section.
Note: the precast roof is already in place and the topping has been poured. So, if I tell them it's no good, there will be a huge confrontation. I have to have some solid evidence if I say it's not adequate. Thanks.






RE: Out of Plumb CMU Wall
Personally, I always use 12 inch block on FEMA shelters regardless of the bearing height.
RE: Out of Plumb CMU Wall
If you are comfortable with it, let it go, 1, if it gets hit by a tornado, who can quantify the 250 psf is correct, and if a cow hits it at 250 mph, is that included in the design? A cow hitting a wall with 250 mph speed and a 250 mph windload on it, more than likely is not going to work.
RE: Out of Plumb CMU Wall
If you want to run an analysis, I'd take a one foot strip of wall and analyze it with the slender wall provisions, building in an estimate of the out of plumbness into your analsyis.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Out of Plumb CMU Wall
RE: Out of Plumb CMU Wall
RE: Out of Plumb CMU Wall
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Out of Plumb CMU Wall
The static analysis of the worst case in either direction is within capacity, so I feel better about letting it stay. The plan right now is to write them up for the poor quality and determine a credit to the owner (including my fee).
Mike, quick question: Is there a specific reason you go to 12" block on your shelters? FEMA 361 references that 8" solid grouted block is adequate for missile penetration. Do you go to 12" just as an added safety factor or something else?
RE: Out of Plumb CMU Wall
As a side note, I have been getting quite a few concrete dome FEMA shelters, too; some have diameters of over 160 ft. It's amazing how efficiently a 4 inch roof can perform at such large diameters. It seems that FEMA is really pushing these hard and is offering funding to build these things. Everyone is ramping up for the IBC 2015 when they will make FEMA shelters required on new schools; there is some question to whether local jurisdictions will adopt this provision.
RE: Out of Plumb CMU Wall
How do they get around the missile impact with the roll up doors? I would think that you would be more susceptible to missile impact and suction with the larger openings.