Distressed CMU exterior wall

[smb4050]

The situation is another expert witness, an architect, is claiming the webs of 12" fluted/corduroy CMU’s have cracked or disintegrated allowing the exterior face of the units to bow out from vertical, and he stated the reason the web(s) cracked was due to freeze thaw due to moisture infiltration into the wall. Using a fiber optic scope he looked inside the CMU cavities and saw the webs were broken, and I take him at his word. The wall definitely has moisture infiltration problems as evidenced in the attached photo. The building was built in 1972 and is located in a northern climate with the average January temperature being around 20F. The exterior faces west and the interior space is storage and loading dock area, but is connected to a heated space (discount department store). The interior face is unfinished and the wall is not insulated. Over the years the building has had little or no maintenance. The building’s structure is steel post and beam with steel joist and deck, and the CMU walls being an infill between columns and to the bottom of the perimeter steel beams. I did not see lateral bracing in the construction documents or in the building. The 12” CMU has horizontal joint reinforcement @ 16” centers. In the attached photo vertical course is a 2” sailor with 2 courses of 8” CMU’s below, covering the perimeter beam. The steel beam has 1/8” x 8” strap masonry clips @ 32” centers at their bottom and web to anchor the masonry to the beam.
I have never seen the web of CMU crack due to freeze thaw cycle, and my concern is the problem is more complex and due in part or solely to stresses from lateral and vertical loads being transmitted into the block. My questions are has anyone seen a similar problem with the exterior face of a CMU separating and if so what was the cause of the separation, and has anyone see the web crack due to moisture freezing?
Hopefully I’ve included enough information for anyone interested in providing any comments.
Thanks

 

[concretemasonry]

Where in the 36 year old building is there a freeze thaw problem? - At what level? Possibly just below the roof line?

Are the block the conventional fluted block with the "flute" projecting beyond the nominal block dimension (usually 4, 5 or 6 flutes per unit) or are they corduroy block (usually 8 flutes per unit) with the flutes within the nominal block dimensions? The terminolgoy varies geographically.

The first things to look at:

1. Did design and specifications for the wall permit/require uncompacted mortar bed joints under the "flutes" and a ledge to collect water and encourage water penetration. - This is a poor design consideration.

2. The details for flashing on the top course of plain block do not show enough vertical exposure to prevent any wind driven rain or drainage from being sucked up into the interior of the wall. - This is a poor design detail.

3. The "flutes" of the corduroy block are not aligned, precluding the use of flush bed joints. - This is either poor construction and/or lack of inspection and control.

4. The top course of the corduroy block (2"?) is recessed, compounding the problem/potential for moisture penetration. - If the course of masonry is 4" thick, a 4" corduroy block should have been used. The exterior dimensions of a corduroy block are to the split face and the actual face shell is usually set back 7/8" from the split surface.

All of these points relate to the design and possibly construction of the building.

The real question of freezing and thawing addresses the weather conditions (temperature & humidity/dew point) and the possibility of acheiving the necessary repeated cycles.

The interesting thing is that freeze/thaw failures require accumulated cycles of freezing and thawing of the SATURATED materials. This only does occur on the exterior where there in the condition of saturation that can be reduced since frezing is a dehydration process. The web of a block is almost impossible to subject it to many cycles, let alone while the CMU are saturated. With a massive hollow wall there is the temperature stability that procludes freeze/thaw of interior portions unless there is a constant supply of moisture.

Feezing and thawing occurs in the winter, and there is little exterior unmelted moisture that can be supplied to a wall with an average temperature of 20F.

Has there been any coating applied to the interior of the wall to prevent condensation (vapor barrier) and passage of moisture from the interior to the exterior or core the cores of the block due to the temperature differential? Usually, in northern climates there is little exterior moisture available to the wall from the exterior in the winter (unless from the roof with melting snow), but interior conditions can provide a source of moisture.

The claim that the webs cracked because of freezing/thawing boarders on the naive or possibly rediculous since this process is one of deterioration and not one of cracking of sound materials. It is very common for block to have vertical cracks in webs and meet ASTM specifications. Obviously, the conpressive strength of the wall is not a problem because of the percentage of solids in a corduroy block and the need to have a strong concrete matrix to split.

This is an intersting situation, but if the only problem is some cracked webs, I would look at detailing or structural conditions.

Just a few observations based on northern concrete and mason building experiences.

Dick

 

[hokie66]

Your photo shows a horizontal separation at the exterior face. Is there a corresponding separation inside? If not, then the webs have broken. But not from freeze thaw cycles. Does this only occur at the top of the wall?

 

[concretemasonry]

hokie66 -

After looking at the photo, I assumed it showed the 3 courses of block as the 2 courses of 8" block and the course of 2" thick units above that. These were the 3 courses covering the perimeter beam. A 2" thick unit is usually not manufactured or possible to manufacture and split, but a modular 3 - 5/8" thick (out to out) is the common unit used with only an extra horizontal cut near the top for a beam flange if necessary.

I assumed (correctly or incorrectly) that the 2" units were laid set back to far (possibly to get support for from the bean or something). In any event, if I am reasonably correct it is definitely an unprofessional detail (either architecturally or construction-wise).

I am still curious why the specifically decided to drill holes and put in a borescope or camera at that point. There must be more to the situation than the photo shows.

I have seem many similar type of buildings in the area through the years with very poor detailing. Most of the time these were on unimportant low cost structures (office-warehouses, etc.) and they problems are not usually pointed out and just go with the low construction cost required. They are usually not engineering gems.

 

[hokie66]

Dick,

I must admit I didn't read the OP thoroughly enough, and now that I have, I am confused even more. smb said the architect was alleging that the webs of 12" blocks splitting had caused the problem, but I don't know from the picture which courses are 2", 8", or 12". I thought all the ribbed blocks in the picture were 12", and that the other blocks were above, but maybe not. A section would help.

 

[smb4050]

Dick you are absolutely correct. To put it bluntly it was and is a cheap building. Poor details combined with a moderate to severe climate and no maintenance for 36 years is a bad combination. Back to my post and questions asked. The interior has not been finished and with no cracks, bowing, etc. I will be back at the building Monday and will look at the interior again and check if there is heat in this area. Yes this is near the top of the wall. This problem has been detected only at one location that I am aware of which is above a garden center roof. The height from the lower roof to the top of the wall is about 8’-0. The attached photo was taken standing on the garden center roof looking north. I didn’t think about the possibility of faulty or poor quality CMU materials. My cynical side thinks the answer to why was a fiber optic scope was used is because the architect’s client is a national company with deep pockets, but I’ll try to find out if there is more information available Monday.
I have access to original construction documents and if anyone is interested I will scan a typical wall section and post it on Monday. It’s been a long time since I’ve been an EIT and I haven’t seen this before and completely agree that freeze thaw cycling causing the problem is remote and perhaps not even physically possible which is why I started the thread. This is an interesting problem.
Thank you everyone your interest and thoughts.
Steve

 

[concretemasonry]

I have seem many buildings with some bad details in my area through the years. I may have actually been in that building a time or two, but the color threw me off a bit. I would imagine it is in MSP or MKE.

Since it is a single location on a large building, I would look at the possibily of poor details combined with sloppy construction (36 years ago) and a more recent roof/water problem to compound the situation.

Freeze/thaw failures do not create cracks in non-bearing concrete products. You must have sound concrete to get a definite crack. The F/T failure mode is a deterioration of the exposed surface and "sanding" of the surface or spalling if it is coated.

Since it is just one isolated spot on a large building, I would not guess there is a material failure since the block for the project may have been made at the same time or intermingled during handling and construction. If the is one bad batch or run, you would have at least several hundred bad block if not many thousands. A plant can produce 50-60,000 block (1 block = .875 sf) per day. It is interesting that when we monitor the ASTM C90 specs, there is no mention of any freeze/thaw (or wetting/drying)durability. There is for SRW block, which are made in the same plants and subjected to more severe conditions.

 

[JedClampett]

A 36 year old building with little or no maintenance in a northern climate with freeze thaw damage? The horror!
Why is this being dealt with as a forensic issue, instead of just fixing it? Was the building recently sold and someone is trying to make a claim against the seller? For the costs of expert witnesses, engineering, etc. the problem could be fixed. If it's rebuilt with someone keeping an eye on things, the problem will go away.
I'll admit it's interesting to get to the bottom of these things, but it's probably a combination of circumstances with a large dose of the unknown.

 

[LobstaEata]

"I did not see lateral bracing in the construction documents or in the building.......The steel beam has 1/8" x 8" strap masonry clips @ 32" centers at their bottom and web to anchor the masonry to the beam."[/color red]

If there is other evidence such as diagonal cracking along masonry joint lines, then one might be tempted to consider that the masonry infill wall is indeed acting as a diaphragm (intentional or not) and resisting lateral loads. As a result, perhaps the block wall diaphragm was not reinforced sufficiently to provide adequate wind restraint. If so, the only direct connection between the laterally induced load and the vertical transfer to the foundation would be through the web connection at the face of block.

 

[hokie66]

Jed,

Sorry you are not interested in knowing why things like this happen, but some of us are. It doesn't matter that the building is 36 years old. If one of my buildings from 1972 has this type of problem, I would want to know about it and understand what I or someone else did wrong.

smb,

Having a look at the details you have would be much appreciated.

 

[msquared48]

Something funny is going on here and my guts tell me this is not freeze-thaw action. I see a lateral shift in an exterior masonry wall, most likely due to loads transverse to the wall = wind or seismic forces, not freeze-thaw.

The position of the longitudinal crack appears to be at the level of a possible diaphragm chord tie to the roof diaphragm beyond the wall. My question would be is the vertical reinforcing in the wall sufficient, deterorated, or compromised?

Mike McCann
MMC Engineering

 

[hokie66]

Mike,

From the OP, I doubt that the wall is reinforced or core filled.

 

[msquared48]

From the picture, I would have to agree with you hokie.

Mike McCann
MMC Engineering

 

[dik]

Can you scan and post the wall section?

Dik

 

[smb4050]

Attached is the wall section. The page with the section at this location is the only one missing, so this section is at the overhead door location. The building dimensions are 350' x 240' with joist spanning 50' and column spacing 32'. The steel beams at this location are W18x40 & W16x31 (22' span) with beam to beam connections being a simply shear connection (standard framed beam connection) with a 5' offset from columns. The Garden Center is 96' long. The entire building is heated, and I didn't see an efforescent on the interior walls. The wall below the Garden Center roof is straight, clean without cracks, and part of this space in finished space and some is in unfinished storage space.
I want to be clear on one item, remember my original post was asking if anyone had seen a CMU web split from freeze thaw cycle because in my 50 plus years I haven't. I am not looking for someone to do my work for me. I find this interesting and enjoy discussing problems and matching wit with other engineers. The repair will be design by someone else.
My guess is (not enough hard data for an opinion) the webs have cracked due to cyclic loading due to both in plane and normal to the exterior wall with unbalance load, vertical and horizontal, from the steel beam adding to the problem.
Dick, you need to go a little farther south.

 

[smb4050]

Sorry didn't get the wall section posted. I didn't design the channel support seen in the previous post. That was done before I got involved. Also, the interior face of the CMU's are smooth, no cracks.

 

[hokie66]

So which courses have the broken webs? From the movement at the bed joint, it would have to start at the second 8" ribbed course from the top, as the top course seems to be hanging onto the beam. When you say there is no interior face cracking, you can't actually see the second course due to the beam.

 

[concretemasonry]

I find it difficult to see where the first attachment (a PB office(?) photo) relates to the detail of the second attachment (a .pdf design detail file). Many things do not agree and make any engineering analysis very difficult.

Please be more specific where the supposed freeze/thaw deterioation web crack occurred in relationship to some kind of drawing detail. The first attachment apparently does not show any 12" split fluted/corduroy block that were in the wall at that location. The drawing also does not accurately indicate the same units as the photos, but that could from be using from "canned" details.

I can see where there could be a substantial lateral force applied to the top 2 courses of 8" plain block with a 2" plain block by the entire roof system if movement and tempertures were not taken into account. This could account for the horizontal displacement.

Incidentally - You may find small vertical cracks at the center of a web of a CMU that are incidental and a part of the manufacturing process. Because the crack occurs before the curing and hydration, it has a minor effect on the bloc that still used be tested and pass the ASTM C90 requirements. Since CMUs are usually so far above the rediculously low ASTM strength requirements this is not a consideration. A camera with lighting may show a crack from the top to about 2" dowm, this can also be seen in units from inventory prior to testing.

Dick

 

[hokie66]

Dick,

I thought the picture and the wall section matched. The horizontal displacement is at middepth of the beam.

 

[dik]

If the separation is at the top I would suspect the eccentric loading on the CMU wall from the steel beam is possibly the cause. I cannot tell from the drawings if there is an expansion space beneath the beam, but the exterior wall photo tends to indicate there isn't.

The photo also shows what I would consider as poor workmanship.

I've only encountered web splitting once in 35 years; it's not common and was at the bottom of a wall caused by poor flashing. I think the Architect is 'all wet'. Freeze thaw deterioration would likely manifest itself by spalling of the surface, ie, a delamination of the concrete surface.

my 2C... Dik