Miami Beach, Champlain Towers South apartment building collapse, Part 07 90

[Seppe]

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[spsalso]

You'd think so, but you'd be unfortunately surprised at how often water gets added to the truck after the testing even takes place.

There was one time they didn't even wait for the concrete testing crew to leave, so the report I received had notes that although the strength characteristics of the tested concrete were within specifications, water was added to the truck AFTER the test cylinders were cast.

Needless to say, a few angry phone calls were had that day, because I didn't receive the report until 7 days after the pour. So not only did I rip the contractor a new one, but I also gave the testing company a piece of my mind for not calling me the second they saw that happen.

So it sounds like you would then certify that the pour was NOT to spec. That would be very interesting.

If adding water is all that common, then it hints that a certifying person should be on site at those times to see that that doesn't happen. Or to "certify" that it did. If it did.

Maybe I am misunderstanding what a PE is supposed to do here. My belief is that he/she designs and specifies much of the structure, inspects the structure during construction to affirm that the plans and specs are being followed, and then affirms same in writing with a stamp added.

Am I wrong somewhere in there? I don't get much involved with structure in my work, but it sure is interesting!


spsalso

 

[spsalso]

I see from pictures posted by Spartan5 back on July 5 that a typical column top poking through the pool deck seems to have been tied to the slab by 4 pieces of rebar embedded in the column, bent 90 degrees, and extending into the slab about a foot.

I haven't a clue how to read what the drawings say SHOULD be there. Is the above what the drawings call for?


spsalso

 

[Colostruct]

Spsalso: So it sounds like you would then certify that the pour was NOT to spec. That would be very interesting.

If adding water is all that common, then it hints that a certifying person should be on site at those times to see that that doesn't happen. Or to "certify" that it did. If it did.

Maybe I am misunderstanding what a PE is supposed to do here. My belief is that he/she designs and specifies much of the structure, inspects the structure during construction to affirm that the plans and specs are being followed, and then affirms same in writing with a stamp added.

Am I wrong somewhere in there? I don't get much involved with structure in my work, but it sure is interesting!

Back in the day, it could be quite a task to be sure that water wasn't added during placement. On important work and big placements we used to have two inspectors available so we could be sure that no one is adding water to the mix while we weren't looking. Some of the truck drivers were very good at hiding it. In my area, I haven't seen that tried in years but I don't often have concrete slabs that are structural and exposed so the push to get a good finish and using water to do it doesn't come up on the structural placements. The exception is large monolithic slabs for shop buildings. I will have help watching those placements. Cheating on the W/C ratio doesn't seem as common as it used to be...here.

BUT. Most Engineers around here don't "stamp" letters that indicate that the work was, actually installed to the specifications. We use terms like we "observed that the installation was in substantial conformance" to the construction documents. Construction is NOT a science and the quality of the construction cannot be assured by observation by the designers. Construction is a partnership of responsibility by the suppliers, designers and laborers. Anyone of the team not up to the task or deliberately cheating can destroy a project and it might not be all that obvious.

It is now pretty common to utilize third party special inspectors. These guys are trained to look at only variation form the plans and are familiar with the placement standards and reinforcing tying and chairs. If it is a large, or critical structure, I will use that process. The IBC requires it for substantial construction.

 

[SwinnyGG]

If adding water is all that common, then it hints that a certifying person should be on site at those times to see that that doesn't happen. Or to "certify" that it did. If it did.

From the point of view of a contractor...

I've done some pretty big pours; I'm currently sitting on a site that we are demobing from on Friday after placing roughly 3500 yards over the course of 12 weeks.

There is always a 'certifying person' on site whose entire job during placement is to evaluate the concrete being placed and verify that it meets project specifications - that being the third party concrete testing technician hired by the owner or general contractor. In my experience the EOR is very rarely present for the placement of concrete. I personally have no problem with that at all; I don't view it as part of their responsibility.

Ultimately, as the General Contractor, we are responsible for the actions of any suppliers or subcontractors on the site, including the guys driving the concrete trucks. The concrete testing agency is responsible for clearly communicating to us whether or not the properties of what they test meet the spec, but decisions about whether concrete is placed (whether it tests in spec or not) are up to us.

So, point is, in JayRod's anecdote I don't believe there's any ire to be aimed at the tester; that GC, however, has zero business placing structural concrete. I hope it was flatwork.

As far as final certifications by the EOR; in my experience, they will typically make a few trips to the site (or many if it's a long duration) to spot check things like rebar quantities and placement, final column dims, etc. At the end of the job they produce their as-builts and we get a letter from them stating something to the effect of 'to the best of my knowledge the structure built at 123 Mountain Lane Drive under City of Denver Permit Number XYZ123 has been constructed in conformance with the construction drawings captured by the approved permit'. That letter is always stamped.

That may just be a thing in my local jurisdiction, though, and it may not be a hard requirement. I'm not an EOR so I don't know the rules, but that's what's typical.

For reference, here's the letter from the last high-rise I worked on:

 

[MarkBoB2]

I thought it would be interesting to show some close-up photos of the debris pile that can be seen on a 1920x1280 pixel non-interlaced display while zooming in on frames snatched from high resolution still photos and videos taken by a drone which are then pasted into a PowerPoint document to enable using its powerful zoom capabilities.

The first photo below shows a close-up of the debris pile just before it was removed to clear the floor for foundation studies. The pile shows objects that were seen in the TicToc video and in the vicinity of column 27, but the objects have been pushed onto the pile from their original positions further away and then the whole pile has been pushed closer to the ramp, causing many of the objects to lie in the driving area at the foot of the ramp. Nevertheless, one can see that the recovery workers have used red spray paint to call attention to several objects of interest further down in the pile. One of these objects of interest that is easily distinguished in the photo is the sheet metal top of an air conditioning unit which lies close to the surface of the pile. One can assume that one of the other objects of interest identified by the recovery workers as lying further down in the pile is the lower part of the same air conditioning unit with the radiator, cooling fan, and refrigerator pump. By looking at multiple frames of the video taken as the drone flies past the pile, one can confirm the identification of the top object and a several additional objects nearby as well as seeing down into the pile to confirm that something of interest is below. But it is not possible to confirm the identity of the object below.

The second photo below shows these same objects as they were being uncovered by a back hoe at the bottom of the collapsed debris pile and before they were consolidated into their own little debris pile. Therefore, their locations in this photo are closer to where they naturally fell during the collapse. One can see that the objects in these locations correspond very closely to the objects seen the same locations in the TicToc video. One can easily see the location of columns 26, 27, M11.1, 28, and 29. One can also clearly see that there is a dark-colored car parked in parking space 26 next to column 26. One cannot see a second car in parking space 27 between that car and column 27. But we know from the TicToc video that one is there, and we can see two objects the fell on the hood of this second car; namely, a davit base and what appears to be a hexagonal weight on a rod. The davit base is easily distinguished from an Osha anchor by having no loop on top and by having three triangular reinforcements welded between the base and the central column. Interestingly, a second hexagonal weight can be found on the other side of the red circle. These objects raise the question of what other work was planned or in progress on the roof.

This photo also shows several objects inside the red circle. Closest to column 27 is what appears to be an air conditioner housing with the top opening facing the camera. The housing looks like it has a bulge on the right side similar to some air conditioning units that have a pump to the side of the radiator core. Behind it lies either a second air conditioning unit with the top facing the camera, or perhaps just the inside radiator core of the unit corresponding to the air conditioning housing in front. One can also see what appears to be either column M11.1 tilted to the right or the cross-beam between column M11.1 and L11.1 with its lower end near column M11.1. Either one could have been produced by the air conditioning unit falling between the car and column M11.1 to cause a wedge-like force, which would have caused a high lateral force on column M11.1 as well as a downward force caused by an object falling on the deck. This lateral force might have been what caused column M11.1 to buckle as seen in the TicToc video.

Also in the red circle at the bottom of the pile near the floor of the driving area next to column M11.1 one see a white object with what appears to be windows. But this object is too small for an automobile. While this object has not yet been identified, it has been found that a similar-looking object called a Belle chamber is used for testing roof surfaces for de-lamination caused by hurricane force winds. The chamber is used to apply a vacuum to a 5x5 foot area of the roof while one looks though the windows to observe how high the roofing material rises as a result of the vacuum. The size of this chamber appears to correspond to the size of the object shown in the red circle. Is it possible that such a chamber was being used or planned to be used to test the roof and left on the roof overnight at the time of the collapse? This needs to be further understood.

The objects in the second photo above can be discerned more clearly if one enhances the photo and zooms in further as shown in the photo below. In this enhanced photo one can more clearly see what appears to be a second air conditioning unit facing the camera at a lower position, which may have been the original object seen next to the broken column M11.1 in the TicToc video. Also seen more clearly are the two hexagonal objects that I believe may be weights, and a davit base. In this photo one can clearly see that the davit base is not an Osha anchor because one can clearly see the triangular reinforcements welded between the base and the central column. Finally, in this enhanced photo one can see traces of what appears to be a scaffold between the two hexagonal weights.

One can see that these photos have much higher resolution than a mere “potato camera”. They also have higher resolution than when viewing the same videos using a cell phone or an interlaced 640x480 pixel desktop display.

If one is still skeptical that air conditioning units cannot have fallen from the roof to be found at the very bottom of the debris pile because they are tied down so well by mechanical straps, electrical power lines, and refrigerant lines that they are secure in a hurricane, consider the following. Photo 4 below shows excerpts from the permit issued on the day of the collapse and from an HOA letter describing the work to be done on the roof. These documents show that not only were Osha anchors to be installed on the roof, but also other work was to be done at the same time including stucco repair, air conditioner replacement, and exhaust fan replacement. We also know that a satellite dish was being installed at the same time by an independent contractor. Given that air conditioning units were being replaced at the same time, it is highly likely that some air conditioning units on the roof were not attached at the time, either new ones waiting to be installed or old ones that had just been replaced. These unattached units may have been the ones that fell and were found at the bottom of the debris pile.

Also, if one is skeptical about hexagonal weights being found at the bottom of the debris pile, consider that the permit mentioned that stucco repair was to be done at the same time. Such repair would have required going over the side of the building with a scaffold held by davits. The davits would have required weights to stabilize the scaffold holding at least one man with repair materials, which would have required somewhere between 500 and 1000 kilograms, or over half a ton. These weights could not have been brought up to the roof by using a davit because they would have required getting the weights close to the base of the building over the deck, which was not built for this load. So the weights would have to be brought up by a crane, which had left the building at the end of the work day. Therefore, could the weights have been stored on the roof overnight and in a location close to the edge of the roof where they could have caused a roof collapse? This needs to be further understood.

 

[spsalso]

It sounds like things MAY have changed since the Coral Gables garage and Champlain South were done.

It seems back then that the PE was the person responsible for field inspection. Now there's different people, and the PE is NOT responsible for field inspection.

It's my belief that the general contractor is the main person responsible for the building. But, especially back in 1980, who did the architect and the PE owe responsibility to? I would expect firstly the owner of the building, and secondly the local government (or perhaps the "licensing entity"), and THEN the general contractor.

I could, of course, be mistaken.

With Champlain South, I think the owner and the general contractor were the same person. So if the contractor wishes to do things a little differently, the owner will not object. So THAT'S all covered.

With Coral Gables, the owner was the local government.

So the question may arise, who WAS the person, if any, that was monitoring the pour of the deck slab at Champlain South? Who WAS the person who was making sure the rebar was done right at Champlain South?


spsalso

 

[Spartan5]

I thought it would be interesting to show some close-up photos of the debris pile that can be seen on a 1920x1280 pixel non-interlaced display while zooming in on frames snatched from high resolution still photos and videos taken by a drone which are then pasted into a PowerPoint document to enable using its powerful zoom capabilities.

Those pictures are grainier than my BMs after I’ve eaten nothing but trail mix for a week.

You can’t even hardly make out the text you’ve written.

 

[gonefishing2]

MarkBoB2,

WOW! Great work..... could you upload the Power Point File, as zooming on this Web Site Sucks as far as resolution.... I am sure there are some nah sayers that will want a 8x10 Glossy for their Office!

BTW< that radiator core is what we in the business call a 'Condenser Coil' on the outdoor unit if in air conditioning mode..... Now that coil takes on another name in heat mode if it is a Heat Pump we are talking about.

 

[CE3527]

SwinnyGG - this is essentially same thing you are talking about but it's based on the formal inspection process that is laid out in the international building code, called "Special Inspections". Under special inspections, the EOR should lay out exactly what gets inspected, by who, how often, and what standard is followed for the inspection. The Special Inspector is typically called Agent 1 and the Materials Testing Agent is typically Agent 2). The EOR can also serve as Special Inspector (depending on jurisdiction). For example on a concrete foundation, usually Agent 1 is going to inspect the rebar size/placement before the pour and the testing agent is the one responsible for checking concrete for slump, air, compliance with batch time to delivery, and taking samples which are later tested for compressive strength. The building does not get its occupancy permit until both the EOR and Special inspector have signed off that construction is fully in compliance with documents.

I don't know much about 1980's building code, and when the "Special Inspections" came into being, but would not be surprised if it was less regimented than it is today.

 

[Demented]

I see from pictures posted by Spartan5 back on July 5 that a typical column top poking through the pool deck seems to have been tied to the slab by 4 pieces of rebar embedded in the column, bent 90 degrees, and extending into the slab about a foot.

I haven't a clue how to read what the drawings say SHOULD be there. Is the above what the drawings call for?


spsalso

Not sure it's what the drawing intended to call for, but yes, it calls for it. The pool deck is considered a roof. I cannot find any other details on this.

While I don't think a car would obliterate a column...

Precision guess work based on information provided by those of questionable knowledge

 

[gonefishing2]

If I was the building owner, I sure would want stucco repair done before I replaced the whole roof? I would think they would install fall protection anchors, and they haul up Swing Stages to do wall repair, then do the re-roof. But this is Miami?

Scaffolding would be required for swing stages as tie down cables could not drape across the parapet wall on the way to the ground for anchor, nor could the parapet walls be considered strong enough to anchor too. And perhaps weights were hanging off side of building, to counter balance the swing stage?

 

[Demented]

Also, if one is skeptical about hexagonal weights being found at the bottom of the debris pile, consider that the permit mentioned that stucco repair was to be done at the same time. Such repair would have required going over the side of the building with a scaffold held by davits. The davits would have required weights to stabilize the scaffold holding at least one man with repair materials, which would have required somewhere between 500 and 1000 kilograms, or over half a ton. These weights could not have been brought up to the roof by using a davit because they would have required getting the weights close to the base of the building over the deck, which was not built for this load. So the weights would have to be brought up by a crane, which had left the building at the end of the work day. Therefore, could the weights have been stored on the roof overnight and in a location close to the edge of the roof where they could have caused a roof collapse? This needs to be further understood.

The man behind the BecauseSurfside channel would be the man to ask about that.
The roofing equipment I posted earlier, is rumoured to have been seen left on top of the building overnight. The hot tank trailer as well. It's not unlikely other stuff was left up top either.
Speculation, no facts.

Precision guess work based on information provided by those of questionable knowledge


Edit:
@thermopile
I'll try and drive up and down the coast tonight and snap some pictures of how they attach scaffolding here.
I'll leave this with you though. Because Florida.

 

[gonefishing2]

Swing stages by Building Integrity

https://www.youtube.com/watch?v=FCGfzFCRkXM

 

[Colostruct]

It sounds like things MAY have changed since the Coral Gables garage and Champlain South were done.

It seems back then that the PE was the person responsible for field inspection. Now there's different people, and the PE is NOT responsible for field inspection.

It's my belief that the general contractor is the main person responsible for the building. But, especially back in 1980, who did the architect and the PE owe responsibility to? I would expect firstly the owner of the building, and secondly the local government (or perhaps the "licensing entity"), and THEN the general contractor.

I could, of course, be mistaken.

With Champlain South, I think the owner and the general contractor were the same person. So if the contractor wishes to do things a little differently, the owner will not object. So THAT'S all covered.

With Coral Gables, the owner was the local government.

So the question may arise, who WAS the person, if any, that was monitoring the pour of the deck slab at Champlain South? Who WAS the person who was making sure the rebar was done right at Champlain South?


spsalso

I think you are asking a question that has a nuanced answer. As a structural engineer, it is my responsibility to design a building that satisfies the code. It is my responsibility to convey that design on construction documents so that design may be executed. The observations of the installation of the work is done by a number of "inspectors". We use special inspectors to observe the placement of concrete (if it is an important structure), the installation of bolts and welds etc. Ultimately, I review all of the special inspectors reports to verify that important aspects of the work were completed, to the best of my knowledge. It is my responsibility to double check that the special inspectors have the qualifications to observe the work before or after it is installed. The code does allow the EOR to perform special inspections if they are qualified to do that. I review EVERY compaction test, EVERY pile load test and EVERY concrete test. I also review the shop drawings. Most of the time, I observe 75% of the installed reinforcing. I observe ALL of the reinforcing where life safety is involved or I have a special inspector do it. But, I don't watch every concrete placement unless it is a large column or a structural slab.

The code has a full section devoted to what aspects of the work require special inspections. That section gets larger every iteration of the code. So, things have changed since the early eighties in the process and the personnel available. In 1979 while I was working as a engineering aid I spent summers crawling all over forms, taking concrete samples, and watching the installation of concrete. I was not a certified inspector as required now but the engineering firm I worked for was serious about observing the construction.

If the firms I worked for in the late 70's and 80's had designed the CTS structure, every single piece of reinforcing would have been looked at by someone from our office. Every single concrete placement would have been continually observed.

But. You ask who is the ONE person responsible for the safety of a building. And, as much as some would like that to be the EOR that just isn't the case. A complex building requires the observations and testing of dozens of professionals. I might direct their work but I am not responsible for it. Does that make any sense?

 

[Optical98]

MarkBob,

Uploading pics to Imgur and then linking makes them a bit clearer, maybe try that..

This platform is rather archaic, have the site Over-Lords considered upgrading? I would imagine with the recent state of affairs of beachfront condos and hotels, this site will get a lot more popular.

 

[gonefishing2]

@Demented, Who needs a 40 foot ladder, when they have a fork lift!

 

[Optical98]

Demented,
When you say "hot tank trailer", is that what I was calling a "tar kettle"? You showed a pic of one that looked ashy and burned, then I added a pic of a black one beside 2 crushed cars. Are these 2 different objects?

Link
Link

 

[Demented]

Yes, the tar kettle. There were multiples on the job site is all I know. Having not seen the stuff on the roof myself, I can't be certain if those were the ones he has been referring to, or the smaller ones we know were on the roof. The location of the maintenance spot and the image you posted to me makes a ton of sense. The ash may just be dust that has stuck to the side between moving, rain, being hosed off, etc.

What I find odd is, why would a crew leave the tar kettle on ground level overnight? That is a 100% sure fire way to get it stolen, especially in Miami.


Precision guess work based on information provided by those of questionable knowledge

 

[Seppe]

It is impossible for me to make a single reasonably informed deduction based on what is shown in MarkBoB2's rubble pile photos.

Literally and figuratively, I'm just not seeing it.

 

[Demented]

The tide is rising. High tide is 7:05PM today.

https://www.youtube.com/watch?v=l_G-tVRV4yI

Precision guess work based on information provided by those of questionable knowledge