Chunk of concrete falling from the ceiling.

[Lambda]

It's just as bad as the title makes it seem.
Today, I came in to school, turned on the backstage lights, and saw a couple of pieces of concrete on the floor. Looking up, I saw one of our Batten72 lights was knocked out of focus and dented. Up on the ceiling, I saw a chunk of concrete missing, at least a foot across.
What apparently happened is that at some point during the night, the chunk of concrete just fell from the ceiling. It hit 2nd electric, and broke into several pieces which then crashed to the stage (damaging the marley floor in one spot).
In the place where the chunk used to be, I could see a piece of rusted-out rebar.
Naturally, this set off alarm bells for us and we called the head of maintenance down to see it. He didn't think it was a very big deal.
Correct me if I'm wrong, but I think this is a huge safety hazard. I mean, if there are pieces of concrete falling from 30 feet up, somebody could get seriously hurt. Or worse, our stage lights could get damaged.
So I started inspecting the rest of the ceiling. I found one more spot where it seems like another chunk of concrete is coming loose. What is going on here? What could cause this? This is making me seriously doubt the structural integrity of this building. We had planned to install more loft/head blocks on the ceiling, for spot linesets. Now, I'm not so sure this is a good idea.

Looking up from where it dropped (note damaged fixture in the foreground):



Close-up of the place it used to be (note heavily rusted rebar, this crumbled to the touch):



This is the loose chunk I found. It sounds hollow when tapped. It shows up best on film when seen in shadow.




So, suggestions on where to proceed from here?

[ScottT]

I mean, if there are pieces of concrete falling from 30 feet up, somebody could get seriously hurt. Or worse, our stage lights could get damaged.

Personally, I would have phrased this the other way around, but that's just me...

So, suggestions on where to proceed from here?

Who maintains your building? I would report this immediately to your supervisor, document everything and then call (or get your boss to) call the insurance company. They'll know how to deal with this, and will (hopefully) end up paying to repair the building.

[chausman]

Personally, I would have phrased this the other way around, but that's just me...

Priorities...

And if possible, keep people off the stage, or at least away from where the other spot you saw is. As ScottT said, while it is sad when a fixture is broken, a dead person or someone seriously injured is worse.

[Lambda]

Priorities...

And if possible, keep people off the stage, or at least away from where the other spot you saw is. As ScottT said, while it is sad when a fixture is broken, a dead person or someone seriously injured is worse.

The fixture thing was but an ironic joke, of course. We can always replace a fixture -- but not a person.
I'd like to keep people off the stage, but we have a talent show tomorrow, and a music concert next week. Neither the student council nor the music director is going to cancel either of those events just because I said it's unsafe.
Tomorrow I'm going to try to talk to somebody higher up in the administration. I really want to have this looked at by an engineer if at all possible, because it's really shaken my faith in this building. I mean, we have a lot of weight hanging putting strain on that ceiling, and needless to say, a total collapse would be a disaster on a grand scale.

I wonder, would it be better for me to pry that second chunk off before it falls of its own accord? I'd really want to hold off on that, though, until a professional takes a look at it.

[Les]

Ah guys, I think he was just making a funny. I laughed, but I'm a little twisted like that.

As for the chunk of concrete - I'd be concerned too. Anything that happens once in a situation like this is likely to happen again. Remember; that concrete ceiling was all done in the same pour. Who knows -- it may be nothing, OR the mixture could have been incorrect, water could be penetrating the concrete, etc meaning it will probably happen again. School maintenance doesn't think it's a big deal? So what's he going to do to ensure that it doesn't happen again?

Your recourse isn't much if you are a student (other than letting people know), but make sure you do that as much as possible. Tell your principal or see if you can get in contact with the district's head of maintenance. Do you have an industrial tech teacher around? See what they think.

Rusted rebar (surface rust at least) isn't a huge concern as it comes from the store rusty and does so further when encased in wet concrete. I can't tell how bad it is in this photo, but it looks a little deeper than surface rust. Could there be a leaking cooling unit above?

Ultimately, a structural engineer needs to at least look at this situation. The school maintenance guy isn't a structural engineer. If he knew a lot about that, he probably wouldn't be a school maintenance worker.

[venuetech]

The cause appears to be the corrosion. the question would be why is the re-bar rusting? how is moisture getting through the concrete to the re-bar?

I would think that it should be inspected by a structural engineer

[chausman]

Ah guys, I think he was just making a funny. I laughed, but I'm a little twisted like that.
.

I know, I laughed too...during a test... but, I do know people who would care more about the fixture, then the people below.

[gafftapegreenia]

I know, I laughed too...during a test... but, I do know people who would care more about the fixture, then the people below.

Depends who was below.

[museav]

That looks like spalling (http://www.pioneermasonry.com/resour...20Spalling.pdf) and from a structural perspective it may not be an immediate concern, the bottom of a slab is generally in tension and the rebar carries much of that load, the 'cover' concrete outside of the rebar is generally more for protection of the rebar than for carrying the load (unlike the top of the slab that may be in compression). However, exposing the rebar can lead to accelerated corrosion of the rebar and increase the potential of the rebar failing during a fire. And even if it is not a structural concern, it has already proven that it is still a safety issue that should be assessed.

[Lambda]

That looks like spalling (http://www.pioneermasonry.com/resour...e Spalling.pdf) and from a structural perspective it may not be an immediate concern, the bottom of a slab is generally in tension and the rebar carries much of that load, the 'cover' concrete outside of the rebar is generally more for protection of the rebar than for carrying the load (unlike the top of the slab that may be in compression). However, exposing the rebar can lead to accelerated corrosion of the rebar and increase the potential of the rebar failing during a fire. And even if it is not a structural concern, it has already proven that it is still a safety issue that should be assessed.

It's a relief to know that the whole building isn't about to fall down. So all that needs to be done, according to that pdf, is to remove the loose concrete, coat the steel with anti-corrosion coating, and apply mortar over that area?

[Ric]

<Tongue in cheek>
You could always place notices up around the stage area " Falling rocks, enter at own risk"
</Tongue in cheek>

Seriously, if it was my workplace I would have barriers up already and no performance would be on the stage until there was a green light given by a structural engineers report.
Safety first !!!

[MPowers]

......... if it was my workplace I would have barriers up already and no performance would be on the stage until there was a green light given by a structural engineers report.......

Ditto! What he said!

No one should be allowed on the stage or any adjacent area covered by the suspect concrete roof structure until it has been checked and repaired. If you have reported this verbally and in writing, with photos, to the various PTB, i.e. school Principal, School maintenance et. al. ( you have sent e-mail and hard copy reports to them, Yes???) as a student there is very little else you can do.

That said, are you willing to incur the potential wrath of the people with the events approaching? If so, contact the local TV station with the most active "watchdog" reporter and give them the info. Stress the issue of concrete chunks falling on the heads of students and faculty. Just a thought.

[Lambda]

Well, I'd definitely cordon off the stage if I had the authority to. I do not. I'm not willing to incur the wrath of the administration by getting the media involved, that's just crazy, and might cause there to be some "problems" with my graduation.
What I am going to do is talk to the principal and facilities manager tomorrow. If they still refuse to do anything about it or to cancel the events, then that's a problem. For tomorrow's talent show, I think I can arrange for them to use only the downstage section of the stage, downstage of the proscenium, that is not covered by the concrete ceiling. The music concert will be another problem.

As an aside, I can't help but think this is partially my fault. It just occurred to me that what I was doing last night was testing the sound system, and seeing how loud I could drive the subwoofer amp before it clipped (quite loud, in fact) and adjusting crossover gain to avoid clipping which has been a problem. Vibrations from that test might well have contributed to the concrete spalling.

[ScottT]

I'm not willing to incur the wrath of the administration by getting the media involved, that's just crazy, and might cause there to be some "problems" with my graduation.

You're a student - my apologies, I did not realize this.

In that case, the PTA is your friend. How would one of them feel if little Suzie had a chunk of concrete drop on her head? Yeah, that's what I thought.

But really, the parent's association is your best friend.

[LXPlot]

As an aside, I can't help but think this is partially my fault. It just occurred to me that what I was doing last night was testing the sound system, and seeing how loud I could drive the subwoofer amp before it clipped (quite loud, in fact) and adjusting crossover gain to avoid clipping which has been a problem. Vibrations from that test might well have contributed to the concrete spalling.

If you had any effect at all, at the worst you just revealed a problem that would have eventually revealed itself. How old is the venue?

Maybe you could talk with the music teachers, and at the very least try and have them arrange themselves away from the second loose section?

[MPowers]

...... I can't help but think this is partially my fault. ......

Trust me, as an engineer, I can assure you that what you did, did not in anyway cause the problem. At worst, it only exposed it.

[Chris15]

I'm no civil or structural engineer but that kinda looks like the symptoms of concrete cancer...

You were going to get a structural engineer in to confirm load capacity before you installed any extra rigging anyway weren't you...

At any rate, the risk of a chunk of concrete falling on someone's head is not one to be taken lightly and agitating through the appropriate channels is probably the best course of action...

[porkchop]

When I was pouring concrete for a living ANY exposed rebar was a reason for the inspector to not sign off on concrete work. ANd that was when the stuff was brand new and full strength. Rebar carries a very significant part of the weight in concrete, especially when you're dealing with a span like a roof. It's certainly possible that this can be patched locally and for a not too terrible price tag, but this is something a professional will have to decide. This is way above your head, but you need to get someone with the necessary authority involved. The principle and facility manager are good starts. If you talk to both of them and they don't seem very bothered by it you might ask one of the many professionals here to make a call to your school's administration.

[DuckJordan]

If they feel nothing needs to be done, definitely go to the media with it. They can't hold your diploma for something like that. Its a huge violation of school safety rules for them to even allow anyone in that space now without a structural analysis done. If they hold your diploma, go to the media again. This shouldn't be taken lightly at all. And honestly if they'd rather have a student injured, and then deal with the insurance + lawsuits + the fact they knew there was an issue, then screw them.

Honestly you testing a sub woofer would not have caused that, it may have made the problem evident. But it would have happened later when someone was underneath rather than over night when no one was there.

[Lambda]

Today I spoke with the principal, showing pictures of the damage and general information about concrete spalling. He's ordered the stage upstage of the main curtain blocked off until an engineer comes and assesses the ceiling.
Tonight's talent show was re-structured a little bit so that no acts take place upstage of the curtain. (Our stage is a cross between a thrust-stage and proscenium theater, it's a proscenium theater with a stage extension about 15" downstage and to the sides of the main curtain)
So, I feel better about that. The upcoming music show is also being re-choreographed to hopefully allow all of it to take place downstage of the curtain as well.

[Les]

Excellent turnout! Good to hear that your admin isn't taking this lightly. Likewise, he's probably impressed with the information you've gathered.

[Lambda]

So the principal had somebody from a construction company come today to look at it. He said it was indeed spalling, caused by a combination of rusting rebar and the rebar having been put too close to the bottom of the form in that spot during construction. He does not believe there is any risk to the structural integrity. We're now waiting on a second opinion from an engineer.
I'm quite glad this is going so smoothly.

[LightTamer]

I feel your pain with just being a student helping out at a school. I'm glad things got taken care of though... If the ceiling was falling at my school, i would have made sure every principle and teacher knew about it, and it looks like you've done the same.

Schools have a very tiny budget... they don't like spending much money on anything. It took me an entire day of talking to principles just to get the AC turned on in the room that our amps and dimmer rack is in. It's an AC about like what you would find in a house, and i was only requesting it run through the heat of the day (about 5 hours from 11AM to 4PM) to take care of the thermal errors we've had out of a few dimmer modules. Getting engineers and repairmen out to take care of things like what you're dealing with costs a good bit, and I'm not surprised the school fought it. I'm glad the principle listened though... The head of maintenance may need a little bit of help though... falling concrete, on a stage, with students under it, okay? Uh... no...

[LavaASU]

In the place where the chunk used to be, I could see a piece of rusted-out rebar.


Close-up of the place it used to be (note heavily rusted rebar, this crumbled to the touch):

From your comment and what I can tell of the photo, it sounds like the rebar is pretty much entirely rusted? Is that correct? If so that would be a big concern to me as the rebar is pretty important structurally and if that spot is rusted to that extent (without having been exposed long term), other sections could be as well.

I would also think that knocking down/removing the other loose piece would be a good idea at some point as it's not really going to be doing anything structurally and may eventually fall. It would also give another section of rebar to examine.

*I'm not a licensed structural engineer and this does need to be looked at by one. Also not saying for you to do anything yourself (though I wouldn't necessarily discourage watching/talking with the experts the school brings in).

[mjw56]

I regret finding this post so late, this one is right up my alley.

So as it has already been mentioned, that is indeed spalling, in this case it was definitely caused by the rusting rebar. The rebar expands as it corrodes which places the concrete in tension (which we all know concrete is very weak in tension) and a piece gets blown out => TAADAA! Spalling occurs. I completely agree with the contractors assessment and would say that there is a much greater hazard from the falling debris than from the exposed rebar/spalled concrete. You can actually go around the ceiling and tap on the surface, you should be able to hear the difference where the concrete is sound, vs. delaminated. This may identify areas that the contractor needs to repair which aren't immediately visible at this time. Good move though to get a structural engineer involved.

To clear up a few things though, the concrete cover on rebar is very important to the overall strength of the system, Reinforced concrete structures rely on the bond between the rebar and concrete to develop tension in the rebar, which counters the compression in the concrete. This balance creates the flexural (bending) strength of the floor slab (or any other RC element). Without adequate cover this bond is greatly weakened and if seen over enough of the slab, serious problems could occur. Secondly concrete tends to get stronger as it ages, i understand that there can be a number of arguments against it, but structural concrete indoors, shouldn't get weaker.

If itll make you feel better i have seen much worse spalling and exposed rebar subject to moving truck loads under state highways, and they're holding up fine. A photo for comparison , this is a 5'x12' box culvert in New Jersey. (notice the ceiling of the culvert) The cause in this case was inadequate cover in an extremely moist environment.


The real question i haven't seen asked yet is, where is the moisture coming from that's rusting those bars?

Sources: BS Civil Engineering, BS Architectural Engineering, (Drexel University), 2 Years Underwater/ Substructure Structural Inspection

[Lambda]

The real question i haven't seen asked yet is, where is the moisture coming from that's rusting those bars?

I suspect the roof. I've not been up there proper myself, but I've looked out at it when inspecting the smoke hatches (that's another one of my threads), and it looks like the drainpipe hole is actually a couple inches raised from the level of the roof. Which would cause water to accumulate up there on top of the 50-year-old tar.
I wanted to, but didn't have time that day, to peek out one of those hatches and see if there was any standing water up there. I'll do that after the next good rain.

[mjw56]

The thing about the moisture is that a leak may have already fully/partially saturated any insulation on the roof. Even if you see no ponding, it will still be getting through the tar and felt and sitting on the slab like a wet sponge. And it will remain wet even when there is no indication of moisture on the roofs surface. The only non-destructive way I've ever seen to find this condition is an infra-red survey. The moist areas show up cold on the images. The more destructive way is to cut a hole in the roof and get in there and see what's going on.

[Lambda]

The thing about the moisture is that a leak may have already fully/partially saturated any insulation on the roof. Even if you see no ponding, it will still be getting through the tar and felt and sitting on the slab like a wet sponge. And it will remain wet even when there is no indication of moisture on the roofs surface. The only non-destructive way I've ever seen to find this condition is an infra-red survey. The moist areas show up cold on the images. The more destructive way is to cut a hole in the roof and get in there and see what's going on.

I don't think there's any insulation to speak of. I think it's (from bottom up) just the concrete, then tar, then crushed stone.

[neotrotsky]

<Tongue in cheek>
You could always place notices up around the stage area " Falling rocks, enter at own risk"
</Tongue in cheek>

Seriously, if it was my workplace I would have barriers up already and no performance would be on the stage until there was a green light given by a structural engineers report.
Safety first !!!

Depends on what house sales look like for that night...

Yes, it's dark and mean but when you work for a living, everyone takes risks :P