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Question time

Maybe some architect or engineer can answer a question I or my father have had for thirty years.

Movies stretch reality all the time. The 1974 film, The Towering Inferno was no different. I saw this film for the first time in 74 or 75 along with my parents and younger brother. This morning HBO has the movie on and seeing the film again reminded me of something.

At the end of the movie the fire is doused by having two water tanks at the top of the skyscraper detonated pouring down one million gallons of water on the fires below. One million gallons would weigh over 8 million pounds Can a 130-140 story building have that much water at the top and still stand?

My father didn't seem to think so when we saw the movie way back when. I would seem to agree, also those tanks would have to be enormous and heavy themselves. Can someone answer the question for me? I'd like to finally solve this mystery.

Here's a You Tube video of the movie's ending. I would seem to think the Plastic explosives needed to blow the tanks would also kill the people in the restaurant below.


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Comments (26)

It would be like having ext... (Below threshold)
Anonymous 5:

It would be like having extra floors, so imagine the largest possible building and subtract a few floors for the weight of the water. But why? The building already has water piping! It would seem so much smarter to just make the pipes bigger. Wouldn't you need the pipes either way? And if they are connected to a water supply....duh....

If for some hard-to-fathom reason it was necessary to have on-site water, why not put it on a lower floor and provide a pump? Why add support for all that weight to every floor?

And I would make it a pool and get some use out of it other than when the building is on fire.

Based on some quick searche... (Below threshold)

Based on some quick searches, it seems the weight of a building the size of one of the the World Trade Center towers is in the range of 200 000 - 500 000 tons. Therefore I don't think 4 000 tons of water at the top of such a building, plus a similar amount again for the tanks, is totally unreasonable. I can think of a reason to have a water tank at the top of a building - the fact you can use it to average out the load on the pumps required - but it wouldn't make sense for them to be that large I think.

I think we need to consult ... (Below threshold)

I think we need to consult one of the world's foremost structural engineers on this -- Rosie O'Donnell.

I, myself, am deeply suspicious of this. On the other hand, since fire can't melt steel, maybe it can hold up 8 million pounds of water.

J.

I can't watch the video at ... (Below threshold)

I can't watch the video at the moment and haven't seen the movie, what do the tanks look like? Size estimate? If they're each a half million gallons they'd need to be like 50' in diameter and 35' tall, if they're skinnier they'd be extremely tall and exposed to way too much wind. As for the weight, you can build a building to support whatever you want, but why would you build a building, a long stick, with an 8.34 million pound (4000+ tons) knob at the end? I'm not into structures at all, but that seems like an awfully big moment to have to support, especially, again, with the sway in skyscrapers. There's probably a very good reason they put fire pumps in the basement to feed sprinklers instead of gigantic water tanks on top of them. Can you do it? Sure. Would you do it? I doubt it rather strenuously.

I don't think you can look ... (Below threshold)

I don't think you can look at it as 'extra floors', which I considered at first. The difference is that 'extra floors' would also be providing structural support both for themselves and the floor above them. Water tanks are just sitting there, a big old sloshy lump (again, the building will sway) at the top of the building. The tanks themselves would need to be much heavier to support the sloshing than normal tanks, so that's even MORE weight that's just sitting there at the end of the stick swaying back and forth. There's quite a difference between another floor or two that is supporting itself via complex trusses and steel girders and having a building that has to not only sway with the wind, but as it sways it takes it's own weight and then more than 4000 tons suddenly sloshing over and adding to the moment every time the wind blows, just after the support structure, the building, has already stopped it's own sway. Again, you could do it, but I can't imagine how much bigger the building would need to be just to support such a design.

Nick is correct that the wa... (Below threshold)
WildWillie:

Nick is correct that the water is used to equalize the pumps at times. But the tanks are there in case of a power outage and the fire pumps cannot push water through the sprinklers. Gravity will force the water down. Yes, I believe the building could hold the weight, but I have to see the size of the tank, because all skyscrapers sway, even is undetectable, but water rippling back and forth at that size will cause some twisting problems. IMHO. ww

Some condo/office tower des... (Below threshold)
hyperbolist:

Some condo/office tower designers do put swimming pools on top of structures as it is much easier to let gravity pump water through a sprinkler system than to send it skywards from a tank in the basement. And a swimming pool is a much more even distribution of weight (with no wind resistance) than tanks with four legs attaching them to a flat surface.

I'm not a structural engine... (Below threshold)
J R:

I'm not a structural engineer, but it is common for buildings to store water either on the roof or inside the "penthouse" level. I believe any building in NYC must supply its own water pressure above the 5th floor, for example, and that is usually done with a relatively small tank maybe 15-20' in diameter and 10-15' high. That's roughly 15,000 gallons.

Now, having said that, 1M gallons is excessive. There's no need for that quantity of water to supply any single building, or even any single complex. That quantity of water would be the per capita daily use for about 6,700 people, and would include all uses including showering, dish washing, lawn care, etc.

So the answer is that a) yes it is possible, b) it is done, but on a much smaller scale than in the movie, and c) storing 1MG on the top of a skyscraper is inefficient and would never be done in practice (IMO).

The 1 million gallons of wa... (Below threshold)

The 1 million gallons of water would weigh over 4100 tons. That seems like an awful load but its not so much in reality. The load isn't carried by the floor but by the whole structure and the weight is transmitted down through the structure to the building's footings.

I looked around and found some estimates that had been bandied about after the collapse of the WTC towers. If those numbers have any validity, a million gallons of water would weigh less than adding another floor to the building.

Falze's premise is in error. If you were going to add tanks to hold 1 million gallons you would put in the structural support to hold them. You wouldn't set them out in the middle of the floor like a dining table.

Whether one would put 1 million gallons on a floor of a skyscraper is an irrelevant question. The movie had the tanks. Maybe the architect wanted lots of pressure.

I am an Architect.Al... (Below threshold)
tyree:

I am an Architect.
Although that amount of weight on the top floor could theoretically be compensated for, the cost would be enormous. Every pound on the top floors multiplies all of the way down the structure. In the hospital I just finished the steel columns in the basement have flanges that are 2" thick, and this building is only 7 floors.

That movie made me angry all of the way through. Undersized wiring, exits blocked with concrete, movie stars with bad hairpieces, it's an abomination. Even if a crooked developer tried to build such a structure, the Architect, Engineers, Building Inspectors and Fire Inspectors all spend months at the construction site watching everything that is going on. I just can't imagine too many electrical engineers "forgetting" that the wiring was supposed to be 14 gauge.
The stupidest line in the history of bad skyscraper inferno films was uttered by Steve McQueen, the fire cheif who said:

Chief O'Hallorhan: You know we were pretty lucky tonight, body count's less then 200. You know, one of these days, you're gonna kill ten-thousand in one of these firetraps, and I'm gonna keep eating smoke and carrying out bodies until someone asks us... how to build them.

Absolute, complete and total BS. Fire Fighters and their knowledge and experience have been part of the construction process in this country for over a hundred years. Good rule of thumb, just about everything in the building code is there because someone died in the past because it wasn't there. The people who use that code every day know that.

9. Frank - it isn't an irre... (Below threshold)
J R:

9. Frank - it isn't an irrelevant question. That's a hell of a lot of money to add as dead weight. (If you add another floor, you can rent out that space.) Furthermore, the water pressure is truly IRRELEVANT to the QUANTITY of water stored. A 50,000 gallon tank that holds water 10' deep provides the same pressure as a 50 gallon tank holding water 10' deep. The difference between the two is how often your pump cycles on and off and how much water is used before water pressure begins to noticeably drop. Or you could simply use hydrostatic tanks.

"The movie had the tanks."

yea, and the other movie...
"had the aliens"
"had cartoon characters"
"had vampires"
"had time travel"

That was the author's point - that just because it was in the movie doesn't mean that it would actually happen in real life.

That they even built that t... (Below threshold)
hermie:

That they even built that tall a building in San Francisco of all places (unless they forgot about earthquakes in California), lets you know that this was just a figment of a Hollywood writer's imagination.

Is this a metaphor for the ... (Below threshold)
epador:

Is this a metaphor for the Obama Campaign or the McCain campaign?

Actually, Frank's imagining... (Below threshold)

Actually, Frank's imagining of my premise is incorrect. If you were going to add tanks to hold 1 million gallons you would put in the structural support to hold them. You wouldn't set them out in the middle of the floor like a dining table.

Not sure where you got that from what I said. All I said is that no matter how you support it, that load has to be, ultimately, transmitted down through the structure because it can't be supported, unless you freeze it, like a penthouse level. Even if you just make a big reinforced 'level' at the top, full of water, it's going to slosh and create the moment issue I described, unless, again, you freeze it. It seems to me it makes little difference how much weight you just add to the top of a building from a downward force perspective, but if you add 4000+ tons of accelerating water to the movement of the building every time it gets breezy, well, let's just say it's a bad idea. I suggest keeping your mindreading attempts to yourself.

Assuming you had a million ... (Below threshold)
Mac Lorry:

Assuming you had a million gallons of water at the top of a skyscraper, would blowing them put out a fire that was well established in several floors below? I don't think it would. The water would flow down elevator shafts and stair wells, but it would need to totally flood the floors below to reach all parts of the fire. Any floor that flooded to the ceiling would allow most of the water to escape out of burst windows rather than draining to the floors below. I doubt there would be any water entering into rooms more than 5 to 10 floors below the water tanks.

I'm not a nuke, but I am an... (Below threshold)
ExSubNuke:

I'm not a nuke, but I am an ex-nuclear submariner (imagine that), and I did some quick math. Supposing that a single cylindrical tank containing 1,000,000 gallons were to take up all possible space of one of the World Trade Center's footprint (208 ft/side therefore a radius of 104 ft), the tank would actually be just under 4 feet tall. That's taking up the WHOLE footprint (minus the corners).

More modest radius dimensions (52 ft radius, taking up a little under half of the space of a floor) gives us ~15 ft tall. A more reasonable size of 60 ft diameter (30 ft radius) gives us 47 ft in height (almost 5 floors assuming 10 ft/floor).

So those are some of the dimensions of a SINGLE tank. A more efficient use of space would be more tanks (as I saw in the movie). Let's assume 4 equal size tanks, for ease of math, let's just split up the 30 ft radius tanks (as I already did the math). Therefore just divide the height by 4 and we get just under 12 ft tall each. Factor in a base for each tank, thickness of the tank walls, and it's reasonable for the tanks to be under 20 ft (2 floors).

Now, as to the sloshing of the tanks from the swaying, that probably wouldn't be Too hard to prevent. A series of internal walls with baffles within would reduce the rate of the water sloshing from one compartment to the next, thereby reducing the fluid hammer.

As others have already stated (and I really don't feel like doing the math right now), the weight isn't unreasonable, the size would take up ~ 2 floors height with plenty of space within the walls.

I started out thinking "1,000,000 gallons?!?! No way." Now that I run the numbers... it actually sounds reasonable.

Whoda' thunk?

I meant to say, I'm not an ... (Below threshold)
ExSubNuke:

I meant to say, I'm not an architect. I was a "nuke". Anywho, you get the drift.

Nice comment tyree. <... (Below threshold)
ODA315:

Nice comment tyree.

Should have been a line in the movie where somebody asks McQueen, "Hey, what does NFPA stand for?"

So instead of the water hit... (Below threshold)

So instead of the water hitting an outside wall it's now hitting a series of inside walls. Not sure how that helps us with our moment problem. It helps us with water hammer, sure, but not the moment problem. But unless the building corrects before the water all gets where it's going it's eventually going to get there and create the moment problem. And if the building does correct before that, you have another whole problem of the building going one way while the 4000+ tons at the end of your stick is still going the other way. I'm guessing you can watch your two half-million gallon tanks belly flop off the top of the building at that point. Again, all do-able, though with enough reinforcement...but, again, no one would do that.

Falze, why would anybody pl... (Below threshold)
hyperbolist:

Falze, why would anybody place tanks on top of buildings? Swimming pools (esp. in penthouses) are the most cost-effective, kill-two-birds-with-one-stone-by-getting-the-jerk-in-8,000-square-feet-at-the-top-to-pay-for-it way of pressurising a sprinkler system in a tower.

There is a condo building going up across the street from my office--"Canada's tallest residential condominium/hotel/retail development"--which is going to be 81 storeys high. The penthouse has a pool in it. Pretty cool in that one side of the pool is Plexiglas, so it will seem like you're about to swim off the edge of a 900 foot high building. In the event of a fire, the pool drains and water is routed to wherever it needs to be.

(Sorry--the point of that i... (Below threshold)
hyperbolist:

(Sorry--the point of that is, nobody needs to put 4,000+ tons of water on top of a building, I don't think.)

why are you asking me? I s... (Below threshold)

why are you asking me? I said in my initial comment that it's not a good idea. nevertheless, that's what the movie depicts. If you want to have a hypothetical million gallons of water to dump on a hypothetical burning skyscraper in a blast and gush of water, the rich guy's swimming pool isn't going to do it. reading comprehension - try it sometime.

I am a process chemist (doi... (Below threshold)
Brian The Adequate:

I am a process chemist (doing the job of a chemical engineer) supporting pharmaceutical manufacturing.

The tanks they show getting wired up are (based on the apparent dimensions of the tank versus the actors) somewhere in between the 4,000 gallon production vessels and the 10,000 gallon storage vessels at my plant. We also have a 1 million gallon underground tank storing fire fighting water. Trust me that the 1 million gallon tank is much bigger than anything you would have as water storage in a real skyscraper.

As for why you have the storage at all, primarily it is that to move the water up to the top of the tower requires a lot of pressure to overcome the force of gravity. It is much easier to run plumbing fixtures off of low pressure lines, so the high pressure pumps feed the tanks at the top of the building (and usually tanks at intermediate levels for taller buildings. With a gravity feed off of these tanks supplying the low pressure plumbing we are all familiar with.

A secondary consideration is that pumps run better when they run steadily. The water tanks act as a wide spot in the line to give surge capacity and compensate for inconsistant demand. The system would be designed to pump the average daily demand, with the tank level rising at low demand times and dropping at high demand. The pumps run steadily which increases the working lifetime and lowers maintainance costs.

Thanks ODA 315Herm... (Below threshold)
tyree:

Thanks ODA 315

Hermie- not a bad thought but generally off base. For very tall buildings the wind load is substantially greater than the earthquake load. In other words, if a 135 story skyscraper can stand up to a 125 mph wind, it can handle an earthquake. Thats a "little" over simplified, but basically correct. Engineering huge structures is complex. Have you seen any of the new designs for twisting skyscrapers? The shape allows the wind to spill over the edges, that means the whole structure can weight less and still stand.

Hey Bill, bring on the next question!

So our answer is that it CO... (Below threshold)
ExSubNuke:

So our answer is that it COULD be done. My question, then, is WHY would you need that much water at a high level, and just how much would it cost?

I just read a puff piece on... (Below threshold)
Douglas2:

I just read a puff piece on a new residential tower in San-Francisco with a giant water tank on the top, and googling found this:
"An innovative device is the liquid tuned damper that tops One Rincon Hill, installed last summer after extensive testing at the University of Western Ontario, London. The water-filled device takes up an entire floor at the top of the tower and resembles a gigantic fish tank. It provides not only dampening of sway in high winds or an earthquake, but also fire protection" from www.constructionequipmentguide.com




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