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Drop (suspended) ceiling tiles are of course quite common, but I am in the process of trying to evaluate the long term safety of a specific kind of suspended tile made of fired clay. enter image description here

When installed it looks like this enter image description here

The tile measures about 12 inches x 9 inches and weighs 2 kilograms.

Now the important point is that the tile is supported only on two ends and therefore a single breadthwise fracture causes it to lose all support. In such cases it has been observed that it may sometimes "hang in" for a few days before it falls out, but I don't think that is necessarily true. This type of tile has been widespread in its use in India for over a century now, and also in parts of Europe. Experienced engineers and architects of repute think this is as safe as any other type of suspended tile ceiling. From its design it seems that is not true. However its widespread usage seems to indicate that I am missing something. Does any structural engineer on the forum have an opinion or observation? Is this really as safe as any other suspended tile? If so what makes it safe despite the observations above? Thanks!

Ram
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    A single fracture in a single element often causes complete failure of that element, in any sort of structure. What we do is design the element to make that single failure unlikely. What we really worry about it when the failure of one element leads to the failure of the next element, which then leads (etc.). This isn't the case for ceiling tiles which aren't connected to each other. – AndyT Feb 02 '17 at 11:28
  • Thanks for your comment. In this case I think we would worry about the failure of a single element too: a single tile that fails could cause a 1+ kilogram piece to come crashing down on someone's head. Unless you have a very low ceiling that would be a problem! – Ram Feb 02 '17 at 11:57
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    Hence "What we do is design the element to make that single failure unlikely". – AndyT Feb 02 '17 at 12:04
  • Agreed, and so the fundamental question is, how do you design a fired clay tile to make such failure unlikely? Even if the tile is manufactured perfectly I suppose a single knock that may be effected while installing such ceiling or performing a house renovation can cause a fracture that may even be hairline in nature and not easily visible (as I have seen). Therefore would it be appropriate to conclude that unless every tile is inspected for hairline fracture after installation we cannot be sure? What about hairline fractures in the supporting lug which are not inspectable after installation? – Ram Feb 02 '17 at 12:20

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If it is tried for so many years with no incidents (or small number of them, that may come from wrong installation) then how can we say it is unsafe? Of course improvements can be made to any design and i will try my best to offer some.

The shape of the tile seems simple and convenient for easy installation and also can be stacked one upon the other for less transportation costs. As with any structure, we want it to be simple and economic. Since this is made of clay, I think a major improvement would be if its resistance to brittle fructure is enhanced, so that even if a crack initiates at some point it doesn't propagate too fast and even if a breadthwise fracture occurs, the tile doesn't break apart and fall down. This can be achieved with some sort of reinforcement, like concrete, where steel rebars reinforce and restore its lacking tensile strength. What sort of reinforcement? I can think of small synthetic fibers, or straw, that has been used since ancient times to reinforce clay bricks. But these fibers can be visible to the surface of the tile. Another possibility is a net of wires, placed in the mid-thickness of the tile. The goal is to prevent the tile from breaking apart and fall down, even if a serious crack develops. The size and type of reinforcement should be based on this requirement, Of course experimental testing should verify these claims.

Another approach could be to fasten the tiles at the wooden members, they rest on. This would be easy if the tiles were made with some holes at their ends (along the little step)

minas lemonis
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  • Involves no special steps to install - the tiles are merely placed between those thin purlins, period. What is more likely is that they can develop a fracture if placed "too hard" or during maintenance work (someone dusting the ceiling or painting/polishing the purlins and gives a tile a small knock) or when someone walks on the roof and the pressure causes a ceiling tile to crack at the lug where it cannot be seen. These can happen with good tiles and proper installation. Infrequent, but not ruled out by design. The real Q is, does one have to inspect all tiles after every maintenance job? – Ram Feb 07 '17 at 17:05
  • It is a matter of accepted risk. If you want to be safe, yes you should take any measures to ensure that all tiles are ok after any serious maintanance. But you can't be sure for events such as an eartquake. I believe if someone sleeps at that room when an earthquake strikes he/she is in serious trouble. In order to mitigate that risk you need a better design or removing them altogether. – minas lemonis Feb 07 '17 at 20:09
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Even if they cracked how would those tiles fall out?

It would take a wide crack for the tile to actually move. A hairline fracture would still have both the cracked faces leaning on each other. I feel like you'd notice significant failure before it fell down(or you're throwing heavy things at your ceiling anyways; so tiles falling down is only one of your worries).

JMac
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  • Interesting - is it possible to scientifically prove/establish that a piece of tile supported at only two ends cannot fall down if it has a hairline fracture in the middle? Or does that require assumptions about the shape of the fracture? – Ram Feb 07 '17 at 17:07
  • @Ram well a second fracture could make failure possible since then a piece can drop out. I'm not sure how easy it would be to prove; but a hairline fracture on it's own shouldn't do too much. – JMac Feb 07 '17 at 17:12
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Just because India has used it for a century does not mean it meets European safety standards. As with any construction material, a factor of safety should applied. In this instance it is good practice, developed over centuries of mistakes and fatalities, to imbue buildings with failsafes.

Were an infant lying on the floor to be hit on the head by such a tile from a height of 2m or more, the consequences could be life threatening and life changing injuries would likely result. Consider the legal implications of that worst-case scenario.

As with all structural design approaches, we look at the structure integrity for the purpose of safe and durable design. Clearly these tiles are durable undisturbed but should the be disturbed that may not be the case.

I would suggest application of fibre reinforcement by way of a mesh. If the tiles are fired and designed to be waterproof then steel mesh but if they are pressed and dried below 85°C, a plastic mesh might do.

In thinking of sustainable design, use of recycled materials may be a better solution. A simple sheet of paper has great tensile properties. Gypsum board is often reinforced this way. Woven paper strips may be a good option.

Let me know what you think

Rhodie
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