strange problems

huangyhg

strange problems
this problem has occurred in a  six story concrete building, 42ft x 100ft. simple plan, regular structure. the strange thing is that all of the sudden the floor marble tiles simply popped out completely.
please see the photograph and plan as attached for illustration
what could be the possible causes.
i personally think that the floor beam below this specific strip has deflected, as there are bending cracks visible in the beam immediately below.
you are possibly correct. can you take levels to check deflection? why has this beam deflected more than the others to cause this problem?
don't overlook concrete slab shrinkage too.
mike mccann
mmc engineering
slab shrinkage ?
the temperature change is not too much. it is a controlled environment. secondly the slab is 5" thick and not large spans involved.

you don't say how old the building is or how long that flooring had been in place.
also where are the joints in the finishes?  there is a possibility that this is simply due to movement stresses within the finishes being released due to one tile de-bonding and then propogating across the floor. - lets hope so.
i concur with sdz - please get a level survey undertaken
i agree with mike..i'd look at shrinkage.
we see this a lot in slabs on grade, less so in elevated slabs, mostly because they are not usually covered with rigid tile.  while it usually occurs early on in the life of a structure, i've seen it take several years to develop.
many times you do not see it simply because the tiles are not bonded well to the slab, but when good bond occurs and remains, this can happen with drying shrinkage in the concrete.  this is likely to manifest itself over larger masses of concrete, because of the larger volumetric shrinkage.  further, rigid tile somewhat "protects" the concrete from drying faster due to ambient dehumidification of hvac systems, thus these areas will be slower to realized comparable drying shrinkage to those exposed or carpet covered.
while some deflection and creep can exacerbate the issue, it is more likely that the drying shrinkage over time has resulted in pent up compressive stresses in the tile and that ultimately cause the tile to shear, either at the tile plane or the thinset/grout plane.  most often these failures occur quickly (though the onset takes a long time)and they can be quite loud, sounding like a gunshot.
if this were a post-tensioned structure or even prestressed, i'd look at strand relaxation or slippage; however, you stated it is a "regular structure", implying conventional reinforcement.
the cracking you see might well be shrinkage cracks, not flexural cracks.  as others have suggested, check the deflections against other beams to see if this location is different.

could be a combination of shrinkage and long term movements (deflection and shortening). this is a common problem with tile bonded to slabs over large areas and inadequate expansion joints. the tile moves with the structure and tries to take on compressive load until it cracks or buckles.
clay tiles generally expand over time (like brick) and the concrete shrinks and creeps.  if the tiles are located in a compression area of the beam, there might be some compression load due to creep.
dik
how old is the building?  possible effects of creep plus shrinkage and deflection.
ron,
nice answer very informative...star for you.  
check also for any visible cracks above or below the concrete slab surface. these type of secondary beams are assumed normally as pinned in design and i think that beam release for becoming pin at support.