huangyhg

vibration and cracks in the building
in couple of days i need to inspect a building on clients request. she says that there are cracks formed in the building in underground parking garage ceiling etc. adjacent to building is a vacant land where some one is trying to grade using a bulldozer dragging a steel beam behind. client says building also vibrates when this grading operation is in progress.
building is 8 years old, see picture attached. isn't building too massive to be disturbed by one grading operation? any tips!

i'd never say never, but it seems unlikely that the relatively small vibration caused by a bulldozer would crack a basement
i can believe the grading operation is casuing the building to vibrate.
a fairly well know case locally is of a hotel's laundry extractor (squeezes the water out of the laundry before it goes to a dryer) vibrating the entire 20 story hotel so bad people could not sleep if they ran it at night. people in large adjacent buildings could feel the vibrations during the day.
the extractor only weighed about 1,000 pounds, but it could get entire buildings vibrating.
vibrations are a whole different game, and should not be underestimate.
that said, i am not sure why these vibrations would casue cracking in a ceiling. it will be awefully hard to prove the grading was the casue of the cracks.
i'm with the other guys. it seems extremely unlikely to me that this operation would cause cracks.
it would be neat to put an accelerometer on the ground and measure the magnitude of the ground accelerations.
it is unlikely that damage is resulting from a grading operation. the vibrations from that are relatively low frequency and in order to cause structural damage would require relatively high magnitudes, which the operation is generally not capable of producing.
monitor the vibration using a sensitive seismograph. these are available for rental and will tell you conclusively that the magnitudes and frequencies are insignificant.

yes, and also look at the cracks very closely. evidence sometimes exists that would show the cracks to be older than the grading operation:
paint that dripped or was spread into the crack.
weathered corners of cracks vs. sharp, feather edges.
evidence of water leakage and calcium staining from inside the crack.

my response just disappeared!
i use a pocket microscope to check the cracks and look for pristine surfaces, discolouration and insect 'stuff' in wider ones.
often cracks are 'discovered' during/after adjacent construction. someone notices a crack that wasn't noticed before and then starts looking and finds others.
the photograph shows a building that appears very rigid and stiff and it is unlikely that it was damaged due to the small energy from the grading operation. as ron notes, the frequency of vibration from the grading would likely be well outside the response spectrum of the building.
good points jae...i should have mentioned those as well (dik, we're just too slow!)since i recently gave a deposition on exactly that subject, having to do with recent change in railroad traffic and alleged structural damage to 4 buildings. we found cracks with old paint in them. even one of the windows was cracked and had the building's previous color paint in the crack.
that is quite a good sized building. the most common cause of cracking in the underground floors is restraint by the basement walls. the resulting shrinkage cracks are not usually structurally significant, but can be a nuisance if water leaks through the cracks from one parking level to the next. i agree with others that vibration from a grading operation would not cause cracking of the floors.

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