Thud (knock) noise coming from area between ceiling and roof

Daven · Sep 03, 2019 10:47 am

Good day. I would appreciate help to try identify source of noise. I am in the top floor of an apartment block, and have a thud (knock) noise, a very definite thud, no warning and no after shudder. Sounds like it's coming from junction between concrete roof slab, external wall and drop ceiling. Very localised. Definitely localised inside ceiling space as it is not muffled.

It happens almost every hour, sometimes up to 5 times in an hour, day and night. I have checked, there are no utilities in the area, no aircon ducts, water pipes or electrics. The only things I can identify in the area where the noise is coming from are 1) slip joint between slab and wall and 2) the steel u latice system used to suspend the ceiling from the slab.

When temperatures are consistent it appears to drop off. As soon as we have variability, it starts up. So one thing I have managed to narrow down, its temp variation related. There is no evidence of structural damage - cracks.

Possible causes.
1) can a flaw in a slip joint cause an instantaneous localised thud to occur with expansion and contraction of a slab, or
2) is it possible that some flaw in installation of the suspended ceiling brackets cause that noise when one has slab contraction or expansion, with the sound being amplified due to the ceiling cavity or
3) is there something else that could be the cause that I need to investigate

As the noise is a definite thud (knock) almost like a valve flap shutting, I would not have thought the slip joint would cause this, as far as the steel u-system is concerned, being steel I would have thought if it was that it would have a cluck noise, not a thud.

I am at a total loss, but need to solve as it is very intrusive.

Any ideas would be appreciated. I am hoping with some ideas I may be able to pin point the cause before I start cutting away ceiling to do detailed visual inspections. At this stage I am at such a loss, the only option I can think of is to open a man-hole and carry out visual observation of area in question.

Saint Mike · Sep 03, 2019 11:30 am

I don't know - but could it be water hammer …

Daven · Sep 03, 2019 11:38 am

Thank you for reply. That would be the most logical and I have considered it, however, the water pipes are located 2 rooms (approximately 10 m away) over from location of noise and dividing walls all go up to slab level, so would not have thought the sound would rebervarate to that extant, unless i am wrong.

StructuralBIMGuy · Sep 03, 2019 12:32 pm

Daven

Good day. I would appreciate help to try identify source of noise. I am in the top floor of an apartment block, and have a thud (knock) noise, a very definite thud, no warning and no after shudder. Sounds like it's coming from junction between concrete roof slab, external wall and drop ceiling. Very localised. Definitely localised inside ceiling space as it is not muffled.

It happens almost every hour, sometimes up to 5 times in an hour, day and night. I have checked, there are no utilities in the area, no aircon ducts, water pipes or electrics. The only things I can identify in the area where the noise is coming from are 1) slip joint between slab and wall and 2) the steel u latice system used to suspend the ceiling from the slab.

When temperatures are consistent it appears to drop off. As soon as we have variability, it starts up. So one thing I have managed to narrow down, its temp variation related. There is no evidence of structural damage - cracks.

Possible causes.
1) can a flaw in a slip joint cause an instantaneous localised thud to occur with expansion and contraction of a slab, or
2) is it possible that some flaw in installation of the suspended ceiling brackets cause that noise when one has slab contraction or expansion, with the sound being amplified due to the ceiling cavity or
3) is there something else that could be the cause that I need to investigate

As the noise is a definite thud (knock) almost like a valve flap shutting, I would not have thought the slip joint would cause this, as far as the steel u-system is concerned, being steel I would have thought if it was that it would have a cluck noise, not a thud.

I am at a total loss, but need to solve as it is very intrusive.

Any ideas would be appreciated. I am hoping with some ideas I may be able to pin point the cause before I start cutting away ceiling to do detailed visual inspections. At this stage I am at such a loss, the only option I can think of is to open a man-hole and carry out visual observation of area in question.

I suggest you get copies of the Structural Engineering Drawings and post back with photos.
The more info you put up the better the reply, which also helps others. hth

Daven · Sep 03, 2019 5:29 pm

Thank you, I do agree, will try and access plans and share. A while back I did look at them, but there was nothing unique about the build.

StructuralBIMGuy · Sep 04, 2019 11:38 am

You are welcome, It may well be thermal Expansion within the roof space
Do a thermal plot using a
BOSCH Thermo camera and detector
Bluetooth the data and image

let me know if you need specifics, I can put up an example
Cheers
Chris

Daven · Sep 04, 2019 11:48 am

Chris, appreciate suggestion. Just a question, if it is thermal expansion, what could cause it to make a thud, I would have thought slab thermo expansion/contraction would run along the full bearing length of the slab on the brickwork, and not be localised.

Reason for asking the noise is a precise sound and in a very specific location, without opening the ceiling I can by standing under the area almost narrow it down to a metre in from a corner. Its almost like an impact of a hammer, but a hollow thud (amplified by space in ceiling), not a crisp knock.

I should have mentioned that I am a structural engineer, problem is I have not practiced in 30 years, so very short on current knowledge.

I do have a sound bite on my phone, not sure how to share it.
Really appreciate help, this is doing my head in.
Thanks
Daven

StructuralBIMGuy · Sep 06, 2019 10:54 am

Daven

Chris, appreciate suggestion. Just a question, if it is thermal expansion, what could cause it to make a thud, I would have thought slab thermo expansion/contraction would run along the full bearing length of the slab on the brickwork, and not be localised.

What you have described sounds familiar (excuse the pun) in cases where Steel composite structural flooring is used?
Hence the need to check the certified engineering drawings against the As Built

Daven

Reason for asking the noise is a precise sound and in a very specific location, without opening the ceiling I can by standing under the area almost narrow it down to a metre in from a corner. Its almost like an impact of a hammer, but a hollow thud (amplified by space in ceiling), not a crisp knock.

Are you able to remove a light fitting or drill and small inspection hole into the ceiling and use an Bosch Cordless Inspection Camera

Daven

I should have mentioned that I am a structural engineer, problem is I have not practiced in 30 years, so very short on current knowledge.

Good to hear then you will have no issues in solving the problem as the science/math is still the same.
OT, I often use FEM Multiphysics simulation presentations and Bim data in illustrating problems and fixes
IMO it is the data collection,technology and BOSCH tool applications that has made the real impact.

I am keen for you to find a resolution

leave a PM or email appsb4UBuild (at) gmail
Cheers
Chris