Residential cracks due to vibration?

[psychedomination]

Hi there,

My company would like me to carry out a structural inspection on someones house as they are complaining that some of our machinery has caused vibration, which created numerous cracks in their house.

I must admit, this job seems like a fool's errand, as even if they have cracks I cannot definitively state that they are the result of vibrations?

Does anyone have guidance on this sort of assessment? Is there a guide on cracks that are typical of vibrations or similar damage?

Any tell tale signs that I should be looking for?

Any guidance or help you can give would be greatly appreciated.

 

[jayrod12]

Look to see if the edges of the cracks look sharp and fresh. Whether there's paint inside the cracks or not.

Looks for sign of previously repaired cracks.

Often people have houses that seasonally shift, then there's some construction nearby and they claim all these new cracks have opened up where they didn't have any before.

The biggest problem is without evidence of condition prior to the vibration they really don't have a leg to stand on.

 

[hokie66]

jayrod is correct. Without a preconstruction condition report, it is impossible to say.

What kind of machinery are you talking about? Piledriver? Vibratory roller?

 

[dik]

It helps to have a small pocket microscope to observe the crack edges. Home owner should be retaining an engineer to provide a report about the cause. Also, it's prudent to do a condition inspection prior to undertaking the work. If you are the potential cause, I would not rely on a report from you. Without a preconstruction report it may be difficult to disprove.

Often the homeowner is not trying something 'fast'. As a result of constuction, the home owner may notice a crack that's been there for decades, and think it is new.

Whenever I've done these types of reports, I inform the homeowner that I'm employed by the other protagonist, but my report will be essentially the same and it doesn't matter who's hired me. This has gotten me into a little difficulty with one particular insurance company (SF) who deny damage as SOP, notwithstanding the cause. I've often suggested that a homeowner retain his own expert.

This is actually part of my standard report template that the homeowner was informed of my impartiality and was advised that he could obtain alternate professional opinion.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[ThomasH]

Hi
Who has the burden of proof in this?
Can you prove that the cracks were there before the vibrations? Can the homeowner prove that they weren't?

If you machinery is still causing vibrations in the building I think you should measure the vibration levels. Those levels might be able to give you an idea regarding the risk for cracks in a building.

When you write "My company" and "our machinery" and ask for advice. I suspect this can become fairly costly for the company. So I think you should ask somebody with experience in this type of work to do the investigation.

Thomas

 

[1503-44]

Assuming you want to fairly address and resolve the engineering aspects of the problem, I think you'd want to objectively determine if the work conducted had the possibility to do the damage. I think it requires more than a crack inspection.

Did the machinery have the capability to do the damage? What loads did the machine apply? What was the range of vibratory frequencies applied. Was the machine operating at full rpm and power? How long was the machine operating in the area? Was the operator experienced doing similar work? Was there any previous experience where similar work was accomplished without any damages done? Should there have been enough reason to take precautions? We're any precautions attempted? What are the elastic properties of the soil and its potential response to the vibratory loads? How far away was the machine from the damaged portion of the structure? Could enough power have been transmitted by the machine over the distance to reach the structure with significant adverse affect? Examine the structure as well. What would have been the estimated load needed to cause the damage? Should the structure have been able to resist the applied loads? Was there a potential prior defect in the structure? Could the loads needed to damage the structure have been applied by the machine? Would those loads have caused the damages if applied?

If you don't answer those questions, you're only going to have ugly photographs to add to the pile of evidence against you.

A black swan to a turkey is a white swan to the butcher ... and to Boeing.

 

[271828]

Vibration that would cause cracking would be uncomfortable to the people. You might probe a little to see if they were made uncomfortable by the vibration.

The preferred metric for this is peak particle velocity (PPV) in in./s. That is just the peak velocity in a plot of velocity over time. PPVs that cause damage typically correspond to pretty high accelerations, higher than say the 0.5 %g limit that is used as the design limit for residential floors.

 

[HouseBoy]

I'd be curious as to what the vibration is doing to "cause" the cracking. (i.e. Is it ground motion or sound waves?)

About looking at the cracks -
How old is the house?
How long has the machinery been in operation?
What size are they?
Is there paint in the crack?

One simple "trick" I use (to try to detect previous repairs) is to shine a bright flashlight across the wall surface at a VERY shallow angle.

 

[Ron247]

Without a close inspection shortly before the work started, conclusions tend to be "best guess" unless you get lucky on some physical evidence.

Sharp cracks can be old if nothing was ever present to dull them. Loose debris in cracks is not as conclusive on a flat surface as it is on a vertical surface. Paint, caulk and sealants are great information but they only prove the cracks where you find them present.

As far as loads from the vibration, their magnitude is not as influential as being in the house during the vibration. If you can sense the vibration, that is not a good sign. Most concrete slabs, drywall and other construction components have stress present without the vibration. For example, should the drywall fracture at 100 psi, but it currently is only 70 psi, all the vibration has to do is add 31 psi to create a fracture. When a concrete slab gets a shrinkage crack, it does not set all the remainder of the slab to 0.0 psi tensile stress. So slabs tend to have tensile stress but not enough to crack them.

I agree that when something makes Owners curious, they go look closely and find cracks they have never seen before. They tend to believe they are new. There are 3 determinations on cracks, 1) new 2) old but has not changed and 3) old but has gotten worse.

I had a customer once who was laying on his couch and saw a thumbnail width crack in his tray ceiling. I will blindly bet any house with a tray ceiling will have one or more cracks and I will win 70% of my bets. Because of this he looked at his entire house very closely and became convinced it was literally falling apart overnight. He called me in a panic and I went out look at his house and found multiple cracks that I could easily prove were old. He had owned the house at least five years and thinks he looked at the house real close before he bought it. One of the bedrooms had the widest crack in the entire house and it had blue paint inside the crack. I asked the owner if he painted the room blue and he said that he did not. The room was blue when he bought the house. He was absolutely convinced that all these cracks were new but he did agree that the one in the blue bedroom was the worst in the entire house. I showed him the blue paint inside the crack and told him that was definitive that the crack was there when he bought the house and he still refused to believe me. I politely asked him to pay me for my time and that I would be leaving because I could not convince him that his house was not falling apart with that logic.