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Infant shaking a crib

Infant shaking a crib

Infant shaking a crib

I'm a test engineer and am seeking advice on how effectively an infant could shake a crib to failure. Shaking loosens hardware like screws (over time) while impact can cause outright failure.  It is known (and quite intuitive) that infants don't have alot of strength.  Still, hardware loosens on cribs but correlation to shaking is anecdotal. The most damaging way to shake a structure (crib) is at forced resonance wherein a small force quickly results in large motions --- motions equal potention for joints to loosen even before outright failure.  I know resonance is learned for walking and for swinging, but at a more advanced age.  Infants like movement, so maybe they would be inspired to get the most movement out of their crib?

My question is this:  For infants, either on all-fours or upright holding onto a crib rail, what is the approximate age at which they can move in resonance with a crib?  Is there a source for information on this topic?

RE: Infant shaking a crib

I bought a used crib and put it together myself and neither of my two kids shook anything loose or apart.

Nonetheless, you should be a ble to swag numbers for infant weight an height from growth tables and swag some numbers for frequencies.  Borrow your friends' baby videos and see what they do.


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RE: Infant shaking a crib

Well, so what I say about anecdotes?  To be upfront, crib injuries related to hardware failure are pretty rare.  But we treat rare with great respect w.r.t infants/children.

I like your idea to review videos of kids in cribs.  

Thank you.

RE: Infant shaking a crib

maybe it's the parents "rocking" the baby to sleep, creating the resonance.  Any reports of this?  As far as hardware coming loose, I would expect expansion and contraction due to temperature fluctuation to play a greater role than infant movement.

Aaron A. Spearin
Engineering Six-S'$

"The only constant in life is change." -Bruce Lee

RE: Infant shaking a crib

I'm not schooled in all the cases and there assigned causes.  But parents have been suspected in some cases, for a variety of reasons.  But I think you make the case that parental "rocking" is possible and of course "rocking" entails resonance.  

Wood shrinkage can cause loosening as the moisture in the crib drops, especially during winter.

RE: Infant shaking a crib

That would seem to depend on the type of fasteners employed, I would think.  My kids' crib used threaded inserts throughout.


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RE: Infant shaking a crib

Here is an idea... Put some rocking chair like legs on the bottom for when they do rock, nothing will come loose! Put a wheelie bar on both sides! You have a rock a by baby crib that is designed for what the rocking baby actually wants...

RE: Infant shaking a crib

Most cribs are high CG, particularly with kid in residence, and putting them on rocker legs is probably asking for even more trouble.


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RE: Infant shaking a crib

geauxinspect is on tract to eliminate the problem I've presented which is can a baby/child be expected to find the resonance of a crib and exploit it (for his/her own pleasure).  IRstuff points out that a crib rocker would be over-center unstable.

I'm guessing their are no human factors types that can point me to a study of baby kinesthesis for perception of resonance. I can still find videos of kids and view the frequency of rocking and estimate whether resonance was achieved.

Thank you all for your interest.

RE: Infant shaking a crib

Another thing to keep in mind, Since I am a father of seven I believe I can say this with a little confidence in my train of though... it would be interesting to know how many failures are from poorly constructed cribs by the parents themselves, if the husband or wife put the crib together as you are probably aware you always start strong and when you are in the middle of the project you are thinking damn I wish this was done...especially if there are other kids in the house and they are trying to help… parent get distracted and maybe doesn’t  tighten every bolt or screw as tight as it should be

RE: Infant shaking a crib

It is good engineering to consider that resonance may be a factor in crib destruction.
The next step may be a reality check. What is the resonant frequency (or frequencies)of a crib?
The answer may be out of the range of frequencies that an infant may reasonably be expected to generate.


It is known (and quite intuitive) that infants don't have alot of strength.
True, but after a few kids and the experience of trying to remove something from an infants grasp, my "intuitive assessment" of the strength of an infant was revised upwards by almost an order of magnitude.

"Why not the best?"
Jimmy Carter

RE: Infant shaking a crib

Waross is on track: measure the frequency.  

Waross:"The answer may be out of the range of frequencies that an infant may reasonably be expected to generate".

True.  And I can measure it.  But who will tell me what frequencies are within range?

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