U hook deforming force

[Ainchains]

I have an unknown grade of steel (Rb85) round U hook with 1.25" diameter legs mounted to serve as an anchor point. One day the hook was found deformed (in the same plane as the legs so the 'U' was now a CJ if that makes sense). the hook was bent, but the legs had not stretched enough to neck down,or buckled so the force must have been just over the yield point (~40+-ksi?). A new hook was installed, and one day it appeared deformed again. I don't who or what is deforming the hook, however out or curiosity when I tried to calc the force to bend but not break the hook, I get results in the millions of # which would exceed the strength of any wire slings or ropes I have around.
can someone explain to me the proper set up of this basic problem for me to solve; it has been eating away at my soul...

 

[desertfox]

Hi Ainchains

Can you provide a picture or diagram?

desertfox

 

[Ainchains]

simple dwg as requested to show the bent hook

 

[kelowna]

Not much info. A pack of pink furious elephants could be doing that damage.

My guess is that you are calculating the force required as a static load, where a much more likely cause is impact loading.

 

[desertfox]

Hi Ainchains

Are both ends of the hook built into the floor or some structure? I was going to suggest use a strain energy method but I see a complication if both ends are built in.
Also How have you gone about calculating the bending force? where have you considered the load to act and finally what are the dinmensions of the hook apart from the 1.25" dia you have give us already.

desertfox

 

[apsix]

I would say with reasonable confidence that your calculation result of 'millions of #' is incorrect.

As desertfox says, more information is required.

 

[TXStructural]

Do you have any idea what was attached when it was deformed?

You could get an approximation by starting at the base and computing what it would take to bend each increment. The load required to deform the shape would approximately be the force required to make the bend in both legs near the embedded end at once. The different bends happen simultaneously, and the ones nearest the base are probably the easiest to determine.

For instance, solid dowels would have a plastic modulus of (pi*d^3)/32 (=0.192 in^3 for 1.25"), and with a yield of 40 ksi (low), it would take:
# of legs(=2) x fy (=40 ksi) x Z (=0.2 in^3) = 15 kip-in
Assume a location of the load to initiate deformation somewhere near the center of the "C" in the "CJ" shape (on the un-deformed shape) and compute a force using this arm.
If the |original "U" shape was 4 inches tall, one might assume a 2.5" lever at the initiation of deformation. This would give 15 k-in / 2.5 in. = 6 kips to initiate a plastic hinge on the two legs at the base.

Obviously, I have over-simplified things, but this should be a rough approximation of what it would take the initiate yield. Once the steel starts moving, it will work harden, but will be moving. If the load was already moving when the force was applied to the U, it would take about 1/2 this amount to start the yield.

**** note that I have used made up values for fy and the location of the applied force****

Also, look carefully at the steel to determine where the load is being applied - determine if it is from something connected to the U (tension to the left or up and left), or it was from impact on the top (which would most likely bend it out of plane.) A close inspection will likely reveal deformation of the surface of the steel.

 

[Bobber1]

Are these lifting hooks and they are picking with a two-legged sling at too flat an angle, giving an extremely high lateral force on the hooks?