BTH-1 2005 combined normal and shear stresses - how to apply

[black79ta]

i am designing a drill casing pulling lug. the lug will never see the loads it is designed for but i want to have a complete design i can stamp and file away.

Question: how do you determine the shear stress that is used in the formula (3-37) that determines fcr? the most conservative way is to use a single plane thru the lug, not sure if that is right.

any thoughts are appreciated,

i have attached a sketch and some calcs so you can follow along my train of thought.

thanks in advance

 

[black79ta]

bump?

i hope i have not enclosed too much information, what i am looking for is the correct interpretation of the formula:

fcr = (fx^2 -fxfy + fy^2 + 3fv^2)^.5 is less than Fcr= Fy/Nd (3-37) from BTH-1-2005

this is the interaction formula for normal and shear stresses.

thanks

 

[ishvaaag]

It is just the comparison stress (I think von Mises) for the plane stress case when (fz=0); this you compare with the limit strength stress by your code.

 

[ishvaaag]

In the case of the old spanish MV-103 (steel code) where I have checked the equation all was set at the factored and limit strength level. It might be otherwise in your code, that I don't have, but would be rare, von Mises is usually seen against limit strength.

 

[black79ta]

ishvaaag, thanks for your response. i will look further into this. the code is "Design of Below-the-Hook Lifting Devices" ASME BTH-1-2005 if anybody is wondering