Bolt torque-safety factor in member relation

[takio]

Hello

When applying recommended torque from clamp manufacturer. (They said the clamp safety factor is 5, when using 109 ft lbs for 0.375 steel member.)
I get safety factor of 1.5~2 in members at bolt joint surface. but my requirement for the member safety factor is 3.
In this case, is this something that I need to worry about? because the manufacturer says it's ok to use the torque for 0.375" thick member.
or, is this something I just should go for a different clamp with less capacity, which means less preload.

I used FEA to see the safety factor.


Thank you

 

[rb1957]

?

are you saying the the plates that the clamp is clamping aren't strong enough ?

another day in paradise, or is paradise one day closer ?

 

[takio]

Hello,
Thank you for your comment again.
Yes that's what I meant,, it's carbon steel material.

 

[rb1957]

what calc are you doing (on the plates) to make you think you're crushing them ?

another day in paradise, or is paradise one day closer ?

 

[TugboatEng]

Are you using the right strength for your material? Carbon steel comes in a wide range of strengths. Common structural steel starts at 36ksi yield while HSLA steel commonly used for lifting equipment is 100ksi.

 

[desertfox]

Hi YOUNGTAKI

How have you established a 1.5 to 2 safety factor in the clamped components?

The manufacturer has designed those clamps to work on structural beams and I would think that They would have considered the steel grades of the beams etc before setting torque values for the clamps.a

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[takio]

Hello all

I ran FEA to see SF on the carbon steel member.
I used Carbon steel yield limit = 46000 PSI
The carbon steel surface area that bolt contacts to : 0.3in^2
Applied preload = 10440 lbf (109 lb-in)
Stress = 34800 psi
SF = 1.3

Thank you for the information on HSLA steel

 

[desertfox]

Hi YOUNGTAKI

I thought it would be the area of the clamp surface in contact with the carbon steel and not the bolt head, I also assumed that the area of the clamp in contact with the carbon steel would be larger than that of the bolt head. If this joint is purely static I don’t see a problem in any case.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[Joe591]

Maybe the safety factor they are quoting is based on UTS and conventional analysis?

 

[rb1957]

why run FEA when you're doing a hand calc (or are you checking your FEA ?)

Is fty the appropriate failure mode ?

another day in paradise, or is paradise one day closer ?