loads due to applying torque to the nut of a threaded bar in the middle of a simply supported beam 2

[jedstress]

Hello,

I am currently working on a fixture which is essentially a beam with upward forces being applied at both its ends. The centre of the beam reacts the total load via a threaded bar which is grounded at its base. The previous derivative of the fixture required that the threaded bar be torqued to 50Nm prior to applying the external vertical forces.

The previous calculations did not account for this additional load due to the pretorque of 50Nm. Should it have been included and if so then should the classical lead screw method be used to evaluate the additional force due to 50Nm? And is it simply a matter of adding the external fore and the torque force to get the actual total load in the system? Please refer to the sketch to elaborate on the setup.

Thank you.

 

[jedstress]

Hotrod10 Thanks alot for the clarification.

The previous report that I inherited had not accounted for this preload and had only stressed it to the applied hydraulic load despite the preload being far greater. And I couldn't even find any requirement for the pretorque yet the instruction manual stated it. It goes to show the importance of fully understanding the loading conditions.
And I fully agree with your previous statement regarding applying the precise required compressive force via the hydraulic route as opposed to the pretorque.
Thus I will most likely suggest the client to pretorque it to an amount roughly equivalent to the hydraulic force just to ensure minimal gapping whilst also helping to minimise changes to the existing report.

Thanks once again for the support at such short notice.

 

[desertfox]

Hi

Whilst I agree with the preload being at least that of the force due to hydraulic pressure, I would like to add that if this fixture is used frequently and the rod is subject to zero stress and then stress do due cylinder pressure, then the screw needs to be analyzed for fatigue.

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

 

[rb1957]

why are you applying so much clamp-up to this ? The nut (whatever you're torqueing) will freely turn until it bears up against the beam.

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

 

[jedstress]

Hi desertfox.
The item is used occasionally and thus fatigue should not be of concern.

Hi rb1957.
The clamp up load has been inherited from the original design and only minor mods have been made to the design. Thus the load is a carry over from the original spec. It has been questioned but client insists on it.