Design with a Moving Load

[JT-1995]

I am looking at a machinery foundation design. Given the machine vendor drawings there is a reciprocating load identified as "10,000LBSF @1.0G". I know the center of mass location of this load. What is bothering me is translating this load into a static load for design. I have spoken to the machine designer and their intention is that there is a 10,000lbf item that is accelerated horizontally from stationary to "full speed" at a 1g acceleration. The item moves at that velocity for a couple feet and then decelerates to zero at 1g. Am I correct in applying F=ma (10,000/32.2)* 32.2) = F=10kip static load (acting horizontal at a location of the center of mass). That seems over simplified. Any help or confirmation is appreciated.

 

[GC_Hopi]

Search the forum there is quite a bit on this topic. Also recommend reviewing ACI 351.3R, foundation for dynamic equipment, and I would ask the manufacturer what they have seem for the foundation on past installation, get some drawings or sketches. No point re-inventing the wheel.

 

[JT-1995]

Thank you for the thoughts GC Hopi. The "foundation" I am designing will start with structural steel legs under the machine and then include the concrete foundation. I will review ACI 351.3R for some guidance, thanks. I have looked through the historical threads and found some general discussions of moving loads but not of the sort I have. Maybe my search terms are not guiding me to the right place.

 

[GC_Hopi]

I could be wrong but it sounds like the moving load is a piston in some sort of machine. I would search the forum for equipment foundation if you search using the term moving load you probably will get a lot of traffic related results.

 

[driftLimiter]

Ya I am curious about the reciprocating rate, and the stroke length of this mass. It feels like to me that the manufacturer owes you and the client some minimum component reactions. If the '10,000 lbf @1.0G' is all you have been given it feels like a lot of risk me.

 

[GC_Hopi]

Here is one post Link. I agree with driftLimiter. Push the manufacturer a little harder, generally they have more info then they let on. I think they consider it IP so they dont share it very easily.

 

[SlideRuleEra]

...10,000lbf item that is accelerated horizontally from stationary to "full speed" at a 1g acceleration. The item moves at that velocity for a couple feet and then decelerates to zero at 1g.

Am I correct in applying F=ma (10,000/32.2)* 32.2) = F=10kip static load (acting horizontal at a location of the center of mass). That seems over simplified. Any help or confirmation is appreciated.

For the magnitude of the horizontal force, yes, 10,000 lbf... it is that simple.

Of course the direction of the 10,000 lb force alternates... one way during acceleration, the opposite way during deceleration.

Also, the duration of the 10,000 lb horizontal force is only during acceleration / deceleration.

And keep in mind that location of the 10,000 lb item is constantly changing during acceleration / deceleration.

That's the short answer. There is a branch of mechanical engineering, kinematics of machinery, that deals with the details.

 

[JT-1995]

I appreciate the feedback. Thank you for your time.