FOUNDATION DESIGN FOR HEAVY MACHINE

[Abdel22]

Hello everyone,

i have a some questions about machine foundation design.

1- do we have to do analysis for wind and seismic for heavy machine( 90000 lb)
or we have to show that overturning FS >1.5 , so no net uplift( but i m not sure witch chapter to use for heavy machine)
2- for anchor bolt, any way to find necessary length or just trial and error.
some reference advice to make anchor as long as possible

Thank you

 

[r13]

1. Yes, both cases need to be addressed, but wind might not govern for heavy equipment, and it is not required for enclosed equipment, except the enclosure. Follow ASCE7 procedures on chapters for nonbuilding structures to get anchorage force.
2. Follow ACI318 App. D for anchorage design.

 

[Abdel22]

Thank you for the clarification,

I did use chapter 13 and chapter 15( non building structures) to get the force.
The force from chapter 15 was more conservative.

i m following ACI318 App. D for anchorage design.
is there any rule of thumb for minimum embedment of anchor? our block foundation gonna be deep( around 4' due to weight of the machine (90000 lb)

Thank you

 

[r13]

If you are intended to use headed anchors, you shall follow App. D to determine the required embedment length to develop the pull out/break out strength required for tension. Or for relatively smaller strength requirement, you may consider using post installed anchors. The manufacture's catalog on its website has all required information.

 

[Abdel22]

Thank you Retired13,

 

[r13]

You are welcome.

One thing to keep in mind, when design anchor in pedestal type structure, the concrete is usually not sufficient due to the limited cross sectional area, therefore, the vertical rebars are to be utilized to provide resistant force. In such case, you need to extend the anchor to below the full rebar tension development length, and let the failure cone intercept that point.

 

[saikee119]

Normally the design of machine foundations has its own code and requires dynamic analysis so that the vibration is controlled by considering the machine, the foundation and the supporting soil all working together.

UK has a simple CP 2012. The German has an excellent DIN 4024 (both Part 1 & 2). The American uses ACI351.

On the holding down bolt the standard practice is to cast the HD bolt with bottom washer and a robust steel grouting tubes so that the top of the HD bolt has some free movement for the machine installation. The tube is grouted finally after the machine has been correctly installed and tightened in line and level first with its own grouted baseplates.

A good practice that I recommend is to follow UK CP 2012 practice to provide a 3D cage because you do need (1) the holding down bolts to dissipate the stresses into the foundation. (2) If your foundation split the you are not bolting the full mass (thereby invalidating your computed participation factor) to vibratory equipment and thereafter there is no cure!

As far as I know the holding down bolts should be supplied by the machine vendor and you may need to cast them with a template to ensure the required accuracies are achieved.

Lastly unless someone points a gun at me I usually specify in the drawing a machine foundation to be cast in one operation without any construction joint but exceptions can be made on certain pedestals.