Concrete slab for machine support 1

[mattcpe]

We are moving into a new building that has a 4" concrete slab. We want to put a 26,000 lb machine in there. The machine sits on 4 legs, equally loaded, so it runs 6,500 lb each. The only thing we have heard is place each leg on a 6" x 6" x 1" steel plate. Do we have to bust out and redo the slab at the legs? What thickness for the slab? How about reinforcement?

An alternative idea was place a steel plate 1" thick under each end, roughly 4 feet long by 2 feet wide would pick up two legs. Would this work? Would we still have to thicken the slab?

 

[jheidt2543]

A few things to consider:

1. What does the machine do? If it vibrates in any way you may have to isolate it from the rest of the building, hence a foundation.

2. What are the machining tolerances? If you must machine to even a modest tolarance, you may have to prevent the machine from deflecting during operations, hence a foundation.

3. Check with the machine's manufacturer, even if it is a used machine, they can tell you if you need to isolate it or restrain it for operation. You run the risk of damaging your machine or the parts it works on and likely both.

4. Generally speaking, the cost of a foundation, while sometimes expensive, is usually only a fraction of the machine cost, to say nothing of the time to refabricate a lot of damaged parts.

Play it safe and do it right, have a structural engineer look at it.

 

[mattcpe]

Thanks for your help. The machine is a 165 ton press brake for bending metal. We will level and anchor it to the floor. Unfortunately, the machine is used and the manufacturer will not give us any information on a required foundation.

 

[jheidt2543]

mattcpe,

First off, even when new, it is like pulling teeth to get information from the machine manufacturers. I would call them back and ask for all the loads that the machine imparts to a foundation. Tell them you don't want them to design it, just give you the loads so you can get someone to design the base. That is the least they can do. Don't take NO for an answer, start with their customer service department (they might get a service contract!) or the engineering department and work your way up the ladder to the guy who will get the information to you.

The few press breaks I'm familiar with have all their forces internal to the break, so 165 ton is not really a foundation load, the load is basically the machine weight plus some impact. They do create some vibration with each "stamp" or "break" cycle. Therefore, you may want to isolate the machine on its' own foudation. I personally would not just bolt it to a 4" thick floor slab. At a minimum I would put it on a 12"-18" pad, flush with the floor and isolated with 1" expansion joint on all four sides.

Good luck!

 

[RDK]

You could saw cut a section of the floor and simply place a new pad, somewhat thicker with any necessary anchor bolts already cast in place.

A 6,500 lb static load is in the range that you get for basement teleposts, these typically sit on pads between 18x18x6 to 30x30x6 with minimum rebar. If there is significant impact loading due to the operation of the equipment then the pad would have to be somewhat larger and most likely reinforced.

What type of soil conditions do you have locally? In a good well-drained well-graded granular soil you can sustain foundation loads of 4,000 lbs per sq ft and up, even in a poor clay you should be able to get 1,000 to 2,000 PSF.

I’d suggest you contact your local friendly civil engineer who is familiar with local conditions and loadings. In any event I would not use the 4” slab of unknown strength and reinforcing. The cost of four small pads is not really significant.

What was the original foundation for this machine?





Rick Kitson MBA P.Eng

Construction Project Management
From conception to completion

http://www.kitsonengineering.com