Reinforcing heavy equipment foundations
Reinforcing heavy equipment foundations
(OP)
I am designing foundations for FAG Mills and Ball Mills. I need guidance on use of nominal reinforcing steel.
Most of the guidelines relate to beams for building construction, or columns up to 1 m square, and to concrete slabs. If I apply those to raft foundations 2 to 3 m thick the numbers are way outside normal comfort zones, and don't make much sense.
The equipment plinths may be 3 m wide x 1 m thick x 5 m high. The vendors say most of the 2,000 ton loads will be vertical with comparatively small dynamic side loads.
Any guidance on the subject would be appreciated.
Most of the guidelines relate to beams for building construction, or columns up to 1 m square, and to concrete slabs. If I apply those to raft foundations 2 to 3 m thick the numbers are way outside normal comfort zones, and don't make much sense.
The equipment plinths may be 3 m wide x 1 m thick x 5 m high. The vendors say most of the 2,000 ton loads will be vertical with comparatively small dynamic side loads.
Any guidance on the subject would be appreciated.





RE: Reinforcing heavy equipment foundations
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RE: Reinforcing heavy equipment foundations
RE: Reinforcing heavy equipment foundations
Contractors, hate the big bars - they have to perform their own (means & methods) structural design just to support the the top mat(s). Often they propose sizable WF columns to support the top rebar - these are completely encased within the foundation.
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RE: Reinforcing heavy equipment foundations
1 - For this size of foundations minimal steel ratios are not applicable. The "comfort zone" is the limited range of values over which rule-of-thumb reinforcement ratios provide realistic guidelines.
Usually the minimum steel requirement is intended to limit unsightly cracks in beams and slabs in building construction. When taken out of context, and extrapolated to 10 times normal values these guidlines break down. Hence the motivation for this thread.
2 - Thanks for the US Guidelines for concrete floor slabs. When dealing with floor loads of 3,000 tons floor slab guidelines are way outside the range of normal recommended practice.
3 - Thanks for the recommendation to use maximum size bars, and planing how to support these as a top mat 2 m above the floor mat. Effectively we need to construct a second floor for this top reinforcing.
The Codes say nothing about minimum percent reinforcing for such applications. The forword to most codes will specifically exclude such unusual structures. However, in today's mining engineering there is nothing unusual about FAG and Ball Mills, except their size.
I would rather put reinforcing where it is required by design, than to fill the concrete void with steel that I don't understand, using rules-of-thumb taken way out of their normal context.
That is why I'm seeking better understanding of such structures, of which there are many forms - even in rafts to multistorey buildings.
RE: Reinforcing heavy equipment foundations
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RE: Reinforcing heavy equipment foundations
RE: Reinforcing heavy equipment foundations
Going the Big Inch!![[worm] worm](https://www.tipmaster.com/images/worm.gif)
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RE: Reinforcing heavy equipment foundations
RE: Reinforcing heavy equipment foundations
If I have a spot footing 4 m square x 2 m deep it will carry 800 ton without any reinforcing at all. To keep shuttering simple we usually cast the full box - providing more concete than is strictly required.
The subsoil could settle a bit but there would be no distress to the concrete. The side of the block could be trimmed back at 45 degrees. But the extra side wedges gives the concrete additional confined compression strength.
Top steel in footings is only needed if there is the possibility of serious stress reversal due to uplift.
If I put two of these units together to form a 4 m x 8 m x 2 m combined footing they would still act as a mass concrete block requiring no reinforcing. However, if I spread the two 800 ton loads by 200 more millimeters, we would get a 4 m x 8.2 m x 2 m block with designer reinforcement, minimum steel ratios, and side face steel. This smells of overkill - but may be justified in some cases.
RE: Reinforcing heavy equipment foundations
BigInch
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RE: Reinforcing heavy equipment foundations
RE: Reinforcing heavy equipment foundations
RE: Reinforcing heavy equipment foundations
As usual, weigh the risks and make a decision - there is no "right" or "wrong", just probabilities and consequences.
www.SlideRuleEra.net
RE: Reinforcing heavy equipment foundations
Oh well, for once, my hands are clean.
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Reinforcing heavy equipment foundations
If you can make it work as unreinforced, then I think the code allows you to put some reinforcement in it for serviceability only.
According to the ACI, just because it has reinforcement doesnt necessarily mean that it is not unreinforced!
RE: Reinforcing heavy equipment foundations
I'm a machinery engineer with over 30 years experence, and would like to offer my 2 cents worth of advice.
For dynamic equipment PLEASE use reinforcing steel, and plenty of it. More than code minimums. Post-tensioning should also be considered for crticial service equipment foundations....that's what we're using to repair our existing 7000HP recip compressor foundations, on the advice of a leading consultant in this field. The CE's who designed the original foundation didn't use enough reinforcing steel.
An alternative solution is to lop off the top 36-48" of the block and replace with a heavy duty structural steel baseplate, to be subsequently filled with concrete.
The cost of having to go in 10-20 years from now and replace machinery foundations in an operating plant can be astronomical. It's not uncommon to have to rebuild a complete new compressor station due to foundation damage...were talking many millions of $$ and lost revenue. Generally speaking, I do NOT like using profiled reinforced concrete foundations as they always seem to fail through under-design and incur huge costs to repair.