Concrete Footing

GA

It all starts with the ground you build on...

It might be great on hard rock foundation, but you may run into trouble if you are building this on sand. Know the ground, start there, and build up.

Additionally, you will need to take freezing/heaving into account. This presumes that the concrete is properly reinforced to take the load and there are no seismic code issues.

KJK is absolutely correct. You need to have a proper Geotechnical Report conducted in order to answer you question, and then some.....

I might add that not enough info was given regarding the in-situ soil conditions, ground water conditions (if any), if wind and seismic considerations included in you loadings? Is the load that you have given the LL + DL service load with or without appropriate ACI modification factors included? Also, what is the MAXIMUM load for any given column, not just the combined loading for the FOUR columns?

Do you even have a clue what you're doing structural engineering wise?

Another GA for KJK!

Do you consider the same factors and vibrations for diesel engine driven generator?.

pnaban, I'm not sure how relevant your question is regarding the OP's query.

At least in the USA if a structure is supporting any type of HVAC equipment or any type of rotating machinery then the AISC or ACI Standards codes take in account vibration or dynamic induced loading, usually through utilization of an Impact Factor. OR, the induced loads can be modeled and the structural element(s) checked for frequency response.

Remember, if the equipment is rotation such as a motor, pump or turbine etc. it can become out of balance......a worse case design scenario, which is prudent. Also, each type of rotating equipment has it's own inherent vibrational frequency....ditto for any structural element.

For rotation equipment support it is customary to use vibration isolators positioned between the equipment base and the supporting structural element to REDUCE the vibration. You cannot remove the vibration entirely. The isolators are fabricated dampeners usually featuring a tuned spring and centrally-located steel guidance shaft, all sandwiched between a top and bottom mount plate, much like an automotive coil spring setup used in the suspension.

I wonder how civil engineers designed and constructed foundations for electric power generators,say,50yrs back when there were no computers or modelling techniques by considering weight,rpm,inertia,vibration etc

A lot of solid engineering research has occurred in government and university laboratories in the past 60-70+ years regarding vibrational analysis and design of structures of all types. Not just here in the US and Canada, but around the world. Much of the research is ongoing and hasn't stopped. And much of resulting formulae and methodology can be computed by hand and a simple handheld calculator.......having a computer to undertake the analysis and design tasks isn't a prerequisite. Same computer software only speeds up the process and alleviates computational errors, but as the saying goes: "garbage in, garbage out" , and ya gotta know what the hell you're doing in the first place (from an educated & experienced structural engineering point of view), especially when it comes to inputting relevant variable factors (ie, guesstimates and assumptions)..........

Your spot on with your answer. I knew a man from Chattanooga, TN. who worked on most of the dams for TVA back in the early 30's. He still had a lot of the paper work from this time showing many hours of calculation using a slide ruler and paper. Quite interesting to discuss the work that went into the designs.

You're quite correct about those dam calculations with slide rule, engineer's scale, and graph/profile paper....the groundwater hydraulics (flow nets under the dams etc) computational gymnastics alone would be mind-boggling!

When I began my stint with the USACE back in the early 80's we had just graduated from the slide rule era and plunged into Fortran software to do the work......lots of steep uphill learning curves!!!! ACKKKKK!!!!!!

Is there a simple method or rule of thumb for calculating foundation details for a diesel driven generator taking into consideration the weight,rpm etc?.

Yes there is, but it will take me some time to look it up in my huge collection of structural textbooks & CDs.

It's a structural engineering methodology that one doesn't use everyday, so please be patient for the next few days. [I'm kind of swamped right now with projects and the Wife's "Honey Do List" of house projects, so I have very little spare time on my hands.....also having to deal with a handful of Contractors working on a daily basis on the house has really eaten up my time somewhat..........]

Try Google search for "structural vibration analysis methodology", or something along those lines.....

If worse comes to worse, treat your entire piece of equipment as a live load and apply a very conservative Impact Factor of 1.33 ~ 1.50. That approach will be very conservative and overkill! Most of the time you can get away with this, unless you have very crappy soils (like clay, etc.) or a very heavy and very big piece of equipment with a tremendous amount of inherent torque values. Also, mount the equipment on a structural steel welded frame and employ 4, 6, 8 or 10 (or whatever it takes, depending on the weight and size of the diesel engine) vibration isolators between the top of the concrete footing (make sure you use leveling plates and non-shrink/non-metallic grout) and the bottom of the steel isolation frame.

Good luck hunting the web....

Mr Pnaban, you must recognize and remember this.

The computer you bought today was "dumber than a rock" until the programmers loaded it with all the "Smarts" collected from the guys who did the work by hand 50 years ago.

pnaban, here's a link an invaluable standard for you to use regarding the design of concrete structures (incl. foundations) and machinery:

[ACI 351-3R-04, standard from the American Concrete Institute].

www.inti.gob.ar/cirsoc/pdf/fundaciones/ACI-351-3R-04.pdf

Do a Google search for any of the following textbooks will end up giving you a lot of useful information. I have many of these texts in printed form. Sorry, I'm not able to scan the books and send you the e-files due to copyright infringement laws. You may be able to download some of the following books for free as e-books (all you have to do is look on the web and hunt for them!). I did this too quickly, so it's up to you to find them.....sorry for the mess! LOL

One of the best references that I am aware for this subject is Soil Dynamics by Prakash. There is an entire chapter dedicated to machine foundations.

There is also a textbook by Suresh and Arya on the topic

Novak, M.: "State of the art in analysis and Design Of Machine Foundations, Soil Structure Interaction", Elsevier Science Publications, 1987, pages 171-192.

Gazetas, G.: "Analysis of Machine Foundation Vibrations: State of Art, Soil Dynamics and Earthquake Engineering", CML Publications, Vol.2.1, 1983, pages 2-42.

Design of machine foundations by SRINIVASALLU

If you would like to isolate the vibrations you have a simple way is presented in pages 46 to 52 of book "Dynamic of Structures", Ray W. Clough and Joseph Penzien, McGraw-Hill.

I hope that helps you!

===Signed,

CaptMoosie, PhD, PE