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I am suppose to design a pile foundation for a machine weighing approximately 50 tons and with an operational loading of 100 tons. 

I ll appreciate your help in terms of guidance & provision of notes...  

 

Thank you..

Edited by Umar Makhzumi
Changed Thread Title so it is more relevant to discussion.

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100 tons is the operational load including weight of the machine? or it will be 100+50=150 tons? Whatever is the case, select a pre-cast pile having capacity more than that. For example select a pile of 200 tons. Regarding pile cap you can model it or design yourself manually. Other members are encouraged to continue and discuss!

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Vertical resistance of piles will depend on soil conditions; insure enough skin friction, or bearing capacity at bottom of pile according to external vertical forces. In case of machine loading, you will also need to provide for ability to shear and bending stresses. Check for punching shear in pile cap.

 

Check out this book for guidance.

https://www.dropbox.com/s/v5ffxjcq4jyqcpt/Pile%20Foundation%20Analysis%20and%20Design_H%5B1%5D.%20G.%20Poulos%20%26%20E.%20H.%20Davis_1980.pdf

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I am suppose to design a pile foundation for a machine weighing approximately 50 tons and with an operational loading of 100 tons. 

I ll appreciate your help in terms of guidance & provision of notes...  

Thank you..

 

What kind of machine is that ? Would the operation of machine induce any dynamic forces in the foundation ? If yes, then pile design is a total different story. The static design of pile is easy. Depending upon what kind of pile you select (friction, end bearing) Consider your pile cap as rigid plate and find reactions at pile locations and design.

 

Thanks.

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It’s a circular Boiler required to be installed at a Pharmaceutical factory... Yes, the referred operational loading is the dynamic load which will be exerted on the pile cap & subsequently on the Piles. With regards to the type of pile, the soil investigation report based on two bore holes drilled upto 40 feet, state that the strata consists of Silty clay up till 25 feet and from 25 to 40 feet, the strata consists of sand and silt. Based on the results obtained from these bores, the Geotech experts have recommended 26 feet deep piles (without indicating the type of Pile). Based on my site experience, I will certainly recommend combine (skin friction & end bearing piles for this case with more concentration towards end bearing)

 

Please share your experience and recommendations.

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Attached are two docs I got from Google; they are lucid and easy to understand and cover examples. Pile Groups (Literature).pdf, Pile_Foundation_Design.pdf

 

With Dynamic loading, the question is not about piles designing only, but in fact, you need to design a foundation system and satisfy vibration limits for the machine. I can share with you typical rule of thumbs for dynamic design of machine foundations. Keep me posted on this as this is my specialty in structures.

 

1) Your utilization for piles should not exceed 45 - 55 % of capacity under static loading. This is to ensure that soil remains fairly elastic and expected behavior is achieved.

 

2) Is the boiler centrifugal or reciprocating machine ? You can check ACI - 351 that talks about minimum ratios of foundation weights to machine operating and their CG Locations for both centrifugal and reciprocating machines.

 

3) Your center of resistance for pile group should be with in 6-7% of machine C.G.

 

4) What is the max vibration limit for the boiler on the foundation level and at the machine CG level ? You normally get this information from the vendor and you proportion your foundation to satisfy those limits.

 

5) I am interested in knowing that how would you do a dynamic analysis for the system ?

 

6) You need to have complete soil investigation report with SCPT test providing shear wave velocities in each soil layer.

 

7) Is the foundation system an elevated one or is at ground level ? It is important to know this as table top machine design needs more engineering input and caution ?

 

8) What is your acceptable Human Perception Limit for the system ?

 

9) Is the foundation system being shared by super structure too. Please provide foundation plan. I want to see what is around your boiler.

 

10) You response of foundation should be outside the operating range of the machine to avoid resonance. (V.Imp) 

 

11) Please reply asap :).

 

Thanks.

Edited by Umar Makhzumi
Modified 10, added 11

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It’s a circular Boiler required to be installed at a Pharmaceutical factory... Yes, the referred operational loading is the dynamic load which will be exerted on the pile cap & subsequently on the Piles. With regards to the type of pile, the soil investigation report based on two bore holes drilled upto 40 feet, state that the strata consists of Silty clay up till 25 feet and from 25 to 40 feet, the strata consists of sand and silt. Based on the results obtained from these bores, the Geotech experts have recommended 26 feet deep piles (without indicating the type of Pile). Based on my site experience, I will certainly recommend combine (skin friction & end bearing piles for this case with more concentration towards end bearing)

 

Please share your experience and recommendations.

When you say end bearing, do you mean "belled piles" ? or "end bearing" with straight shaft piles ?

What pile diameters are you expecting ?

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Pls. contact at info@rockwellgrp.com for comprehensive civil/structural engineering, geo-technical and foundation engineering solutions, Regards, Asif Saeed, Director-ROCKWELL Group (Pakistan)

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Pls. contact at info@rockwellgrp.com for comprehensive civil/structural engineering, geo-technical and foundation engineering solutions, Regards, Asif Saeed, Director-ROCKWELL Group (Pakistan)

 

Asif, this is a free forum for educational purpose only. We don't allow any advertisements. Any post not related to topic falls under spam and therefore is not allowed.

 

Please review Forum Posting Rules at http://www.sepakistan.com/topic/1344-forum-posting-rules/#entry2660

 

Thanks.

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If vendor drawing for a particular machine shows values of Static Load & Dynamic Load, is static load "weight of machine"?

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If vendor drawing for a particular machine shows values of Static Load & Dynamic Load, is static load "weight of machine"?

Generally that is correct. However, Torque is considered as a static load too and is reported with other static loads.

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Dear Umar Bhai,

 

I have to design Tabletop Elevated Foundation for Turbo-Alternator. I have vendor drawings with static and dynamic loads identified to be applied on various points. Now my question: What is static and dynamic load, and how am I to convert them into masses/weights so that I can find to frequencies [fn = 2*pi*(k/m)^0.50].

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Dear Umar Bhai,

 

I have to design Tabletop Elevated Foundation for Turbo-Alternator. I have vendor drawings with static and dynamic loads identified to be applied on various points. Now my question: What is static and dynamic load, and how am I to convert them into masses/weights so that I can find to frequencies [fn = 2*pi*(k/m)^0.50].

 

You need to calculate the unbalance load and apply that as a dynamic force based on the speed of machine. What kind of company you work for and what software are you using ?

 

Thanks.

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I am working for a consultant in Karachi and we use SAP2000.

 

If I calculate the unbalanced load, then should I add it with dynamic load provided by vendor/supplier? or only apply the vendor's dynamic load?

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I am working for a consultant in Karachi and we use SAP2000.

 

If I calculate the unbalanced load, then should I add it with dynamic load provided by vendor/supplier? or only apply the vendor's dynamic load?

Use the vendor provided unbalanced load and perform a Modal Time History Analysis in SAP2000 to see what your vibrations are.

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Can I have DYNA5 software to download. I need to calculate the stiffness constants and damping constants.

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Can I have DYNA5 software to download. I need to calculate the stiffness constants and damping constants.

You need DYNA5 to get pile impedance(stiffness + damping) values. DYNA5 would calculate these values for your pile group considering group effects. You should convert the group values to single pile, and use them in SAP2000 as a One Node/Joint link and do the Modal Time History Analysis. Find your critical modes and check structure for resonance. If your amplitudes are lower than vendor allowable, you are good.

Tell you company to buy DYNA5.

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Dear Umar Bhai,

 

Modal analysis of a Table-top foundation has been done on SAP2000, with following result:

 

Frequency of foundation in mode-12 (last mode)  =  25.72 Cyc/sec. (Mode-12 has maximum frequency value)

 

Turbine's Frequency      =  117 Cyc/sec.

Generator's Frequency  =    25 Cyc/sec.

 

Plz comments

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12 Modes are very few and I believe is the default number in settings. You should run your modal analysis for at least 300 modes or 95% of Static Dead.

 

Check your magnitudes for cases of Turbine Operating and Generator Operating and superimpose them to see if the total doesn't exceed vendor limit at points specified by vendor. Since your operating frequencies are different for both turbine and generator, you should have two files for each case operating with pile impedances referring to the speed of forcing function.

 

Regarding Modal Analysis,

You have to see two bandwidths. First one is from 0.8-1.2 of your Generator Operating Speed; which would be 20 Hz to 30Hz and the second bandwidth will be from 0.8-1.2 of Turbine Operating Speed. For each case, note all the modes that fall into the bandwidth. Then run Modal Time History Function by equating your forcing function to the frequency of the mode(that's how you check resonance). Superimpose the results for each operating case and if they are below the vendor allowable limit at the points vendor has specified. you are good.

 

Thanks.

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Do u ve manual (or can u refer to a manual or book) for this procedure?


Also, I have designed mat foundation (not piles) for this table-top.


Please elaborate this point "Then run Modal Time History Function by equating your forcing function to the frequency of the mode(that's how you check resonance)".

Attached is modal analysis result for frequencies of Turbine & generator. I am confused as to what should I do with analysis. Should I apply turbine loads & generator loads separately in two SAP2000 files? Or as I have done here by combining both in same single file?

I would appreciate any and all kinds of inputs.

Tabletop foundation - Modal Analysis Result.pdf

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I would like to see the definition of your Time History Function? Explain to me how are you applying your loads in SAP2000 for the given frequency of operation and that would contain answer to 

"Please elaborate this point "Then run Modal Time History Function by equating your forcing function to the frequency of the mode(that's how you check resonance)"."

 

 

Moreover, attach snapshots of your SAP200 file so that I can see if you are modelling it correctly.

 

Thanks.

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Attached is zip file containing info of loads and model picture. I do not have "Time-history Function Data" of my project.

 

Thank you anyways for the input.

TTF.zip

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