Foundation Design Philosophy for Rotating Equipment References has been taken from, Home Vertical Vessel/Tower Horizontal Horizontal Vessel Vess el Tube & Shell Exchanger Rotating Equipment Storage Tank on Ring Beam Equipment on Skid Pipe Rack Transformer Transformer Pit Pi t Anchor Anchor Bolt Bolt Stack Foundation Help & More Help Feed Back About me Site Link
1. Design Desi gn of structures structures and foundations foundations for vibrating machines by S. Arya, Arya, M. O'Neill and G. Pincus Pincus 2. Foundation analysis analysis and design by J. E. Bowels 3. Dynamics of bases and foun foundations dations by D. Barkan Desi gn of Machine Foundations Foundations - Lecture Notes of Professor M.H. El Naggar, Department of Civil E ngineering, 4. Design The The University of Western Ontario, London, Ontario, Ontario, C anada, N6A 5B 9 In this page I will talk about the rigid block foundation for Centrifugal (Pump) and Reciproca ting machines (Compressor). We a re considering consideri ng the the concrete block i s infinitely rigid and thus a lump lump mass model can be considered i n computer 3D modelling. To start the design of a block foundation, we need need to follow the following steps to collect the design data: Step-1 : Review of pump pump / compressor drawing (Vendor Equipment Drawing) The The machine data perti pertinen nentt to the dynamic dynamic analy a nalysis sis and design of the block foundation should should be obtained ob tained from vendors. Plan dimension of pump / compressor base frame Height of rotor / shaft center line from the bottom of skid Anchor Anchor bolt bolt location location,, size size and and embedmen embedmentt depth depth Weight of machine parts and the rotor parts (pump / compres sor rotor and motor rotor) Location of center of gravity both vertically and horizontally Operating speed of machines and power rating of motor (RPM) Magnitude and direction directi on of unbalanced unbalanced forces. forces . For reci procating machines both primary and secondary unbalanced unbalanced forces and couples and respecti ve CG locations needs to be checked. Limit Limi t of deflection and vibrati vibration on amplitudes at center line line of rotor. Step-2 : Collection of Geotechnical Geotechnical / soil data (P l discuss with soil consultant consultant and look into project design criteria) The The Geotechnical Geotechnical data are a re used for evaluating evaluating the soil / pile sti stiffn ffness ess and damping coefficients, coeffi cients, and are required for both static and dynamic dynamic design de sign and analysis analysis of of o f block foundations. foundations. Following soil parameters a re required: Soil weight density Poisson's ratio Dynamic shear modulus (G) Shear wave velocity (v s) Dynamic modulus modulus of sub-grade re action (k s ) Allowable Allowable soil soil bearing bearing pressure pressure or pile load load carryin carrying g capacity for design of foun foundation dation Step-3 : Categorization Categori zation of rotating machines machines based on machine machine speed: The The rotating machines are categorized bas ed on machine speed. Following are different categories of machines: Low Speed machine: The low speed machines operate at a speed range of less than 500 RPM. High tuned foundations, having first natural frequency more than machine's operating speed, should be designed for this type of machines. In In this this case c ase machine do not pass the resonance resonance during machine start up and and coast down conditio condition. n. Intermediate Intermediate speed machine: mac hine: The The intermediate speed machines operate at a speed range 500 RPM to 1000 RPM. Foun Fo undations dations should be designed desi gned for this type of machines high tuned tuned or low tuned side whchever whchever more practica l. If the the foundation foundation is low tuned, tuned, dynamic amplitude shall be checked during start up and coast down condition. conditi on. High Speed machine: The high high speed machines operate a t a speed range of more than 1000 RPM. Low tuned foundations, having first natural frequency less than machine's operating speed, should be designed for this type of machines. In In this this case c ase machine will pass the resonance resonance during machine start up and coast down condition. Dynamic amplitude shall be checked during start up and c oast down condition. You need need to ensure that there there is i s no adverse effect to machine operati on during the resonant resonant conditions. Variable Variab le Speed machine: T The he variable variable speed machines operate at a speed range as prescribed prescrib ed by vendor. Foundations should be designed for this type of machines high tuned or low tuned side whchever more practical. A detail dynamic analysis analysis of foundation is required for a range of machine machine operating speeds to ensure that the the dynamic dynamic design des ign criteria criteri a are met. Step-4 : Preliminary sizing of foun foundations: dations: A block foundat foundation ion consists consists of massive massive concrete concrete blocks, piers and and mat foundat foundation. ion. The The preliminary preliminary sizinng sizinng of block should be bas ed on the following: Weight of the block foundation should should be at leas t 4 times the weight of reciprocati ng machines and 3 times the weight of ce ntrifugal ntrifugal machines. The The width of foundation foundation should be at least 1.5 times ti mes the vertical di stance from the bottom of foundation to the center line of the shaft / rotor.
of the soil foundation or pile group resi stance. Horizontal eccentricity should be limited to 5% of the corresponding foundation dimension. For a rigid mat, following criteria to be followed: Minimum thickness of the mat will be 600 mm or 1/5 th of least foundation dimensions or 1/10 th of largest foundation dimensions, whichever is greater . Maximum thickness of the mat will be 1500 mm Minimum thickness of mat, t = 0.0012 x (k s x (a)4)1/3 ft, ks = soil dynamic modulus of subgrade reaction, lbs/in3, from soil report, a = maximum cantilever projection ( inches), measured from face of block (Refer: Foundation analysis and design by J E Bowles)
Step-5 : Requirement for dynamic analysis of foundations: Dynamic analysis of concrete foundations are not required for all the foundations supporting rotating equipment. You need to refer your project design cri teria for the conditions for dynamic analysis. F ollowing are the general criteria for not performing any dynamic analysis of foundation supporting rotating equipment: Dynamic analysis is not required if the weight of machine is less than 25kN. Dynamic analysis is not required if the power rating of motor is less than 200hp. If you are not doing any dynamic analysis of concrete block foundation, then follow Step-4 for foundation sizing and put it into 3D model for any interference check. If you are doing the dynamic analysis of concrete block, then follow the following steps. Step-6 : Calculation of un-balanced forces for dynamic analysis of foundations: If unbalance force is not mentioned in the Vendor equipment drawing, then you will calculate the force as follows: Un-balance force for pump: F pump = mp-rotor x e x w2 Un-balance force for motor: F motor = mm-rotor x e x w2 Where, mp-rotor = weight of pump rotor,
m m-rotor = weight of motor rotor
w = circular frequency = 2 x pi x (f / 60), f = speed of machine from vendor drawing (RPM). e = rotor eccentricity, depends on machine speed Eccentricity Table ( Refer reference -1) Machine
Operating Speed (f in RPM)
Eccentricity e (mils)
Pump / compressor
f < 3000
(1.8-10 7) / (f)2
Pump / compressor
f > 3000
(12000/f) 1/2
Motor
f < 1500
1.5
Motor
1500< f < 3000
1
Motor
f > 3000
0.5
Now you are having all the information to start the foundation analysis and design. You can put all the above data in any computer software program (say - Dyna5) or use any text books to calculated the natural frequencies of foundation. You can also use the different tables that I have attached here ( click for the table). Natural frequency analysis of foundation: This rigid block has six degree of freedom. So, you will calculate all the following uncouple natural frequencies:
1. 2. 3. 4. 5. 6.
Sliding Frequency along horizontal X-direction Sliding Frequency along horizontal Y-direction Sliding Frequency along vertical Z-direction Rocking Frequency about X, rotational mode Rocki ng Frequency about Y, rotati onal mode Rocking Frequency about Z, rotational mode
When the CG of foundation system is far above the foundation base, coupling effect needs to be considere d to calculate the foundation natural frequency. In this case sliding mode and rocking mode frequencies overlap each other and as a result foundation dynamic analysis may be more critical. You can calculate the coupled natural frequency using the formula mentioned in the table. Coupled condition: 1. Slidi ng along X & Rocking about-Y and 2. Slidi ng along Y & Rocking about X Once, analysis is completed, please check the foundation for the following conditio ns: Resonance Frequency Check: Calculate resonanace frequency and check that the ratio of machine frequency vs resonance frequency (f / f d) is either less than 0.8 or greater than 1.2 in all six degrees of freedom. Resonance frequency can be calculated as follows: f d = f n / (1-2 x D 2)½ where, f n = foundation natural frequency, D = Damping ration (see table 5 and 12) Soil Bearing Pressure / Pile Capacity Check Soil bearing pressure or pile load should not exceed 75% of the allowable. Please avoid any foundation upliftment in seismic / wind condition. Maximum Velocity check: Maximum velocity should fall in "Good Condition" per table-1 of attached table Environmental condition Maximum displacement amplitude of vibrati on at foundation level should lie within or below "Zone-B" of figure -1 and it should fall below the Zone "Troublesome to persons" of fig ure -2 in the attached table. Reinforcement: Reinforcement shall be provided per project approved design code. However, you can use minimum reinforcement as follows: 0.2% rebar on all face of concrete block and mat. 1% rebar for all concrete pedestal. Rebar spaci ng should not be more than 300 mm. Anchor Bolt: Anchor bolt shall be checked for start-up and coast down contion. For a typical pump foundation drawing click here I hope this page will be very helpful to you to understand the basic design of a Pump foundation.
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Copyright 2009. All rights reserved. Please do not print or copy of this page or any part of this page without written permission from Subhro Roy. Disclaimer: This page is prepared based on experience on Civil Engineering Design. All definitions and most of the explanations are taken f rom different t ext books and international design codes, which are referenced in the contents. Any similarity of the content or part of with any company document is simply a coincidence. Subhro Roy is not responsible for that.
