machine foundations 1
DESCRIPTION
FoundationsTRANSCRIPT
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KNS4553 SOIL DYNAMICS
KANIRAJ SHENBAGA
UNIVERSITY MALAYSIA SARAWAK
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By the end of this course, the students should be
able to design machine foundations complying with
design criteria, evaluate liquefaction potential of
saturated soil, suggest preventive measures,
evaluate lateral earth pressures during earthquakes,
and recommend vibration isolation measures.
Learning Objective 3
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By the end of this course, the students should
be able to investigate contemporary practices
and issues on applications of soil dynamics in
machine foundations and earthquake
engineering and prepare technical reports of
the investigations.
Learning Objective 4
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Machine Foundations
KNS4553 Soil Dynamics
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Block foundation
A pedestal of concrete on which the machine rests.
Box or caisson foundation
A hollow concrete block which supports the machinery at the top.
Wall foundation
A pair of walls which support the machinery at the top slab.
Frame foundation
A frame work of columns, beams, and slabs. The machinery is
supported on the top deck slab.
Types of Machine Foundations
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Block Foundation
http://mechanicaldatahelp.blogspot.com/2011/05/machine-foundations-ii.html
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Based on operating speed:
Low to medium frequencies (< 500 rpm)
Medium to high frequencies (300 to 1000
rpm)
Very high frequencies (> 1000 rpm)
Types of Machines
1 rpm = 1 revolution per minute = 2π radians per minute
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Reciprocating engines (50 to 250 rpm),
compressors, and large blowers:
Low to medium speed machines; Usually
supported on a block foundation
Diesel engines and gas engines:
Medium to high frequency machines
Machines Producing Periodical Forces
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High speed internal combustion engines,
electric motors, and turbo generators:
Very high speed machines
Turbo generators are usually supported on
frame foundations, and others on block
foundation.
Machines Producing Periodical Forces
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Electric Motor Support
http://www.bing.com/images/search?q=images+of+machine+foundations&view=detail&id=51A66497BBA89E6F0328D059EF7FC06D35167732&first=0&qpvt=images+of+machine+foundations&FORM=IDFRIR
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Turbogenerator Foundation
http://www.bing.com/images/search?q=images+of+turbogenerator+frame+foundations&view=detail&id=56716CD0DE953A83499DDE5748D03F17FCB7D873&first=0&FORM=IDFRIR
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Turbogenerator Foundation
http://www.coyne-et-bellier.fr/en/dun/sin/fiche_lavrion_industrie.html
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Forge hammers and presses:
Usually supported on block foundation
For the construction of a large hammer
foundation see:
http://www.fluekiger.ch/american-
english/our-new-drop-forging-
hammer/index.html
Machines Producing Periodical Forces
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Typical configurations of the mounting systems in hammer foundations: (a) one-mass foundation, (b, c), two-mass foundation with springs and dampers
http://origin-ars.els-cdn.com/content/image/1-s2.0-S0022460X03010198-gr1.gif
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Direct spring support of a Forging Hammer http://www.gerb.com/en/arbeitsgebiete/arbeitsgebiete.php?ID=151
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Loading diagram giving the magnitude and
position of static and dynamic loads exerted by
the machine on the foundation
Power and operating speed of machine
Details of grooves, openings, ducts, embedded
parts, etc., in the foundation
Soil data
Data for Machine Foundation Design
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Design Requirements
KNS4553 Soil Dynamics
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A machine foundation should satisfy two criteria:
a) Static load criteria
b) Dynamic load criteria
Design Criteria
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a) The foundation should be properly located
(location criterion).
b) It must be safe against failure by rupture of soil
(bearing capacity criterion).
c) The foundation must not excessively (settlement
criterion).
Static Load Criteria
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a) No resonance should occur.
Resonant frequency must be very large or very small compared to the operating speed of the machine.
b) The amplitude of motion (displacement or rotation) must be within permissible limits under service conditions.
Permissible limits: Prescribed by manufacturers of machine, Code provisions, Empirical guidelines (for preliminary design)
Dynamic Load Criteria
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Richard’s Chart for Limiting
Amplitudes of Displacement
in Vertical Vibration
How to use the chart
• Determine the amplitude of
displacement.
• Locate the point on the chart.
• Evaluate the response of persons
to the vibration.
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When response limits are defined simultaneously by
values of displacement, velocity, and acceleration,
the plot is called a response spectra for vibration
limits.
Response Spectra
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Point A corresponds to: Frequency = 10 cps Displacement = 10-4 inch Velocity ≈ 0.007 in/sec Acceleration = 10-3 g
A
B
Point B corresponds to: Frequency = ? cps Displacement = ? inch Velocity ≈ ? in/sec Acceleration = ? g
Note: Limits based on amplitude of quantity
Response Spectra for
Limiting Amplitudes
of Motion in Vertical
Vibration
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Barkan’s Recommendations
Type of machine Permissible amplitude of
displacement, mm
Low speed machinery (500 rpm) 0.20 – 0.25
Hammer foundation 1.00 – 1.20
High speed machinery (a) 3000 rpm Vertical vibration Horizontal vibration (b) 1500 rpm Vertical vibration Horizontal vibration
0.02 – 0.03 0.04 – 0.05
0.04 – 0.06 0.07 – 0.09
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Blake’s Recommendation
AA: Dangerous. Shut it down now
to avoid danger
A: Failure is near. Correct within
two days to avoid breakdown.
B: Faulty. correct it within 10 days
to save maintenance dollars.
C: Minor faults. Correction wastes
dollars.
D: No faults. Typical new
equipment
Note: Limits based on peak to peak value of quantity
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Blake’s Service Factors
Service Factorsa
Single-stage centrifugal pump, electric motor, fan
1
Typical chemical processing equipment, Noncritical
1
Turbine, turbogenerator, centrifugal Compressor
1.6
Centrifuge, stiff-shaftb; multistage centrifugal pump
2
Miscellaneous equipment, characteristics Unknown
2
Centrifuge, shaft-suspended, on shaft near basket
0.5
Centrifuge, link-suspended, slung 0.3
Service Factor indicates the importance of a machine in the installation.
Example 1: A centrifuge has a 0.01 in (0.250 mm) amplitude at 750 rpm. The value of the service factor is 2. The effective vibration therefore is 2 X 0.01 = 0.02 in (0.50 mm). This point falls in Class A in the chart. The vibrations, therefore, are excessive, and failure is imminent unless the corrective steps are taken immediately.
Example 2: A link-suspended centrifuge operating at 1250 rpm that has 0.003 in (0.075mm) amplitude with the basket empty. The service factor is 0.3, and the effective vibration is 0.0009 in (0.0225mm). This point falls in class C and indicates only minor fault.
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A machine operates at a circular frequency of 31.4
rad/s and causes its foundation to vibrate vertically
at an amplitude of displacement of 0.13 mm in steady
state vibration. Evaluate the response of persons to
the vibration using:
(a) Richart’s chart, and (b) response spectra.
Exercise 1
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Barkan’s Recommendations
The foundation must be preferably placed above water level to reduce propagation of vibration.
The machine foundation should be placed at a lower level than the surrounding structures and be separated from adjacent structures.
The combined centre of gravity of machine and foundation, and the centroid of the base area should as for as possible lie in the same vertical line.
There must be scope to incorporate future corrections in the base area or mass of the foundation if it becomes necessary due to inadequate performance of the foundation.
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Dynamic Analysis of Block Foundations
KNS4553 Soil Dynamics
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Degrees of Freedom of Block Foundations
In general, 6 degrees of freedom
3 translational modes (Vertical, Longitudinal, Lateral)
3 rotational (Rocking, Pitching, Yawing)
For cylindrical foundations, only 4 degrees of freedom due to symmetry
2 translational modes (Vertical, Sliding/Horizontal)
2 rotational modes (Rocking, Torsional/Yawing)
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Dynamic Analysis Approaches
Empirical and semi-empirical formulae
Soil-as-spring approach
Elastic half-space approach
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Empirical and Semi-empirical Formulae
Formulae available for vertical vibration only.
Damping is neglected. Therefore, resonant frequency is equal to natural frequency. (Keep operating speed away from natural frequency.)
The formulae do not consider amplitude of displacement. Not possible to check whether within permissible limits.
Can be used for approximate preliminary calculations, not for final design.
Units as specified in the formulae should be used.
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Converse Formula
𝒇𝒏 = 𝟑. 𝟏𝟑𝟖𝟒𝟎𝜸
𝑮𝟏. 𝟔𝟒 −
𝑷𝒅𝑾
+ 𝟎. 𝟓𝟓𝑮𝒓𝒐𝑾𝒗
fn = natural frequency, cps
= unit weight of soil, pcf
G = shear modulus of soil, psi
Pd = maximum dynamic load, lb
Wv = static weight of vibrator or machine, lb
ro = radius of foundation or of an equivalent circular area in the case of rectangular foundation, in
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Alpan’s Formula
𝒇𝒏 =𝜶
𝑾𝑨𝟏/𝟒
fn = natural frequency, cpm
W = static weight of machine and foundation, kgf
A = contact area of foundation, m2
= a constant (3,900 for peat; 69,000 for plastic clay;
82,000 for sand; 111,000 for sandstone)
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A foundation block and machine weigh 12,000 kgf.
The foundation has a base area of 10 m2. If the block
foundation rests on sand, make a preliminary
estimate of its natural frequency.
Exercise 2