Machine Foundation Analysis and Design
 

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1 GENERAL DESIGN REQUIREMENTS
Foundations shall be cast on a 50 mm thick lean concrete layer.
Top of concrete foundations shall be at least 200 mm above the high point of paving.
In order to allow the adjustment of pumps exchangers, drums, columns, steel structures etc., during the casting of the foundation, the top of piers shall be left at least 25 mm below the final level. Surfaces under base plates for equipment and structures shall be rough to increase grout bonding. Non shrinking grout shall be used for filling between concrete foundation and baseplates. For large base plates this minimum shall be increased up to 50 mm. Concrete bases for steel plates shall extend at least 25 mm beyond the border of the plate. Minimum distance between the axis of the anchor bolt and the foundation edge shall be:

120 mm for 14 <= f <= 24 mm
150 mm for 27 <= f <= 45 mm
200 mm for f > 45 mm
Where f = bolt diameter

Anchor bolts shall be positioned within the reinforcing bar cage.
As a general rule anchor bolts shall be installed before concrete casting. If necessary, adequate pockets shall be provided in the foundation where anchor bolts can be installed later. Pockets shall be filled using non-shrinking grout.
Foundation for vessels on skirt shall have the area within the skirt sloped for drainage and an embedded pipe or opening in the grout discharging outside the skirt.
Minimum concrete cover shall be:
Exposition (Minimum concrete cover)
Concrete cast egainst and permanently exposed to earth. (70 mm)
Concrete exposed to earth but cast in forms (50 mm)
Concrete exposed to weather
For bars <= 16 mm (40 mm)
For bars > 16 mm (50 mm)
Concrete no exposed weather nor in contact with ground:
Walls and slabs (20 mm)
Beams and Columns (40 mm)
Shells, folded plate members:
For bars <= 16 mm (15 mm)
For bars > 16 mm (20 mm)
Minimum distance between reinforcing bars shall not be less than 1 time the maximum diameter of bar or 25 mm
Minimum sliding safety factor shall be 1.50, assuming the coefficient of friction given in the soil report. With the exception of those cases in which the horizontal force depends on the weight of soil (e.g.: retaining walls), such weight shall not be considered if it increases stability.
Minimum overturning safety factor shall be 1.50 during erection and 1.8 in operation. Soil contribution shall be considered as per 6.2.
100% of foundation base area shall be in compression during operation. During erection such percentage may be reduced to 85%.
2 FOUNDATIONS AND STRUCTURES FOR VIBRATING MACHINERY
2.1 Scope
The following mandatory requirements shall govern the design and testing of supporting structures and foundations for heavy machinery.
2.2 Definitions
Heavy machinery is any equipment having reciprocating or rotary masses as the major moving parts (such as reciprocating or rotary compressors, horizontal pumps, engines and turbines) and having a gross plan area of more than 2.5 m² or a total weight greater than 25 KN.
2.3 Design criteria for all heavy machinery
Dynamic modules of elasticity (E') in MPa for use in the dynamic analysis shall be as indicated in DIN 1045.
Modulus of elasticity (E) or shear modulus (G) of soil to be used in dynamic shall be as indicated in the soil report.
Soil bearing pressure shall not exceed 50% of the net allowable values for static loads.
Shrinkage and thermal expansion effects shall be taken into account. In order to prevent Cracking, minimum concrete reinforcing shall be 50 kg/m cubic meter. All reinforcement shall be triaxially arranged.
The Following rules shall be considered in foundation design:
• Foundation design shall consist of clean simple lines;
• Pockets where vapors could accumulate shall not be permitted;
• beams and columns shape should be uniform and rectangular;
• Slender elements shall not be used.
All parts of machine supports shall be independent from the adjacent foundations and buildings. Concrete floor slabs, adjacent to machine foundations, shall be spaced a minimum of 10 mm from the foundations.
The space between slab and foundation shall be filled with a flexible joint filler and sealer.
The thickness of the foundation slab, in meters, shall not be less than:
Thk = 0.6 + L / 30
Where:
For one machinery train:
L = longest dimension of the foundation slab (m);
For two or more machinery trains supported by a common foundation:
L = the greater of:
width of the common slab;
Maximum slab segment length assigned to any train.
In any case minimum thickness of foundation slab shall not be less than 1/10 of its maximum dimension.
The height of supports above grade shall be the minimum required to accommodate suction and discharge piping configuration.
2.4 Design criteria for reciprocating machinery
Design foundation for reciprocating machinery shall be carried out in accordance with the following criteria:
a. Total foundation weight shall be at least 5 times the total machinery weight.
b. Horizontal eccentricity in any direction between the centroid of mass of the machine-foundation system and the centroid of the base contact area shall not exceed 5% of the respective base dimension.
c. The center of gravity of the machine-foundation system should be as close as possible to the lines of action of the unbalanced forces
d. Compressor foundations shall include integral supports for the pulsation bottles.
e. Groups of reciprocating machinery could be tied together with a common foundation slab when allowed by their location and service.
Dynamic design shall be as follows :
a. Natural frequencies in the modes being excited shall preferably be out of the range of 0.7 to 1.3 times the disturbing frequencies of any machine on the foundation. If it is not possible fulfill this prescription, frequency within the above mentioned range can be accepted if the maximum amplitudes shall within the limits listed in the following point e;
b. Damping shall not be higher than 5%;
c. Primary forces, couples and moments shall be applied at machine speed to calculate primary amplitudes.
d. Secondary forces, couples and moments shall be applied at twice the machine speed to calculate secondary amplitudes.
e. Total amplitude shall be calculated by combining, in phase, primary and secondary amplitudes. Total peak-to-peak amplitude on the foundation shall exceed 0.05 mm.
2.5 Design criteria for rotary machinery
Rotary machinery may be supported either on a direct foundation or an elevated structure. Structure and foundation supporting rotary machines shall be designed in accordance with the requirements of DIN 4024, 1988 ed.
Foundation and elevated structures shall be dimensioned applying the criteria mentioned in this specification and in accordance with the prescriptions included in par. 7 of DIN 4024. Furthermore weight of basement (foundation and elevated structure) shall be at least 3 times the weight of the machinery.
Elevated structures for rotary machinery shall be as follows:
a. Machinery loads shall be directly over vertical supports, where possible.
b. Within the weight requirements of the foundation, the upper table and the foundation slab shall be as rigid as possible in the horizontal plane.
c. The weight of the foundation slab shall not be less than the combined supported weight of the upper table, columns, walls and machines.
 Static design for all types of foundations shall take into account the following loads:
a. Dead weight of machines and their base plates
b. Transversal forces representing 25% of the weight of each machine, including its baseplate, applied normal to its shaft at a point midway between the end bearings.
c. Longitudinal forces representing 25% of the weight of each machine, including its baseplate, applied along the shaft axis.
d. Total transversal and total longitudinal forces per b. and c. above shall not be considered to act concurrently.
Dynamic design for all types of foundations shall be as follows:
a. Barkan`s theory shall be utilized to carry out the calculations of natural frequencies and amplitudes.
b. All natural frequencies shall be out of the range of 0.7 to 1.4 times operating speed of any machine supported thereon; where this frequency ratio restriction is impractical or uneconomical, frequency ratios within the above range will be accepted, provided the amplitudes meet the requirements of point
h); short circuit couples, oil whirl frequency, rotor critical speeds and background vibration shall also be considered.
c. Transverse bents or walls should be designed so that their vertical natural frequencies agree within 5%.
d. Torsional, transverse and longitudinal horizontal natural frequencies should be determined considering the whole structure. Individual transverse bents or walls should have same transverse horizontal frequencies.
e. Multi-degrees of freedom shall be considered if a single degree of freedom system will not lead to a reasonable mathematical representation of the structure.
f. Loaded beam, slab and frame natural frequencies in both horizontal and vertical directions, where possible, shall be above any machine speed. If beams, slabs or frames must be designed to have natural frequencies below machine speed, allowance must be made for the stiffening effect of the base plate and the machine.
g. Amplitudes shall be determined using dynamic forces from each rotor, calculated as follows:
Dynamic force = Rotor weight x Rotor Speed (rpm)
6000
h. Total amplitude on the structure of foundation in any direction shall not exceed the values indicated in
the following table:
ALLOWABLE AMPLITUDES
ROTOR SPEED (RPM) PEAK TO PEAK AMPLITUDE (MM)
0-999 0.023
1000-1149 0.020
1150-1299 0.018
1300-1499 0.015
1500 and above 0.013
2.6 Design criteria of light vibrating machinery
Following mandatory requirements shall govern the design of supporting structures and foundations for light vibrating machinery.
Light vibrating machinery is any equipment having reciprocating or rotary masses as the major moving parts (such as reciprocating or rotary compressors, horizontal pumps etc.) and having both a gross plan area less than 2.5 m² and a total weight less than 25 KN.
For light vibrating machinery dynamic design shall be neglected. Static design of foundations shall be performed according to clause 7.4 of this specification, but weight of foundation must be at least 3 times the total rotary machines weight or 5 times the total reciprocating machines weight.
Minimum concrete class shall be f´c= 21 N/mm².
3 LOADING OF MACHINE FOUNDATIONS
3.1 Static loads
3.1.1 Dead loads
3.1.2 Live loads
3.1.3 Wind loads
3.1.4 Seismic loads
3.1.5 Static operating loads
3.1.6 Special loads for elevated-type foundations
3.1.7 Erection and maintenance loads
3.1.8 Thermal loads
3.2 Rotating machine loads
3.2.1 Dynamic loads due to unbalanced masses
3.2.1a Dynamic load provided by the manufacturer
3.2.1b Machine unbalance provided by the manufacturer
3.2.1c Machine unbalance meeting industry criteria
3.2.1d Dynamic load determined from an empirical formula
3.2.1e Machine unbalance determined from trip vibration level and effective bearing stiffness
3.2.2 Loads from multiple rotating machines
3.3 Reciprocating machine loads
3.3.1 Primary and secondary reciprocating loads
3.3.2 Compressor gas loads
3.3.3 Reciprocating inertia loads for multicylinder machines
3.3.4 Estimating reciprocating inertia forces from multicylinder machines
3.4 Impulsive machine loads
3.5 Loading conditions

Calculation Reference
Design for Machine Vibration
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FOUNDATIONS AND STRUCTURES FOR VIBRATING MACHINERY
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Rotating machine loads
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Submitted On:
16 Jun 2014
Submitted By:
BABACAN
File Date:
16 Jun 2014
File Author:
Turan Babacan
File Version:
1.0
File Size:
213.02 Kb
File Type:
xlsx
Downloads:
417
Rating:
stars/5.gifTotal Votes:10
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Comments  

 
#5 rbj 2016-06-23 02:26
How are the excitation forces determined that are to be input into the software ?

rbj
 
 
#4 JohnDoyle[Admin] 2014-12-07 12:56
 
 
#3 mbhatti 2014-12-06 21:37
I like Machine Foundation and many others. How can I use them for English Units like Fett and pounds etc and not metric???

Thanks

Max Bhatti
 
 
#2 CedarCorp 2014-11-26 00:18
Wondering about whether the checks for the foundation/equipment ratio changes for rotary (3 x machine weight) and reciprocating (5 x machine weight) - right now it seems locked to 5 x weight for reciprocating
 
 
#1 JohnDoyle[Admin] 2014-06-16 17:35
Not content with covering all aspects of civil and structural engineering I see you are starting to encroach on the ground of the mechanical engineer! Amazing stuff Turan (again!)
 

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