Section 4 — Structures and Foundations

Support Structures and Foundation for Heavy Machinery

IPE Engineering Practice IPE-EP-4-2-8

Document number: IPE-EP-4-2-8 · Section: 4 — Structures and Foundations

SCOPE

• This Practice covers mandatory requirements governing the design and testing of support structures and foundations for heavy machinery.
• Any deviation to this Practice must be approved by the procedure described in EP 1–1–3.
• An asterisk (*) indicates that a decision or approval by the Owner or the Owner’s Engineer is required, or that additional information is furnished by the Purchaser.
• A revision bar indicates all changes made to this Revision.
• Documentation required for structures supporting heavy machinery is given in Table 2.

2.0 REFERENCES

The latest edition of the following Standards and Publications are referred to herein.

STANDARDS AND PUBLICATIONS

3.0

3.1

3.2

3.3

3.4

3.5

3.6

3.7

4.0

4.1

4.1.1

DEFINITIONS

Contractor - Company or business that agrees to furnish materials or perform specified services at a specified price and/or rate to the Owner.

Heavy Machinery - Rotating equipment having reciprocating or rotary masses as the major moving parts (such as reciprocating or rotary compressors, pumps, engines, and turbines), and having a gross plan area of more than 20 square feet or a total weight greater than 4,000 pounds.

Inspector - A Inflection Point Engineering, LLC appointed engineer or inspector.

Light Machinery - All rotating equipment that is not classified as Heavy Machinery. Owner - Inflection Point Engineering, LLC.

Owner’s Engineer - A Inflection Point Engineering, LLC appointed engineer.

Purchaser - The party placing a direct purchase order. The purchaser is the Owner’s designated representative.

DESIGN

Requirements for All Heavy Machinery

Dynamic modules of elasticity of concrete (EI) for use in dynamic analysis shall be:

E '  79000 where f '  28  day compressive strength, psi

• Soil bearing pressure shall not exceed 50 percent of the net allowable values for static loads. For piled foundations, no reduction in allowable pile capacity is required.
• The effects of shrinkage and thermal expansion shall be taken into account. To prevent cracking, minimum concrete reinforcing steel shall be 84 lb./cu. yd., except for the foundation slabs, which shall have at least 50 lb. of reinforcing steel/cu yd. All reinforcing shall be tri-axially arranged.
• To prevent fatigue failures, all sections shall be proportioned to resist the sum of static dead and live loads, plus three (3) times dynamic loads.
• Foundation design shall consist of standard, simple shapes. Beams, columns and slabs shall be of uniform rectangular shapes. Pockets where vapors could accumulate are not permitted.
• All parts of machine supports shall be independent of adjacent foundations and buildings. Concrete floor slabs, adjacent to the machine foundation, shall be spaced a minimum of 1/2 in. from the foundation. The space between the two shall be filled with a flexible joint filler and sealer.
• The thickness of the foundation slab, in feet, shall not be less than:
•  L

30

Where, for one machinery train :

L  longest side of the foundation slab, feet

For two or more machinery trains on a common foundation :

L  greater of the width of the common slab, or, length of the longest slab segment assigned to any one train, feet

• The height of the support above grade shall be the minimum required to accommodate suction and discharge piping.
• Reinforced concrete foundations shall be designed in accordance with EP 4–2–3 and the requirements of this Practice.
• Additional Requirements for Reciprocating Heavy Machinery
• Reciprocating machinery and associated pulsation bottles shall be supported directly on a rigid foundation. The support foundation for the bottles shall be integral with the compressor foundation. Mounting plates shall be anchored into the foundation.
• Rigid Machinery foundations shall be designed as follows:
• The 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.

• The center of gravity of the machine–foundation system shall be as close as possible to the lines of action of the unbalanced forces.
• Groups of reciprocating machinery shall be tied together with a common foundation slab when the net result is reduced amplitudes.
• Static design shall take into account the following:
• Weight of all machines on the foundation.
• Unbalanced forces and couples, as specified by the machine manufacturer.
• Dynamic design shall be as follows:
• Primary forces, couples and moments shall be applied at machine speed, over the full range of specified operating speeds, for calculation of primary amplitudes.
• Secondary forces, couples and moments shall be applied at twice machine speed, over the full range of specified operating speeds, for calculation of secondary amplitudes.
• Total amplitudes shall be calculated by combining, in phase, primary and secondary amplitudes. Peak–to–peak amplitudes on the foundation shall all be less than 0.002 inches.
• (*)If the Owner’s Engineer gives prior written approval, damping may be considered in amplitude calculations when ratios of structural natural frequencies to excited forcing frequencies in the range of 0.70 to 1.30 cannot be practically avoided.
• Either of the following two damping forms are permitted for amplitudes within the following limits:
• Form 1: Damping ratio C/Cc

Limits: C/Cc for torsional mode of vibration  2/3 of the sum of theoretical geometrical plus internal damping, but in no case > than 0.25

C/Cc for all other modes of vibrations  1/3 of the sum of theoretical geometrical plus internal damping, but in no case > than 0.25

Where: C = modal damping constant

Cc =

2 = modal critical damping value

k = modal spring constant m = mass

• Form 2: Damping characteristics 

Limits: Since  = 2 C/Cc , it shall be limited to twice the limits specified in Form 1 for values of C/Cc

Where:  = logarithmic decrement of damping

• Additional Requirements for Rotary Heavy Machinery
• Rotary machinery shall be supported either directly on a rigid (block type) foundation, or on an elevated structure.
• Static design for either type foundation shall take into account the following loads:
• The dead weight of the machines and their baseplates.

• Lateral 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.
• Longitudinal forces representing 25% of the weight of each machine, including its baseplate, applied along the shaft axis.
• The total lateral and total longitudinal forces above shall not be considered to act concurrently.
• Dynamic design for either type foundation shall be as follows:
• Amplitudes shall be determined using dynamic forces from each rotor, calculated as follows:

Dynamic Force  (Rotor Weight)(Rotor Speed, rpm)

6000

• When there is more than one rotor, amplitudes shall be computed with the rotor forces assumed in–phase and 180° out–of–phase to obtain, respectively, the maximum translational and torsional amplitudes.
• The total peak–to–peak amplitude on the structure or foundation in any direction, shall not exceed the values found in Table 1.
• Rigid foundations for rotary machinery shall be designed per applicable sub-paragraphs in 4.2.2 and 4.2.4 of this Practice.
• Elevated structures for rotary machinery shall be designed as follows:
• Machine loads shall be directly over vertical supports.
• Beams and slabs shall have a minimum span.
• The upper table and the foundation slab shall be rigid in the horizontal plane.
• The foundation slab shall not weigh less than the combined supported weight of the upper table, columns or walls, and the machines (including baseplates).
• All structural natural frequencies shall be outside of the range of 0.70 to 1.30 times any operating speeds of supported machine(s). Short circuit couples, oil whirl frequency, rotor critical speeds, and background vibration shall also be considered.
• Transverse bents or walls shall have the same vertical natural frequencies, within  5%.
• Torsional and transverse horizontal natural frequencies shall be determined considering the whole structure. Individual transverse bents or walls shall have same transverse horizontal natural frequencies, within  5%.
• Multi–degrees of freedom shall be considered if a single degree of freedom system will not lead to an acceptable mathematical representation of the structure.

• Loaded beam and slab natural frequencies in both the horizontal and vertical directions shall be greater than any machine speed, where possible. If beams or slabs must be designed to have natural frequencies below machine speed, allowance must be made for the stiffening effect of the baseplates and the machines.

TESTING

• (*)A test program to determine the dynamic response of elevated supporting structures is required. The test program may be reduced in scope, or waived, pending review by the Owner of the dynamic analysis.
• The test program shall be sufficient to determine if natural frequencies exist near machine operating speeds and to predict the approximate operating amplitudes.
• (*)Proposed testing procedures shall be given to the Owner’s Engineer for approval, at least 60 days before testing.
• Testing shall commence immediately after mounting the machinery, and as long before in- service startup as possible, in order to provide maximum time for corrective measures if vibration problems are discovered.
• (*)Results of the tests shall be documented and submitted to the Owner’s Engineer for determination of acceptance and the need for corrective measures.

6.0 TABLES

TABLE 1

MAXIMUM PEAK–TO–PEAK AMPLITUDE

TABLE 2 DOCUMENTATION REQUIREMENTS

FOR SUPPORT STRUCTURES AND FOUNDATIONS FOR HEAVY MACHINERY PER EP 4–2–8

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