Machine foundations

Types of machine foundations and their usages

1. Machine Foundations IQBAL 17512008 Alternate Hydro Energy Systems AHN 512

2. Introduction Type of Loads Static load – due to weight of machine and weight of foundation itself Dynamic load – nature of dynamic load depends on type of machine Type of machines 1. Reciprocating machines Produce periodic unbalanced force Engines, Compressors etc. Less than 600 rpm Sinusoidal unbalanced force 2 . Impact machines High impact load for small duration Forge hammers etc. 60 to 150 blows per minute 3. Rotary machines Medium and high speed machines e.g. turbo-generators, rotary compressors Generally 1500 to 10000 rpm

3. Types of foundations 1. Block type 2. Caisson or Box type 3. Wall type

4. Block type foundations Block type foundations consists of a pedestal resting on a footing have has large mass and a small natural frequency. For reciprocating type machines, block type foundations are generally used.

5. Box type foundation consists of a hollow concrete block. The mass of this foundation is less than the block type, as it is hollow. The natural frequency of the box type machine foundation is increased. Box type foundations

6. Wall or Frame type of machine foundation consists of vertical columns with horizontal frame at their tops. It is used for larger machines. The machines are rested on top of the frames. The vertical and horizontal members of this foundation can be constructed by different materials. Wall type foundations

7. Vibrational analysis of Machine foundation For single degree of freedom System Where E = Young’s modulus u = Poisons ratio A = area of contact

8. For six degree of freedoms

9. •Cross Hole Test (CHT) •Down hole test (DHT) •Spectral Analysis of Shear wave ( SASW) •Block Vibration Tests Laboratory tests: •Resonant Column test •Cyclical Tri axial Test The above test are conducted usually by a Geotechnical Contractor and appropriate values are recommended by him in the Geotechnical report How to determine the Soil Parameters?

10. Indian Standard on design and construction of foundation for rotary machines IS: 2974 (part 3) 1992 code of practice is for foundation designing of rotary machine. Salient features of Code of practice Necessary Data Design Criteria Concrete foundation design

11. Necessary Data Data provided by machine manufacturer General description about the machine, outline dimensions, driving and driven machine, rated output Detailed loading diagram showing details of transfer of loads and their point of application Details of dynamic loads and couples- their location, magnitude and direction O perating speed, critical speed Mass moment of Inertia of driving and driven machine about principal axes Allowable displacements at machine bearing points during normal operation Data on ground and site conditions Soil profile and soil characteristics up to the depth of three times the expected plan dimension of foundation Dynamic properties of soil The relative position of water table below ground level at different times of the year

12. Design Criteria The machine foundation should be isolated from other foundations It should be able to carry the superimposed loads without causing shear or crushing failure No resonance should occur between the natural frequency of the foundation–soil system and pulsating load The amplitude of vibrations does not exceed the safe value Limitations of amplitude of vibration 1. to avoid damage to machinery 2. to avoid damage to neighbouring structures 3. to avoid discomfort to person 4. to avoid soil settlement

13. The above are only approximate values. Actual permissible should be given by the Machine Vendor/Manufacturer Vibration Limit in machine foundation design For Rotary machine For Reciprocating machine

14. Concrete block foundation are generally designed for reciprocating machines and wall type is used for rotating turbo-generator machines. Pile foundations may be used where the soil conditions are unsuitable to support a block foundation. F oundation mass = 2.5 to 3 times of rotatory machine mass Foundation should extend by at least 150 mm on all sides of machine base frame. The pressure developed in the soil loads due to static loads should not exceed 75% of the allowable safe bearing capacity. Concrete foundation design

15. Table top turbo-generator foundation Table top turbo-generator foundation with vibration Isolators Wall type foundation with isolators

16. IS Codes IS 2974 – 5 parts, of which part 1, 3 and 4 are for reciprocating and rotating machines IS 5294 – Method of test for determination of soil dynamics properties IS 7207 – Design of generator foundation for hydroelectric power station

17. R eferences Varanasi Rama Rao, Machine F oundations in oil and gas industry, Chennai Office www.theconstructor.org/geotechnical/general-requirements-of-machine-foundations/7244 www.theconstructor.org/structural-engg/machine-foundation-vibration-analysis/14777 BIS (1992). “IS 2974 (Part 3): 1992—Indian Standard Design and Construction of Machine Foundations—Code of Practice, Part 3: Foundations for Rotary Type Machines (Medium and High Frequency) (Second Revision)”, Bureau of Indian Standards, New Delhi Dr Priti Maheshwari , Machine Foundations, Module - 02 Lecture – 4, Department Of Civil Engineering, IITR Sukanta Adhikar , Turbo-generator foundation