The design of machine foundation is carried out for evaluating vibration characteristics of the foundation system cautiously. The machine manufacturer supplies the appropriate data essential for the design and development of the machine foundation of machine before creating the design. All parts of machine foundation are created for extreme stresses because of the poorest combination of vertical loads, torque, longitudinal and transverse forces, stresses because of dissimilarity in temperature and the foundation dead load. In case, the machine foundation layout is partially constructed with beam and column construction, straight bars are placed both at top and bottom of the beams and the gaping of the stirrups should be nearby. The primary foundation block must contain the calculated thickness and should be reinforced both at top and bottom, although the reinforcements are not compulsory from design considerations.
General standards of machine foundation design are provided below :-
There should be adequate mass of the foundation block to absorb vibrations and as well as withstand resonance among the machine and the adjoining soil. This is possible with the increased weight of foundation block according to the power of the engines. It is recommended that for every break horse power of multicylinder engines, a lowest 725 kg. weight of foundation should be arranged for gas engines, 565 kg. for diesel engines and 225 kg. for steam engines. This value is raised by 40 to 60% for the single cylinder engines. As a thumb rule, the weight of the foundation must be minimum 2½ times the weight of the entire machine.
To get rid of the variation in settlement, the dimension of the machinefoundation should be perfect so that the subsequent force move through the centre of gravity of the base contact area as a result of the weight of the machine and the weight of the foundation.
The foundation should have been solid enough to maintain required strength as the smallest deflection of foundation can lead to significant bearing troubles.
There should be a gap around the machine foundation so that the vibration is not delivered from the machine to the adjacent parts of the building to separate it from the adjoining parts of the building.
Overhanging cantilevers should not be used in most cases. If it is not possible, they should have been designed for stability and hardness against vibrations.(6) All units of machine foundation are arranged with reinforcement passing both ways along the surface of the concrete block. The concrete cover to the reinforcement must not be below than 75 mm at the bottom, 50 mm on sides and 40 mm at the top. For foundation developed with steam turbo-generators, cover for the reinforcement at bottom, side and top of base slab must not be below 100 mm.
The amount of reinforcement in foundation units should not be below 2 kg per cu. m of concrete toward impact type or reciprocating type of machines, 50 kg per cu. m of concrete for rotary type of machines and 100 kg per cu. m of concrete for steam turbo generators.
M 150 to M 200 grade of concrete should be applied in the foundations and mostly the-entire block should be concreted in one process devoid of construction joints.
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Published By
Rajib Dey
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