DHARM876 GEOTECHNICAL ENGINEERING20.17 Explain the essentials of the Elastic half-space theory for the design of machine foundations.
20.18 Explain briefly the salient components of ‘Mass-spring-dashpot model’ for the analysis of ma-
chine foundations.
20.19 Describe how the unbalanced inertial forces are calculated for a reciprocating machine (a) with
a single-cylinder, and (b) with two cylinders with crank angles 0° and π/2.
20.20 What are the special considerations for the design of ‘Impact Machines’?
20.21 Explain the design criteria for the foundation of an impact machine.
20.22 Explain Barkan’s empirical approach for the design of foundation for an impact machine.
20.23 Explain the basic kinds of ‘Vibration Isolation’.
20.24 Describe briefly different methods of active isolation and of passive isolation.
20.25 A machine weighing 500 kN is mounted on a concrete block resting on soil. The base area of the
block is 25 m^2 , and the weight is 100 kN. The coefficient of elastic uniform compression of the soil
is 1.1 × 10^5 kN/m^3. Calculate the natural frequency of the system.
20.26 The coefficient of elastic uniform compression of a soil is obtained as 24,000 kN/m^3 using a plate
of diameter 4 m. Estimate its value if a plate of 2.4 m had been used.
20.27 The exciting force in a constant force type of excitation was 120 kN. The natural frequency of the
machine foundation is 4 Hz. The damping factor is 0.36. Determine the magnification and trans-
mitted force at an operating frequency of 10 Hz.
20.28 The resonant frequency of a block is observed as 18 Hz. The amplitude at resonance is 1.25 mm.
The dynamic force exerted at 18 Hz is 4.5 kN. If the weight of the block is 18 kN, what is the
damping factor?
20.29 The following data refer to a single cylinder reciprocating machine:
cranks radius = 100 mm
Length of connecting rod = 300 mm
Operating speed = 1500 rpm
Weight of reciprocating parts = 45 N
Weight of rotating parts = 9 N
Calculate the maximum unbalanced force generated by the machine.
20.30 The following particulars refer to the foundation for an impact machine:
Weight of ram = 12 kN
Height of fall = 1000 mm
Weight of anvil = 300 kN
Efficiency of fall of ram = 90%
Coefficient of restitution = 0.5
Steam pressure 600 kN/m^2
Area of piston = 0.12 m^2
Limiting frequency of anvil = 240 rad/s
Natural frequencies of the combined system = 270 rad/s and 45 rad/s
Design the foundation.