Boiler Components

FOUNDATIONS FOR VIBRATING MACHINES

Special Issue, April-May 2006, of the Journal of Structural Engineering, SERC, Madras. INDIA

SHAMSHER PRAKASH Professor Emeritus Civil, Architecture and Environmental Engineering University of Missouri Rolla Rolla, MO, USA

VIJAY K. PURI Professor Civil and Environmental Engineering Southern Illinois University Carbondale, IL, USA

ABSTRACT The paper discusses the methods of analysis for determining the response of foundations subjected to vibratory loads. The design of a machine foundation is generally made by idealizing the foundation- soil system as spring-mass –dashpot model having one or two degrees of freedom. Most machine foundations are treated as surface footing and the soil spring and damping values are determined using the elastic-half space analog. The spring and damping values for response of embedded foundations can also be determined from the elastic half space concept as per Novak‟s work. The soil spring and damping values can also be obtained following the impedance –compliance function approach. The paper also presents a brief discussion of the predicted and observed response of machine foundations . INTRODUCTION Machine foundations require a special consideration because they transmit dynamic loads to soil in addition to static loads due to weight of foundation, machine and accessories. The dynamic load due to operation of the machine is generally small compared to the static weight of machine and the supporting foundation. In a machine foundation the dynamic load is applied repetitively over a very long period of time but its magnitude is small and therefore the soil behavior is essentially elastic, or else deformation will increase with each cycle of loading and may become unacceptable. The amplitude of vibration of a machine at its operating frequency is the most important parameter to be determined in designing a machine foundation, in addition to the natural frequency of a machine foundation soil system....