Practical Design of Machine Foundation Subjected to Harmonic Loading by Rotating Equipment with Varying Frequency

Abstract

This paper presents a practical design of machine foundation subjected to varying harmonic loads. The dynamic analysis of machine foundation is performed using an analytical method. The varying harmonic loads are generated by varying the speed of the machine as per the performance requirements of the plant, which essentially results in operating the machine at or near the resonance. The vertical vibration and coupled horizontal and rocking vibrations are represented using Lysmer’s and Hall’s analogs, respectively. The equations of motions are formulated considering the vertical motion and coupled horizontal and rocking motion of the foundation soil system in the lumped parameter approach. The analytical formulation is capable of considering the moments generated due to the eccentricity of loads (i.e., static weights of the machine and foundation). A computer program is developed using FORTRAN to obtain the practical solutions for the machine foundation soil system. The maximum amplitudes of the vertical and horizontal displacements of the case study example are 22.5 and 110.68 μm, respectively, for the operating frequencies ranging from 2.5 to 12.1 Hz. The performance of the induced draught fan foundation is evaluated using the General Machinery Vibration Severity Chart, the guidelines given in the publication Foundations for Machines: Analysis and Design, and the American Concrete Institute standard ACI 351.3R-04. These charts and guidelines help in assessing the performance of the machine foundation system during operation of the plant. Based on the results, the performance of the machine foundation system is rated as “good” to “very good” and “fair” to “slightly rough” category based on the obtained vertical and horizontal amplitudes of the displacements respectively. Based on the measured data, it is noted that the evaluated performance parameters are well within the operating parameters of the machine foundation system.