Experimental Research on Vibration Dampers and Insulators

The study of vibration insulation presented· in what follows is an original research undertaken in connection with the general problem of preventing vibration in structures, as applied in particular to the terminal improvements of the Pennsylvania Railroad at Philadelphia, Pa., now (1928) under construction. In order to study the transmission of vibration it was necessary to have two vibrating systems to act as transmitter and receiver, respectively. Each of these elastic systems had its own vibration characteristics. Moreover, the insulator placed between them was also elastic and resilient and, therefore, added a third vibrating element. Loads were also transmitted through this threefold composite system, which had a further effect in modifying the vibration characteristics. It is a notable fact, however, that no practical solution has yet been found of the vibration characteristics of such a primary element as a simple beam of uniform cross-section under load. Simplifying assumptions, such as neglecting the mass of the beam, or assuming that it is unloaded, have always been found necessary to a mathematical solution, and these make the results of such analysis of little practical value. Moreover, such experimental studies of vibration insulators as have appeared, have also been of a very special nature and so limited in scope as to warrant no general conclusions. It is evident, therefore, that the present study is of a somewhat pioneer nature in a difficult field of growing practical importance. It is believed that the essential features of the problem have been kept distinct, and that practical results have been brought to light concerning the general problem of vibration control.