Experimental Investigation of Large Helical Coil Springs for Ground-Shock Attenuation

Abstract

Critical installations require that shock inputs of 50 G or higher be attenuated to less than 1 G. This can be accomplished by very soft helical coil springs, used in various arrangements relative to the center of gravity of the isolated units. The lack of experimental data on springs of extreme sizes—3-in. bar diameter—and their application for vertical and lateral shock protection was the reason for this investigation. Two specific applications are presented for helical coil springs: the first, an underground bottom spring-supported building in which the springs have to take simultaneous vertical and lateral deflection under combined vertical and lateral loads during full shock input; the second system, a pendulum suspension-type with four struts, each consisting of four springs in series, parallel arrangement. Design criteria for the springs, the measurement of their lateral and vertical load rates, and experimental stress analysis, with equipment developed for the purpose of testing large springs under high static and shock loads, are described and compared with the results of analytical investigations for stress distribution in the circular cross sections of helical compression springs under different loading conditions.