Mechanics of Rubber Bearings for Seismic and Vibration Isolation by James M. Kelly, Dimitrios Konstantinidis

The multilayer rubber bearing is an apparently simple device that is used in a wide
variety of industries that include civil, mechanical and automotive engineering. It is so
ubiquitous that it may be difficult to believe that it is a relatively recent development,
having been used for only about fifty years. The idea of reinforcing rubber blocks by
thin steel plates was first proposed by the famous French engineer Eug`ene Freyssinet
(1879–1962). He recognized that the vertical capacity of a rubber pad was inversely
proportional to its thickness, while its horizontal flexibility was directly proportional to
it.

He is best known for the development of prestressed concrete and for the discovery of
creep in concrete. It is possible that his invention of the reinforced rubber pad was driven
by the need to accommodate the shrinkage of the deck due to creep and prestress load,
while sustaining the weight of a prestressed bridge deck. He obtained a French patent
in 1954 for his invention, and within a few years the concept was adopted worldwide
and led to the extraordinary variety of applications in which multilayer rubber bearings
are used today.

These reinforced rubber bearings in their various forms are a source of fascinating
problems in solid mechanics. It is the combination of vertical stiffness and horizontal
flexibility, achieved by reinforcing the rubber by thin steel plates perpendicular to the
vertical load, that enables them to be used in many applications, including the seismic
protection of buildings and bridges and the vibration isolation of buildings and machinery.
The horizontal, vertical, and bending stiffnesses are important to the design
of bearings for these applications and for predicting the buckling load, the interaction
between vertical load and horizontal stiffness, and the dynamic response of structures
and equipment mounted on the bearings.

We will cover the theory for vertical stiffness in Chapter 2 and for bending stiffness
in Chapter 3.

Some of the results in these two chapters are new. The results of Chapters
2 and 3 are used to predict the stresses in the steel reinforcing plates in Chapter 4.
The analysis used to calculate these stresses is new to this text and was only recently
developed by the authors. Also new and original to this text is the development of a
theory for these stresses when the effect of the bulk compressibility of the rubber is
included, which is necessary for seismic isolation bearings, but usually not for vibration
isolation bearings.

In Chapter 5 we study the stability of these bearings