ABSTRACT
Although earthquake base isolation by means of HDNR is a relatively new technology, the use of natural rubber pads in structures extends back over a century. Natural rubber is attacked by oxygen and ozone, but for bulky components (such as earthquake isolation bearings) the effects are only superficial over timescales up to 100 years; large items made from appropriate formulations are relatively immune even to superficial attack. Furthermore the natural material subjected to a constant load is not susceptible to time-dependent crack growth. The bulk properties of suitably formulated natural rubber materials have been found to remain relatively stable over many years [12]. Evidence suggests this is not the case for all engineering elastomers [13].
