Realistic modelling of earthquake-isolation bearings

Abstract

The physical properties of rubber components are greatly influenced by the techniques used in their manufacture. Normally, high-order strain energy (density) functions are required in finite-element analyses (FEAs) to represent elastomeric behaviour. Natural rubber is bonded to steel in alternate layers to produce earthquake-isolation bearings and these bearings are predominantly subjected to compression and shear. In compression, rubber is thought to behave in compliance with a simple neo-Hookean strain energy function, whilst tests in shear provide only information about low-order functions. This suggests that it may be possible to model the bearings with a comparatively simple equation. Natural rubber test-pieces were manufactured by three different processes over a range of hardness. Initially, a Flory–Rhener test was applied to each compound to establish the variation in cross-link density. Uniaxial, compression and tension tests were carried out on specimens produced by compression, transfer and injection moulding. Neo-Hookean and two-term Ogden models were determined for each compound for input to FEA. Simultaneous shear and compression loads were applied to a rectangular block comprising rubber and steel layers. Results from this test were compared with a plane-stress finite-element model. In conclusion, recommendations are made for the manufacture, computer modelling and testing of the bearings.