Evaluation of the Shear Modulus of Elastomeric Bridge Bearings Using Modal Data

The current methods for the determination of the shear modulus for elastomeric bearings consist of the testing on a rather small part of the specimen cut from the manufactured bearing. Hence, such tests are destructive and at the same time, may not essentially represent the corresponding properties of the full size specimen with sufficient accuracy, due to the so-called "size effects." Here, a modal-based nondestructive test method has been proposed which requires a rather simple modal testing apparatus and can be applied to find some important dynamic characteristics of the elastomeric bearings as well as its shear modulus. After the derivation of the dynamic characteristics of the specimens from modal analysis, the shear modulus has been obtained from modal analysis in conjunction with finite element analysis with different material properties that requires a series of finite element analyses based on a simple trial and error procedure. Four test specimens have been used and several tests have been carried out on each. Two of the test specimens were new elestomeric bearings and the other two were used bearings which have been in service for 35 years. The results demonstrate that the proposed method is a suitable manner in which important characteristics of the elastomeric bearings can be quantitatively obtained. Comparison of the results obtained from this method and conventional tests by ASTM have been discussed and some comments have been given on the results of tests on the new and old specimens.