Test Methods for Elastomeric Bearings on Bridges

The report discusses the material properties of elastomers for bridge bearings and the factors that influence these properties. The development of tha AASHTO specifications between 1961 and 1992 on elastomeric bearings are also summarized. In addition, various sizes of bonded natural rubber blocks were tested in compression, tension, shear, and combined compression and shear. Load deformation relationships were obtained from all tests and mechanical properties of compressive modulus, tensile modulus, and shear modulus were calculated. Test results indicated that specimen size affects the material properties of an elastomer. Furthermore, the measured shear modulus values were not affected by various level of compressive stress.

The ASTM quad shear test for shear modulus of elastomeric material in bridge bearings was evaluated by comparing the shear modulus from the ASTM test method with the results of full-size bearings manufactured from the same material. The comparison showed that the ASTM test can give significantly different results from the full-size tests; the difference depends on the size of the quad shear test specimen, the method of attachment and testing the full-size specimen, and the method of determining the shear modulus from the quad shear test. The ASTM quad shear test gave poor correlation with the full-size test when high hardness materials were used.