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Performance Related Parameters of Elastomeric Bearings

Kumar, Alok

2000

The effects of laminate misalignment, creep, aging and explosive decompression on the performance of steel laminated elastomeric bearings were investigated. Natural rubber and neoprene at two hardness levels (durometer 50 and 70) were used in the study of laminate misalignment, creep and aging while the effects of explosive decompression were studied on nitrile. Combined limits on vertical misalignment, edge cover misalignment and laminate inclination in the form of an interaction equation were systematically developed by means of computer simulated virtual experiments using the finite element method. The results showed that the tolerances given in AASHTO M241 are well below the laminate misalignments that affect the performance of the bearings. The creep behavior was investigated by means of full-scale tests. The results showed that creep of elastomeric bearings is important and the boundary conditions play an important role in controlling the long-term deformation. Since full-scale creep tests are time consuming, uneconomical and specific to the bearings tested, a practical method was developed to predict creep of elastomeric bearings using six-hour stress relaxation data obtained from a dual lap shear relaxation test. The effects of aging on shear stiffness were studied by conducting accelerated heat aging tests on four different sizes of shear specimens. As the size increased the percent change in shear stiffness decreased drastically. The results extrapolated to full-size bearings at ambient temperature using Arrenhius relationship predicted that the change in shear stiffness was insignificant. It was concluded that the standardized aging tests performed on thin specimens in tension mode per ASTM D573 assess superficial aging only and does not represent the aging behavior of elastomeric bearings. Therefore ASTM D573 can be eliminated from AASHTO specifications. For elastomeric bearings used as moment-free connections in offshore pipelines transporting high-pressure hydrocarbon fluid/gas mixture, a new test method was developed to study the effects of explosive decompression. Three rubber layer thicknesses tested under extreme exposure conditions showed that under similar environmental and loading conditions, thicker rubber layers were more susceptible to Explosive Decompression Damage (EDD) and with adequate confinement of rubber, the effects of EDD can be reduced to acceptable levels.

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