United States Department of Transportation
i
Evaluation of Tapered Bridge Bearing Pads
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2021-03-01
[PDF-19.87 MB]
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Alternative Title:Evaluation of Tapered Bridge Pads
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Edition:Final Report
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Abstract:Steel-reinforced elastomeric bearing pads are widely used in bridge construction to vertically support girders on piers while also accommodating translational and rotational girder deformations caused by live loads and temperature changes. To support sloped girders, flat bearing pads of uniform thicknesses are typically used with either tapered steel shim plates or an inclined concrete bearing seat. Tapered pads have the potential to reduce both construction time and cost by eliminating the need for tapered steel plates or the need to slope concrete beam seats to match the girder slope. Limited research, however, has been performed to investigate the effects of taper on relevant design properties of bearing pads such as axial stiffness, shear stiffness, horizontal restraining force and displacement generated in tapered pads under pure compression, and shear strain at slip. In order to evaluate these properties, tapered pad configurations with varying plan view dimensions, elastomer thicknesses, and slope angles were developed by modifying elastomer thicknesses and shim orientations of standard FDOT flat pads. An experimental test setup and testing protocol was then developed to test tapered bearing pads and flat pads (control specimens). In this report, results are presented from the experimental testing that was performed to quantify the effects of taper on the design properties of bearing pads. Results obtained from the study revealed that shear stiffness was not significantly influenced by the introduction of taper angle, or the direction of shear along the length of pads. The shear stiffness of tapered pads remained within approximately 15% of the shear stiffness of corresponding flat pads. However, axial stiffness, horizontal restraining force, and horizontal displacement in tapered pads were found to depend on the taper slope angle. Axial stiffness decreased with increase in taper slope, and horizontal restraining force and displacement increased with increase in slope. Based on the collected experimental data, generalized equations were developed to aid in the estimation of axial stiffness, shear stiffness, horizontal restraining force, and horizontal displacement. The effect that taper slope has on shear strain at pad slip was also investigated. Tapered pads bearing against concrete surfaces were found to satisfy the AASHTO requirement of minimum 0.5 shear strain before slip. However, tapered pads bearing against steel surfaces generally did not satisfy this requirement. Future research is recommended to evaluate different options to prevent premature slip of tapered pads on steel surfaces. For the design of mechanical anti-slip devices such as keeper plates, relevant design forces may be computed using horizontal pad restraining force equations developed and presented in this study.
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