LRFD Design Criteria for Cotton Duck Pad Bridge Bearing.

摘要

Cotton duck pads (CDP) are preformed elastomeric pads consisting of thin layers of elastomer interlayed with layers of cotton duck fabric. Manufactured under Military Specification MIL-C-882-E, CDP are known to be quite stiff and to have large compressive load capacity. Because of this great stiffness, the translational movement and rotational capacity of CDP have been severely limited. Very few tests have been performed on these pads to examine their behavior, and, as a consequence, the design limits for these pads have been based historically on models for plain unreinforced elastomeric bearing pads (PEP), with the additional constraint caused by the larger bearing stiffness added to the model. As a consequence, although CDP are permitted significant compressive load capacity in the American Association of State Highway and Transportation Officials (AASHTO) Load and Resistance Factor Design (LRFD) and Standard Specifications, they are allowed virtually no translational movement or rotational capacity in these same specifications. The AASHTO limit on translational movement capacity is less serious than that on rotational capacity, because CDP are often used with polytetrafluorethylene (PTFE) sliding surfaces, which can accommodate significant translation even though the CDP is very stiff. The AASHTO limitation on rotation is very severe, however, because it makes difficult the accommodation of construction tolerances with CDP applications. The severity of this rotational limit is the primary focus of this research study.