Cotton duck bearing pads (CDP) are sometimes used to support loads and accommodate movements and rotations at bridge bearings. CDP are preformed elastomeric pads consisting of thin layers of elastomer interlaid with fabric, and they are manufactured under military specifications with limited guidance from the AASHTO. The behavior of these CDP bearing pads was experimentally evaluated to establish design models for predicting this behavior, to determine the variation in behavior expected with different bearing pad manufacturers, and to develop design recommendations. This research is a follow-up study of an earlier research program sponsored by Arkansas State University.
CDP bearing pads from three different manufacturers were tested, and the test program included dynamic and static (or monotonic) tests of bearings in shear, compression, and rotation. In general, the static tests were used to evaluate strength, stiffness, deformation limits, and general pad behavior. The dynamic tests examined durability and performance under repeated loading and deformation.
The results of this test program were used to develop design recommendations, and an appendix includes a draft of proposed wording for modification of the AASHTO LRFD Specifications to include these design recommendations. In addition, a spreadsheet was developed in Microsoft EXCEL to accomplish the calculations necessary to complete the design.