Bearings are important bridge elements that must be considered when evaluating potential ways to extend overall bridge service life. Elastomeric bearings have proven durability but with certain combinations of load and movement, their capacity to accommodate the required load and translation can be exceeded. Additional movement capacity can be provided by means of sliding surfaces. Many bearing types, including cotton duck pads and high-load multirotational bearings, also use sliding surfaces to accommodate bridge movements. Currently, polytetrafluorethylene (PTFE) is the material commonly used for sliding surfaces; however, this material wears under certain service conditions. Higher performing materials are available that can provide significantly greater wear resistance and enhanced service life. Two such high-performing sliding surface materials were investigated to study and predict their service life: ultrahigh-molecular-weight polyethylene (UMWP) and glass-filled reinforced PTFE (GFR-PTFE). This paper describes research and proof-of-concept testing to determine the feasibility of achieving increased service life with bearings that use sliding surfaces for movement through the use of alternative high-performing materials in lieu of conventional plain PTFE. This paper describes the experimental testing program, which compared material wear and coefficient of friction (COF) over a range of parameters including contact pressure, rate of movement, and accumulated total movement. Both UMWP and GFR-PTFE showed significantly greater wear resistance than conventional PTFE when subjected to initial testing with high contact pressure (20.7MPa or 3,000psi) and high rate of movement (63.5cm/min or 25in./min), but also exhibited higher COFs. Plain PTFE was shown to wear at a very high rate under the initial testing parameters, resulting in substantial thickness loss within less than 2mi of accumulated sliding length. Glass-filled reinforced PTFE exhibited the best wear resistance with no material thickness loss in initial testing over approximately 8mi of accumulated sliding length. Ultrahigh-molecular-weight polyethylene exhibited some initial thickness reduction, which may have been related to material compressibility. The testing confirmed the effects of both contact pressure (P) and rate of velocity of movement (V) as contributing factors to sliding-surface wear. For PTFE and GFR-PTFE, the testing also showed a direct correlation between the rate of material wear and the factor of P times V (PV), where increased levels of PV resulted in increased rates of material wear. Also, wear rates at these PV levels were nearly uniform. There were also levels or thresholds of PV below which the rate of material wear was very low or nearly zero. (C) 2015 American Society of Civil Engineers.
