United States Department of Transportation
i
Testing and Analysis of the Effects of Infiltrated Water and Ice on Friction Pendulum Bearings
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2023-02-17
[PDF-26.48 MB]
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Abstract:Field contamination of friction pendulum system (FPS) isolation bearings (water, ice, dirt and other debris) has been observed in several Alaskan bridges during routine bridge inspections. Characterization testing was performed on four FPS bearings in clean/dry conditions as well as wet, frozen and soil-filled. Three of the four were double pendulum bearings (DPBs); two of these formerly in-service abutment bearings from the Susitna River Bridge and one new matching Susitna DPB. The fourth was a new single pendulum bearing (SPB) representing the Robertson River Bridge abutment bearing. The experimental configuration utilized could not constrain the bearing top plate against rotation, so dynamic behavior was influenced by bearing rotation. Evidence was presented to support the hypothesis that water/ice and bearing top plate rotation cause dynamic variation of the bearing friction, which can manifest as a change in the bearing post-yield stiffness. In addition, these same effects can constrain multi-pendulum bearings to slide unevenly on top and bottom surfaces, or constrain the bearing from sliding on one surface altogether, which effectively doubles the post-yield stiffness. Analysis of the Susitna River Bridge under several different contamination scenarios showed that peak bearing displacement and forces can be substantially affected by contamination, but the pier column forces to a lesser extent. Changes are proposed to some of the property modification factors used in bounding analysis procedures as part of the bearing design process
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