Effects of Ice and Water Contamination on Friction Pendulum Bearings
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Authors
Grijalva Alvarado, Rolando
Issue Date
2024
Type
Dissertation
Language
Keywords
Double Pendulum , Friction Pendulum , Ice Contamination , Seismic Isolation
Alternative Title
Abstract
Over the past few years, there have been several reports on water contaminated Friction Pendulum System (FPS) bearings across the country. Additionally, there is a concern in Alaska that water will freeze inside the bearing during the winter, potentially restraining the slider from moving along the bottom concave surface. The motivation for this project comes from the lack of experimental work to examine the effects of ice and water in FPS bearings. This is the first comparative study on ice and water contaminated FPS bearings against clean FPS bearings. The overall goal of this study is to determine how ice and water contamination affect the bearing frictional properties and overall response of isolated bridge structures. To do so, four bearings were tested: one was a new single pendulum bearing with the same characteristics as the abutment bearings from Robertson River Bridge, two were formerly in-service double pendulum bearings from the abutments of Susitna River bridge and the fourth bearing was a new bearing with the same characteristics as the two formerly in-service bearings. Displacement controlled harmonic sine wave protocols, that included constant amplitude sinewaves and ramping sinewaves, were used to load the bearings and generate hysteresis loops, which were then used to characterize the bearings. Furthermore, ice breakaway force was quantified in order to assess additional shear force demands due to ice breakaway. For ice contaminated tests, the bearings were frozen overnight in-place using dry ice, after the axial load was applied. Furthermore, in double pendulum bearings (DPB), independent displacement of each sliding surface was measured. Experimental results showed that water contamination decreases coefficient of friction by about 40% compared to clean bearings. Furthermore, three sliding regimes were observed on DPBs during tests: sliding on one surface, sliding evenly distributed between both sliding surfaces and uneven sliding between both sliding surfaces. Sliding in one surface only causes single pendulum behavior, essentially doubling the bearings post-yield stiffness. Behavior between single and double pendulum behavior was observed for uneven sliding. Furthermore, it was hypothesized that, in addition to ice or water contamination, concave plate rotation could be inducing sliding in one surface. However, rotation data was inconclusive. Ice contaminated tests showed a consistent ice breakaway force of about 80kN. Furthermore, a spine model of Susitna River bridge was developed in OpenSees to assess the effects of ice contamination on the overall response of the bridge, where experimental ice strength backbone curves were used to develop ice contaminated bearings material models using OpenSees existing materials and elements. The analysis showed ice contamination does not have an important impact on substructure shear force and therefore need not to be considered through the design process. However, Susitna River bridge piers are massive and very stiff, which might have made it insensitive to increases in bearing shear force. Thus, future research using different substructure configurations is recommended.