Effect of Water Immersion on the Seismic Isolation Performance of Castable Polyurethane Bearing

Abstract

This study performs a 120-day water aging simulation on castable polyurethane (CPUE) bearings and tests them at 30-day intervals for vertical load-bearing performance and 100% horizontal shear performance. The results indicated that the CPUE bearings achieved full water aging after 120 days of water immersion. Besides, the vertical stiffness, horizontal shear stiffness, and equivalent damping ratio decreased by 10.3%, 16.8%, and 10.0%, respectively. Moreover, the study investigates the hydrolysis mechanism of CPUE bearings using Atomic force microscopy (AFM) and cross-linking density (NMR) tests. Subsequently, it develops models for unaged CPUE bearings (CPUE-un) and fully water-aged bearings (CPUE-aged), selecting unaged test results for CPUE-un and the test results from 120 days of water immersion for CPUE-aged. Within the study context, a representative high-pier continuous girder bridge serves as the basis for evaluating the effects of seismic conditions on the CPUE-un and CPUE-aged bearing bridge systems. The findings demonstrate that water-aged CPUE experiences significant material softening, with bearing deformations increasing by 14.99%, 34.06%, and 46.65% at 0.3, 0.6, and 0.9 g peak ground acceleration (PGA), respectively. The likelihood of damage to water-aged bearings increased under seismic influence, while the impact on piers was less pronounced. This research provides a valuable reference for the application of CPUE bearings in humid environments.