Seismic fragility and uncertainty mitigation of cable restrainer retrofit for isolated highway bridges incorporated with deteriorated elastomeric bearings

Overcoming the deterioration of aging infrastructure has aroused increasing concern in recent years, particularly, problem of deteriorated elastomeric bearings has emerged as one of the greatest challenges in maintenance and reliability strategies for isolated highway bridges. Though the abundant applications of cable restrainers to provide alternative measure against bearing deterioration and reduce the risk of bridge collapse due to deck unseating, the performance of cable restrainer retrofit is not well understood because of the complicated and nonuniform deterioration process of elastomeric bearings. This paper presents an in-depth seismic fragility and variation analysis to evaluate cable restrainer retrofit for isolated highway bridges, with a special emphasis on the introduction and mitigation of structural response uncertainty caused by the deteriorated lead rubber bearings (LRBs) and cable restrainer retrofit. Firstly, the mechanical properties of deteriorated LRBs and cable restrainers including the associated parameter uncertainty were modeled based on the consideration of past relevant researches. Subsequently, seismic response of a simplified model of a typical continuous girder isolated highway bridge subjected to various scaled earthquake ground motions was computed to statistically evaluate the effect of typical uncertainties of the mechanical behavior of deteriorated LRBs and cable restrainers upon the risk of global seismic failure of the bridge. Finally, the contribution of cable restrainer retrofit in mitigating the vulnerability and response uncertainty of structural components is quantitatively assessed by comparing the cases with and without the application of cable restrainers. The statistical assessments not only reveal the effect of restrainer cable retrofit at the earthquake levels for design standards, but also consider the levels of seismic events greater than consideration in the design, incorporating the seismic performance uncertainty introduced and enlarged by the aging deterioration of LRBs.