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<p>The influence of deep foundation configuration on pier-level seismic fragility under near-fault ground motions remains insufficiently quantified. This study evaluates how alternative foundation systems modify the probabilistic seismic response of reinforced concrete bridge piers in simply supported bridge configurations, where column ductility demand typically governs seismic performance. Nonlinear time-history analyses incorporating soil–structure interaction effects are conducted for piers supported on conventional caisson foundations and composite caisson-pile foundations (CCPF). Probabilistic seismic demand models are developed to establish lognormal fragility functions corresponding to ductility-based damage states defined through section-level material response. The results indicate that CCPF systems reduce pier exceedance probability by 55–68% across all damage states relative to caisson-only foundations at PGA = 0.5&#xa0;g, with caisson depth identified as the dominant design parameter governing probabilistic pier-level response. The findings provide comparative pier-level fragility functions for caisson and CCPF systems and highlight the critical role of foundation depth in performance-based seismic evaluation of bridge substructures subjected to near-fault excitation. The influence of foundation flexibility becomes more pronounced at moderate-to-high intensity levels where nonlinear behavior dominates.</p>

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Pier-level seismic fragility of RC bridges on caisson and composite caisson-pile foundations under near-fault ground motions

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年6月21日

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  • Jibendra Misra,
  • Netra Prakash Bhandary

摘要

The influence of deep foundation configuration on pier-level seismic fragility under near-fault ground motions remains insufficiently quantified. This study evaluates how alternative foundation systems modify the probabilistic seismic response of reinforced concrete bridge piers in simply supported bridge configurations, where column ductility demand typically governs seismic performance. Nonlinear time-history analyses incorporating soil–structure interaction effects are conducted for piers supported on conventional caisson foundations and composite caisson-pile foundations (CCPF). Probabilistic seismic demand models are developed to establish lognormal fragility functions corresponding to ductility-based damage states defined through section-level material response. The results indicate that CCPF systems reduce pier exceedance probability by 55–68% across all damage states relative to caisson-only foundations at PGA = 0.5 g, with caisson depth identified as the dominant design parameter governing probabilistic pier-level response. The findings provide comparative pier-level fragility functions for caisson and CCPF systems and highlight the critical role of foundation depth in performance-based seismic evaluation of bridge substructures subjected to near-fault excitation. The influence of foundation flexibility becomes more pronounced at moderate-to-high intensity levels where nonlinear behavior dominates.