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<p>Semi-ruined reinforced concrete frame structures (RCFSSS), formed after mainshock-induced damage, are highly vulnerable to secondary collapse during aftershocks, posing serious threats to trapped occupants and rescuers. To enable real-time risk assessment, this study proposes an integrated early-warning framework that combines scaled shaking table experiments, high-fidelity FEM–FDEM simulations, and dynamic response indicators. Two 1:15 scale RC frame models were tested to reproduce typical seat-type and pancake-type secondary collapse modes under sequential mainshock–aftershock excitations. A new dynamic indicator, the Cumulative Absolute Vertical Velocity (CAVV), was introduced to quantify vertical instability. Across 360 simulation cases, CAVV curves consistently exhibited a three-stage evolution. The first inflection point, with a mean value of 1150 mm/s, was identified as an effective early-warning threshold for cases that ultimately underwent secondary collapse. A real-time decision algorithm was developed by integrating CAVV triggering with vertical displacement (VD) feedback for adaptive threshold updating, improving warning accuracy and responsiveness. The proposed framework provides a scientific basis for real-time secondary collapse warning of RCFSSS and offers practical support for post-earthquake emergency response and rescue operations.</p>

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Experimental and numerical study on real-time early warning of secondary collapse in semi-ruined RC frame structures under aftershocks

  • 期刊论文

  • 发表日期：

    2026年2月13日

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  • Defeng Xu,
  • Feifei Sun,
  • Yue Liu,
  • Jixin Wen

摘要

Semi-ruined reinforced concrete frame structures (RCFSSS), formed after mainshock-induced damage, are highly vulnerable to secondary collapse during aftershocks, posing serious threats to trapped occupants and rescuers. To enable real-time risk assessment, this study proposes an integrated early-warning framework that combines scaled shaking table experiments, high-fidelity FEM–FDEM simulations, and dynamic response indicators. Two 1:15 scale RC frame models were tested to reproduce typical seat-type and pancake-type secondary collapse modes under sequential mainshock–aftershock excitations. A new dynamic indicator, the Cumulative Absolute Vertical Velocity (CAVV), was introduced to quantify vertical instability. Across 360 simulation cases, CAVV curves consistently exhibited a three-stage evolution. The first inflection point, with a mean value of 1150 mm/s, was identified as an effective early-warning threshold for cases that ultimately underwent secondary collapse. A real-time decision algorithm was developed by integrating CAVV triggering with vertical displacement (VD) feedback for adaptive threshold updating, improving warning accuracy and responsiveness. The proposed framework provides a scientific basis for real-time secondary collapse warning of RCFSSS and offers practical support for post-earthquake emergency response and rescue operations.