Resonance-Induced Damage Evolution and Lateral Collapse in a Core–Outrigger Structure: Event-Guided Modal Tracking

Long-period resonant excitation can amplify local damage and promote global instability in tall core–outrigger structures. This study presents an event-guided reanalysis of the shaking-table collapse response of a 28-level, 1/40-scale model representing a 56-story steel-building prototype. Wavelet-transform-assisted independent component analysis identifies transient response features and their spatial concentration; sliding-window independent component analysis tracks the dominant response shape; and synchrosqueezed wavelet analysis characterizes its frequency evolution. These results are integrated with local strain and displacement measurements. An early state-change feature emerged near the upper outrigger at approximately 3.0 s, followed by strain and impact responses near the 13th model level at 3.3 s. The short-time dominant period increased from 0.571 to 0.666 s (16.64%). Subsequent events concentrated near levels 13–15, while upper-structure horizontal deformation became more pronounced after 5.3 s. Strong transient activity at 7.4–7.6 s coincided with reduced stability of local modal separation, followed by rapid growth in roof-vertical displacement mainly after 8.5 s. The combined evidence traces the progression from localized deterioration to increasing upper-structure movement and eventual lateral collapse. These findings highlight the value of event-guided analysis for interpreting the collapse response of a previously damaged scaled specimen under resonant excitation.