Background
Existing tree-risk assessment focuses on static ultimate-load criteria and neglects cumulative fatigue from everyday wind loading. Yet decay-accelerated fatigue is the dominant cause of branch failure and windthrow in mature urban trees during storms.
Approach
Six core modules integrated end-to-end:
- FE dynamic analysis (ABAQUS) — 6 geometries (H=6, 8 m × DBH=15, 20, 25 cm), tapered B31 beams
- Kaimal-spectrum wind time series — longitudinal mean+turbulence + lateral turbulence (σv = 0.75σu), biaxial loading
- Rayleigh damping (ζ = 2%)
- Rainflow cycle counting + Miner's linear damage rule
- Concentric-hollow decay stress amplification model
- Regional Weibull wind speed distributions
Key Results
| Metric | Value | |---|---| | Maximum dynamic amplification factor (DAF) | 7.71 (H=8 m, DBH=15 cm) | | Peak stress (same condition) | 138.7 MPa — exceeds ginkgo MOR | | Lower-bound fatigue life for decayed reference tree (Jeju typhoon regime) | ~1.4 yr | | Fatigue-life spread across 5 Korean sound species | up to several hundred thousand-fold (MOR differences) | | Basal stress reduction in soft clay | up to −64.5% (vs fully fixed base) |
Implications
- Slender trees (high H/DBH ratio) fail statically before fatigue — static thresholds should be checked first during inspection.
- Decay detection and species selection are the primary determinants of fatigue safety.
- Clay soil reduces basal stress but raises overturning risk under extreme loads — a clear trade-off.
- Regionally differentiated inspection standards are warranted (e.g., capital region vs Jeju typhoon belt).
Related solutions
- Street-Tree Safety · Fatigue Diagnosis — this framework is the engine behind the advisory deliverable.