Tree Rigging Shock (Dynamic) Load
Estimated peak dynamic load and the multiplier over static weight when a piece is dropped and caught on a lowering line.
Example
You enter
- Static weight of the piece (lb) 500
- Free-fall before the line tightens (ft) 3
- Rope in the system (ft) 30
- Rope elongation at load (%, dynamic ~5-20) 5
You get
- Stretch (ft) 1.5
- Estimated peak load 1618
- Dynamic multiplier over static 3.24x
Details, formula, and sources
From the drop, rope length, and elongation.
stretch = elong/100 x rope_length; peak_load = static x (1 + sqrt(1 + 2 x drop / stretch)); multiplier = peak / static. An energy / elastic-catch estimate.
Arborist rigging dynamic-loading research (Detter, Rust, Donzelli, named generically) and ANSI Z133-2017 by name; first-principles energy balance.
The energy-balance shock-load relation is public mechanics. ANSI Z133-2017 is a published consensus standard.
Math aid for personal verification. Stop work and consult the qualified person on site if any number does not match the field condition.
Field names used by the API: static_weight_lb, drop_ft, rope_length_ft, elong_pct, stretch_ft, peak_load_lb, multiplier
- Rope elongation dynamic-rated rope ~5-20% at the working loadrope manufacturer data
- Elastic catch energy balance assuming a linear-elastic rope; a hard catch is worsearborist rigging research