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
Checked against published worked examples from: Arborist rigging research / ANSI Z133-2017.
Details, formula, and sources
ScopeFrom the drop, rope length, and elongation.
Formula or tablestretch = elong/100 x rope_length; peak_load = static x (1 + sqrt(1 + 2 x drop / stretch)); multiplier = peak / static. An energy / elastic-catch estimate.
Source and editionArborist rigging dynamic-loading research (Detter, Rust, Donzelli, named generically) and ANSI Z133-2017 by name; first-principles energy balance.
Free accessThe energy-balance shock-load relation is public mechanics. ANSI Z133-2017 is a published consensus standard.
What governsMath aid for personal verification. Stop work and consult the qualified person on site if any number does not match the field condition.
API field namesstatic_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