Aug 28 • General discussion
Understanding dynamic loading
In tree work, dynamic loads are forces that are not constant or static. They are created by movement and are significantly greater than the weight of the object itself. Understanding and managing dynamic loads is crucial for safety during tree removal, pruning, and rigging operations.
How Dynamic Loads Are Created
Dynamic loads in tree work are typically created when a cut limb or section of trunk is allowed to free-fall for any distance before being caught by a rigging system.
* Shock Loading: This is the most common cause of a dynamic load. When a piece of wood falls a certain distance before the rope goes taut, it generates an impact or "shock" load on the system. The force of this impact can be many times the weight of the piece itself.
* Swinging/Pendulum Effect: When a load swings back and forth after being caught, it creates dynamic forces on the anchor point and the rigging line. The swinging motion can multiply the forces acting on the system.
* Wind and Movement: Even a standing tree is subject to dynamic loads from wind, which causes it to sway and bend. Arborists must consider these inherent forces when evaluating a tree's structural integrity.
Estimating and Calculating Dynamic Loads
While precise calculation is complex, a simple rule of thumb and a basic formula can help arborists understand the forces at play.
* Dynamic Load Formula: A simplified formula for a "negative" or free-falling load is:
F = W \times \frac{H}{D}
Where:
* F = Peak dynamic force
* W = Weight of the log/branch
* H = Distance the load falls before the rope catches it
* D = Distance the rope stretches or the system decelerates the load
* The "H Factor": The most critical takeaway from this formula is the importance of the fall distance (H). A piece of wood weighing 100 lbs that free-falls for 5 ft can generate the same force as a much heavier piece that only falls for 1 ft. This is why arborists try to limit free-fall distance as much as possible.
Managing Dynamic Loads with Equipment
Specialized equipment is used to absorb and dissipate the energy from dynamic loads, protecting the tree and the gear.
* Rigging Rope: Arborist rigging ropes are designed with some stretch to absorb the shock of a dynamic load. This elasticity is crucial for lengthening the deceleration distance (D) in the formula above, which dramatically reduces the peak force.
* Friction Devices: Tools like the Port-A-Wrap, Porty, or Good Rigging Control System (GRCS) are essential for managing dynamic loads. They use friction to control the descent rate of the rope, allowing the ground crew to "let it run" and gradually stop the load over a longer distance, rather than abruptly halting it.
* Rigging Blocks and Pulleys: These devices are not just for lifting. They distribute forces, protect the rope from abrasion, and can be used in different rigging configurations to direct the load and manage forces more safely.
* Anchor Points: Choosing a strong, healthy branch union or the main trunk as an anchor point is the first line of defense against dynamic forces.
2
1 comment
Understanding dynamic loading
powered by
skool.com/tree-jobs-1775
Networking and skill sharing platform for tree workers aspiring and skilled alike.
Suggested communities
Powered by