The same questions crop up time and time again if a tree is being restored to be safe for traffic and pedestrians using tree cabling systems:
In most cases branches/stems are supported using dynamic cabling. This is installed as horizontally as possible and ideally as triangle cabling. This type of cabling supports all wind load directions.
Static cabling is only installed if a branch is cracked. This is also installed as horizontally as possible and as triangle cabling.
Wide branches or branches where cabling against side wind loads is not possible are secured using static support/load cabling. With this the tree cabling runs as vertically as possible and is not to prevent breakage but to prevent it from “falling to the ground” afterwards.
As a rule, no complicated calculations or analysis are required here. In practice we rely on arborists’ decades of practical experience. The ZTV Baumpflege standard’s notes on breaking loads for crown bracing apply here.
German treecare standard (ZTV Baumpflege) note on calculating dynamic tree cabling systems:
(measured at the base at the time of installation)
|Minimum breaking load
for the warranted service life, installed at least in 2/3
of the branch/stem length to be cabled
|up to 40 cm||2,0 t (cobra 2t)|
|between 40 and 60 cm||4,0 t (cobra 4t)|
|between 60 and 80 cm||8,0 t (cobra 8t)|
|over 80 cm||Special situations to be decided on a case-to-case basis|
German treecare standard (ZTV Baumpflege) note on calculating static crown bracing and load/support cabling systems:
Double the values for tree cabling systems that are to keep part of a tree still or absorb permanent loads.
It is also recommended that the German treecare standard (ZTV Baumpflege) recommendations are followed here.
If the installation is on one level, then dynamic or static cabling is installed at least at 2/3 of the height of the branch to be cabled.
If the installation is on two levels (with split forks), then static cabling is installed at least at 1/4 of the height and dynamic cabling is installed in 2/3 of the branch to be cabled.