Force vector analysis of bracing systems
The table below compares three methods for using an anchor point to suspend a load of 10kN from an anchor point on a lateral branch .
Redirected main line
In this setup , the main line is redirected twice , with an included angle of 120 ° at each redirect .
Ignoring the effects of friction in the pulleys , the force applied at each redirect has a magnitude of approximately 10kN acting , with the greatest component of the force acting as compression along the arm of the stem .
Floating anchor
This method uses a floating anchor , with the anchor line redirected at the same locations and angles as the setup above .
The magnitude of load has doubled due to the 2:1 mechanical advantage applied to the primary anchor .
Consequently , the magnitude of force increases at each anchor , but the direction remains approximately the same .
Bracing
Finally , we can consider the use of a single bracing sling .
Assuming the sling is entirely static ( branches are not static beams ), the resultant force acting on the branch anchor is the same as with the method above .
The force on the top anchor has also not increased in magnitude , however the direction is almost the worst possible , at approximately 80 ° to the arm of the stem .
The impact of compound bending is shown at point A . Multiple bending moments are applied to a single point in the tree ’ s structure . Acting together , these significantly increase the likelihood of failure at that point .
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