Load Sharing and Multiplying Effects of Angles
When creating a multi-point anchor, the goal is to spread the load over multiple points so that no one point is taking a significantly large portion of the load. There is a concept used in rock climbing anchor building called equalization. Equalization means to “equalize or make equal” the load across multiple points. In practice, equalization is next to impossible for highline anchors. There is no way to make every anchor point across a multi-point anchor equally share a load. This is why we use the term “load sharing”.
You can test this yourself by tugging on the legs of an anchor after constructed. We guarantee you’ll be able to feel differences in load across each leg of the anchor. This is a result of the angles created by multiple anchor points in relation to the masterpoint. It is also due to the friction created in the system by the anchoring material used (rope or spanset) when passing or rubbing along itself or over the terrain. When creating a highline anchor it is best to test each leg as you’re pulling tension in the highline. Testing while you’re pulling tension allows you to shift the leg strands around (pull and tug on them to make sure everything settles correctly in place) so that they share load as effectively as possible.
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Multiplying Effects of Angles in Anchors
The angles within a multi-point anchor system are important component to consider because an angle that is too open or above 60 degrees actually starts to multiply the load placed on the anchor points in a significant way. The wider the angle, the greater the amplification. Simple studies show that the load in a 2 bolt anchor system (like one used for rock climbing anchors) start to grow when the angle’s go beyond 60 degrees. For example an angle of 60 degrees from the masterpoint results in a 58% load transfer to each bolt, not 50% like one could assume in a 2 bolt anchor. A 90 degree angle results in a load transfer of 70% to each bolt, and it goes up from there. When building a multi-point anchor it is best to look at the angle created by the two outermost bolts or points. To keep things simple, make sure this angle is at 60 degrees or below. This will ensure that any other angle within the anchor is far below 60 degrees. Ways you can manipulate the angle include the location of each point or bolt within the anchor and how far out you’d like the masterpoint to be from the anchor points.