Break Test of BGebs Knot

Written By: Lance Piatt

Break Test of BGebs Knot

Abstract

Our intent was to test a beat up, old GREEN spanset (rated at vertical pull WWL 5,300 lbf; MBS 26,500) to failure using the BGebs Knot in conjunction with the RamLock. This information will be used to evaluate the overall efficiency of the BGebs Knot when compared against the spansets vertical pull MBS.

The BGebs Knot is tied by stuffing a loop of Spanset (aprox 12”) through the large diverter hole in the RamLock. After looping the tail end of the spanset around the anchor tree, it is then inserted through the bite that was passed through the diverter. Once through the 12” bite, the RamLock is then pushed through the tails loop creating a small knot behind the RamLock. It looks reminiscent of a girth hitch.

Method

The BGebs Knot was tied in conjunction with the RamLock. The departure angle from the knot to the anchor pins was approximately 70-80 degrees. This was done to mimic a similar departure angle that is common in tree anchors.

A PURPLE spanset was used as the load bearing webbing within the RamLock because we figured no webbing would be strong enough to bring the GREEN spanset to failure.

A stainless steel pin was used in the RamLock. A load was applied to the system via the PURPLE spanset with a 225 K lbf piston giving us a graphical readout of the load over time.

Results

The first rupture came at 17,340 lbf. One of the strands running through the RamLock broke near the knot (ie. Span 1 from Fig 2). Though, the anchor did not fully fail. The machine load dropped to 2,000 lbf. then continued to ramp. The second span (ie. Span 2 from Fig 2) failed at just below 15,500 lbf. ending the experiment. The overall efficiency of the BGebs Knot using an MBS of 15,500 lbf., when compared against the vertical pull MBS at 26,500 lbf. was 58%.

A PURPLE spanset was used as the load bearing webbing within the RamLock because we figured no webbing would be strong enough to bring the GREEN spanset to failure.

Observations and Insight

The GREEN spanset used was one of the most beat up slings that was floating around the rigging house; meaning it was used, very used. As the hydraulic piston started ramping, the knot slowly began to tighten on itself eventually becoming very solid. No major signs of fatigue were shown until the first failure of one of the spans running through the RamLock. The second span absorbed the load from the first and continued to hold at the knot. It looked as though the knot isolated the spans when under high tension. So, when the first span failed the entire spanset didn’t go flying. The load continued to rise until the second span failed within the RamLock at a seemingly similar location.

Observations and Insight Continued…

We think the reason why the loops failed independently is because they were not loaded 100% evenly. It’s possible one span was a bit longer than the other. The shorter span loaded first, thus broke first. The second span then “caught” the load and continued to hold until its eventual failure just below 15,500 lbf.

This condition may not hold true in situations where the departure angle is very low, say 40 degrees or below. The knot may not hold because the spanset angles within the knot may be reduced, thus resulting in a lower holding strength.

Also, we were able to exceed the proposed MBS of the RamLock by using a spanset. The spanset has enough volume in it to prevent the normal modes of failure to occur. SlackTech is in no way, suggesting that the RamLock be brought to these loads under any circumstances.

Author and Tester, Jason Fautz is CEO and Founder of SlackTech/Balance Hardware

He can be reached at Email: jason@slacklinetechnology.com

http://slacklinetechnology.com

SlackTech is a company devoted to slacklining. Our company was founded in May of 2013 literally in a campground, the Smith Rock State Park Bivouac to be exact. It was a result of being frustrated with the systems and hardware available for slacklining. Because our initial group was (and still consists of) a ragtag group of slackers, climbers and general dirtbags, we had a lot of time to sit and complain about how we thought things should be. Eventually, we got to the point of saying, “lets freaking do something about it!” Luckily, our rag tag group of slackers, climbers and dirtbags also had education and professional experience in manufacturing engineering, product design, machining, advanced physics, computer programming and some of that legal stuff. We figured we knew enough collectively to make things work.