A Review of Webbing Anchor Research THOMAS EVANS, SARAH TRUEBE SAR - - PowerPoint PPT Presentation

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A Review of Webbing Anchor Research THOMAS EVANS, SARAH TRUEBE SAR - - PowerPoint PPT Presentation

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A Review of Webbing Anchor Research THOMAS EVANS, SARAH TRUEBE SAR 3 HTTP://SARRR.WEEBLY.COM/ Need 5 year research program Learned a lot Other available research Are our results consistent with theirs? Need a meta analysis

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THOMAS EVANS, SARAH TRUEBE SAR3

HTTP://SARRR.WEEBLY.COM/

A Review of Webbing Anchor Research

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Need…

  • 5 year research program

○ Learned a lot

  • Other available research

○ Are our results consistent with theirs?

  • Need a meta analysis

○ Compare all research ○ Determine consistency ○ Bigger picture?

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Methods

  • Performed a literature review

○ Found papers on webbing anchors ○ Read them ○ Synthesized data ○ Drew bigger conclusions

  • Added some more testing data

○ Data published in the paper

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Methods: What Was Included

  • Strength/properties of 1” tubular nylon webbing anchors

○ Based on a literature review of testing data ○ Does not include multipoint anchors

Not included here Included here

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Sources of Data (10)

  • Evans, Thomas, Stavens, Aaron, 2011, Empirically Derived Breaking Strengths for Basket Hitches and Wrap

Three Pull Two Webbing Anchors, Proceedings of the International Technical Rescue Symposium, Fort Collins, Colorado, November 3-6, 2011

  • Evans, Thomas, Stavens, Aaron, McConaughey, Sherrie, 2012, Causal Mechanisms of Webbing Anchor

Interface Failure and Failure Modes, International Technical Rescue Symposium, Seattle, Washington, November 1-3, 2012

  • Evans, Thomas, 2013, Empirical Observation of Anchor Failure Points in Old and Retired Webbing,

International Technical Rescue Symposium, Albuquerque, New Mexico, November 7-10, 2013

  • Evans, Thomas, Truebe, Sarah, 2015, A Review of Webbing Anchor Research, International Technical Rescue

Symposium, Portland, Oregon, November 5-8, 2015

  • Kovach, Jim, 2007a, Webbing Wisdom, FireRescue, May 2007
  • Kovach, Jim, 2007b, Does Nylon Lose 15% of Its Strength When Wet? Proceedings of the International

Technical Rescue Symposium, Golden Colorado, November 2-4, 2007

  • McKently, John, Parker, Bruce, 2000, One Inch Webbing Anchor Tests, International Technical Rescue

Symposium, Tucson, Arizona, October 20-22, 2000

  • Mortimer, Roger, Angel, David, 2014, Baskets versus the Basket+, equivalence of strengths, International

Technical Rescue Symposium, Denver, Colorado, November 6-9, 2014

  • Moyer, Tom, 1998, Rope and Gear Testing, Salt Lake County Sheriff's Search and Rescue, Posted on: http:

//user.xmission.com/~tmoyer/testing/pull_tests_11_98.html

  • Pylman, David, Spinelli, Philip, 2013, Drop Testing Versus Slow-Pull Strength Testing, International Technical

Rescue Symposium, Albuquerque, New Mexico, November 7-10, 2013

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Methods: Deliverables

  • Developed three deliverables

○ A table that lists each study

  • Evaluate the studies for yourself

○ A synopsis table

  • Results at a glance

○ A list of my conclusions

Anchor Type Average Strength (kN) Standard Deviation (kN) Maximum Strength (kN) Minimum Strength (kN) Webbing Loop 21.1 3.3 25.0 16.2 Webbing Loop (old webbing) N/A N/A 24.6 13.4 Girth Hitch 23.2 1.2 24.6 21.3 Wrap 2 Pull 1 27.4 3.3 32.9 24.5

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Results

  • We will present synopsis results only
  • If you want details:

○ See ITRS paper tables ○ http://sarrr.weebly.com/

  • Easy to miss big picture in the details!
  • Remember

○ 1 inch tubular nylon webbing ○ New webbing unless stated otherwise

Old webbing anchor

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Results: Anchors clipping one webbing strand

Anchor Type Average Strength (kN) Standard Deviation (kN) Maximum Strength (kN) Minimum Strength (kN) Webbing Loop 21.1 3.3 25.0 16.2 Webbing Loop (old webbing) N/A N/A 24.6 13.4 Girth Hitch 23.2 1.2 24.6 21.3 Wrap 2 Pull 1 27.4 3.3 32.9 24.5

Webbing Loop Girth Hitch Wrap 2 Pull 1

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Results: Anchors clipping one webbing strand

Anchor Type Average Strength (kN) Standard Deviation (kN) Maximum Strength (kN) Minimum Strength (kN) Webbing Loop 21.1 3.3 25.0 16.2 Webbing Loop (old webbing) N/A N/A 24.6 13.4 Girth Hitch 23.2 1.2 24.6 21.3 Wrap 2 Pull 1 27.4 3.3 32.9 24.5

All Above 21 kN

Webbing Loop Girth Hitch Wrap 2 Pull 1

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Results: Anchors clipping one webbing strand

Anchor Type Average Strength (kN) Standard Deviation (kN) Maximum Strength (kN) Minimum Strength (kN) Webbing Loop 21.1 3.3 25.0 16.2 Webbing Loop (old webbing) N/A N/A 24.6 13.4 Girth Hitch 23.2 1.2 24.6 21.3 Wrap 2 Pull 1 27.4 3.3 32.9 24.5

Low standard deviations suggests results are relatively consistent

Webbing Loop Girth Hitch Wrap 2 Pull 1

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Results: Anchors clipping one webbing strand

Anchor Type Average Strength (kN) Standard Deviation (kN) Maximum Strength (kN) Minimum Strength (kN) Webbing Loop 21.1 3.3 25.0 16.2 Webbing Loop (old webbing) N/A N/A 24.6 13.4 Girth Hitch 23.2 1.2 24.6 21.3 Wrap 2 Pull 1 27.4 3.3 32.9 24.5

All above 13 kN

Webbing Loop Girth Hitch Wrap 2 Pull 1

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Results: Box and Whisker Plots

  • Displays descriptive statistics
  • Compare data sets rapidly
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Results: Anchors clipping one webbing strand

Webbing Loops Webbing Loops (old webbing) Girth Hitch Girth Hitch (wet webbing) Wrap 2 Pull 1

N=10 N=6 N=5 N=5 N=2 N=1 N=67 N=7 N=2 N=5 N=3 N=3 N=5

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Results: Anchors clipping one webbing strand

Mixed weak points:

  • The knot
  • The connector

(carabiner, screw link, etc.)

Anchor Type Weakest Point Webbing Loop At knot with a big internal angle, at carabiner when pulled end to end Girth Hitch At carabiner and at knot Wrap 2 Pull 1 At carabiner Webbing Loop Girth Hitch Wrap 2 Pull 1

Knot

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Results: Anchors clipping one webbing strand

Which one to use?

  • It depends…
  • Not very strong
  • Questionable for rescue loads

Anchor Type Strengths Weaknesses Webbing Loop Fast to rig, uses little webbing Can slip down or around

  • n an object

Girth Hitch Fast to rig, the anchor stays in place Uses twice the webbing as a loop Wrap 2 Pull 1 Uses less webbing than a girth hitch but more than a loop, the anchor stays in place Uses more webbing than a loop, slowest to rig of the three one strand anchors

Webbing Loop Girth Hitch Wrap 2 Pull 1

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Results: Anchors clipping two webbing strands

Basket Hitch Basket Hitch + One Wrap Basket Hitch + Connector Basket Hitch + Overhand Focal Knot

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Results: Anchors clipping two webbing strands

Wrap 2 Pull 2 Redundant Double Loop Redundant Wrap 2 Pull 1 Wrap 3 Pull 2

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Results: Anchors clipping two webbing strands

All anchors are strong enough

Anchor Type Average Strength (kN) Standard Deviation (kN) Maximum Strength (kN) Minimum Strength (kN) Wrap 2 Pull 2 42.4 1.5 50.0 38.8 Redundant Double Loop 39.8 2.9 42.9 35.9 Redundant Wrap 2 Pull 1 45.1 1.5 46.6 43.1 Basket Hitch 41.8 3.7 50.0 32.1 Basket Hitch (wet webbing) 39.1 3.4 Not Reported 28.9 Basket Hitch (old webbing) N/A N/A 38.4 26.3 Basket Hitch + One Wrap 42.8 3.5 46.2 38.4 Basket Hitch + One Wrap (wet webbing) 36.9 3.4 Not Reported 26.6 Basket Hitch + Connector 41.1 2.6 44.1 36.3 Basket Hitch + Overhand Focal Knot 35.5 0.1 35.6 35.4 Wrap 3 Pull 2 39.6 4.1 52.0 31.5 Wrap 3 Pull 2 (old webbing) N/A N/A 38.1 23.8

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Results: Anchors clipping two webbing strands

Anchor Type Average Strength (kN) Standard Deviation (kN) Maximum Strength (kN) Minimum Strength (kN) Wrap 2 Pull 2 42.4 1.5 50.0 38.8 Redundant Double Loop 39.8 2.9 42.9 35.9 Redundant Wrap 2 Pull 1 45.1 1.5 46.6 43.1 Basket Hitch 41.8 3.7 50.0 32.1 Basket Hitch (wet webbing) 39.1 3.4 Not Reported 28.9 Basket Hitch (old webbing) N/A N/A 38.4 26.3 Basket Hitch + One Wrap 42.8 3.5 46.2 38.4 Basket Hitch + One Wrap (wet webbing) 36.9 3.4 Not Reported 26.6 Basket Hitch + Connector 41.1 2.6 44.1 36.3 Basket Hitch + Overhand Focal Knot 35.5 0.1 35.6 35.4 Wrap 3 Pull 2 39.6 4.1 52.0 31.5 Wrap 3 Pull 2 (old webbing) N/A N/A 38.1 23.8

Low standard deviations suggests results are relatively consistent

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Results: Anchors clipping two webbing strands

All anchors are strong enough: All above 23 kN

Anchor Type Average Strength (kN) Standard Deviation (kN) Maximum Strength (kN) Minimum Strength (kN) Wrap 2 Pull 2 42.4 1.5 50.0 38.8 Redundant Double Loop 39.8 2.9 42.9 35.9 Redundant Wrap 2 Pull 1 45.1 1.5 46.6 43.1 Basket Hitch 41.8 3.7 50.0 32.1 Basket Hitch (wet webbing) 39.1 3.4 Not Reported 28.9 Basket Hitch (old webbing) N/A N/A 38.4 26.3 Basket Hitch + One Wrap 42.8 3.5 46.2 38.4 Basket Hitch + One Wrap (wet webbing) 36.9 3.4 Not Reported 26.6 Basket Hitch + Connector 41.1 2.6 44.1 36.3 Basket Hitch + Overhand Focal Knot 35.5 0.1 35.6 35.4 Wrap 3 Pull 2 39.6 4.1 52.0 31.5 Wrap 3 Pull 2 (old webbing) N/A N/A 38.1 23.8

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Results: Anchors clipping two webbing strands

Basket Hitches W3P2 Redundant Double Loop Redundant W2P1 Basket Hitch + Connector Basket Hitch + Overhand Focal Knot Basket Hitch + Wrap W2P2

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Results: Anchors clipping two webbing strands

  • Weak point is at the connectors
  • Compressed strand is the weakest point
  • Knots in limbs are not the weak point for most anchors
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Results: Anchors clipping two webbing strands

Which one to use? It depends…

Anchor Type Strengths Weaknesses Wrap 2 Pull 2 Takes less webbing than other anchors, is multidirectional Can slip around on the anchor, takes a while to rig Redundant Double Loop Anchor is redundant, and consumes a lot of webbing Can slip around on the anchor, takes a long time to rig Redundant Wrap 2 Pull 1 Anchor stays in place, and is redundant Requires the most webbing, takes a lot of time to rig Basket Hitch Uses less webbing than other two stranded anchor options, is very fast to build Slips around the anchor, is unidirectional, not redundant Basket Hitch + One Wrap Stays in place, fast to rig Uses more webbing, slower to rig, is not redundant Basket Hitch + Connector Uses less webbing than other two stranded anchor options, is very fast to build, is multidirectional Slips around the anchor, requires two carabiners, is not redundant Basket Hitch + Overhand Focal Knot The focal knot makes the anchor redundant Is weaker, takes longer to rig, slips on the anchor Wrap 3 Pull 2 Multidirectional, stays in place Takes a lot of webbing to rig, cinches down on conical anchors, and it takes more webbing than basket hitches, is not redundant

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Results: Anchors clipping three webbing strands

Anchor Type Strength (kN) Standard Deviation Maximum (kN) Minimum (kN) Wrap 4 Pull 3 59.5 3.3 61.7 55.7 Wrap 4 Pull 3 (wet webbing) 58.2 3.5 60.3 54.1 53.9 3.1 56.7 50.5

All above 53 kN

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Results: Anchors clipping three webbing strands

Anchor Type Strength (kN) Standard Deviation Maximum (kN) Minimum (kN) Wrap 4 Pull 3 59.5 3.3 61.7 55.7 Wrap 4 Pull 3 (wet webbing) 58.2 3.5 60.3 54.1 53.9 3.1 56.7 50.5

Low standard deviations suggests results are relatively consistent

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Results: Anchors clipping three webbing strands

Anchor Type Strength (kN) Standard Deviation Maximum (kN) Minimum (kN) Wrap 4 Pull 3 59.5 3.3 61.7 55.7 Wrap 4 Pull 3 (wet webbing) 58.2 3.5 60.3 54.1 53.9 3.1 56.7 50.5

All above 50 kN

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Results: Anchors clipping three webbing strands

Anchor Type Weakest Point Wrap 4 Pull 3 At carabiner, the compressed webbing strand Wrap 4 Pull 3 (wet webbing) At carabiner, the compressed webbing strand

Weak point is the compressed webbing strand at the connector

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Results: Anchors clipping three webbing strands

N=3 N=3 N=3

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Synopsis Results

Single Webbing Strand Anchors Double Webbing Strand Anchors W4P3

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Synopsis Results

  • How to get more strength

○ Add another strand of webbing ○ Obvious… ○ Configuration

less important

< <

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Synopsis Results

  • Anchors with a single strand clipped

○ Less strong than anchors with two strands (obvious…) ○ Weak point is the knot or connector

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Synopsis Results

  • Anchors with two strands clipped

○ All are strong enough regardless of configuration ○ Weak point is at the connectors ○ Compressed strand is the weakest point ○ Knots in the limbs are not the weak point for most anchors

Not here

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Synopsis Results

  • Anchors with three strands clipped

○ Really strong! ○ Weak point is at the connectors ○ Compressed strand is the weakest point

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Synopsis Results

  • If a focal knot is added

○ Strength is reduced ○ It is the weak point ○ Anchor still strong enough

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Synopsis Results

  • Reducing webbing pinch increases strength
  • Getting webbing wet reduces strength

○ Not enough to matter

  • Dynamic tests yield greater variability

than slow pull tests

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Rigging Consequences: Single Strand Anchors

  • Girth hitches and wrap 2 pull 1’s

○ Can be reconfigured to anchors twice as strong

  • Basket Hitches or Wrap 2 Pull 2’s

Girth Hitch Basket Hitch Basket Hitch + Connector Or Wrap 2 Pull 1 Wrap 2 Pull 2

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Rigging Consequences

  • Any anchor with 2 or 3 strands clipped is strong enough

○ All have more than a 10:1 SSSF for a 1 or 2 kN load

  • Pick best anchor

○ e.g., speed, lack of webbing, lack of gear, etc.

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Rigging Consequences

  • Knots (bends) can go anywhere

○ Protect knot if you want to untie anchor easily ○ Be tolerant of where knots are rigged

Or Or Basket Hitch Wrap 3 Pull 2

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Conclusions

  • Data driven decision making can improve rigging
  • Please read the citations!
  • Please contribute to the research!
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Acknowledgements

  • Everyone who has done research!!
  • CMC provided

○ Laboratory time ○ Laboratory equipment ○ Staff time

  • PMI provided the webbing
  • Cedric Smith for running the equipment/time
  • Loui McCurley for facilitating webbing donation
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Questions?

Thomas Evans, Sarah Truebe SAR3

http://sarrr.weebly.com/ cavertevans@gmail.com

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Results: Anchors clipping two webbing strands

Weak point: At connector, compressed webbing strand, knot is not weak point!!!!

Anchor Type Weakest Point Wrap 2 Pull 2 At carabiner, the compressed webbing strand Redundant Double Loop At carabiner and knot Redundant Wrap 2 Pull 1 At carabiner, the compressed webbing strand Basket Hitch At carabiner, the compressed webbing strand Basket Hitch (wet webbing) At carabiner, the compressed webbing strand Basket Hitch (old webbing) At carabiner, the compressed webbing strand Basket Hitch + One Wrap At carabiner, the compressed webbing strand Basket Hitch + One Wrap (wet webbing) At carabiner, the compressed webbing strand Basket Hitch + Connector At carabiner, the compressed webbing strand Basket Hitch + Overhand Focal Knot At focal knot Wrap 3 Pull 2 At carabiner, the compressed webbing strand Wrap 3 Pull 2 (old webbing) At carabiner, the compressed webbing strand