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

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 ○ Compare all research ○ Determine consistency ○ Bigger picture?

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

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

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

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

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

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

Results: Anchors clipping one webbing strand Anchor Type Average Standard Maximum Minimum Strength Deviation Strength Strength (kN) (kN) (kN) (kN) Webbing Loop 21.1 3.3 25.0 16.2 Webbing Loop N/A N/A 24.6 13.4 (old webbing) 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 Girth Wrap 2 Loop Hitch Pull 1

Results: Anchors clipping one webbing strand Anchor Type Average Standard Maximum Minimum Strength Deviation Strength Strength (kN) (kN) (kN) (kN) Webbing Loop 21.1 3.3 25.0 16.2 Webbing Loop N/A N/A 24.6 13.4 (old webbing) 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 Girth Wrap 2 Loop Hitch Pull 1

Results: Anchors clipping one webbing strand Anchor Type Average Standard Maximum Minimum Strength Deviation Strength Strength (kN) (kN) (kN) (kN) Webbing Loop 21.1 3.3 25.0 16.2 Webbing Loop N/A N/A 24.6 13.4 (old webbing) 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 Girth Wrap 2 Loop Hitch Pull 1

Results: Box and Whisker Plots ● Displays descriptive statistics ● Compare data sets rapidly

Results: Anchors clipping one webbing strand Webbing Loops Girth Hitch Girth Hitch Webbing Loops (old webbing) (wet webbing) N=5 N=2 N=10 N=2 N=3 N=6 N=67 N=5 N=5 N=3 N=5 N=7 N=1 Wrap 2 Pull 1

Results: Anchors clipping one webbing strand 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 Knot Mixed weak points: -The knot -The connector (carabiner, screw link, etc.) Webbing Girth Wrap 2 Loop Hitch Pull 1

Results: Anchors clipping one webbing strand Anchor Type Strengths Weaknesses Webbing Loop Fast to rig, uses little Can slip down or around webbing on an object Girth Hitch Fast to rig, the anchor Uses twice the webbing as stays in place a loop Wrap 2 Pull 1 Uses less webbing than Uses more webbing than a a girth hitch but more loop, slowest to rig of the than a loop, the anchor three one strand anchors stays in place Which one to use? -It depends… -Not very strong -Questionable for rescue loads Webbing Girth Wrap 2 Loop Hitch Pull 1

Results: Anchors clipping two webbing strands Basket Basket Hitch Basket Hitch + Basket Hitch Hitch + One Wrap Overhand Focal Knot + Connector

Results: Anchors clipping two webbing strands Wrap 2 Redundant Redundant Wrap 2 Wrap 3 Pull 2 Pull 2 Double Loop Pull 1

Results: Anchors clipping two webbing strands Anchor Type Average Standard Maximum Minimum Strength (kN) Deviation (kN) Strength (kN) 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 39.1 3.4 Not Reported 28.9 (wet webbing) Basket Hitch N/A N/A 38.4 26.3 (old webbing) Basket Hitch + One Wrap 42.8 3.5 46.2 38.4 Basket Hitch + One Wrap 36.9 3.4 Not Reported 26.6 (wet webbing) Basket Hitch + Connector 41.1 2.6 44.1 36.3 Basket Hitch + Overhand 35.5 0.1 35.6 35.4 Focal Knot Wrap 3 Pull 2 39.6 4.1 52.0 31.5 Wrap 3 Pull 2 N/A N/A 38.1 23.8 (old webbing) All anchors are strong enough

Results: Anchors clipping two webbing strands Anchor Type Average Standard Maximum Minimum Strength (kN) Deviation (kN) Strength (kN) 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 39.1 3.4 Not Reported 28.9 (wet webbing) Basket Hitch N/A N/A 38.4 26.3 (old webbing) Basket Hitch + One Wrap 42.8 3.5 46.2 38.4 Basket Hitch + One Wrap 36.9 3.4 Not Reported 26.6 (wet webbing) Basket Hitch + Connector 41.1 2.6 44.1 36.3 Basket Hitch + Overhand 35.5 0.1 35.6 35.4 Focal Knot Wrap 3 Pull 2 39.6 4.1 52.0 31.5 Wrap 3 Pull 2 N/A N/A 38.1 23.8 (old webbing) Low standard deviations suggests results are relatively consistent

Results: Anchors clipping two webbing strands Anchor Type Average Standard Maximum Minimum Strength (kN) Deviation (kN) Strength (kN) 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 39.1 3.4 Not Reported 28.9 (wet webbing) Basket Hitch N/A N/A 38.4 26.3 (old webbing) Basket Hitch + One Wrap 42.8 3.5 46.2 38.4 Basket Hitch + One Wrap 36.9 3.4 Not Reported 26.6 (wet webbing) Basket Hitch + Connector 41.1 2.6 44.1 36.3 Basket Hitch + Overhand 35.5 0.1 35.6 35.4 Focal Knot Wrap 3 Pull 2 39.6 4.1 52.0 31.5 Wrap 3 Pull 2 N/A N/A 38.1 23.8 (old webbing) All anchors are strong enough: All above 23 kN

Results: Anchors clipping two webbing strands Basket Hitch W2P2 Basket Hitches W3P2 + Overhand Focal Knot Redundant W2P1 Basket Hitch Redundant Basket Hitch + Wrap Double Loop + Connector

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