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Log Load Wrapper Security System
Background During the past several years SDTDC conducted seven developmental field experiments to test the log load strapping concept. The first experiment took place in Deerlodge, Montana. Plastic packaging straps were used on a load of lodgepole pine to determine if they offered a potential as a theft deterrent. The concept was tried using ½-inch wide plastic straps. Very limited testing was conducted. It was determined that the ½-inch strapping was not suitable when used as a single wrap around the load. Its durability and strength proved to be marginal when wrapped around the load seven times. Since synthetic webbing and hardware that is rated for 3,000 pounds and higher working tensions is commercially available, SDTDC decided not to continue to test plastic straps and evaluate the use of synthetic webbing. The second SDTDC experiment was conducted in Terra Bella, California. Webbing rated for a 3,000-lb working load was applied to log loads of 25 to 30 logs per truck. The SDTDC log truck was used for the test and the logs were loaded on the truck at the mill. Two commercially available ratcheting buckles were used on each strap for strap attachment and tensioning. Three evenly spaced straps were used to bundle each load. Conventional steel cable wrappers were also used on each load in compliance with current State Law. The following was learned as a result of work:
This testing was conducted to help determine if strapping would be an effective theft deterrent. At the time SDTDC believed that strapping would not be very cost effective on loads of less than 50 logs. The testing was conducted on smaller diameter logs. Lodgepole pine logs with 65 to 70 logs per load were used during these tests. Loaded trucks arrived at the mill after hauling the logs for about 80 miles. By this time the load was well settled which supported the testing objectives. The load was strapped on the truck in three places; about 3 feet forward of the aft bunk, in the middle, and about three feet aft of the forward bunk. Using a cheater bar on a mid-strap ratchet, tensions upward of 4,000-lbs were applied to each strap. A choker was then placed around the butt end of a log that was approximately 1/3 of the way down the load from the top of the load. The choker was hitched to a wheeled loader and the loader slowly reversed until the choker was taut. When the loader started pulling on the log it slipped out of the load with very little resistance. The loader’s engine was barely above idle as it pulled the log from the load. This experiment was performed in a mill yard on a soft soil surface. The loader was a CAT 938G, which weighs roughly 29,000-lbs and has a break out force (similar to drawbar pull) of 25,000-lbs. It is considered to be at the light end of medium weight class loaders. Strap tension does not translate directly into force against a log in a load. The logs at the top corners of the load will see the most direct force from the strap and at the very best they will only convert 70% of the strap tension to direct force against the adjacent log. Adjacent logs will see increasingly less of this load and logs closer to the center of the load will see even less strap-induced force against them. Strap tension is not uniform either since friction losses occur at every contact point. Even with 3 straps, tensioned to 20,000-lbs each, a net minimum 50,000-lbs of force against each log in the load would not be possible. The conclusion is, load bundling with straps is not an effective theft deterrent to a highly motivated thief. April 2000 testing at SDTDC: The SDTDC experimental log truck with a load of approximately 45 mixed conifer logs that had been loaded on the truck more than two years prior to this test. The load had been used for several SDTDC projects including strapping prior to this testing. The load had traveled well over 700 miles. It is by far the driest, most settled load one would ever find on a commercial log truck. The logs were loaded in a staggered fashion with the butt ends alternating between the front and rear of the load. Three 4-inch straps were secured around the load and tensioned above their working load limit of 8,000-lbs with the assistance of a 32-inch extension handle on the existing 11-inch ratchet handle. This provided a net lever arm of 43-inches. In general practice, OSHA does not allow more than a 30-inch lever to be used with conventional chain binders. The mechanical limits of the buckle ratchet mechanism were approached when in excess of 8,000-lbs of strap tension was applied to each strap. A log located near the middle of the load was selected. It had been loaded butt-forward which made it much more difficult to pull out of the load toward the rear. A 3/8-inch steel chain was wrapped around the log end and coupled to a small front-end loader. An 20,000-lb dynamometer was attached to the chain to measure the pull force. When the loader pulled on the log it started to move through the load without to much resistance. The dynamometer showed a peak force of 1,200-lbs after the log had been pulled out of the load about 8 to 9 feet. Static (breakaway) friction is the highest, and the log slid more easily once it started to move. This experiment was repeated with a different log loaded butt-forward with three 2-inch straps tensioned to 5,000-lbs each. Peak pullout force was measured at 1,400-lbs. The fact that this was not the same log brings in too many unknown variables to make an objective comparison. However, it is interesting that it required more force to pull the log held by 2-inch straps. The 4-inch ratchets used for the testing cost $98 each and 35-ft of the 4-inch webbing used for each strap costs $124 resulting in a net cost per strap of $222. The 2-inch straps used with their ratchet buckle cost $35 each.
Two tests were conducted by SDTDC during the Spring and Fall of 2001 in Terra Bella, California. The first test was conducted to determine what strength of 2-inch commercially available webbing would be most suitable for use to secure log bundles. Webbing greater than 2-inch wide had been determined by earlier tests to be very expensive and cumbersome to use. Ideally, the lowest strength webbing suitable would result in the lowest cost per strap. Webbing with breaking strengths of 3,000 lbs and 10,000-lbs of tension respectively were selected for testing. The ratchet buckles used for both were the same and were rated to withstand up to 10,000-lbs of tension before failure. Bundles were prepared as described for the earlier testing conducted in Cody, Wyoming. The bundles were dropped 5-ft after they were removed from the log truck. The 3,000 lb rated webbing failed the 5-ft drops. The 10,000 lb tension rated webbing survived and then was subjected to a 8-ft drop which it also survived and maintained the bundle. The ratchet buckles used survived all of the testing (see figures 3, 4 and 5).
The second test, conducted in the Fall of 2001, was to determine the integrity of, and any design changes required, of prototype, sealable tensioning buckles fabricated to SDTDC specifications by a California manufacturer (see figures 7 and 8). The testing was conducted using the prototype buckles with 10,000-lb rated webbing. The buckles were subjected to both 5-ft and 8-ft drops. They survived intact both series of drops. Some minor damage to the buckles was observed. For comparison, a 8-ft drop was done using conventional and currently approved steel cable/chain wrappers secured by a chain binder. These wrappers were rated at a breaking strength of 20,000-lbs of tension. One of these wrappers failed causing the bundle to come apart. More testing would be required to determine if this failure is significant. The outcome of this testing was a revised design requirement for the prototype buckles. These 2001 tests have been documented on a video which is available from SDDTC for viewing by interested persons (see figures 6,7, 8 and 9). Since these 2001 tests, SDTDC purchased 140 sealable buckles from the manufacturer for use in tests conducted during the summer and fall of 2003. This testing was conducted to determine field performance, durability and use problems of the SDTDC Wrapper Security System when it is used, as intended, during actual sale transport and log mill operations. A timber sale was located in Region 4 for the testing of the concept. Strapping and tensioning buckles were provided by SDTDC to the timber sale operator/purchaser and the seals were furnished by the local Forest. An agreement was made between both parties (Forest Service & Purchaser/Contractor) to treat the testing as an actual timber sale contract situation. Trucks were loaded at the sale site, sealed and transported to the mill, off loaded with a machine that removed the whole load safely (with straps intact) and decked it for later release by the Forest Service.
The objective of this testing was to determine whether the SDTDC Wrapper Security System, as designed, is suitable for use by the Forest Service during timber sale operations, and will perform satisfactorily under operational conditions when used for it’s intended purposes. This operational field evaluation allowed SDTDC and its testing cooperators to identify any problems that would limit or prevent the use of the system for timber sale operations. The evaluation was conducted as follows
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