Arboriculture & Urban Forestry 37(2): March 2011 Arboriculture & Urban Forestry 2011. 37(2): 67–73 67 Dead-end Stop Terminated Tree Support Cable Systems E. Thomas Smiley Abstract. Supplemental support systems are used to reduce the risk of failure of codominant stems. The goal of this study was to evaluate dead-end stop terminated cables used in trees and to compare the strength of small tree cable systems. Field evaluations comparing eyebolt and Wire Stop® anchored ca- bles found an enlargement of the hole through the branch in 39% of the Wire Stop terminations with a mean size of 6 mm. Static break tests found that the strength of cable system varied with the strength of the wood and system configuration. From a system strength perspective in oak: bent eye screw lags < welded eye screw lag = single swage stop = single swage stop with washer < double swage stop with washer = eyebolt. In pine, bent eye screw lags = weld- ed eye screw lag = single swage stop < single swage stop with washer < double swage stop with washer = double swage stop with fender washer < eyebolt. Key Words. Codominant Stems; Eyebolts; Ferrule; Guys; Junction Failures; Lags; Support Cable; Swage Stops; Tree Failures; Tree Support System; V-crotch; and Wedge. A codominant stem is a forked branch with nearly equal diam- eters, arising from a common junction and lacking a normal branch union (ISA 2009). Codominant stem junctions tend to be one of the weakest portions of a tree’s structure (Gilman 2003; Smiley 2003; Kane 2007; Kane et al. 2008; Kane and Clouston 2008). Supplemental support systems are installed to limit the movement of codominant stems so that the junc- tion is not stressed to the point of breakage (Thompson 1935; Thompson 1936; Mayne 1975; Smiley et al. 2000; James et al. 2002; ANSI 2006; Smiley and Lilly 2007). The supplemen- tal support typically used in North America for this purpose is a cable system that consists of a length of seven strand galva- nized Extra High Strength (EHS) steel cable terminated with a thimble and manufactured cable grip. The termination is an- chored to the tree using eyebolts (including nuts and washers), lag threaded hooks (J-lags), or lag threaded eyes (Mayne 1975; Smiley and Lilly 2007). Cables, grips, thimbles, lags or bolts all come in different sizes to accommodate different tree and cable sizes. Therefore, to install a cable the arborist must have from six (two lags, two thimbles, two grips) to ten (two eyebolts, two nuts, two washers, two thimbles, two grips) pieces of hardware to terminate and anchor each cable for each branch size class. In a nonscientific survey, arborists knowledgeable in tree support systems from major commercial arboriculture com- panies, universities, and arboricultural consulting firms were asked for their observations on cable system failures (author’s unpublished data 2010). Specifically, if they had seen failure of eyebolts installed in support systems and if they had seen prob- lems associated with the overgrowth of cable terminations. One of the 17 arborists reported having seen the failure of an eye- bolt. That arborist explained that the bolts broke due to faulty installation and side loading. Three of the 17 arborists surveyed reported having seen failures associated with overgrown cables. All of these failures were related to cable corrosion. The arbor- ists reported that the more common cable failures they have seen were at the apex of the manufactured grip and when a lag hook/ eye opened or lag was pulled out of a branch. Grip failures were attributed to a lack of a thimble at the time of installation or the thimble falling out of the termination after it was installed. In recent years, a number of dead-end stop termination sys- tems have come to the arboricultural market, such as Wire Stop® (Steve Tillitski, Rigguy Inc., Athens, GA, U.S.), Endz (George Mellick, Shelter Tree, Wrentham, MA, U.S.), and Wedge-Grip™ Dead End (Preformed line products, Mayfield Village, OH, U.S.). These terminations are installed by inserting a cable in a hole through the branch and anchoring the cable with one of these devices on the side opposite of the working section of the cable. Stop-terminated systems claim the benefits of using a smaller di- ameter hole for the cable, since the hole only needs to be the diameter of the cable; simplified installation of the system since they have fewer parts; stocking of fewer parts since stops are selected for cable diameter, not branch diameter; and providing equal or greater strength than alternative products. Manufacturer pull tests of the Wire Stop indicate that the cable will fail be- fore the Wire Stop (Steve Tillitski, pers. comm.). Dead-end stop terminations consist of one or two major parts for each end of the cable. These systems eliminate two of the arborist identified weak points of the traditional cable system, the grip and lags. There is no mention of the cable size required for small trees or shrubs less than five centimeters in diameter in the ANSI A300 Standard (ANSI 2006). However, there are many large shrubs and small trees planted in the landscape that have codominant stems and therefore would benefit from support systems. An inexpensive and aesthetically un- obtrusive cable system would be desirable for these plants. While there may be benefits to dead-end stop terminat- ed systems, there are several questions that need to be an- swered, including: how does the strength of the termina- ©2011 International Society of Arboriculture
March 2011
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