140 Brian Kane: Withdrawal Resistance of J-Lags from Three Hardwood Species L.) growing in a row at the Urban Horticulture Center (UHC) in Blacksburg, VA, U.S. (USDA hardiness zone 6B). For red oaks, mean diameter (± standard deviation) at the height of in- stallation was 14.9 ± 1.49 cm. A pilot hole 1.6 mm in diameter less than the diameter of the J-lag was drilled into each tree, and J-lags were installed in accordance with the A300 Standard (Anonymous 2006). In September and October 2005, 90 J-lags were installed, divided equally between two shank diameters (6.4 mm and 9.5 mm) and in approximately equal proportions between two species [sugar maple (Acer saccharum Marsh.) (n = 39) and paper birch (Betula papyrifera Marsh.) (n = 51)] grow- ing in a forest in Pelham, MA, U.S. (USDA hardiness zone 5A). On sugar maple and paper birch, J-lags were installed approxi- mately 1.5 m above ground. Mean diameter (± standard devia- tion) of sugar maples and birches into which J-lags 6.4 mm in diameter were installed was 8.9 ± 0.95 cm and 8.7 ± 1.31 cm, respectively. Mean diameter (± standard deviation) of sugar maples and birches into which J-lags 9.5 mm in diameter were installed was 24.6 ± 8.16 cm and 18.7 ± 4.72 cm, respectively. At the UHC, all J-lags were withdrawn after one year because the trees were being removed for a new research project. At the site in Pelham, MA, J-lags from trees of both species were removed in the autumn of 2006, 2007, and 2009; in autumn 2008 J-lags were removed from only paper birches. In January 2010 at the site in Pelham, additional trees of both species were harvested and 30 J-lags 12.7 mm in diameter were installed and immedi- ately extracted. Mean diameter (± standard deviation) of sugar maples and birches into which J-lags 12.7 mm in diameter were installed was 43.2 ± 1.18 cm and 39.8 ± 0.61 cm, respectively. After trees were felled, a log (0.6 m long) that was centered on the J-lag was removed from each tree. A paraffin coating was applied to the cut ends of logs, which were then stored for up to 30 days at 4.5°C prior to testing. Logs were removed from re- frigeration and exposed to room temperature (22°C) for one hour immediately before testing, but wood temperature at the time of testing was not measured. Logs were secured in a universal test- ing machine (Figure 1a) (Model 30/G, MTS, Eden Prairie, MN, U.S.) to ensure that the apex of the “J” of the lag was in line with a tensile load applied at 5.1 mm/min. until the J-lag withdrew from the wood (withdrawal) or failed without withdrawing (lag failure). To apply the load, a hardened steel bolt similar in diam- eter to the cable that would typically be used with each size lag being tested was fastened between two ends of a chain (Figure 1b). The maximum load as well as the shank diameter and em- bedded thread length of the J-lag were recorded. A cube of wood 25 mm on a side was cut from each log near the J-lag, and its mass and volume were measured immediately after testing, as well as after drying in an oven at 50°C for three days to attain approximately 12% moisture content. From these measurements, moisture content and oven-dry specific gravity of the wood were calculated as described by Simpson and TenWolde (1999). In the winter of 2006-2007, after attempting to withdraw J-lags installed in 2005, it was apparent that lags failed, rather than withdrawing from the logs. Consequently, 66 additional J-lags were installed, divided nearly equally between lags 6.4 mm (n = 43) and 9.5 mm (n = 38) diameter in fresh logs from sugar maple (n = 34) and paper birch (n = 32). J-lags were in- stalled to three partial thread lengths: 12.7 mm, 25.4 mm, and b Figure 1. a) Bolt of wood secured to testing machine, and b) partially installed lag being withdrawn. a ©2011 International Society of Arboriculture
May 2011
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