Nailplated timber trusses are widely used in residential housing. However, there is limited evidence of use or research on the application of nailplated trusses in exposed environments. It is common knowledge to the nailplated truss industry that weather-exposed trusses experience a phenomenon referred to as “nailplate backout”, where the nailplates separate from the timber surface due to the shrink-swell mechanism of the timber in response to its varying moisture content. This paper investigates the performance of innovative nailplated joints on: (1) stopping moisture-driven backout and (2) increasing the capacity of the joints, when compared to currently used joints, after exposure to severe moisture cycling. Three different experimental sets of joints were manufactured to achieve these outcomes, with Set 1 and Set 2 containing 100 splice and 100 butt joints while Set 3 had 40 splice and 40 butt joints. Sets 1 and 2 have a re-designed tooth profile where: (1) Set 1 combined a polyurethane adhesive with a modified nailplate tooth designed to allow the adhesive to penetrate the timber and (2) Set 2 implemented a hook in the middle of the nailplate teeth to grab the timber when the nailplate tries to separate from the timber, either from moisture induced backout or from loading. Polyurethane adhesive was also used in Set 3 but on an un-modified tooth profile. To evaluate the efficiency of the new nailplates, control joints with unmodified nailplates were manufactured for each set and tested. All joints were subjected to severe accelerated moisture cycles inside an air-driven kiln with the temperature being kept constant 70 °C and the relative humidity varied between 15 and 95%. The cycles consisted of a 7-h wetting and an 18-h drying period. For Sets 1 and 2, the tensile capacity of the joints was measured after 0, 3, 6, 9 and 12 moisture cycles, while for Set 3, it was only measured after 0 and 12 cycles. The backout was recorded after each moisture cycle for Sets 1 and 2 and after 12 cycles for Set 3. The average backout of Set 1 and Set 2 control joints after 12 severe cycles was 1.13 mm and 1.01 mm, respectively, while the addition of glue and a hook reduced the backout to 0.56 and 0.92 mm, respectively. In terms of capacity, the adhesive in Set 1 increased the capacity for the splice joints and butt joints by 43% and 13%, respectively. In Set 2, the hook only marginally increased the capacity of the splice joints by 13% and reduced the average butt joint capacity. Observations were made regarding the failure modes of the joints. The addition of the adhesive and hook to the nailplate teeth resulted in more joints failing due to the capacity of the timber rather than due to the nailplate separating from the timber during the tensile testing.

中文翻译：

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创新的镀钉接头承受加速湿气循环的能力

镀指甲木桁架广泛用于住宅。但是，在裸露的环境中使用钉板桁架的使用或研究的证据有限。钉板式桁架行业的常识是，暴露于天气的桁架会经历一种称为“钉板退回”的现象，其中钉板由于木材因其不同的水分含量而产生的膨胀-膨胀机制而与木材表面分离。 。本文研究了创新的钉板式接头在以下情况下的性能：（1）在遭受严重的水分循环后，与目前使用的接头相比，停止了水分驱动的回退，以及（2）增加了接头的承载能力。制造了三种不同的实验关节组以实现这些结果，组1和组2包含100个接头和100个对接接头，而组3包含40个接头和40个对接接头。组1和组2具有重新设计的齿廓，其中：（1）组1将聚氨酯粘合剂与修饰的钉板齿相结合，旨在使粘合剂能够穿透木材，并且（2）组2在树皮的中间装有钩子当钉板试图与木材分离时，无论是由于潮湿引起的回弹还是由于负载，钉板齿都会抓住木材。聚氨酯胶粘剂也用于第3组，但齿形未改变。为了评估新钉板的效率，为每组制造并测试了未修饰钉板的对照关节。在空气驱动的窑炉中，所有接缝都经历了严重的加速湿气循环，温度保持恒定在70°C，相对湿度在15％至95％之间变化。循环包括7小时的润湿和18小时的干燥时间。对于第1组和第2组，在0、3、6、9和12个水分循环后测量了接头的拉伸能力，而对于第3组，仅在0和12个循环后进行了测量。在第1组和第2组的每个水分循环后以及第3组的12个循环后记录回落。在经过12次严重循环后，在添加胶水的同时，第1组和第2组对照关节的平均回落分别为1.13 mm和1.01 mm。和一个钩子分别将回落量减少到0.56和0.92毫米。在容量方面，第1组中的胶粘剂使对接和对接的容量分别增加了43％和13％，分别。在第2组中，钩子仅稍微增加了拼接接头的承受能力13％，并降低了平均对接接头承受能力。对关节的破坏模式进行了观察。在钉板齿上添加粘合剂和挂钩会导致更多的连接失效，这是由于木材的承载能力而不是由于在拉伸测试期间钉板与木材分离所致。