自攻螺絲木構造接點的剪力行為與解析公式驗證

Abstract

本研究主要探討木構造接點的剪力行為，其中，接點係由國產材組成並採自攻螺絲作為橫貫緊固件，透過剪力試驗評估接點的抗剪強度、韌性、及破壞模式，測出的剪力強度將拿來跟Eurocode 5的計算結果比較，藉以檢討公式之於國產建材的適用性。首先，本研究篩選適合用於建築結構的國產材和自攻螺絲，用以製作接點試體。國產材包含針葉木結構材福杉、柳杉、和屬於闊葉木的相思樹，自攻螺絲為台灣製造商代工的產品，挑選5種常用而細部處理略有不同的螺絲。以這些參數為基礎，共規劃16種接點，每種接點有9個試體，計144個剪力試體。剪力試驗的結果顯示，樹種會影響接點的剪力行為甚鉅，相思樹由於有較高的密度，因此其承載力與韌性都明顯比柳杉、福杉來得大。使用螺紋間距3mm的自攻螺絲的接點，其剪力強度和韌性分別比使用5mm螺距的試體高了10%、7%。使用全牙自攻螺絲鎖固的接點，其剪力強度與韌性也比半牙螺絲分別高出9%、7%。在使用墊片的情況下，接點的剪力強度與韌性皆可提升約7%。相較之下，鑽尾形式對於接點力學行為的影響較小。比較實驗值和Eurocode 5的計算結果後發現，Eurocode 5的評估結果偏保守，儘管仍有調適的空間以兼顧安全性與經濟性，這套評估方法可適用於國產建材並確保足夠的安全係數。  This study is focused on the shear behaviour of dowel-type timber joint composed of domestic wood and self-tapping screw. A series of shear test is intended for evaluating the shear capacity of timber connections. Then, the testing results are compared to the analytic values based on Eurocode 5’ formula. The comparison contributes to verify the feasibility of the formula for domestic materials, including wood and screw. This study selects viable timber and self-tapping screw to manufacture various timber joints. The wood comprises softwood and hardwood for structural purposes, while the self-tapping screw consists of 5 different profiles in terms of screws’ tailing and threading. Depending on these parameters, the shear test includes 16 types of timber joints and each type consists of 9 specimens. The testing results demonstrate that the species of wood influence the shear behaviour significantly. With greater density, the hardwood reveals higher capacity and ductility compared to softwood. Thread’s spacing and the threading length influence joints’ shear behaviour as well. The self-tapping screw with 3mm spacing of the thread increase the ultimate shear strength and ductility by 9% and 7%, respectively, compared to the specimens with 5mm-spacing screw. When applying fully threaded screw, the joints exhibit 9% higher shear capacity and 7% greater ductility than those with half-threaded screws do. According to the comparison between testing and analytic results, Eurocode 5 method conservatively predicts the joints’ capacity. Although the formula may need further modification for Taiwanese materials, the calculation results ensure considerable safety margin for timber joints.