金屬連結件應用於CLT接合之剪斷性能評估

木材對於環境負荷小，為綠建材之首選，採用國產造林木同時亦能降低碳足跡。針對中高層樓建築之市場潛力，木質結構技術面臨創新及整合系統化加工之挑戰。在新型的木構造系統中，CLT係透過集成元直交層積排列提高材料之剛性性質，並作為大型厚板材應用於結構中，其接合部之性質為重要影響因素，透過金屬連結件及扣件之搭配可提高接合部之塑性率及能量散逸性能。考量施工效率之同時，自攻螺絲具有易於安裝及不須預鑽孔之優勢。故本研究採國產柳杉材製成CLT，設計不同之金屬連結件並引用結構用自攻螺絲扣件進行結構體之接合，以剪斷試驗進行接合性能之評估，以提供給國內相關業者設計參考用。　　試驗之CLT試材以43年生國產柳杉材經製材及窯乾後製成尺寸為880 × 110 × 30 mm之集成元，透過打音分等並配置成Mx60-5-5異等級構成之柳杉CLT，另外，採用南方松作為表層集成元，製成異樹種CLT改善表面強度並比較其性能差異。CLT製造膠合劑採用間苯二酚－酚甲醛樹酯搭配粉末狀聚甲醛硬化劑使用。CLT進行牆－牆接合及牆－樓板接合試驗。連結件採用鋁合金設計，以平板型、T型及L型等三種連結件型式進行試驗。自攻螺絲扣件採用M6 × 90 mm及M8 × 120 mm之兩種規格，使用數量分為12、18與28支。合計20種接合條件，採用雙剪斷方式進行試驗，並採用2D-DIC觀察接合部受力變形之過程。　　接合部破壞結果顯示破壞可區分為CLT破壞、自攻螺絲破壞與鋁合金連結件破壞等三個部分。其中在集成元纖維方向平行於受力方向之多支自攻螺絲使用數量之接合條件有表面集成元剪斷破壞發生；在直徑6 mm自攻螺絲發生螺帽剪斷破壞，自攻螺絲之降伏破壞模式分為單剪之mode 6，及雙剪之mode III與mode IV之組合，以及三者合併之組合；在直徑8 mm自攻螺絲及多支使用數量之接合條件易發生連結件剪斷破壞。　　比較不同樹種CLT之接合性能並無顯著之差異；在連結件方面顯示T型連結件之接合具有較佳之剪斷容量性能，而平板型連結件接合之初始剛性及塑性率高於T型及L型連結件接合，以L型連結件接合則顯示有較大之位移量，而自攻螺絲直徑間差異則不明顯。自攻螺絲使用數量為顯著的接合影響因子，使用較多自攻螺絲數量者在剪斷容量、初始剛性及能量散逸性能皆有增加，並降低位移量；多重比較分析顯示T型及平板型連結件之接合有較佳之接合性能，而L型連結件之接合，則以使用28支直徑6 mm之自攻螺絲接合條件具有較為優異之性能。　　以2D數位影像相關分析，比對實際試驗接合部變形破壞情形，在εyy、εxy、ε1、ε2皆能觀察出發生大量變形時之特徵，故以數位影像相關分析應變分布圖可有效評估實際試驗之變化。　　可利用加速規測定CLT接合部構件產生破壞時之振動加速度，進而推估各構件之破壞情形，本研究解析木材劈裂所發生之振動，進而可判定CLT產生初期破壞之階段為剪斷降伏容量之51.36％或最大剪斷容量之25.49％時，並伴隨構件間的受力摩擦。

關鍵字

柳杉；直交集成板；接合剪斷性能；金屬連結件；自攻螺絲

並列摘要

Wood has become the first choice for green building materials due to its small environmental load, energy saving and carbon reduction. The use of domestic plantation timber can also reduce the carbon footprint. For the market potential of mid- and high-rise buildings, wood-frame construction technology faces the challenge of innovation and integrated processing system. In the new wood construction system, CLT (Cross laminated timber) improves the stiffness properties of materials by cross laminated combination. Used as a large thick plate in the structure, the connection characteristics become an important factor, and both the ductility factor and energy dissipation performance of the connector can be improved by the combinations of the metal joint and the fastener. For considering construction efficiency, self-tapping screws have the advantage of being easy to install and without pre-drilling. Therefore, this study uses the C. japonica to make CLT, with different types of connectors and self-tapping screws on the CLT structure, and estimates connect performance by shear tests. Results can be the reference for the designers and building industry. 　　The lumber of CLT is made of 43-year-old C. japonica and through kiln dried and cut to form the laminae of size 880 × 110 × 30 mm. The C. japonica CLT, which is a heterogeneous-grade construction of Mx60-5-5, and grading is classified by a top-tone approach. In addition, the southern pine was used as the surface layer of CLT to make the mixed species CLT to improve the surface strength and compare its performance. CLT is glued by the resorcinol-phenol formaldehyde resin with powdered polyformaldehyde hardener. The types of CLT assembly test include the wall-wall and wall-floor connections. The connetors are made of aluminum alloy, and designed with three types: flat type, T type and L type. Self-tapping screws are provided with M6 × 90 mm and M8 × 120 mm sizes and set in 12, 18 and 28. There are a total of 20 connecting conditions. The test was carried out by double shearing, and the process of deformation of the connection was observed by 2D-DIC. 　　The failure of the connection shows that the failure mode can be divided into three parts: CLT failure, self-tapping screw failure and aluminum alloy connector failure. Wherein the connection condition of a large amount of self-tapping screws used in the direction of the laminae fiber parallel to the force is that the surface laminae shear failure occurs. The screw nut shear failure occurs in the condition of self-tapping screw with a diameter of 6 mm. The failure mode of the self-tapping screw is divided into single shear of failure mode 6, double shear of failure mode III and IV, and a combination of the three. In the case of a self-tapping screw with a diameter of 8 mm and multi-use amount, the connector is probably with shear failure. 　　For the comparison of the CLT with different species, there is no significant difference in the connection performance. In terms of the connector, T type has the best shear capacity for the connection. The initial stiffness and ductility factor of flat type are higher than those of the T type and the L type. L type has the most displacement for the connection, and it’s not obvious different between the diameters of the self-tapping screws. The amount of self-tapping screws used is a significant connection influence factor. When using a large amount of self-tapping screws, the shear capacity, initial stiffness and energy dissipation of a connection are increased, and the displacement is reduced. Multiple comparative analysis showed that the connetor of the T type and flat type had better shear-resisting performance for the connection. However, while the connector of the L type showed superior performance using 28 self-tapping screws with a diameter of 6 mm. 　　Compare 2D digital image correlation analysis with the condition of connection failure of experimental results, it shows that the failure characteristic could be observed based on εyy, εxy, ε1, and ε2. Therefore, strain distribution from the digital image correlation analysis can effectively estimate the connection changes in the actual testing condition. 　　The accelerometer can be used to measure the vibration acceleration when the CLT connection is failing, thereby estimate the damage of each member. This study analyzed the vibration of wood splitting and then determined that the initial stage of CLT failure was 51.36% of yield shear capacity or 25.49% of maximum shear capacity, accompanied by friction between members.