柳杉材以刺鐵板接合之疲勞行為

The Fatigue Behaviors of Japanese Cedar Jointed by Metal Plate

王怡仁(Yi-Ren Wang)

《林產工業》 17卷2期 (1998/06) Pp. 263-276

https://doi.org/10.6561/FPI.1998.17(2).2

摘要

大型木結構之接合常使用金屬連結器，如釘、螺栓、刺鐵板及各種式樣的鐵片或角鐵來連接樑柱、地樑、板和柱等結構間的接合。主要在於此等金屬連結器取得方便且能提供適當的接合強度。本研究利用刺鐵板接合省產柳杉造林木，探討其疲勞行為及破壞模式。所用刺鐵板為60×120×0.8 mm之結構用冷軋鋼板，齒長則分為長（12 mm）和短（9 mm），而齒密度則有疏（每平方吋4齒）和密（每平方吋8齒）共計四種刺鐵板，柳杉為2×4＂。接合方式均使刺鐵板的長軸和荷重方向相同，荷重方式計有引張和靜曲，引張又依木理方向分為平行木理和垂直木理方式。實驗方式為先將各接合以靜態荷重進行至破壞，記錄其破壞荷重，然後由靜態試驗結果選取短密刺鐵板以引張平行木理和引張垂直木理方式進行動態試驗，荷重基準為靜態破壞荷重的20%、30%、40%和50%。荷重形式為以荷重基準為波峰而0為波谷頻率為105 Hz的正弦波。在引張垂直木理方向的靜態試驗，各刺鐵板的破壞荷重相近，引張平行木理方向則以短密刺鐵板接合效果較好，靜曲試驗也以短密刺鐵板有較大的彎矩抵抗。在設計荷重處、極限滑動處及初始斜率等三者所求得的剛性相同荷重下刺鐵板間並無顯著差異。靜態試驗中發現接合處破壞模式大約有三種：齒拉出、齒鐵板變形和齒剪斷。其破壞模式單獨或混合出現。在動態引張平行木理試驗則發現到疲勞破壞的次數在荷重基準為30%'，40%和50%，分別為61550、38065和11126次。而20%荷重基準時則試驗至25萬次仍未破壞，顯示疲勞荷重應在20%荷重基準以下。在動態引張垂直木理試驗則40%和50%荷重基準時分別破壞在60960和43358次，且變異很大。但在30%荷重基準則大部份未破壞，顯示其疲勞限度荷重應在30%以下。至疲勞破壞的次數均隨荷重基準增加而降低。破壞模式都先由齒剪斷，繼而被拉出為多。

關鍵字

柳杉 ； 刺鐵板 ； 接合強度 ； 動態行為

並列摘要

Wood connectors such as nail, bolt, lag screw, metal plate and other connectors are usually used in fabrication of roof truss, floor truss and walls due to their ease of fabrication and low cost. The domestic Japanese cedar lumber is connected by metal plate in order to study the failure behaviors and failure mode in this study. The metal plate is made from cold rolled steel plate with the dimension of 60×120×0.8 mm. The tooth length are 9 and 12 mm, and the tooth density are 4 and 8 teeth per square inch. The long axis of the metal plate in the joint is placed in parallel to the loading direction when loaded in tension. The 2×4＂ lumbers are jointed in parallel or perpendicular to each other with the metal plate in wide side. The lumbers jointed in parallel are loaded either in tension or in bending to obtain their static maximum load. The lumbers jointed in perpendicular to each other are loaded in tension alone to obtain static maximum load. According to the maximum load and the failure mode, the metal plate with 9mm tooth length and tooth density of 8 teeth/in^2 are used in fatigue test. The load levels are 20%, 30%, 40% and 50% of the static maximum load. The load function is a non-reversed 1.5 Hz sinusoidal wave with the load level as its peak. The fatigue test was carried out until failure occur or test cycles to 1/4 million. The maximum static load of four metal plates tested in the lumbers jointed perpendicular to each other do not have significant difference. However, the 9mm with 8 teeth/in^2 metal plate showed higher static tension load and bending moment in the case of parallel grain joint. Three stiffness calculated at design load, at critical slip and from initial slope showed no significant difference among metal plates. Three major failure modes observed are tooth withdrawal, metal plate yield and shear of tooth. The cycles to failure for the parallel grain joint under 30%, 40% and 50 % load levels are respectively 61550, 38065 and 11126 with large variation. Load level of 20% of static load do not fail after 1/4 million cycles. For the perpendicular case, the cycles to failure for 40% and 50% are 60960 and 43358, but no failure occur for 30% load level after 114 million cycles, the results indicated that the fatigue limit for parallel joint might be under 20% load level, and under 30% load level for perpendicular joint. The failure is always initiated by shear of teeth followed by pulling out of wood for the fatigue tests.

並列關鍵字

metal plate ； fatigue test ； Japaness cedar ； failure mode