中國傳統建築直榫木接頭力學行為研究

Abstract

本研究針對台灣傳統大木結構的金柱與通梁的榫卯接合方式作反覆載重與單向側推實驗。實尺寸約30年生的人工林杉木，梁柱徑級為30 cm，榫卯嵌合度即縫隙為0。實驗中最大彎矩Mmax與旋轉勁度K定義榫頭的強弱，其中發現榫長增長會使受力面積增大，其中又以穿榫最大，而一般構件設計防止水平拔出的踏步燕尾榫，也比同榫長的單向直榫抵抗彎矩大，而最大彎矩Mmax大者旋轉勁度K亦大。研究中亦探討梁柱構材形狀、榫長、榫接種類等因子對於接合強度的影響，並將實驗結果與前人分析作比較，比較實驗方式，尺寸影響與模型推導結果是否有所差異。 研究結果發現榫卯接頭有以下特性：(1)構件容許很大的位移量；(2)中央滑移段尚有木材本身摩擦所造成的力矩抵抗，實驗進行至該循環力量最大值時，施以相反方向的力，圖形有反翹(力量提升)的現象；(3)中央會產生一段滑移現象，因此嵌合度對接頭力學行為有很大的影響；(4)每個循環進行第二次時力量均較第一次小，表示木材纖維受到擠壓發生變形；(5)下一循環的第一次曲線會沿著上一循環的第二次曲線上升。

The main purpose of this study was to investigate mechanical behavior of tenon and mortise wood joints by cyclic loading and lateral loading in Taiwan traditional wood structure. Related studies were less in our country, and most of them were tested on small size of furniture or reduction the size in the same ratio. The tested components were 30-year-old woods of artificial China fir, and the diameters of post and beam were 30 cm, and the tenon fitness was 0. The maximum moment and rotational stiffness were defined as joint strength. Experimental results revealed that increasing tenon length would increase bearing area, and especially the “through tenon” was the strongest. The strength of “stepped dovetail tenon” which was the common joint to resist lateral force was stronger than that of the “straight tenon” with the same length. The following characteristics of the tenon and mortise joints were found：(1)Wood components could allow much displacement. (2)The strength of cyclic loading would increase as opposite force affected the joint. (3)According to the slip, the tenon fitness would affect the mechanical behavior of joint. (4)The moment of the second cycle was lower than that of the first cycle. (5) In next cyclic loading, the curve of the first cycle would be along the curve of the second cycle in previous cycle.