台灣產杉木工字樑之應力分布

Stress Distribution of I-beam Fabricated with China-fir Lumber in Taiwan

葉民權(Min-Chyuan Yeh) ； 王村(Bor-Tsuen Wang)

《林產工業》 22卷2期 (2003/06) Pp. 119-128

摘要

本研究係採用省產杉木造林木所組成之工字樑應用於樓板托樑系統之探討，樑翼材之尺寸為38×89、38×140及38×180 mm，樑深為300 mm，樑翼與樑腹構材之組合採用16d箱用釘，間距分別為8、10、12 cm，並以環氧樹脂膠合劑于界面補強。工字樑試材長3.6 m，以三分點載重進行靜曲試驗，跨距/樑深比11.7。試驗結果顯示，在最大靜曲破壞的30%條件下，於載重跨距範圍內，以應變片測定所得樑斷面之應變分布呈線性關係；同時在下樑翼構材所測得之拉伸應變值較上樑翼者高出17.8%。在釘接與膠合之界面兩側的相鄰樑翼構材與樑腹構材，其應變值相差約-19.6%～+39.5%。以38×89 mm作為樑翼構材之工字樑彎曲剛性較佳。上下樑翼構材在表裏側的應變量平均差異分別為12.3%及21.9%。破壞時在剪斷跨距範圍樑翼所產生之剪斷應力，為樑腹構材斷面中央位置之最大剪斷應力之36.3%，在樑翼與樑腹接合介面之剪斷應力則為最大值之72.5%。利用ANSYS有限元素分析軟體，探討離支點60 cm處的工字樑斷面應力分布，以固體元素配合無缺點木材之彈性係數值模擬結果較實測者為低較為保守。

關鍵字

杉木 ； 工字樑 ； 彎曲性質 ； 有限元素方法

並列摘要

China-fir is a fast-grown species and is used as materials for the assembly of I-beam for the application of flooring system. The sizes of flanges include 38×89, 38×140, and 38×180 mm and the depth of beam is 300 mm. The flanges and web were assembled with 16d box nails in nail spacing of 8 cm, 10 cm, and 12 cm, respectively, and with the application of epoxy adhesives. I-beam with 3.6 m in length was subjected to four-point loading for static flexural tests with a span/depth ratio of 11.7. The linear relationship of strain distribution on the cross section of I-beam can be found within the shear span based on the measurements of strain gages at the level of 30% of maximum load. It is indicated that there is 17.8% higher for tensile strain on lower flanges than that of compressive strain on upper flanges. The variation of -19.6% to +39.5% in strain measurements between flanges and adjacent web resulted due to the influence of the sizes of flanges on the stiffness of I-beam formed by nail joints and adhesives. Better improvement on the stiffness can be found in the case of I-beam fabricated with 2×4 flanges. The difference of strain measured at both sides of top and bottom flanges are 12.3% and 21.9%, respectively. The simulation on the stress distribution on the cross section of I-beam 60 cm from support within the shear span is performed. The maximum shearing stress occurred in the middle of web member is about 2.55 MPa. The shearing stress on the web near the interface is reduced to 72.5% of the maximum shearing stress. The shearing stresses on the flanges are only 36.3% of the maximum shearing stress. The flexural behavior of I-beam is modeled with a finite element method of the ANSYS software and solid 45 elements are employed. The more conservative results were obtained as the modulus of elasticity evaluated from small clear wood employed in the modeling.

並列關鍵字

China fir ； I-beam ； Flexural property ； Finite element method