省產針葉樹結構材容許應力值之探討

Investigation on Establishing Allowable Strength Properties for Domestic Structural Coniferous Lumber

葉民權(M. C. Yeh) ； 林建宗(C. C. Lin) ； 蘇裕翔(Y. S. Su) ； 魏振財(C. T. Wei)

《林產工業》 15卷3期 (1996/09) Pp. 391-414

摘要

本研究之目的在發展一套省產針葉樹結構用木材之容許應力設計值，期望藉由這套模式的推展，能夠進一步探討國內實施木結構設計的可行性。研究中係根據ASTM標準所規範結構用材之容許應力程序作為主體架構，將省產主要針葉木材，利用標準試材之機械強度值，經過適當之合併及分等，並經過電腦計算而得一木材容許應力設計值系統。本研究將省產針葉樹十九種依強度歸納為四類，每類樹種再區分為結構輕框架、結構托樑與板材、樑與縱桁、柱與角材等四種用途別，各用途別又區分為一等材及二等材。省產針葉木材之各項無缺點強度值是決定於複合離散因子，而最後各項容許應力設計值調降幅度以拉伸強度為最大，彈性係數為最小。與現行設計規範比較時，所推導之靜曲強度設計值較能顯示因等級不同所產生的強度差異，而平行木理壓縮強度設計值則較能得到因樹種類別不同所產生的強度差異。彈性係數因木材用途類別而有差異而現行規範中則無此特點，有關垂直木理壓縮強度設計值則建議現行規範中可作合理的調高，至於本研究所建立的拉伸強度設計值則較為保守。

關鍵字

容許應力 ； 分等 ； 木材機械性質

並列摘要

The purpose of the study is to develop an allowable design properties system for structural lumber of coniferous species grown in Taiwan. The establishing procedures for allowable stress are mainly according to ASTM Standards. The design values are constructed based on mechanical properties data from standard testing specimens after the species are properly combined and lumber grading system is scheduled. There are four groups of species combinations classified based on nineteen species, and each species combination is divided into four types of usage: structural light framing, structural joist and plank, beams and stringers, post and timber , which in turn classified as no. 1 and no. 2 grades. It is noted that the clear wood strength values is determined mainly on composite dispense factors for each species combination. The design values for tensile strength show the greatest reduction from the clear wood strength, while the modulus of elasticity has the least reduction. As comparing to the current design specification, the suggested design values of bending strength shows better performance due to grades, and the suggested design values of compressive strength in the direction parallel to the grain shows better performance due to proper species combination. The design values of modulus of elasticity varies with the lumber usage classifications, while the current design specification is lack of similar features. It is suggested that the compressive strength in the direction perpendicular to the grain may be assigned with higher values, and the tensile strength may be assigned with lower values for curent design specification.

並列關鍵字

Allowable stress ； grades ； mechanical properties of wood