摘要
为揭示环境湿度变化引起的木材含水率非均匀性分布对胶合木构件内部湿应力的影响规律,从材料层面测试了变湿度条件下290个国产杉木木材的平衡含水率,以及横纹径向和横纹弦向干缩性、湿胀性、水分扩散系数、抗拉强度和弹性模量等物理力学性能参数,并从理论层面利用有限元模拟分析周期性变湿度条件下层板厚度对杉木胶合木湿应力的影响。研究结果表明:利用Nelson方程能够较好地拟合变湿度中杉木的平衡含水率;杉木横纹径向干缩和湿胀性均小于横纹弦向,横纹径向水分扩散系数、抗拉强度和弹性模量均高于横纹弦向,这决定于横纹径向排列的木射线以及管胞径面壁上大量纹孔导致的实质物质减少的微观构造;减小层板厚度有助于降低胶合木湿应力,当层板厚度由40 mm降至20 mm时,构件内部最大湿应力降低19.32%,但其最大值仍高于木材横纹抗拉强度,湿应力的降低程度不足以避免构件的横纹开裂;木结构工程设计和应用中必须考虑其他有效的方法减小湿应力以避免木材横纹开裂。
It is well known that stresses caused by different moisture contents of wood affect the strength and stiffness,which influences the loading capability and durability of wood components in wooden structures.The influence of non-uniformly distributing moisture content of wood caused by varying relative humidity in the surrounding environment on moisture stress in glued laminated timber was examined and analyzed by the experimental tests and theoretical simulation in this study.A total of 290 Chinese fir wood specimens was tested to determine the influence of varying relative humidity on wood physical and mechanical properties,including equilibrium moisture content,perpendicular-to-grain tangential shrinkage,perpendicular-to-grain tangential swelling,perpendicular-to-grain radial shrinkage,perpendicular-to-grain radial swelling,perpendicular-to-grain tangential moisture diffusivity coefficient,perpendicular-to-grain radial moisture diffusivity coefficient,perpendicular-to-grain radial tensile strength,perpendicular-to-grain tangential tensile strength,perpendicular-to-grain radial modulus of elasticity,and perpendicular-to-grain tangential modulus of elasticity.The influence of laminae thickness on moisture stress in glued laminated timber manufactured with Chinese fir wood was simulated using the finite element method.The results showed that the equilibrium moisture content of Chinese fir in varying humidity could be simulated well using the conventional Nelson equation.The perpendicular-to-grain radial shrinkage and swelling properties of Chinese fir specimens were lower than the perpendicular-to-grain tangential ones,while the tangential moisture diffusivity coefficient,tensile strength and modulus of elasticity were higher than the radial ones,which were attributed to the microstructural characteristics,including wood rays and pits in radial cell walls.The reduction of laminae thickness led to a decrease in the moisture stress in glued laminated timber.When the thickness of laminate was reduced from 40 mm to 20 mm,the moisture stress decreased by 19.32%.However,the maximum moisture stress was still higher than the tensile strength,which might cause transverse fracture.Therefore,it was desired to use other additional effective methods in engineering timber design to reduce humidity stresses.
作者
岳孔
宋旭磊
程秀才
赖延军
贾翀
陆伟东
刘伟庆
YUE Kong;SONG Xulei;CHENG Xiucai;LAI Yanjun;JIA Chong;LU Weidong;LIU Weiqing(College of Civil Engineering,Nanjing Tech University,Nanjing 211800,China;Nanjing Institute of Product Quality Inspection,Nanjing 210019,China;College of Materials Science and Engineering,Nanjing Forestry University,Nanjing 210037,China)
出处
《林业工程学报》
CSCD
北大核心
2019年第4期35-40,共6页
Journal of Forestry Engineering
基金
国家重点研发计划(2017YFC0703501)
关键词
杉木
胶合木
湿应力
平衡含水率
微观构造
Chinese fir
glued laminated timber
moisture stress
equilibrium moisture content
microstructure
