正交胶合木(CLT)梁剪应力分析及其层间剪切强度测试
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摘要
【目的】探索正交胶合木(CLT)矩形截面梁剪应力计算公式,为测试CLT梁层间剪切强度提供理论依据。【方法】根据胡克定律及梁的弯矩与剪力的微分关系,计算3层、5层和7层CLT梁及同向胶合木梁的层间剪应力,给出CLT梁剪应力计算公式,比较CLT梁及同向胶合木梁的剪应力分布特征。【结果】CLT梁层间正应力间断,但层间剪应力是连续的;对于CLT矩形截面梁,其剪应力沿截面高度变化趋于均衡,不再遵循抛物线分布; CLT短跨距梁在三点弯曲加载中,依次发生垂直层滚动剪切破坏、层间剪切破坏和平行层弯曲破坏;短跨距梁三点弯曲载荷-位移曲线的最高峰值载荷为CLT发生层间剪切破坏载荷,其值稳定、易于读取;铁杉CLT梁层间剪切强度与其平行层弹性模量呈正相关。【结论】CLT梁层间剪应力和最大剪应力与CLT层数、平行层与垂直层弹性模量比值E_L/E_T(或E_L/E_R)有关; 3层、5层和7层CLT矩形截面梁的最大剪应力均发生在梁截面中性轴上,其值分别为1.5倍截面平均剪应力的92.8%、86.7%和92.6%;短跨距梁三点弯曲法是一种有效测试CLT层间剪切强度的方法。
【Objective】 The formula for calculating the shear stress of the cross laminated timber(CLT) rectangular beam was explored to provide a theoretical basis for testing the interlaminar shear strength of CLT.【Method】 Interlaminar shear strength of three-, five-and seven-layers CLT beams and glulam beams was calculated by Hooke's law and on the basis of the differential relationship between beam's bending moment and shear stress. Shear stress calculation formula of CLT beams was developed, and its distribution characteristics of CLT beams and glulam beams were also compared.【Result】 Interlaminar normal stress of CLT beam was interrupted, and shear stress between layers was continuous. Shear stress for rectangular section CLT beams along the height of the section tended to equalize and no longer followed the parabolic distribution. In center-point bending loading for short-span CLT beams, rolling shear failure in vertical layer, interlaminar shear failure and bending failure in parallel layer occurred in turn. The maximum load of the center-point bending load-displacement curve for CLT short-span beams was the interlaminar shear failure load, it was stable and easy to read. Interlaminar shear strength of Hemlock CLT was positively correlated with elastic modulus of parallel layer.【Conclusion】 Interlaminar shear stress and the maximum shear stress of CLT beams were related to the number of CLT layers and the ratio of elastic modulus of parallel and vertical layers E_L/E_T(or E_L/E_R). The maximum shear stresses of three-, five-and seven-layers CLT rectangular beams occurred on the neutral axis of the beam section, and their values were 92.8%, 86.7%, and 92.6% of the 1.5 times section average shear stress, respectively. Short-span beam three-point bending method was an effective method of testing the interlaminar shear strength of short-span CLT beams.
【Objective】 The formula for calculating the shear stress of the cross laminated timber(CLT) rectangular beam was explored to provide a theoretical basis for testing the interlaminar shear strength of CLT.【Method】 Interlaminar shear strength of three-, five-and seven-layers CLT beams and glulam beams was calculated by Hooke's law and on the basis of the differential relationship between beam's bending moment and shear stress. Shear stress calculation formula of CLT beams was developed, and its distribution characteristics of CLT beams and glulam beams were also compared.【Result】 Interlaminar normal stress of CLT beam was interrupted, and shear stress between layers was continuous. Shear stress for rectangular section CLT beams along the height of the section tended to equalize and no longer followed the parabolic distribution. In center-point bending loading for short-span CLT beams, rolling shear failure in vertical layer, interlaminar shear failure and bending failure in parallel layer occurred in turn. The maximum load of the center-point bending load-displacement curve for CLT short-span beams was the interlaminar shear failure load, it was stable and easy to read. Interlaminar shear strength of Hemlock CLT was positively correlated with elastic modulus of parallel layer.【Conclusion】 Interlaminar shear stress and the maximum shear stress of CLT beams were related to the number of CLT layers and the ratio of elastic modulus of parallel and vertical layers E_L/E_T(or E_L/E_R). The maximum shear stresses of three-, five-and seven-layers CLT rectangular beams occurred on the neutral axis of the beam section, and their values were 92.8%, 86.7%, and 92.6% of the 1.5 times section average shear stress, respectively. Short-span beam three-point bending method was an effective method of testing the interlaminar shear strength of short-span CLT beams.
引文
曹瑜,王韵璐,王正,等. 2016. 国外正交胶合木(CLT)建筑技术的发展与展望. 林产工业, 13(12):3-7.(Cao Y,Wang Y L,Wang Z, et al. 2016. Application and research progress of overseas cross-laminated timber(CLT) construction.China Forest Products Industry, 13(12):3-7.[in Chinese])
邵蓓珠,马功勋. 1988. 剪力对梁变形影响分析. 南京化工学院学报, 10(3):78-84.(Shao B Z,Ma G X. 1988. Analysis of effect of shear on deformation of beams.Journal of Nanjing Institute of Chemical Technology,10(3):78-84.[in Chinese])
王韵璐,曹瑜,王正,等. 2017. 加拿大铁杉正交胶合木弯曲性能预测与评估.林产工业, 44(7):15-20.(Wang Y L, Cao Y, Wang Z, et al. 2017. Prediction and assessment of Canadian hemlock CLT bending performance. China Forest Products Industry, 44(7):15-20.[in Chinese])
王韵璐,王正,王建和. 2017. 国内外新一代重型CLT木结构建筑技术的研究进展. 西北林学院学报, 32(2):286-293.(Wang Y L,Wang Z,Wang J H. 2017. Research progress of the new generation of heavy CLT wood structure building technology.Journal of Northwest Forestry University,32(2):286-293.[in Chinese])
谢文博,王正,高子震,等. 2018. 正交胶合木(CLT)性能测试及其分析.林产工业, 45(10):40-45,49.(Xie W B,Wang Z, Gao Z Z, et al. 2018. Performance test and analysis of cross-laminated timber(CLT). China Forest Products Industry,45(10): 40-45,49.[in Chinese])
S.铁摩辛柯, J. 盖尔著. 1978. 材料力学. 胡人礼,译.北京:科学出版社, 146-164.Timoshenko S,Gere J. 1978. Mechanics of material.Hu R L, translated.Beijing:Science Press,146-164.[in Chinese])
Hindman D P, Bouldin J C. 2015. Mechanical properties of southern pine cross-laminated timber. Journal of Materials in Civil Engineering, 27(9):101-110.
Schickhofer G.2010.Cross laminated timber(CLT) in Europe-from conception to implementation,presentation. University of British Columbia, Department of wood Science, Vancouver,Canada.
Ggnon S, Pirvu C. 2011. CLT handbook: cross-laminated timber. USA:FPInnovation.
Sikora K S, McPolin D O, Harte A M. 2016. Effects of the thickness of cross-laminated timber (CLT) panels made from Irish Sitka spruce on mechanical performance in bending and shear. Construction and Building Materials,116(7):141-150.
Wang B J, Pirvu C, Lum C. 2011. Cross-laminated timber manufacturing. Chapter 2. Canadian CLT handbook. FPInnovations, Special Publication SP-528E, 18.
邵蓓珠,马功勋. 1988. 剪力对梁变形影响分析. 南京化工学院学报, 10(3):78-84.(Shao B Z,Ma G X. 1988. Analysis of effect of shear on deformation of beams.Journal of Nanjing Institute of Chemical Technology,10(3):78-84.[in Chinese])
王韵璐,曹瑜,王正,等. 2017. 加拿大铁杉正交胶合木弯曲性能预测与评估.林产工业, 44(7):15-20.(Wang Y L, Cao Y, Wang Z, et al. 2017. Prediction and assessment of Canadian hemlock CLT bending performance. China Forest Products Industry, 44(7):15-20.[in Chinese])
王韵璐,王正,王建和. 2017. 国内外新一代重型CLT木结构建筑技术的研究进展. 西北林学院学报, 32(2):286-293.(Wang Y L,Wang Z,Wang J H. 2017. Research progress of the new generation of heavy CLT wood structure building technology.Journal of Northwest Forestry University,32(2):286-293.[in Chinese])
谢文博,王正,高子震,等. 2018. 正交胶合木(CLT)性能测试及其分析.林产工业, 45(10):40-45,49.(Xie W B,Wang Z, Gao Z Z, et al. 2018. Performance test and analysis of cross-laminated timber(CLT). China Forest Products Industry,45(10): 40-45,49.[in Chinese])
S.铁摩辛柯, J. 盖尔著. 1978. 材料力学. 胡人礼,译.北京:科学出版社, 146-164.Timoshenko S,Gere J. 1978. Mechanics of material.Hu R L, translated.Beijing:Science Press,146-164.[in Chinese])
Hindman D P, Bouldin J C. 2015. Mechanical properties of southern pine cross-laminated timber. Journal of Materials in Civil Engineering, 27(9):101-110.
Schickhofer G.2010.Cross laminated timber(CLT) in Europe-from conception to implementation,presentation. University of British Columbia, Department of wood Science, Vancouver,Canada.
Ggnon S, Pirvu C. 2011. CLT handbook: cross-laminated timber. USA:FPInnovation.
Sikora K S, McPolin D O, Harte A M. 2016. Effects of the thickness of cross-laminated timber (CLT) panels made from Irish Sitka spruce on mechanical performance in bending and shear. Construction and Building Materials,116(7):141-150.
Wang B J, Pirvu C, Lum C. 2011. Cross-laminated timber manufacturing. Chapter 2. Canadian CLT handbook. FPInnovations, Special Publication SP-528E, 18.