带纵缝木梁抗弯承载力及修复方法研究

Flexural and Shearing Capacities of Longitudinally Cracked and Retrofitted Wood Beams

摘要:

木结构构件由于荷载和温、湿度变化等作用易在端部及中部发生平行于构件纵轴的裂缝，导致缝端应力集中以及削弱裂缝两侧木材的变形协调，进而降低承载力.开展了带纵缝木梁足尺试件弯曲加载试验和木材清样小试件材性实验，考虑了不同试件材性的差异和木材材料强度的尺寸效应，确定了纵缝长度和位于梁截面高度处的位置等参数对木梁承载力的影响，并分析了采用新型自攻螺丝修复后带纵缝木梁的承载力恢复性能.研究表明，纵缝位于木梁剪弯段截面中部的影响最大，承载力下降可达46.2%；在弯剪段施加自攻螺丝的修复效果最好，其修复率随自攻螺丝间距增大而减小.采用200 mm间距时木梁承载力修复率可达1.12.

关键词:木梁; 纵缝; 抗弯承载力; 自攻螺丝; 修复率; 尺寸效应

Abstract:

Wood structural members are prone to endsplitting and cracking along the longitudinal axis, due to external loading and changes of humidity. Such cracks can impair the structural integrity and lead to stress concentration in the vicinity of the crack tips, thereby significantly reduce the load carrying capacity of the wood members. This paper presents the results of fullscale bending tests with longitudinally cracked wood beams. With consideration of the variation of specimen quality and the size effect of wood strength properties, the influence of crack length and position along the crosssectional height on the bending resistance of the wood beams was identified. The retrofitting effect of selftapping screws was also investigated considering different provisions and spacings. It was found that the longitudinal cracks within the shear span and at the midheight of the crosssection can lead to the biggest decrease (46.2%) of the bending resistance, and the selftapping screws are most efficient (retrofitting ratio of 1.12) while applied to the shear span and the retrofitting effect may decrease with the increasing of the screw spacing.

Key words:wood beams; longitudinal cracks; bending resistance; selftapping screws; retrofitting efficiency; size effect