竹胶板双剪螺钉连接的承载性能与破坏机理

Loading behavior and failure mechanism of plybamboo-sheathed doubleshear screwed connections

【目的】以常规木基结构板材作夹板的夹板剪力墙在侧向力作用下易出现板边撕裂和钉子拔出破坏,严重制约其抗侧力性能。采用竹胶板作为中心夹板、以自攻螺钉代替常规钉连接件,可在夹板剪力墙中形成墙骨-竹胶板-墙骨的双剪螺钉连接效果,有望改善上述不利破坏。【方法】为探究该方法的可行性,以6组竹胶板双剪螺钉连接试件为研究对象,开展了单调和低周反复加载试验,分析了竹胶板厚度和加载方向变化对其破坏模式、弹性刚度、强度、延性系数等力学特性的影响,明确了其在往复加载过程中的损伤累积规律。【结果】尽管竹胶板双剪螺钉连接不能完全避免板边撕裂和螺钉拔出破坏,但已充分利用了自攻螺钉的高抗弯和抗拔性能,所表现出的极限承载力比由常规木基结构板材和圆钉制作的双剪钉连接高72.4%以上。增大竹胶板厚度有益于提升双剪螺钉连接的极限承载能力,但对弹性刚度的影响并未表现出显著规律。在低周反复荷载作用下,竹胶板双剪螺钉连接中的自攻螺钉易过早发生弯曲疲劳剪断,以致其极限承载力、极限位移和延性系数明显比单调加载时低。综合试验损伤观测和累积损伤指数(D),将竹胶板双剪螺钉连接的损伤划分为五个等级:基本完好(D<0.10)、轻微损伤(0.10≤D<0.20)、中度损伤(0.20≤D<0.60)、严重损伤(0.60≤D<0.80)和失效(D>0.80)。【结论】分别采用竹胶板和自攻螺钉替代木基结构板材和和常规钉连接件,是提升夹板剪力墙抗侧力性能的一种可行方法。

【Objective】The lateral performance of the midply shear wall sheathed with common wood-based structural panels was severely limited by the failures of sheathing edge-tear and nail withdrawal.Replacing wood sheathing panels and common nails with plybamboo panels and self-tapping screws,respectively,might be a novel method to avoid such failures,which can generate lots of stud-plybamboo-stud dolube-shear screwed connections in midply shear walls.【Method】In order to evaluate its feasibility,six groups of plybamboo-sheathed double-shear screwed(PSDSS)connections were tested under monotonic and cyclic loads.The influence of plybamboo sheathing thickness and loading direction was investigated,with respect to the failure modes,elastic stiffness,ultimate strength,and ductile ratio.Cumulative damage of the connections under cyclic loads were also assessed.【Result】The PSDSS connections can’t completely avoid sheathing edge-tear and screw withdrawal failures,but can take full use of the high bending and withdrawal capacity of the self-tapping screws.The PSDSS connections have an over 72.4%higher ultimate strength than the doubleshear nail connections with common wood sheathings.Increasing the plybamboo sheathing thickness can increase the ultimate strength of PSDSS connection,but has no distinguishable effect in the elastic stiffness.Under cyclic loads,PSDSS connections mainly fail due to the premature bending fatigue of the screws,resulting in a substantial reduction in the ultimate strength,peak-point displacement and ductile factor compared to those under monotonic loads.Based on the observed damage and the calculated damage index(D),the damage levels of PSDSS connections is summarized into:none(D<0.10),minor(0.10≤D<0.20),moderate(0.20≤D<0.60),severe(0.60≤D<0.80)and failure(D>0.80).【Conclusion】The combined use of plybamboo sheathing and self-tapping fastener is a viable method of increasing the lateral performance of midply shear walls.