日本柳杉木构件内嵌钢填板销连接横纹承载性能

Bearing Performance of Dowel Connection with Slotted-in Steel Plates in the Structural Component of Japanese Cedar under Load Perpendicular to Grain

【目的】研究日本柳杉木构件内嵌钢填板销连接在横纹荷载作用下的破坏机制和承载性能,为木结构梁、柱构件金属件连接时梁端销连接设计提供依据。【方法】在梁端部开槽钻孔后将单个钢销连接到内嵌钢填板,分别对日本柳杉锯材梁和胶合木梁进行横纹荷载作用下的弯曲剪切加载试验,按照日本通行数据分析方法确定销连接短期承载力标准值,并与5个不同国家标准规定的屈服荷载计算值进行比较。【结果】加载初期,荷载-位移曲线呈线性关系,构件处于线弹性阶段,随着位移增加曲线呈非线性,构件进入弹塑性阶段,当位移增加到一定数值,梁端出现初始脆性开裂,荷载瞬间急速减小,随后荷载又随位移增加再次上升,加载至极限状态时,梁构件产生劈裂破坏丧失承载力;最终的破坏形态为梁构件沿销孔水平剪切面开裂、销连接屈服模式Ⅲ型;通过足尺试验得到断面尺寸120 mm×240 mm锯材梁和胶合木梁的钢填板单个销连接短期承载力标准值取决于屈服荷载,分别为8.6和13.7 kN,初始开裂对应的荷载平均值分别为15.0和21.1 kN,屈服荷载平均值分别为14.50和15.00 kN,最大荷载平均值分别为27.0和30.8 kN。【结论】胶合木梁钢填板销连接的最大荷载和屈服荷载平均值均大于锯材梁,且变异系数明显小于锯材梁,含水率低而变异小,从而导致试验获得胶合木梁销连接的短期承载力标准值明显高于锯材梁,当销连接作为中小断面梁柱构件的主要连接方式时,宜选用强度等级确定、质量合格的胶合木作为木构件,比锯材具有更高的连接承载力。梁端销连接节点承载力与单个销连接承载力和销数量具有良好的相关性,可作为梁柱节点梁端销连接设计依据。销连接部位发生销屈服后木材开裂,初始开裂取决于木材抗剪强度、横纹抗拉强度和销所在的梁高部位以及销孔到梁端的距离,发生初始开裂后钢销仍能起到支撑作用,连接节点延性较好;锯材梁和胶合木梁短期承载力标准值与标准中规定的屈服荷载公式计算值吻合度较好。各国标准中关于脆性破坏计算公式均能较好预测销连接木材的脆性破坏,与试验值比较,日本标准对于劈裂破坏的计算值最为接近,欧洲和加拿大标准的计算结果更趋于保守,我国现行标准在销连接设计中尚未考虑木材的脆性破坏,今后应进一步研究完善销连接计算公式和参数,更好地保证木构件连接安全可靠度。

【Objective】In the paper,testing in the full size structural beam connected with a dowel(drift pin)to the slotted-in steel plates in the loading direction of perpendicular to the grain of the beam was done to study the failure mechanisms and load-bearing performances of the dowel joint of Japanese cedar beam.The research was conducted to provide basic data for the design of dowel joint at the end of the beam in the post and beam structure.【Method】After slotting and drilling at the end of the beam,a single dowel was connected to the slotted-in steel plates.The bending shear testing under load perpendicular to the grain was carried out on the Japanese cedar beam of sawn timber and glued laminated timber(glulam)in the same size,respectively.According to the general analysis method in Japan,standard percentile values of load-bearing in the short term of dowel joint in the beam were determined,and compared with the calculated values based on the yield load specified in 5 different national standards.【Result】In the initial loading,the load-displacement curve had a linear relationship in a linear elastic stage.As the displacement increased,the curve became nonlinear and entered the elastoplastic stage.When the displacement increased to a certain value,initial brittle cracking occurred at the end of the beam,and the load was suddenly reduced rapidly,and then the load rose again.When loaded to the limit state,the beam member split and lost its bearing capacity.Cracks along the horizontal shear plane of the pin hole in the beam component happened with yield modeⅢin the final failure.The standard percentile value in the short-term bearing capacity of the single dowel joint in the slotted-in steel plates at the end of beam of the sawn timber and glulam beams with a cross section of 120 mm×240 mm depended on the yield load,which was 8.6 kN and 13.7 kN,and the average load value corresponding to the initial cracking was 15.0 kN and 21.1 kN,the average yield load was 14.50 kN and 15.00 kN,and the average maximum load was 27.0 kN and 30.8 kN,respectively.【Conclusion】The average value of maximum load and the yield load of a single dowel connection of glulam beams was greater than that of the sawn timber beams,and the coefficient of variation was significantly smaller than that of the sawn timber.The moisture content of glulam beams was relatively low and less variation.The above reasons resulted in the standard value of pin joint load of glulam timber a little higher than that of sawn timber,i.e.a higher connection bearing capacity.When the dowels were used as the main type of connectors for post and beam components,glulam with certificated strength grades as the wood component might be preferable to sawn timber.The bearing capacity of the pin connection in the beam end had a good correlation with the bearing capacity of the single pin connection and the number of pins,which could be used as the design basis of the beam-column joints with metal connectors.The cracking of the wood after pin yielding occurred.The initial cracking depended on the shear strength or perpendicular tension strength of the wood and the pin hole position at the end of beam.After the initial cracking,the dowel could still play a supporting role,which kept the joint a good ductility.The standard percentile values of bearing capacity of sawn timber and glulam beam by test data had a good correspondence with the calculated value of the yield load formula specified in the several standards.The calculation formulas of brittle failure in the standards from various countries could predict the brittle failure of the pin connection.Compared with the testing values,the calculation values of the cleavage failure in the Japanese standard were closer,and the calculation results of the European and Canadian standards were more conservative.The brittle failure in the design of the wood connection in our current standard had not been considered fully.In the future,further research should be done related to the calculation formula and parameters of the dowel connection to better ensure the safety and reliability of the wood components connection.