腹杆节间间距对平行弦木桁架承载性能的影响

研究腹杆节间间距对平行弦木桁架承载性能的影响，控制融余强度，形成平行弦木桁架强度及质量控制的理论支撑。采用Smsolve结构力学求解器对桁架进行内力分析，并对构件进行承载能力与稳定性验算，得到桁架腹杆节间间距临界值。采用静力加载方式，对平行弦木桁架挠度、轴向应变以及破坏形式进行测试，对2种工况模拟变形趋势与试验结果进行对比分析。结果表明，腹杆节间间距0 mm与65 mm的桁架，极限荷载平均值分别是设计荷载的5.26倍和3.49倍，均满足设计要求，且节间间距0 mm桁架的承载力高于节间间距65 mm桁架，2种桁架变异系数均较小，表现出较小的离散性。当达到极限荷载时，2种工况的跨中挠度值相差不大；节间间距0 mm桁架，跨中与两加载点处挠度值相差不大，变形较小；节间间距65 mm桁架，跨中与两加载点处挠度值相差1.5倍，此工况试件极限荷载均超过3倍设计荷载，满足规范设计要求。比较2种工况下桁架变形形式，可以看出节间间距0 mm桁架整体变形较小，有较高的承载能力。试验证明桁架破坏形式主要为节点齿板拔出，而导致桁架失效，破坏位置主要出现在两侧端部、跨中、加载点下端节点位置，与模型分析相一致。分析认为平行弦木桁架有较好的强度储备，在满足构件承载能力、稳定性的情况下，腹杆节间间距可在65 mm范围内进行调节，桁架失效主要发生在齿板连接节点处。

Influence of the Spacing between Webs on the Bearing Capacity of Parallel String Truss

The influence of web spacing on the bearing capacity of parallel chord wood truss was studied to find out the theoretical support for the strength and quality control of parallel chord wood truss by controlling the residual strength.Smsolve structural mechanics solver was used to analyze the internal force of the truss,and the bearing capacity and stability of the members were checked to get the critical value of the spacing between the webs of the truss.The deflection,axial strain and failure modes of parallel chord wood truss were tested by static loading method.The deformation trends of the two conditions were compared with the test results.The results demonstrated that the average ultimate loads of the truss with 0 mm and 65 mm web spacing were 5.26 times and 3.49 times of the design load,respectively.The bearing capacity of the truss with 0 mm web spacing was higher than that of the truss with 65 mm web spacing.The variation coefficients of the two trusses were small and showed small dispersion.When the ultimate load was reached,the mid-span deflection values of the two working conditions were not very different;the mid-span deflection values of the truss with 0 mm inter-node spacing were not very different from those of the two loading points,and the deformation was small;the mid-span deflection values of the truss with 65 mm inter-node spacing were 1.5 times different from those of the mid-span and the two loading points,and the ultimate load of the specimens under this working condition was more than 3 times of the design load,which met the design requirements.Comparing the deformation forms of the truss under the two working conditions,it could be seen that the overall deformation of the truss with 0 mm inter-node spacing was smaller and had higher bearing capacity.The test proved that the main failure mode of truss was pulling out the tooth plate of the joint,leading to the failure of the truss.The failure location mainly occurred at the end of both sides,the middle span and the lower end of the loading point,which was consistent with the model analysis.The analysis showed that parallel chord wood truss had better strength reserve.Under the condition of satisfying the load-bearing capacity and stability of components,the spacing between web members could be adjusted in the range of 65 mm.The failure of the truss mainly occurred at the joints of the teeth plate.