接头偏移对弧形管桁架结构受力性能的影响研究

Research on the Effect of Joint Deviation on the Mechanical Performance of Arc-Shaped Tubular Truss

在空间管桁架结构中,施工时为避免弦杆杆件连接接头与腹杆的相贯节点重合导致焊缝集中,常采用将弦杆接头按需要进行偏移的施工方法。当结构中存在不同曲率的弧段时,接头偏移将导致结构局部发生改变,与设计模型产生偏差,且会影响变曲率弧形管桁架的受力性能。为探究接头偏移对弧形管桁架结构受力性能的具体影响,选择实际工程项目模型,按照常用施工方案对弦杆接头部分进行偏移处理,并计算对比偏移前后模型的受力情况。选择结构中不同位置、具有代表性的两榀桁架模型进行分析,在弧段曲率改变处选择合适的杆件,根据腹杆相贯情况,计算理论最小偏移量,并添加安全距离,取整得到接头处实际最小偏移量。分别按照最小偏移量、2倍最小偏移量、3倍最小偏移量调整原模型,并考察在自重工况和最不利组合工况下接头处上下弦杆、腹杆和接头相邻弦杆的轴力、弯矩、应力情况。结果表明:杆件轴力主要受整体结构设计和杆件截面的影响,不因接头偏移产生明显改变;接头两端弧段曲率不同时,当接头偏移后,其位置与杆件原位置产生偏心距,导致接头两端杆件所受轴力在此产生弯矩,使接头处弦杆受到的弯矩增加;在轴力无显著变化的情况下,弯矩增加,杆件应力对应增大;最小偏移量时,杆件弯矩增幅最高可达200%,应力可增加10%~15%;3倍最小偏移量时,接头处弦杆的应力在自重工况下增幅达到70%,最不利组合工况下增幅达到100%;偏心增大时,弦杆弯矩大幅提升,在3倍最小偏移量时,接头处个别弦杆应力比超过1,此时对应的接头偏移导致的偏心距为0.15~0.3 m,且在各种工况下,该危险杆件的应力都有明显增幅,在最不利荷载组合工况下有破坏危险。得到结论:1)接头偏移对变曲率弧形管桁架结构杆件轴力无明显影响;2)弯矩随接头偏移带来的偏心距的增加大幅增大;3)轴力与弯矩共同作用下,接头偏移使杆件应力对应增大,对整体结构造成安全隐患。施工时应对实际弦杆接头偏移情况进行验算或在设计阶段考虑接头偏移影响,消除结构的潜在危险。

In spatial tubular truss structure,in order to avoid the concentration of weld seams caused by truss chord connections and tubular nodes,the construction method of joint deviation is often used.When segments with different arc curvature exist,joint deviation leads to local changes of the structure and difference from the designed model,which will affect the mechanical performance of the tubular truss with variable arc curvature.To explore the specific influence of joint deviation on the mechanical performance of arc-shaped tubular truss structure,a practical engineering project model is selected,deviation to the chord joint according to the common construction plan is applied,the force of the model before and after the deviation is calculated and compared.Specifically,two representative truss parts at different positions in the structure are analyzed.According to the intersection of diagonal members,the theoretical minimum offset of the appropriate members where the arc curvature changes is calculated.The actual minimum offset at the joint is decided with safety distance and rounded.The model is adjusted to the minimum offset,two times minimum offset,and three times minimum offset respectively.The axial force,bending moment,and stress of upper and lower chord members,diagonal members and the adjacent chord members at the joint are compared under self-weight load condition and the most unfavorable load condition.The results showed that the axial force of the member was mainly affected by the overall structure design and its cross section,which was not obviously affected by the joint offset.The offset of the joint deviation generates eccentricity between the members at the joint with different arc curvature compared to the designed tubular truss model.The eccentricity caused the axial force on the members at both ends of the joint to generate a bending moment,which would increase the bending moment of the chord members at the joint.When the axial force did not change significantly,the bending moment increased,the stress of the member increased correspondingly.With the minimum offset,the bending moment of the chord members at the joint could increase up to 200%and the stress could increase by 10%-15%.With three times minimum offset,the stress of the chord members at the joint would increase by 70%under the self-weight load condition,and 100%under the most unfavorable load condition.When the eccentricity increased,the bending moment of the members at the joint also increased greatly.At three times minimum offset,the stress ratio of some chord members at the joint exceeded 1,and corresponding joint deviation resulted in an eccentricity of 0.15-0.3 m.Under various working load conditions,the stress of the member increased significantly,which might cause damage under the most unfavorable load condition.The conclusions are as follows:1)the joint offset has no obvious effect on the axial force of the members in the structure;2)bending moment increases greatly with the increase of eccentricity caused by joint offset;3)under the joint action of axial force and bending moment,the joint offset increases the stress correspondingly,causing hidden dangers to the overall structure.During construction,the deviation of the actual chord joint should be checked or the influence of the joint deviation should be considered in the design stage to eliminate the potential danger of the structure.