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

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.