Effect of Brace-to-Chord Angle on Performance of Unstiffened Circular Hollow Section X-Joints under Brace Axial Force
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摘要: 为了研究支主管夹角对X形圆钢管相贯节点轴向受力性能的影响，进行相关试验来校验有限元模型，以有限元为手段分析了支主管夹角对X形节点在支管轴力作用下的传力特性和承载力的影响；根据有限元参数分析结果，对支主管夹角较小的节点的承载力提出了改进建议. 研究结果表明：节点试件的破坏模式为相贯线附近主管管壁局部屈曲；当支主管非正交但夹角大于60° 时，节点的传力特性与支主管正交节点的相近，符合Togo模型的假定，现行规范中的夹角正弦的倒数项能精准地反映夹角对节点承载力的影响；但当节点的支主管夹角小于45° 时，其传力特性与Togo模型的假定有较大的差异，夹角正弦的倒数也低估了支主管夹角对节点承载力的提高，对于夹角接近30° 的节点甚至低估了30%；因此建议当夹角小于45° 时，在规范已有的节点承载力计算式的基础上乘以修正系数.Abstract: In order to study the effect of brace-to-chord angle (BCA) on the performance of unstiffened circular hollow section (CHS) X-joints under brace axial force, experimental test was carried out to verified finite element (FE) model. Then FE parameter analysis were used to study the effect of BCA on the stress transfer and bearing capacity of the X-joints under brace axial force, and the capacity prediction accuracy of the X-joints with small BCA was improved. The results show that the failure pattern of test is local buckling of chord wall near brace-to-chord intersection. The incline X-joints (brace-to-chord non-orthogonal) with BCA greater than 60° have the similar stress transfer characteristic to that of the brace-to-chord orthogonal X-joints, which is consistent with the assumption of the Togo model. Moreover, the reciprocal of the sine of BCA (RSBCA) in the current specification can accurately reflect the influence of BCA on the capacity. However, the stress transfer characteristics of the incline X-joints with BCA less than 45° are quite different from the assumption of the Togo model, and RSBCA underestimates the beneficial effect of BCA on the capacity of these X-joints (even 30% for the X-joint with BCA near to 30°). Hence, it is recommended to multiply a correction coefficient on the existing capacity prediction formula of these CHS X-joints with BCA less than 45°, to improve the prediction accuracy.
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图 5 有限元和试验所得轴力-局部变形对比
Figure 5. Brace compression-local deformation comparison between test and FE results
图 7 支主管夹角对节点传力的影响
Figure 7. Effect of brace-to-chord angel on the load transfer under brace axial force
图 9 支主管非正交对节点轴压承载力的影响
Figure 9. Effect of brace-to-chord non-perpendicularity on the capacity of CHS X-joints under brace compression
表 1 试件的几何特征
Table 1. Geometry of the specimen
试件 D/mm d/mm T/mm t/mm β γ τ θ/(°) XPA 244.6 202.8 8.0 6.8 0.83 15.3 0.85 90 
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表 2 钢管材性试验结果（平均值）
Table 2. Test results of steel tubing properties (average value)
钢管直径（壁厚）/mm fy/MPa fu/MPa E/GPa ζ/% 244.6（8.0） 375.3 545.1 209 32.7 202.8（6.8） 372.1 550.3 213 31.3
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表 3 θ
对节点受压承载力的影响 Table 3. Effect of θ on the Puc
项目 90° 75° 60° 45° 30° Puc/kN 419.9 441.3 516.4 671.3 1013.2 Pucsin θ/kN 419.9 426.3 447.2 474.7 506.6 Pucsin θ/Puc90 1.00 1.01 1.06 1.13 1.21
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表 4 θ对ηt的影响
Table 4. Effect of θ on the ratio ηt
D/mm fy/MPa β γ θ/（°） Put/kN ηt 245 375 0.83 15.3 75 901.1 1.04 245 375 0.83 15.3 60 1016.4 1.05 245 375 0.83 15.3 45 1291.3 1.09 245 375 0.83 15.3 30 1860.5 1.12 250 345 0.90 10.0 75 2646.2 0.96 250 345 0.90 20.0 45 1491.1 0.98 250 345 0.90 40.0 30 932.2 1.11 250 345 0.70 10.0 45 1891.7 1.12 250 345 0.70 20.0 30 1062.8 1.34 250 345 0.70 40.0 75 107.6 1.03 250 345 0.40 10.0 30 1650.6 1.27 250 345 0.40 20.0 75 202.9 1.01 250 345 0.40 40.0 45 106.2 1.00
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