High strength steel (HSS) is commonly available in the form of steel plates. The built-up box tube with sharp corners which is welded from four steel plates is usually fabricated for construction. The stress concentration factor (SCF) is crucial for the determination of the hot spot stress range which governs the high-cycle fatigue resistance of tubular joints. This paper presents experimental and finite element (FE) investigations on the SCF of HSS fabricated box X-joints. Four X-joints which are fabricated from built-up box tubes with a nominal yield stress of 890 MPa are tested under brace axial compression. The SCFs at typical hot spot locations are obtained using strip strain gauges. A FE model which has been validated against the test results is employed to conduct the parametric study on totally 112 fabricated box X-joints. The loading cases of brace and chord axial loading are covered. The effects of brace to chord width ratio, chord width to wall thickness ratio and brace to chord wall thickness ratio on the SCFs at the hot spot locations are revealed. The CIDECT SCF formulae are shown to be not suitable for the fabricated box X-joints under brace and chord axial loading. More accurate SCF equations are proposed to calculate the SCFs at the hot spot locations of the box X-joints.

高强度钢（HSS）通常以钢板形式获得。通常用建筑用的四块钢板焊接制成的带有尖角的组合式箱管。应力集中系数（SCF）对于确定热点应力范围至关重要，该范围决定着管接头的高周疲劳强度。本文介绍了HSS制成的箱形X形接头的SCF的实验和有限元（FE）研究。在支撑轴向压缩下测试了四个由标称屈服应力为890 MPa的组合式套管制成的X形接头。使用条形应变仪获得典型热点位置处的SCF。使用已针对测试结果进行验证的有限元模型对总共112个制造的箱形X接头进行了参数研究。涵盖了支撑和弦杆轴向载荷的载荷情况。揭示了支撑与弦宽之比，弦宽与壁厚之比以及支撑与弦壁厚之比对热点位置处的SCF的影响。CIDECT SCF公式显示不适合在支撑和弦轴向载荷下制造的箱形X形接头。提出了更精确的SCF方程来计算盒形X接头热点位置处的SCF。