Numerical analysis on dynamic stress and vibration for tubular joints of welded steel pipes under axial loads

Reported researches rarely focus on dynamic stress concentration factors (SCF) of tubular joints between the chord and brace, where the chord is a square pipe, and the brace is a circular pipe. Tubular joints between a square pipe and circular pipe are widely applied in spatial structures as a support structure. Therefore, tubular joints of welded steel pipes under axial loads were studied numerically for determination of dynamic stress concentration factors (SCF). Finite element models were setup for a total of 165 tubular joints with various configurations, obtaining dynamic stress distributions of each model along the joint. Dynamic stress concentration factors on the brace and the chord were extracted respectively. Relations between sizes of dynamic stress concentration factors between the joint and structural parameters were discussed. The computational model was finally validated by the experimental test. The experimental curve was basically consistent with the finite element at the elastic stage of loading, indicating that the computational model at the elastic stage was very accurate. The paper mainly studied dynamic stress distribution of the tubular joint of welded steel pipes under an excitation load at the elastic stage, so the finite element model could be used to replace experimental test. SCF was 180° symmetric under different parameters. This angle was located at the crown point of tubular joints, while the welded steel pipe structure was a symmetric structure relative to the longitudinal plane. In addition, the chord and brace had SCF peaks at the angles of 90° and 270° because the two points were located at the saddle point of the tubular joints. Under angles of 0° and 180°, the SCF had obvious valley values because the two points were located at crown points of tubular joints. Finally, the vibration performance of the tubular joint was also analyzed. Vibration displacement could be reduced obviously through reinforcement of tubular joints with the collar plates. Axial pre-tensile forces would increase vibration displacement on top and bottom positions of the chord pipe. This paper can provide an important reference for the improvement of the dynamic stress concentration of joints of welded steel pipes.