Load combination effects on stress and strain concentration of completely overlapped tubular K(N)-joints

The stress and strain concentration of a completely overlapped tubular K(N) joint specimen under lap brace axial (AX), in-plane (IPB) and out-of-plane bending (OPB) is experimentally investigated. The combination effect of these loadings on the stress concentration of the joint is also studied. The test results showed that the maximum strain concentration factor of the joint under AX and OPB occurs at the saddle of through brace near the lap brace. For the joint under IPB, it occurs at the crown heel of lap brace. The peak hot spot stress (HSS) of the joint under combined loading is found occurred at a position between the crown and the saddle of members. A comparison of HSS showed that the equation proposed by Gulati et al. agrees reasonably well but the design recommendation, API RP2A, over predicts the test data. In the numerical analysis, the finite element model with 8-node thick shell element simulates very well the joint specimen. It is concluded that the existing equation for simple joints based on a superposition of stresses of basic load cases is suitable for predicting the stress concentration of completely overlapped tubular K(N)-joints under combined loading.