ULTIMATE STRENGTH OF DOUBLE-TEE TUBULAR JOINTS: INTERACTION EFFECTS

Twenty-seven double-tee tubular joints were tested under branch axial compression, in-plane bending, and out-of-plane bending, and various combinations of these branch loads. These test results along with other test results were used to study the effect of the {dollar}beta{dollar} ratio on the interaction of branch loads in DT tubular joints. It was found that {dollar}beta{dollar} did have an effect on the joints' interaction behavior.; Comparison of an equation which accounted for {dollar}beta{dollar}, with other proposed equations, using a data base of 65 T and DT interaction tests, showed that the proposed equation was the most accurate however the accuracy of all three equations was very similar. Hoadley's equation provided a lower bound to the data, and is recommended for design based on its simplicity.; Results of replicate branch axial and OPB tests on {dollar}beta{dollar} = 1.0 joints indicated that the distance between the weld toes at the saddle points, or gap, has a significant effect on the behavior of {dollar}beta{dollar} = 1.0 joints. It was found that the compressive capacity of the joint can be predicted when the gap is treated as a column. Based on this analysis and because measurements showed a significant variation in the gap sizes on nominally identical joints, it is recommended that the variation in the gap be accounted for in the factor of safety applied to a mean design equation.; A simplified finite element model was developed to analyze the ultimate strength behavior of tubular joints to provide additional insight into joint behavior. Comparison of the results of the finite element analysis and the experimental data showed that the model is both accurate and economical.