Strength of DT Tubular Joints with Brace and Chord Compression

The effects of chord axial compressive stress on the ultimate strength of a DT joint subjected to brace compression have been studied both experimentally and numerically. Three experimental load cases were considered, one with brace compression only and the other two with different chord axial stress. Two methods were used in the numerical work to apply the chord and brace loadings: (1) Proportional loading; and (2) nonproportional loading. The former method was adopted in the experimental work. The results confirmed that the ultimate strength of DT joints can be reduced significantly when chord axial stress is present. Nonlinear finite-element (FE) analysis on the joints was found to overestimate ultimate loads, especially for high chord loads. A comparison between the current results and the API design rules has shown that, even with the two safety factors removed, the API equation gives ultimate brace compression loads that are conservative up to chord utilization values of ∼0.5.