Single sided welds are used widely in many areas around the world for brace-chord connection in tubular joints. Possible occurrence of crack initiators in the weld root where the weld inspection is very difficult is the main concern for fatigue design of single sided weld lines.
Conventional fatigue design for tubular joints is usually based on estimation of the stress concentration factors (SCFs) on the external weld toes using parametric equations, calculation of the associated hot spot stress and obtaining the fatigue damage ratio using S-N curves. For single sided welds there is a general understanding in engineering practice that the SCFs on internal weld roots are usually much less than those on the weld toes and hence there is no need to check the fatigue damage on the weld roots. Knowing that S-N curves are more onerous for the internal weld root, for areas with high SCF on the internal weld root or with the improved S-N curves on the external weld toe, more attention should be paid to possible fatigue crack initiation from the internal weld root.
This paper studies the ratio of SCF at the internal weld root to that at the external weld toe using existing parametric equations. Geometrical setups and loading conditions for the high ratio of internal to external SCFs are highlighted and sensitivity of the results to input parameters are discussed in detail.
In many areas around the world particularly in Gulf of Mexico, Far East and the Middle East, single sided welds have been used successfully as the principal method for brace to chord connection in tubular joints. In this method, brace edges in the brace-chord connection area are single beveled and then the brace is welded to the chord filling up the gap only through external surface of the brace. Typical weld details of a single sided weld around a brace-chord connection in a tubular joint are shown in Fig. 1.