Stress intensity factor for a tubular T-joint with grouted chord

The hot spot stress concentration factors (SCFs) for an as-welded tubular joint can be reduced by infilling the chord member with cementious grout, with associated improved fatigue strength for the grouted joint. However, inconsistent fatigue test results of grouted tubular joints are found in the published literature, which cannot be justified by hot spot stress approach. In order to obtain a better understanding for the fatigue performance of grouted tubular joints, a comprehensive fracture mechanics study is carried out for the reported fatigue test on as-welded tubular T-joint and another joint with grouted chord. The stress intensity factors (SIFs) of the two joints are determined by numerical method and then by empirical method. The SIF results are found to be consistent and in agreement of the fatigue test results. The presence of infilled grout in the chord is found to reduce the SCF, and lower the degree of bending (DOB). For tubular joints with weld toe fatigue cracking, the hot spot stress with lower DOB is associated with larger crack driving force and is more damaging than that with higher DOB. Hence, for fatigue assessment of grouted tubular joints it is essential to include the effect of DOB, which is ignored in hot spot stress S–N approach recommended in some current design codes.

► Fracture mechanics study is conducted on grouted and as-welded tubular T-joints. ► The stress intensity factors (SIFs) determined agree with the fatigue test results. ► Grouted T-joint has less stress concentration but lower degree of bending (DOB). ► The effect of low DOB should be considered for current hot spot stress S–N method.