Fatigue behavior of very high strength (VHS) circular steel tube to plate T-joints under in-plane bending

• We study the fatigue behavior of VHS steel tubes to plate T-joints under in-plane bending.
• Stress concentration factors were obtained through linear extrapolation at the weld toe.
• The fatigue life of the T-joints was determined using the hot spot stress approach.
• VHS tubes showed better fatigue life than cold formed CHS T-joints.

This paper investigated the fatigue behavior of very high strength (VHS) steel tubes (t<2 mm) to steel plate T-joints under cyclic in-plane bending. VHS tubes, with a yield stress of 1350 MPa and an ultimate tensile strength of 1500 MPa, were welded to G350 steel plates using the GTAW welding method. Three different failure modes were observed. Stress concentration factors (SCFs) ranging from 1.2 to 2.2 were obtained through linear extrapolation at the weld toe. The fatigue life of VHS (t<2 mm) to plate T-joints subject to in-plane bending was determined using the hot spot stress approach with a stress concentration factor SCF=2.0 and the existing fatigue design equation in CIDECT Design guide No. 8. VHS tubes (t<2 mm) showed better fatigue life than cold formed CHS (2 mm≤t<4 mm) to plate T-joints when welded to plates and loaded under in-plane bending. A class of 102 was proposed for fatigue design of VHS-plate T-joints under in-plane bending based on the current steel design standards.