FATIGUE LIFE ASSESSMENT OF INCLINED WELDED JOINTS IN STEEL BRIDGES SUBJECTED TO COMBINED NORMAL AND SHEAR STRESSES

The paper presents fatigue life assessment of inclined welded joints with a new geometric configuration in steel bridges. Fatigue tests on full penetration load-carrying fillet cruciform welded joints with inclination angles of 0 degrees, 15 degrees, 30 degrees, and 45 degrees subjected to uniaxial cyclic loading are performed. Hot spot normal and shear stress ranges are obtained by a linear extrapolation, and a sensitivity analysis is carried out to determine the appropriate mesh size. The fatigue life results predicted by the equivalent stress range method, DNV(Det Norske Veritas), Eurocode 3, and IIW(the International Institute of Welding) are compared with test results. The results show that the fatigue cracks in all of the specimens initiate at the weld toe but propagate in different directions. There are two cracking types: (a) cracking along the weld (theta=0 degrees, 15 degrees); (b) cracking perpendicular to the direction of the applied load (theta=30 degrees, 45 degrees). The fatigue life increases with an increase in the inclined angle due to a decrease in the normal stress range perpendicular to the weld. The fatigue life tends to be overpredicted by Eurocode 3 at the large inclination angle. The FAT90 used by DNV is more conservative than the FAT100 recommended by Eurocode 3 and IIW, so that the fatigue life is underestimated. It is concluded that the equivalent stress range method and IIW are in good agreement with the fatigue test results. The equivalent stress range method is more suitable to assess the fatigue life of inclined welded joints subjected to combined normal and shear stresses due to the ease of implementation and low computational cost. The fatigue design curve of FAT100 is recommended for the equivalent stress range method.