Fatigue experiments on very high strength steel base material and transverse butt welds

Very High Strength Steels (VHSS) with nominal strengths up to 1100 MPa have been available on the market for many years. However, the use of these steels in the civil engineering industry is still uncommon, due to lack of design and fabrication knowledge and therefore limited inclusion in codes. Moreover, in a fatigue loaded VHSS structure absolute and relative stress variation will be higher compared to stresses in structures made of lower grade steels. According to current design codes the fatigue strength of welded connections mainly depends on the applied detail, plate thickness and machining condition, not on steel grade. Recently experiments on plates made of S690 and S1100, with and without transverse butt welds, have been performed in order to study the fatigue strength. Test results show that the characteristic fatigue strengths of plates with and without transverse butt weld lay well above the values according to EN 1993-1-9, mainly because of higher slope of the S-N curves. Crack initiation phase of S1100 specimens is relatively long compared to S690 specimens, while crack propagation is relatively short. An efficient application of VHSS in welded connections requires high fabrication quality and avoidance of large stress concentration in joints.