Influence of the base Material Strength and Edge Preparation on the Fatigue Strength of the Structures Made by High and Ultra-high Strength Steels

In recent years the high and ultra-high strength steels have been developed and applied for light-weight constructions such as the structural members of mobile equipment in order to reduce weight and fabrication costs as well as to contribute to the performance. In many applications, especially in the use of ultra-high strength steels, the welds are tended to locate outside of the highly stressed regions and use the post weld improvement for the critical welds. This means that the non-welded sections are in load-carrying positions and have to take into the consideration in the design of the structures.Novel test results have shown that the fatigue strength of the base material increases by increasing the yield strength of steel and the maximum fatigue class in the design codes FAT 160 and a slope, m=5, is conservative when the yield strength of steel is equal and higher than 355 N/mm2. Only standard EN 13001-3-1:2012 allows applying for the higher fatigue classes by increasing the yield strength in cranes.In this paper the fatigue test results from high and ultra-high strength strip rolled steels are presented and compared with the fatigue classes in standard EN 13001-3-1:2012. Also a cross-member brace connection to main chord flange in vehicle chassis is presented as a design example.