FATIGUE-STRENGTH OF WEATHERING STRUCTURAL -STEELS AFTER MANY GEARS OFATMOSPHERIC EXPOSURE

Objective. Weathering structural steels, which in bare condition displ ay elevated resistance to atmospheric corrosion compared with unalloye d steels, are used preferably in steel structures and, in particular, in bridge construction as they present economic and maintenance-relate d advantages. However, there have been concerns that their fatigue str ength might be diminished because of the corrosion process. Thus arose the task of gathering quantitative data concerning the relationship b etween fatigue strength and the influence of long-term weathering. Sum mary. In a cooperative effort between four German steel companies and Fraunhofer-Institut fur Betriebsfestig- keit (LBF) in Darmstadt, the f atigue behaviour of test pieces of general-purpose structural steel S3 55J2G3 (St 52-3) and weathering structural steel S355J2G1W (WTSt 52-3) exposed atmospherically at two industrial locations for up to 20 year s was determined as a function of the test piece form (non-welded, wel ded) and duration of exposure. The fatigue strength of the non-welded test pieces decreases by as much as 30 % within a two-year atmospheric exposure period (and by as much as 35 % over exposure periods up to 2 0 years), in which respect the weathering structural steel has at all times exhibited less corrosion than the general-purpose structural ste el. The fatigue behaviour of welded test pieces is more important for the dimensional design of components. The stress permissible for shape d elements such as butt-joints and transverse stiffeners remains indep endent of the duration of atmospheric exposure. The reason for this is that the influence of the corrosion is masked by the fatigue-strength -diminishing effect of the undercuts made during welding. The results of the research help to provide robuster calculations for structures b uilt of weathering structural steel, including cases involving alterna ting stress. The current rules on approval and dimensional design do n ot uniformly and adequately take account of the fatigue behaviour as a function of the exposure duration.