PSI - Issue 57

Matthias Winkler et al. / Procedia Structural Integrity 57 (2024) 510–517 Matthias Winkler / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction Bridge cranes are used in most industrial companies and constitute a crucial link in the process chains of whole industries. The crane runway girders are exposed to cyclic loading due to the lifting of the hoist loads and the moving of the crane bridge. Therefore crane runway girders must be designed against fatigue failure. For new structures exist national design codes that codify the fatigue design e.g. with the nominal stress concept acc. EN 1993-6 ( EN 1993-6 , 2010) and EN 1993-1-9 ( EN 1993-1-9 , 2009). Beginning with the installation of the crane, the crane runway is in the regular use and has a design working life, for example 25 or 50 years. Within this time span it must be inspected to detect possible damages like loose bolts or fatigue cracks. The inspection intervals are dependent from the partial safety factor γ Mf that is used in the verification to reduce the fatigue resistance Δσ C of the investigated detail. However, after the end of the design working life the crane runway is in an unregulated phase due to missing standards that codify the handling of pre-damaged components. In Germany it is estimated that around 40% of new bridge cranes are installed on existing crane runways, many of them have probably exceeded their design working life (Seeßelberg, 2019). Therefore to help assessing pre-damaged welded connections of cyclically loaded steel components an research project (Dürr and Winkler, 2024) is carried out by the University of Applied Sciences Munich. In the course of this project several approaches regarding strengthening and repairing pre-damaged structural details are investigated. Next to post-weld treatments like grinding or hammer peening applied to pre-damaged or repaired weld seams, different application methods of steel cover plates like fitting bolts, lockbolts, adhesives and self-tapping screws are tested. In this publication the previous results of the work package “Strengthening of pre -damaged components without visible cracks ” will be presented. 2. Strengthening of pre-damaged components without visible cracks 2.1. Fatigue strenght-increasing post-weld treatments There are numerous post-weld treatments e.g. grinding and hammer peening that are proven to increase the fatigue strength of welded components. The treatments are normally applied to new constructions (as-welded condition). In the course of the research project (Dürr and Winkler, 2024) the efficacy of fatigue strength-increasing treatments used on pre-damaged components was investigated. In this chapter the procedures grinding and hammer peening that were experimentally investigated are briefly introduced. It should be noted that both methods are only applicable to structural details where root cracks can be excluded, see Figure 1, and that the improvement factors in the IIW recommendations and the prEN-standard are only applicable to new structures in the as-welded condition.

Figure 1. Suited and unsuited constructional details for post-weld treatments like grinding or hammer peening

2.1.1. Grinding By grinding the critical material in the vicinity of the weld toe is removed. For this purpose angle and burr grinder can be used. With this treatment the notch radius at the weld toe is enlarged resulting in lower notch stresses and thus a higher fatigue resistance of the welded connection. The positive effect of grinding the weld toe is considered in the IIW-recommendation (Hobbacher, 2016) with an improvement factor of 1.3 and a maximum possible FAT class of 112 (nominal stress concept).