The increasing requirements for welded constructions in terms of lightweight-design enforce the use of high-strength materials and computer aided engineering. As a starting point for the dimensioning of a new construction variant, a precise knowledge of the occurring stresses during operation is required. An essential part of the present work is dedicated to the development of a methodology for a determination of occurring, complex and time-variable operating loads, based on experimental measurements and numerical stress analysis. For this purpose, the local stress state of an existing crane structure is investigated and verified experimentally by strain gauges and measured at six defined positions in real operation of the forestry device. For further calculation of the initiated forces at the end of a crane, an approach based on Moore-Penrose-inverse is used. Therefore, divided into three basic load cases, a nominal load was applied at all technically possible cylinder positions. Determined by numerical analysis, the nominal stress values at the measurement positions were evaluated. A script which calculates the applied forces using the Moore-Penrose-inverse and the recorded measurement data was created, thereby featuring an automated calculation of the transient loading forces. Previous studies have shown the potential of high-frequency peening methods (HFMI) as fatigue enhancing post-treatment in lightweight welded steel designs. A verification of this technique is performed based on fatigue tests of welded and HFMI-treated, high-strength steel specimen. Due to variable block testing and a calculation of the equivalent local stress, a significant influence of the load spectrum is evaluated on the life cycle span. Finally, a life time calculation of a selected detail of the investigated forest crane design is performed in consideration of HFMI-treatment. In this case, the beneficial applicability of the presented methodology is shown, whereby a service strength improved lightweight design of crane structures is obtainable.