PSI - Issue 77

Miloslav Kepka et al. / Procedia Structural Integrity 77 (2026) 272–278

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These spectra can be described by the following equation: = � 1 −� , , � � ∙ 0 0 - total number of harmonic cycles in the loading spectrum - cumulative number of loading cycles corresponding to the stress amplitude level , , - maximum stress amplitude in the loading spectrum ν - shape parameter (exponent) of the loading spectrum The parameter ν characterizes the nature of the loading process acting on the structure:

(1)

ν = ∞: loading with constant amplitude ν = 2: stationary random Gaussian process ν = 1: superposition of multiple random Gaussian processes An increase in the value of ν indicates a more severe (aggressive) loading spectrum, leading to earlier onset of fatigue damage. 4. Measuring campaign and its evaluation One of the principal objectives of the presented work was the derivation of a standardised load spectrum for the design and testing of welded joints in thin-walled body structures of city buses. The operational data employed were obtained through cooperation of the University of West Bohemia and Research and Testing Institute Pilsen Ltd., whose staff regularly participate in the measurement of operational loads on various types of buses. The data originated from measurements conducted in the cities of Pilsen and Bratislava on three types of vehicles (all of them trolleybuses): SKODA 27Tr: The tested articulated trolleybus is manufactured by Skoda Electric, which employs a body supplied by the Polish producer Solaris Bus & Coach. This 18-meter-long trolleybus may be equipped either with a battery system or with an auxiliary diesel engine. SKODA 36Tr: This is a single low-floor trolleybus produced by Skoda Electric, utilising a body manufactured by the Turkish company Temsa. The trolleybus is 12 meters in length and equipped with batteries that enable it to cover distances of up to 15 km without overhead traction lines. SKODA SOLARIS 24M: This articulated trolleybus was again developed in cooperation between Skoda Electric and Solaris Bus & Coach. It is distinguished by an unconventional design incorporating two articulation joints, which makes it possible to achieve an overall vehicle length of 24 meters. All measured vehicles are in the photos in Fig. 4.

Fig. 4. Measured vehicles.

In the bodywork of such vehicles, the most critical locations in terms of stress levels (and thus the risk of fatigue damage) are typically found in the areas of doors and windows. These regions were instrumented with strain gauges for the measurement of deformations. Measurements were routinely performed using dozens of strain gauges. For