PSI - Issue 28

Pedro Andrade et al. / Procedia Structural Integrity 28 (2020) 279–286 P. Andrade et al. / Structural Integrity Procedia 00 (2019) 000–000

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2.2. Walking tests The sample staircase, as can be observed from Table 1, has a fundamental frequency equal to 13.9 Hz, which is lower than the cut-off frequency of 16 Hz suggested by Andrade et al. (2017a) and Santos et al. (2019) and, therefore, with a possibility of resonance effects to occur. Considering that pedestrians walk on staircases with step frequencies ranging approximately from 2.0 to 4.5 Hz (Bishop et al. (1995), Davis et al. (2009) and Kasperski & Czwikla (2012)), ascending and descending at 3.5 Hz (4 th sub-multiple of the staircase fundamental) could generate a resonant build up and amplify the staircase response. However, the objective of this study is to compare the Direct Integration and Modal Superposition when computing human induced vibrations, the two different time domain analysis methods being comparable in the same basis, regardless the staircase responses. Hence, walking tests and vibration measurements were performed for step frequencies more commonly used by pedestrians in their daily routines, i.e. ascents at 2.0 Hz.

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Fig. 1. Flight of steps: (a) real staircase; (b) FE staircase model.

Table 1 – Experimental and numerical vibration modes. Modes Experimental Numerical Nº Shape Frequency (Hz) Frequency (Hz) 1 Vertical 13.9 13.9 2 Vertical 14.5 14.9 3 Torsion 20.9 23.4 4 Torsion 21.9 26.5 5 Torsion 22.4 27.1 6 Torsion 23.2 29.3