PSI - Issue 78

Riccardo Maurizio Ambrogio Baltrocchi et al. / Procedia Structural Integrity 78 (2026) 9–16

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2.3. Numerical Analyses

A series of analyses, both linear and nonlinear, are performed with Straus7 on all configurations. In particular: • Linear Static Analysis (LSA) • Natural Frequency Analysis (NFA) • Spectral Response Analysis (SRA) • Sectional Analysis • Non-Linear Time-History Analysis (NLTHA) • Incremental Dynamic Analysis (IDA). All analyses are performed on the elements, taking into account the loads and material properties described above, for a total of 340 analyses. The results of each analysis are presented and discussed below, highlighting the main aspects of each element in all the configurations considered, both coupled and uncoupled, and linear and non-linear. The maximum span bending moment M Ed of each structural element in seismic load combination (EC0, § 6.5.3) is calculated for both elements. The value associated to the Ondal member is 956.64 kNm; the value associated with the beam is 5612.16 kNm. 3.2. Natural Frequency Analysis The NFA is used to calculate the natural frequencies and corresponding vibration modes of the structure (G+D Computing, 2010), obtaining periods and participant mass factors m p associated with the main modes of vibration. For uncoupled elements, the first 15 modes are considered, but only the fundamental period is later used. For coupled systems, the first 30 modes are determined. In particular, the Ondal member and the I-shaped beam have similar fundamental period values of 0.400 s and 0.383 s, associated to m p of 84.21% and 92.38%, respectively. Thus, it is noted that there may be design conditions with very similar first-mode periods between the beam and the Ondal member. The identified periods are close, suggesting a possible dynamic interaction effect. This dynamic interaction is indeed confirmed by analyzing the coupled configuration, where all the members are modelled with half span due to symmetry. In this case, not only the first, but also the following modes have non negligible values of m p , exceeding 5%. The deformed shape for the coupled configuration for modes 1, 5 and 26, i.e. those with non-negligible m p , are shown in Fig. 2. The first natural mode involves the in-phase oscillation of beam and roof elements along the span (Fig. 2a), while those at the supports remain stationary, with a period of 0.54 s; subsequently, the 5 th mode is local with the oscillation of the Ondal members at the supports (Fig. 2b), while mode 26 relates to the out-of-phase oscillation of beam and roof elements along the span (Fig. 2c). 3. Results and Discussion 3.1. Linear Static Analysis

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Fig. 2. NFA results – coupled configuration: (a) mode 1, (b) mode 5 and (c) mode 26.