PSI - Issue 78

Noemi Di Rienzo et al. / Procedia Structural Integrity 78 (2026) 1474–1481

1475

1. Introduction The network of reinforced concrete bridges constructed in the aftermath of World War II continues to support a significant share of vehicle and rail traffic in Europe and around the world. Following several decades of utilisation, these structures are now suffering from increasing degradation phenomena and nowadays are certainly subject to levels of stress higher than those for which they were conceived. This critical scenario, also associated with changed structural demand, has led to several collapses in recent years (Zhang et al., 2022), highlighting the urgent need for rapid assessment methods capable of directing resources to structures that require in-depth investigations or priority interventions. Within this framework, Experimental Modal Analysis (EMA) and, even more, Operational Modal Analysis (OMA) have become widely utilised methodologies for fast identification of the global dynamic properties of bridges. The primary benefit of the latter approach is the rapidity and low level of service disruption with which a global assessment of the structure can be obtained. The main output of EMA/OMA, i.e., natural frequencies and modal shapes, is fundamental for calibration of numerical models, health assessment, and can potentially represent a starting point for the development of large-scale approaches to fragility estimation of structure stocks. In this context, predictive empirical formulations based on limited set of parameters could be particularly useful. The present study analyses seventeen simply supported or continuous ordinary or prestressed reinforced concrete bridges, whose characteristics in terms of experimental modal shapes and frequencies are reported in the literature. Hybrid analytical-empirical formulations for the first frequencies related to flexural vertical modes of the decks are developed showing that simplified modelling of the structure provides robust and reliable values that can then be used for assessment. 2. The literature dataset The bridges analysed in this study are seventeen cases for which vibrational modes and frequencies were estimated based on OMA or EMA. The structures examined belong to different international geographic contexts, including bridges located in Italy, United States, Tunisia, India, United Kingdom, South Korea, Spain and Iran, thus providing a representative overview of the different design and construction solutions adopted in the road and rail infrastructure sector. The dataset sources are outlined in Table 1. This table details the main geometric and mechanical characteristics (static scheme, number of spans, total length TL , span length SL , deck width DW , and total deck - including girders and slab - cross-sectional area A , as well as its second moment of area I and the elastic modulus of the concrete E ), in addition to the experimental natural frequencies ( f OMA ) related to the first and second vertical flexural modes (Fig. 1) experimentally identified. It is worth noticing that, where available, the values of elastic module reported in Table 1 were obtained from direct (e.g. compressive tests on core samples) or indirect (e.g. sonic and ultrasonic tests) measurements, or design data. On the contrary, if this information was missing, the field was left empty. Also, for continuous decks, the span lengths of all the spans are reported in the table.

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Fig. 1. First two modes for (a) simply supported, and (b) three-support beams.