RIASSUNTO.Le piastre ortotrope sono state applicate ai ponti di grande luce a partire dal periodo immediatamente successivo alla Seconda Guerra mondiale a causa dei numerosi vantaggi che esse presentano, come il peso contenuto, l'elevata resistenza, il ridotto numero di connessioni con l'impalcato, la durabilità, la rapidità costruttiva e l'economia dovuta alla manutenzione durante il ciclo di vita. Lo studio della fatica nelle piastre ortotrope è iniziato circa venti anni fa, da quando sono state diagnosticate le prime rotture per fatica. Da allora sono stati condotti un vasto numero di studi e indagini, ottenendo risultati interessanti. Si è scoperto che la maggior parte delle rotture per fatica si verificano in corrispondenza delle connessioni saldate, ovvero le giunzioni rib-to-deck, rib-to-diaphragm, e rib-to-diaphragm-to-deck (plate) (RDDP). Questa tipologia di connessioni è sensibile alla nascita di fratture per fatica dovute agli accumuli di tensione ed alle tensioni residue nelle connessioni saldate. In questo articolo viene presentato e analizzato un caso studio di rottura a fatica nelle connessioni saldate, dove è più probabile una frattura, attraverso una modellazione numerica di una piastra ortotropa con un software ad elementi finiti (FE). Inoltre viene affrontato il tema del miglioramento delle tecnologie adottate per limitare i problemi di fatica. I risultati di queste analisi possono rappresentare un proficuo contributo per la progettazione a fatica delle piastre ortotrope.ABSTRACT. Orthotropic decks were applied to the long span bridges after World War II due to several advantages, such as light weight, high strength, few deck joints, durability, rapid construction, life-cycle economy. The fatigue problem of orthotropic decks was realized twenty years ago since fatigue failure was found. In the past two decades large amount of studies and investigations were carried out and fruitful achievements were obtained. It was found that most of the fatigue cracks were occurred at the welded connection details, such as rib-to-deck plate, rib-to-diaphragm, and rib-to-diaphragm-to-deck plate (RDDP). These connections are sensitive to fatigue cracking due to high concentrated stress and residual stress at welded connections. In this paper practical fatigue failure cases at the welded connections, ease to occur fatigue cracking, are presented, and analyzed through a numerical modeling of orthotropic deck via FE (finite element) software. Furthermore, the improvement technologies of fatigue are also discussed. The results of the analysis can be contributed to the evaluation of the fatigue design for the orthotropic deck.

The hydroplaning propensity on the steel bridge deck pavement (SBDP) is higher than ordinary road pavements. In this study, the objective is to develop a hydroplaning model to evaluate the hydroplaning behaviors for SBDPs. To achieve this goal, a finite element (FE) model of a 3D-patterned radial tire model was developed at first, and the grounding characteristics of tire on the SBDP were calculated as an initial condition for the follow-up hydroplaning analysis. The X-ray CT scanning device and Ostu thresholding method were used for image processing of pavement surface topography, and the 3D FE model of SBDP was established by the reverse stereological theory and voxel modeling technique, which can accurately reconstruct the pavement morphology. A fluid model was established to simulate the dynamic characteristics of water film between the tire and SBDP. On this basis, the tire–fluid–pavement interaction model was developed based on the CEL (Couple Eulerian–Lagrangian) algorithm, and it was verified by the hydroplaning empirical equations. Finally, the hydroplaning behaviors on the SBDP were studied. The findings from this study can provide a tool for hydroplaning evaluation on SBDPs, and will be helpful to improve the driving safety of SBDP in rainy days.

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