Several failures of recurved concrete crownwalls have been observed in recent years. This work aims to get a better insight within the processes underlying the loading phase of these structures due to non-breaking wave impulsive loading conditions and to identify the dominant failure modes. The investigation is carried out through an offline one-way coupling of computational fluid dynamics (CFD) generated wave pressure time series and a time-varying structural Finite Element Analysis. The recent failure of the Civitavecchia (Italy) recurved parapet is adopted as an explanatory case study. Modal analysis aimed to identify the main modal parameters such as natural frequencies, modal masses and modal shapes is firstly performed to comprehensively describe the dynamic response of the investigated structure. Following, the CFD generated pressure field time-series is applied to linear and non-linear finite element model, the developed maximum stresses and the development of cracks are properly captured in both models. Three non-linear analyses are performed in order to investigate the performance of the crownwall concrete class. Starting with higher quality concrete class, it is decreased until the formation of cracks is reached under the action of the same regular wave condition. It is indeed shown that the concrete quality plays a dominant role for the survivability of the structure, even allowing the design of a recurved concrete parapet without reinforcing steel bars.@en

Jack-ups are mobile structures widely employed in the offshore industry as drilling rigs or installation/maintenance vessels (e.g. for offshore wind farms). To assure safety at each location, site-specific assessment is required to predict the performance of the unit during installation and operations. The response of jack-ups to environmental loads is highly affected by the interaction between all footings (spudcans) and the underlying soil, an interaction still challenging to describe under general 3D loading. This work emphasises the potential of 3D continuum simulations to capture non-linear soil-structural interaction in jack-up units. An integrated jack-up–spudcans-soil 3D finite element (FE) model is set up by including strain-hardening soil plasticity and geometrical non-linearity (P−Δ effects). After preliminary calibration of soil parameters, the FE model is successfully validated against literature results, namely obtained through (i) small-scale centrifuge experiments and (ii) numerical simulations based on macroelement foundation modelling. The validated FE model is then used to inspect several implications of soil modelling assumptions, as well as the response of the jack-up to relevant 3D loading combinations. The results presented support 3D continuum modelling as a suitable approach to analyse spudcan fixity and, overall, the operational performance of jack-ups. Despite higher conceptual/computational difficulties, fully 3D simulations can valuably complement the insight from (rare) integrated physical modelling, and contribute to the improvement of soil-spudcan macroelement models.

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