PSI - Issue 48

Nemanja Ilić et al. / Procedia Structural Integrity 48 (2023) 318 – 325 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction For decades the structural assessment of ship’s hull girder is performed in the elastic domain of the stress - strain curve. The structural response is evaluated upon the stress criterion, which is the portion of the yield limit of the material. Such approach considers the safety margin with respect to yielding (but not for overall collapse), according to the classification societies rules or other corresponding regulative in both sea-going and inland waterway vessels (IWV) sectors. Therefore, structural response in all loading conditions has to meet the criterion, see Motok et al. (2022). However, ships could undergo extreme events occurring once in a lifetime which might cause catastrophic failure such as, for instance: loss of the ship’s capacity, loss of the ship, environmental disaster, etc. This can be caused by excessive bending moments due to extreme waves, grounding, collisions, allisions or other excessive loading conditions unpredicted in the design phase. Therefore, it is of utmost importance to obtain the “so - called” ultimate strength of the ship’s hull gird er (or ultimate capacity, hull capacity). Ultimate strength is the maximum bending moment (ultimate bending moment) after which the ship hull is intended to experience structural collapse. There are numerous investigations in literature related to the ultimate strength of sea-going ships. Traditionally, ship structural integrity is assessed using classification societies’ prescribed rule -based procedures and additionally, direct calculations; for instance, ones from BV (2020) or LR (2020). Ultimate strength has been analysed with respect to random material and geometric properties, see Vhanmane and Bhattacharya (2011). A summary of factors influencing ultimate strength calculated using progressive collapse method is evaluated by Olmez and Bayraktarkatal (2016). Analysis of box beams ultimate strength considering impact is performed by Xu and Guedes Soares (2020). Also, effect of local corrosion on hull capacity was investigated, see Vu and Dong (2020). Nonetheless, methods for ultimate strength calculation and progressive collapse are systematically presented in Hughes and Paik (2010), Yao and Fujikibo (2016), Paik (2018), ISSC (2018). One of the methods used, a progressive collapse analysis (PCA), is already incorporated in regulative for the bulk carriers and oil tanker, see IACS (2022). However, there are no corresponding standards and regulations for IWV. Moreover, according to authors knowledge, no complete investigations are published regarding the IWV ultimate strength , except one delivered by Ilić and Momčilović (2023), performed for an inland container barge. This gap needs to be examined since there are numerous structural collapses encountered in EU inland navigation sector in recent years, due to grounding, lifting of the grounded vessels, overloading, etc. For more on IWV accidents review, see Bačkalov et al. (2021). Inland cargo vessels, especially ones operating on the Danube, generally tend to have large length to height and length to draught ratio, when compared to the sea-going vessels. Dimensions are, among other constraints, governed by the presence of the locks, breadth and depth of the river, distance between bridge and water level. Due to climate changes, these ratios are becoming more extreme since low water navigation becomes extended and thus, vessels need shallower draughts , see Momčilović (2021) . From the structural design point of view, large length compared to the reduced height directs towards the longitudinal strength issues and thus, reduced ultimate strength. Danube inland vessels have unusually large service life (up to 50, even 60 years) compared to sea-going ships (up to 25 years). Thus, age related degradation of the structure speeds up the potential collapse of the ship. The goal of this paper is to transfer the ultimate strength calculation practice from sea-going to the inland waterway sector, and moreover, to present the benchmark calculation results for typical inland cargo vessel navigating on Danube and Rhine. Ultimate strength here is evaluated using progressive collapse analysis (PCA) method. Such results are compared with the results obtained by some of the simplified approaches: first-yield, first-collapse and Paik - Mansour method. 2. The vessel Inland chemical tanker is chosen for the purpose of the analysis. The vessel has double hull and is longitudinally framed, except at the side, where transverse framing is produced. The width of the double side is 1000 mm. The height of the double bottom is in the range of 750 – 850 mm, going from center to side bottom girder. Web frame spacing is 1890 mm. All longitudinals are made of bulb profiles. Material of the structure is mild steel with modulus of elasticity and yield stress, respectively: 206000 N/mm 2 , 235 N/mm 2 . Simplified lateral plan and cross section of the vessel are illustrated in Fig. 1, while the vessel main particulars and element dimensions are given in Table 1 and Table 2.