Research Information System
INT-NAM 2014 2nd International Symposium on Naval Architecture and Maritime, İstanbul, Turkey, 23 - 24 October 2014, vol.1, no.1, pp.639-648
The estimation of the ship hull girder ultimate strengths under vertical bending moments as close to real behavior is vital both for design stage or seagoing life. It depends on a number of factors including the strength of the structural material, initial distortions, the dimensions and layout of the structural elements, the element discretization (idealization) of hull girder section and the tendency for local structure to buckle under compressive loading. In this study, the main target is investigation of the effect of hull girder section element discretization on ultimate hull girder strength estimation with using progressive collapse analysis-based HULT code developed by authors. In HULT, the load-end shortening curve relationships of structural members such as single plates, single stiffeners, plate-stiffener combination beam-column elements, stiffened panel elements and hard corner elements of hull girders under vertical bending moment have been determined by numerically, empirically and analytically. For these calculations "limit state design approach", "membrane stress approach", orthotropic panel approach" and the rules of IACS-CSR have been used. The stress-strain behaviors of initially deflected single plates, single stiffeners, plate-stiffener combination elements with different type and geometry and stiffened panel elements are obtained by von-Karman & Marguerre plate equations, IACS-CSR single step procedure with simplified analytical formulas and updated orthotropic panel approach calculations, respectively. Then, the progressive collapse calculations have been performed using the determined load-end shortening curves. Finally, ultimate strength of hull girder has been obtained as the peak value of moment-curvature curve, saying the maximum load carrying capacity under maximum vertical bending moment. HULT is composed of limit state design approach allowing not only stresses of local and global structure arising from design loads but also real loads beyond these consist of several conditions and variables that cease to fulfill tasks of structures. HULT's calculation flow use progressive collapse analysis approach with Smith Method but different element discretization allowing historical effects of stress-strain relationships consist of yield, buckling, collapse and post-collapse. In this paper, hull girder ultimate strength results of HULT and IACS-CSR calculations with different element idealization scenarios are presented for five benchmark ship cross sections and are compared with each other and previously published results. Critical collapse moment values of midship cross sections are calculated and shown to agree well with the results of previous studies. The comparisons demonstrate the overall reliability of HULT's prediction of structural strength. Results also show that HULT’s accuracy is comparable to other ultimate strength methods. Besides, some deficiencies identified are emphasized and recommendations are made to improve HULT’s accuracy and reliability for ship designs and safety during sealife.