Reliability analysis of hull girder ultimate strength for large container ships under whipping loads
Guijie Shi, Dawei Gao
Abstract
The two incident reports for MSC (Mediterranean Shipping Company) Napoli in 2008 and MOL (Mitsui O.S.K. Lines) Comfort in 2015 both pointed out that whipping response was one main reason for inducing the catastrophes. Subsequently, International Association of Classification Societies (IACS) proposed a Unified Requirement (UR) S11A for ultimate strength evaluation of container ships, and main classification societies also updated their guidelines for whipping response. However, there are big differences in these requirements, and the safety level of ultimate strength under whipping loads is still unclear. This article is to find the effect of the whipping loads on hull girder reliability. Two large container ships 14500TEU and 19000TEU designed by China Classification Society (CCS) Rules are selected as case studies. Hull girder ultimate capacity in mid-ship section under hogging conditions is adopted as the dangerous failure mode, which is predicted by the increment-iterative method in IACS Common Structural Rules (CSR). The whipping effect on hull girder reliability is accounted for by a factor attaching on wave-induced moment. Then, a new evaluation criterion is proposed to evaluate hull girder ultimate strength for container ships under whipping loads, and sensitivity analysis of whipping effect is carried out. The conclusions in this article can provide a guidance for revising rule requirements in classification societies and optimising container ship structural design.