The ship ' s hull is a thin - walled box girder structure composed of stiffened panels . the overall failure of a ship hull girder is normally governed by buckling and plastic collapse of the deck , bottom , or sometimes the side shell stiffened panels . therefore , the analysis of buckling and ultimate strength of ship panels in deck , boltom , and side shells is very important and necessary for the safety assessment of ship structure . in stiffened panels , local buckling and collapse of plating between stiffeners is a basic failure mode , and thus it would also very important to evaluate the buckling and ultimate strength interaction of plate elements under combined loads 船体梁的总体失效通常取决于甲板、船底板，有时候是舷侧加筋板的屈曲和塑性破坏。因此，对于衡量船体结构的安全性而言，对甲板、底板、舷侧板进行屈曲和极限强度分析是十分重要且必须的。对于加筋板而言，加强筋间的板格之局部屈曲和失效是最基本的失效模式。
With this understanding , this paper chooses the longitudinal strength of hull girder as the disabled mode , by the calculation of fpso , predicts the ultimate strength and effective lifetime of the hull . expected results of examples are obtained , which provide the analysis data for the further risk assessment 在此前提下，本文选择了船体梁纵向强度失效模式，通过fpso实船计算，分析消化了理想单元法程序软件，预报了船舶极限强度和安全有效寿命期，并用一阶二次矩方法对完整受损船体的结构安全性进行了可靠性的评估，取得了预想的结果，为进一步实施综合安全评估提供了分析数据。
In the hogging condition , double bottom and the side shell remain the ultimate bucking strength , deck and upperwing tank remain the yield stress , and the other parts keep elasticity . then the key to calculate the ultimate strength of ship hull girders is to ascertain the ultimate bucking strength of the stiffened panels . in this regard , the developed formulation is designed to be more sophisticated than previous simplified theoretical method for calculating the ultimate strength of stiffened panels under combined in - plane bending and lateral pressure . fabricatio n - related initial imperfections ( initial deflections and residual stresses ) are included in the panel ultimate strength calculation as parameters of influence . all possible collapse modes involed in collapse of stiffened panels , including overall buckling collapse , column or beam - column type collapse , tripping of stiffeners and local bukling of stiffened web are considered 确定了船体梁整体破坏时的剖面应力分布之后，关键在于确定板架的极限屈曲强度。本文充分考虑了在纵向弯曲、横向压力作用下加筋板可能发生的几种破坏模式，即板架的整体屈曲破坏、梁柱形式的破坏、筋的侧倾、腹板的屈曲并同时考虑了初始焊接残余应力、初挠度的影响，使其更精确的计算加筋板的屈曲强度。对于加筋板中加强筋腹板的局部屈曲，采用解析法推导出筋的腹板的挠度方程及其边界条件，求解相应的方程，从而计算出腹板的局部屈曲应力。
