Ultimate Strength And Structural Reliability Analyses On Large-span Decks

Longitudinal large-cabin structures are commonly used in the aircraft carriers,attack ships,large ro-ro ships,ro-ro passenger ships and oil tankers.No transverse bulkheads,pillars or other support structures are used in the cabin.As a result,the main deck at the top of the cabin is characterized as the large-span deck which is not only used as the transport deck to bear the loads induced by vehicles,aircrafts and green water,but also works as the strength deck to withstand the huge longitudinal loads.Hence,higher requirements on the ultimate capability are put forward on the large-span deck than the conventional deck.In addition,more and more attentions are drawn on the ship structural assessment based on the reliability theory due to the various uncertainties associated with the structure's material properties,structural size and loads.However,the current domestic and international ship structural standards lack specific analysis guidelines for the ultimate strength and reliability analyses of large-span decks.Both the non-linear finite element simulation and experimental method are adopted in the thesis to study the ultimate strength of large-span deck,and the structural reliability theory is applied to analyze the probabilities of failure and sensitivity factors of the large-span deck.The combination of deterministic and probabilistic methods provides a meaningful reference for the rational design of new large-span decks.The main research contents and achievements are summarized as following:(1)The stability theory and muti-span collapse theory are applied to perform the stability analysis according to which the optimal sizes of longitudinal and transeverse stiffeners of the slender large-span deck are concluded,considering the requirements of buckling strength and minimum structural weight.Based on the obtained optimal stiffeners,analytic methods are used to calculate the compressive ultimate strength under different collapse modes by discretizing the large-span deck into stiffened plates.The minimum value of calculated ultimate strength is selected as the critical strength to provide criteria for strength assessment.(2)A rational numerical scheme based on the non-linear finite element method(FEM)for analyzing the ultimate strength is summarized by the comparison with the published experimental results.In addition,studies are carried out to investigate the effects of the structural type of transverse beam,deck span,lateral loads,permanent plastic deformation and local openings on the ultimate strength of large-span decks.Finally,a rational deck structural type is determined.(3)Based on the obtained rational deck structure,this study formulates the experimental scheme for analyzing the longitudinal ultimate strength of large-span deck,which includes the model design,loading device design,experiment process and results processing.The rational FEM and experimental method are obtained by comparing and verifying the results of FEM and the experiment.Furthermore,a method for forecasting the ultimate strength of an actual large-span deck is proposed,which is able to solve the limitation that the similar theory cannot be used in the accurate prediction of nonlinear problems.(4)Advanced First-order Second-moment method and Monte Carlo Simulation are applied to perform the structural reliability analyses to generate results on the safety indices and sensitivity factors by compiling the Fortran subroutine.The limit state equation of large-span deck is established based on the reliability theory and FEM results.Besides,the formula for structural reliability assessment is proposed based on the results of the partial safety factors with varying failure probabilities,which is recommended to directly check the structural safety level under the given loads.The formula is of practical value to the structural design and practical projects.