• Proceedings of the KWS Conference
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• 2010.05a
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• pp.58-58
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• 2010

The purpose of this study is to evaluate the structural safety at the topside weldment of hull structure, which was welded after launching. For it, the variations of residual stress and distortion at the topside weldment with loading conditions such as hull girder hogging bending moment after launching and free initial loading state was evaluated by using FEA. And the maximum stress range at the weldment under design loads specified by classification society was evaluated by FEA. In this case, the residual stress and welding distortion at the topside weldment was assumed to be initial imperfection. In accordance with FEA results, regardless of initial loading condition, tensile residual stress was found. However, the residual stress and welding distortion at the topside weldment produced under hogging condition was less than those of topside weldment under free loading state. That is, the amount of residual stress at the topside weldment decreased with an increase in the amount of tension load caused by hogging condition. It was because the compressive thermal strain at the topside weldment produced during welding was reduced by tensile load. However, the maximum stress range at the topside weldment under maximum hull girder bending moment was almost similar regardless of initial loading condition. So, if the problem related to the soundness of weldment is not introduced by initial load, the effect of initial loading condition during welding on fatigue strength of topside weldment could be negligible.

• Structural Engineering and Mechanics
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• v.69 no.2
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• pp.193-204
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• 2019

This paper presents results from experimental and numerical studies on the response of steel-concrete composite box bridge girders under certain localized fire exposure conditions. Two composite box bridge girders, a simply supported girder and a continuous girder respectively, were tested under simultaneous loading and fire exposure. The simply supported girder was exposed to fire over 40% of its span length in the middle zone, and the two-span continuous girder was exposed to fire over 38% of its length of the first span and full length of the second span. A measurement method based on comparative rate of deflection was provided to predict the failure time in the hogging moment zone of continuous composite box bridge girders under certain localized fire exposure condition. Parameters including transverse and longitudinal stiffeners and fire scenarios were introduced to investigate fire resistance of the composite box bridge girders. Test results show that failure of the simply supported girder is governed by the deflection limit state, whereas failure of the continuous girder occurs through bending buckling of the web and bottom slab in the hogging moment zone. Deflection based criterion may not be reliable in evaluating failure of continuous composite box bridge girder under certain fire exposure condition. The fire resistance (failure time) of the continuous girder is higher than that of the simply supported girder. Data from fire tests is successfully utilized to validate a finite element based numerical model for further investigating the response of composite box bridge girders exposed to localized fire. Results from numerical analysis show that fire resistance of composite box bridge girders can be highly influenced by the spacing of longitudinal stiffeners and fire severity. The continuous composite box bridge girder with closer longitudinal stiffeners has better fire resistance than the simply composite box bridge girder. It is concluded that the fire resistance of continuous composite box bridge girders can be significantly enhanced by preventing the hogging moment zone from exposure to fire. Longitudinal stiffeners with closer spacing can enhance fire resistance of composite box bridge girders. The increase of transverse stiffeners has no significant effect on fire resistance of composite box bridge girders.

• International Journal of Naval Architecture and Ocean Engineering
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• v.3 no.1
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• pp.95-104
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• 2011

As sea state harsher in the ocean space, more large motion and wave loads occurs on ships hull by non-linear phenomena. To consider nonlinear effect on ships hull in the structural design verification, the direct calculation method with numerical approach is used rather than rule values for the reliable accuracy. In this paper, the non-linear wave loads analysis in time domain is performed by using a Rankine Panel Method together with numerical schemes. Linear calculations have been carried out based on DNV CSA-2 notation to generate the motion responses and wave loads of large ships. By short and long term analysis, the design wave amplitudes are selected for the nonlinear analysis. The maximum wave induced bending moment in hogging and sagging conditions are calculated in the nonlinear analysis. Also, the green water effect on the wave induced vertical bending moment was investigated. The results show the vertical bending moments are more influenced by green water in sagging condition than in hogging condition due to green water loading.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.38 no.4
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• pp.307-316
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• 2002

In order to evaluate the deformation and stiffness of frame structure for fishery, composed of unit platforms which made of two concentric high density polyethylene buoys fixed by clamps and belts and rubber hinge components, under wave, the structural analysis for the square type of the structure was carried out by using finite element methods. The accurate physical properties of rubber hinge components determined by material tests were an important parameter to evaluate more reliable structural stability for the structure. The idealization to beam element with equivalent stiffness and rubber element with linearity for rubber hinges was necessary for the modeling of rubber component which has hyper-elastic characteristics. In addition, it was shown that the structural response of the structure under wave was larger in the hogging condition than that of in the still water or in the sagging condition.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.3
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• pp.1-10
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• 2022

For the composite section of corrugated steel sheet and concrete, which is often used in soil structures, a conservative design method based on the ultimate strength state is still applied due to the difficulty of the analysis of compatibility condition. In this study, plastic analysis was performed on the flexural and axial strength of the composite section using two limit state design methods, LRFD and LSD. As a result of the analysis of the experimental results, the LRFD analysis value was interpreted as a conservative results for compressive strength, and it was analyzed that the effect of the concrete compressive strength was greater than the steel ratio of the steel plate. The flexural strength was analyzed to be in good agreement with the experimental results by the LSD analysis. From the parametric analysis on the design variables, the hogging moment, which is affected by the tensile strength of the steel plate, slightly decreased the increasing rate of the strength due to the influence of the bolts connection, but the sagging moment linearly increased according to the increment of steel reinforcement ratio.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2002.11a
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• pp.107-112
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• 2002

Basically, ship structure consists of the plate members, and a strength of overall ship structurnds on the stiffness and strength of ship platings. If buckling which causes to deflect ship plate members occurs, the stiffness of ship plate markedly decreases, and thus buckling has a serious effect on the stiffness or strength of overall ship structure. Buckling is one of the most important design criteria when we scantle structure members. In the present study, a inplane rigidity of a compressed ship plate above buckling load is proposed. The proposed inplane rigidity is available in the elastic or elasto-Plastic ranges in order to can out a more efficient and reliable design.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.7
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• pp.1267-1273
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• 2022

Although the Korea shipbuilding industry has recently been receiving most of the orders for ships in the world, production processes are being disrupted due to a shortage of manpower at the production site. This is because the workers quit the shipyard as both work and wages were reduced due to the long slump in the shipbuilding industry. The main reason for the increase in orders was the large-scale orders for Qatar LNG carriers, and the situation in which the technical specifications required for ships are becoming more complex is also working to an advantage. Because the contract delivery time is of utmost importance for ships, the dock launch plan is the most important management item among the shipyard's major processes. The structure to be built in the dock may be a hull that has left the design work or a finished vessel, and in some cases, it is often at the level of some blocks of the hull. When launching, the hull is affected by the hogging or sagging moment due to the fluid force, and securing the safety of the structural strength of the block connection is of utmost importance. In a normal process, the connecting member launches after welding has been completed, but in actual shipbuilders, quick decision-making is needed on the conditions for securing structural safety to comply with the docking schedule. In this study, a detailed analysis method and applicability using a bending stress evaluation method and finite element analysis modelling were analyzed to rationally judge the above-mentioned problems from an engineering point of view. The main contents mentioned in the thesis can be used as good examples when conducting similar structural strength evaluations in the future.

• Journal of Navigation and Port Research
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• v.31 no.3 s.119
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• pp.235-245
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• 2007

Stiffened steel plates are basic structural members on the deck and bottom structure in ship, offshore. It has a number of one sided stiffeners in either one or both directions, the latter structure was called grillage structure. At the ship structural desgn stage, one of the major consideration is evaluation for ultimate strength of the hull girder. In general, it is accepted that hull girder strength can be represented by the local strength of the longitudinal stiffened panel. In case of considering hogging condition in a stormy sea, stiffened panel was acting on the bottom structure under axial compressive load induced hull girder bending moment, also simultaneously arising local bending moment induced lateral pressure load. In this paper, results of the structural analysis have been compared with another detailed FEA program and prediction from design guideline and a series analysis was conducted consideration of changing parameters for instance, analysis range, cross-section of stiffener, web height and amplitude of lateral pressure load subjected to combined load (axial compression and lateral pressure load). It has been found that finite element modeling is capable of predicting the behaviour and ultimate load capacity of a simply supported stiffened plate subjected to combined load of axial compression and lateral pressure load It is expected that these results will be used to examine the effect of interaction between lateral pressure and axial loads for the ultimate load-carrying capacity based on the Ultimate Limit State design guideline.