Code Development for Ship Structures—A Demonstration

1997 ◽  
Vol 119 (2) ◽  
pp. 114-119 ◽  
Author(s):  
A. E. Mansour ◽  
P. H. Wirsching ◽  
B. Ayyub ◽  
G. White
Keyword(s):  
Failure Modes ◽  
Safety Margin ◽  
Limit States ◽  
Hull Girder ◽  
Load Combination ◽  
Plate Buckling ◽  
Design Variables ◽  
Critical Detail ◽  
Safe Side ◽  
Future Publication

A demonstration summary of a reliability-based structural design code for ships is presented for two ship types: a cruiser and a tanker. One reason for the development of such a code is to provide specifications which produce ship structure having a weight savings and/or improvement in reliability relative to structure designed by traditional methods. Another reason is to provide uniform safety margin for ships within each type. For both ship types, code requirements cover four failure modes: hull girder bulkling, unstiffened plate yielding and buckling, stiffened plate buckling, and fatigue of critical detail. Both serviceability and ultimate limit states are considered. Because of limitation on the length, only hull girder modes are presented in this paper. Code requirements for other modes will be presented in future publication. A specific provision of the code will be safety check expression, which, for example, for three bending moments (still water Ms, wave Mw, and dynamic Md), and strength Mu, might have the form, following the partial safety factor format: γsMs+γwMw+γdMd≤φMu γs, γw, γd, and φ are the partial safety factors. The design variables (M’s) are to be taken at their nominal values, typically values in the safe side of the respective distributions. Other safety check expressions for hull girder failure that include load combination factors, as well as consequence of failure factors, are considered. This paper provides a summary of safety check expressions for the hull girder modes.

scholarly journals Design safety margin of a 10,000 TEU container ship through ultimate hull girder load combination analysis

2016 ◽  
Vol 46 ◽  
pp. 78-101 ◽  
Author(s):  
E. Alfred Mohammed ◽  
S.D. Benson ◽  
S.E. Hirdaris ◽  
R.S. Dow
Keyword(s):  
Safety Margin ◽  
Container Ship ◽  
Hull Girder ◽  
Load Combination

Influence of Human Error on Structural Reliability

2017 ◽  
Author(s):  
Eric Brehm ◽  
Robert Hertle ◽  
Markus Wetzel
Keyword(s):  
Human Error ◽  
Structural Reliability ◽  
Failure Modes ◽  
Structural Model ◽  
Limit State ◽  
Design Procedure ◽  
Material Strength ◽  
Limit States ◽  
The Impact

In common structural design, random variables, such as material strength or loads, are represented by fixed numbers defined in design codes. This is also referred to as deterministic design. Addressing the random character of these variables directly, the probabilistic design procedure allows the determination of the probability of exceeding a defined limit state. This probability is referred to as failure probability. From there, the structural reliability, representing the survival probability, can be determined. Structural reliability thus is a property of a structure or structural member, depending on the relevant limit states, failure modes and basic variables. This is the basis for the determination of partial safety factors which are, for sake of a simpler design, applied within deterministic design procedures. In addition to the basic variables in terms of material and loads, further basic variables representing the structural model have to be considered. These depend strongly on the experience of the design engineer and the level of detailing of the model. However, in the clear majority of cases [1] failure does not occur due to unexpectedly high or low values of loads or material strength. The most common reasons for failure are human errors in design and execution. This paper will provide practical examples of original designs affected by human error and will assess the impact on structural reliability.

Comparative Design of Orthogonally Stiffened Plates for Production and Structural Integrity—Part 1: Size Optimization

1994 ◽  
Vol 10 (03) ◽  
pp. 146-155
Author(s):  
Nicholas Hatzidakis ◽  
Michael M. Bernitsas
Keyword(s):  
Structural Integrity ◽  
Plate Theory ◽  
Plate Thickness ◽  
Stiffened Plates ◽  
Size Optimization ◽  
Element Analysis ◽  
Total Cost ◽  
Plate Buckling ◽  
Design Variables ◽  
Overall Buckling

Five alternative configurations of orthogonally stiffened plates are compared in order to identify the total cost optimum design including material and fabrication cost. Size optimization is performed within the limitations of structural component standardization for each of the five alternatives. The five optimal structures are then compared in terms of weight, fabrication, and total cost. Discrete sizing optimization is performed in this paper with two design variables, i.e., plate thickness and standardized beam cross section. Constraints are imposed on secondary and tertiary stresses computed by finite-element analysis (FEA); and on primary stresses to prevent plate buckling, stiffener tripping, and overall buckling. Confidence is established in the FEA results by making comparisons with FEA results using the effective breadth method and orthotropic plate theory. Producibility constraints dictated by standardization in shipyard practice are imposed as well.

Limit State of Torsion of Ship Hulls with Large Hatch Openings

2001 ◽  
Vol 45 (02) ◽  
pp. 95-102
Author(s):  
Yuren Hu ◽  
Bozhen Chen
Keyword(s):  
Cross Section ◽  
Structural Reliability ◽  
Limit State ◽  
Safety Margin ◽  
Plastic Shear ◽  
Torsional Moment ◽  
Limit States ◽  
Ship Hulls ◽  
Design Values ◽  
Bound Theorem

The limit state of torsion of ship hulls with large hatch openings is studied. A method to determine the distribution of the plastic shear flow on the hull cross section in the limit state by using the lower-bound theorem is presented together with the corresponding linear programming problem. The limit torsional moment of the hull cross section is obtained based on the distribution of the shear stress in the limit state. Three example limit states for typical containerships of different sizes with large hatch openings are calculated. The calculated limit torsional moments are compared with the design values of wave torque calculated by using the equations given by main classification societies in their rules. A rough estimate of the safety margin is obtained. The results show that for large containerships, it is necessary to pay attention to the safety with respect to torsion. The present method can serve as an effective tool in structural reliability analysis of ships with large hatch openings when the failure mode of torsion is taken into account.

scholarly journals Buckling Analysis and Section Optimum for Square Thin-Wall CFST Columns Sealed by Self-Tapping Screws

2019 ◽  
Vol 2019 ◽  
pp. 1-14
Author(s):  
He Zhang ◽  
Kai Wu ◽  
Chao Xu ◽  
Lijian Ren ◽  
Feng Chen
Keyword(s):  
Bearing Capacity ◽  
Failure Modes ◽  
Steel Plate ◽  
Local Buckling ◽  
Steel Tube ◽  
Thin Wall ◽  
Type Section ◽  
Plate Buckling ◽  
Thin Walled ◽  
Cfst Columns

Two columns of thin-walled concrete-filled steel tubes (CFSTs), in which tube seams are connected by self-tapping screws, are axial compression tested and FEM simulated; the influence of local buckling on the column compression bearing capacity is discussed. Failure modes of square thin-wall CFST columns are, first, steel tube plate buckling and then the collapse of steel and concrete in some corner edge areas. Interaction between concrete and steel makes the column continue to withstand higher forces after buckling appears. A large deflection analysis for tube elastic buckling reflects that equivalent uniform stress of the steel plate in the buckling area can reach yield stress and that steel can supply enough designing stress. Aiming at failure modes of square thin-walled CFST columns, a B-type section is proposed as an improvement scheme. Comparing the analysis results, the B-type section can address both the problems of corner collapse and steel plate buckling. This new type section can better make full use of the stress of the concrete material and the steel material; this type section can also increase the compression bearing capacity of the column.

Reliability analysis of wood I-joists

1993 ◽  
Vol 20 (4) ◽  
pp. 564-573 ◽  
Author(s):  
R. O. Foschi ◽  
F. Z. Yao
Keyword(s):  
Reliability Analysis ◽  
Carrying Capacity ◽  
Failure Modes ◽  
Limit State ◽  
Load Carrying Capacity ◽  
Limit States ◽  
Element Analysis ◽  
Strength Limit ◽  
Reliability Method ◽  
Load Carrying

This paper presents a reliability analysis of wood I-joists for both strength and serviceability limit states. Results are obtained from a finite element analysis coupled with a first-order reliability method. For the strength limit state of load-carrying capacity, multiple failure modes are considered, each involving the interaction of several random variables. Good agreement is achieved between the test results and the theoretical prediction of variability in load-carrying capacity. Finally, a procedure is given to obtain load-sharing adjustment factors applicable to repetitive member systems such as floors and flat roofs. Key words: reliability, limit state design, wood composites, I-joist, structural analysis.

Random Combination Factors for Still Water and Wave Bending Moments

2019 ◽  
Author(s):  
Wenbo Huang
Keyword(s):  
Statistical Analysis ◽  
Weibull Distribution ◽  
Ship Hull ◽  
Combined Processes ◽  
Bending Moments ◽  
Hull Girder ◽  
Random Combination ◽  
Load Combination ◽  
Characteristic Values ◽  
Wave Models

Abstract Based on the extreme value of the primary loads of ship hull girder instead of characteristic values, the more reasonable load combination factors are defined. In order to evaluate the random variation of newly defined load combination factors, based on Ferry-Berges & Castanheta (FBC) and Poisson square wave models, the still water bending moments (SWBM), vertical wave bending moments (VWBM) and their combined processes are simulated to get the random realizations of load combination factors. The statistical analysis results show that the load combination factors take the value of 1 with the highest probability and can be well fitted by the Weibull distribution. Such information should be incorporated appropriately in the reliability analysis of ship hull girder.

Reliability analysis for critical reaction forces of lumber members with an end notch

1996 ◽  
Vol 23 (1) ◽  
pp. 202-210 ◽  
Author(s):  
Ian Smith ◽  
Ying Hei Chui ◽  
Lin Juan Hu
Keyword(s):  
Structural Reliability ◽  
Reaction Force ◽  
Service Condition ◽  
Design Criterion ◽  
Timber Species ◽  
Limit States ◽  
Beam Design ◽  
Design Variables ◽  
Property Data ◽  
Reaction Forces

The basis of new design provisions for avoidance of brittle failures in sawn lumber members with an end notch is explained. Linear elastic fracture mechanics and structural reliability concepts are combined with material property data to determine appropriate forms of equations for limiting the reaction force, when a notch is made on either the tension or compression face of a member. Following from this, the factored reaction force resistance of a member designed to the 1994 edition of the CSA Standard 086.1 "Engineering design in wood (limit states design)" depends upon the depth of the member and the geometry and size of an end notch if the notch is located on the tension face. A new property, the specified reaction force strength, which is a measure of the capability of the material to resist fracture, is taken to be independent of the timber species and stress grade of the lumber. Design variables such as duration of load and moisture service condition influence assignments of factored reaction force resistances for members end notched on the tension face. When a notch is located on the compression face of a member the resistance is simply the factored shear resistance of the residual cross section. As in previous editions of CSA Standard 086.1, notches are not permitted to have a depth greater than 0.25 times the depth of the section. Key words: lumber, fracture, structural reliability, notched beam, design criterion.

An approach to weight optimization of a spur gear

2016 ◽  
Vol 231 (2) ◽  
pp. 189-202 ◽  
Author(s):  
S Panda ◽  
BB Biswal ◽  
SD Jena ◽  
D Mishra
Keyword(s):  
Optimum Design ◽  
Failure Modes ◽  
Differential Evolution Algorithm ◽  
Spur Gear ◽  
Weight Optimization ◽  
Element Analysis ◽  
Design Variables ◽  
Stress Region ◽  
Objective Function Values ◽  
Optimum Solution

Lightweight is one of the most important criterion in the optimum design of gear set for motorsport and aerospace application. A tradeoff between optimum weight and failure modes of gear is a subject of interest for researchers and the industry. In the present work weight of a single-stage spur gear set is optimized. This nonlinear constrained optimization formulation has been solved by using differential evolution algorithm. A total of six design variables corresponding to gear geometry and material property are considered. The results obtained are compared with those of published heuristics like genetic algorithm, simulated annealing, and particle swarm optimization algorithm, respectively. The optimization is performed in such a way that the design variables satisfy all constraints at optimum solution. Apart from this, several constraints related to scoring are included in the optimization. The constraint violation study is performed to prioritize the constraints. The sensitivity analysis is carried out to see the effect of manufacturing tolerances of design variables on weight of the gear set. The optimality of the solution has been ensured through the convergence study. The optimization reveals that the reported results are also encouraging in terms of objective function values and CPU time. In addition, the optimum design variables obtained through the weight optimization of spur gear set are used for preparation of a CAD model. Then the stress analysis using finite element analysis is performed on the gear set to identify the critical stress region in the optimized gear set.

On Determination of Acceptable Safety Class in Design of Pipe-In-Pipe (PIP) Systems

2014 ◽  
Author(s):  
Soheil Manouchehri ◽  
Guillaume Hardouin ◽  
David Kaye ◽  
Jason Potter
Keyword(s):  
Failure Modes ◽  
Structural Integrity ◽  
Oil And Gas ◽  
Gas Production ◽  
Point Of View ◽  
Insulation Material ◽  
Limit States ◽  
Oil And Gas Production ◽  
Operational Conditions ◽  
Outer Pipe

Pipe-In-Pipe (PIP) systems are increasingly used in subsea oil and gas production where a low Overall Heat Transfer Coefficient (OHTC) is required. A PIP system is primarily composed of an insulated inner pipe which carries the production fluid and an outer pipe that protects the insulation material from the seawater environment. This provides a dry environment within the annulus and therefore allows the use of high quality dry insulation system. In addition, from a safety point of view, it provides additional structural integrity and a protective barrier which safeguards the pipeline from loss of containment to the environment. Genesis has designed a number of PIP systems in accordance with the recognized subsea pipeline design codes including DNV-OS-F101 [1]. In section 13 F100 of the 2013 revision, a short section has been included in which PIP systems are discussed and overall design requirements for such systems are provided. It has also been stated that the inner and outer pipes need to have the same Safety Class (SC) unless it can be documented otherwise. This paper looks at the selection of appropriate SC for the outer pipe in a design of PIP systems based on an assessment of different limit states, associated failure modes and consequences. Firstly, the fundamentals of selecting an acceptable SC for a PIP system are discussed. Then, different limit states and most probable failure modes that might occur under operational conditions are examined (in accordance with the requirements of [1]) and conclusions are presented and discussed. It is concluded that the SC of the outer pipe of a PIP system may be lower than that of the inner pipe, depending on the failure mode and approach adopted by the designer.

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