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 Structural Reliability Analysis of Ship Hulls Accounting for Collision or Grounding Damage

2020 ◽  
Author(s):  
Branka Bužančić Primorac ◽  
Joško Parunov ◽  
C. Guedes Soares
Keyword(s):  
Reliability Analysis ◽  
Structural Reliability ◽  
Limit State ◽  
Random Variables ◽  
Bending Moment ◽  
State Equation ◽  
Limit States ◽  
Moment Capacity ◽  
Ship Hulls ◽  
Structural Reliability Analysis

AbstractClassical structural reliability analysis of intact ship hulls is extended to the case of ships with collision or grounding damages. Still water load distribution and residual bending moment capacity are included as random variables in the limit state equation. The probability density functions of these random variables are defined based on random damage parameters given by the Marine Environment Protection Committee of the International Maritime Organization, while the proposed reliability formulation is consistent with international recommendations and thus may be valuable in the development of rules for accidental limit states. The methodology is applied on an example of an Aframax oil tanker. The proposed approach captures in a rational way complex interaction of different pertinent variables influencing safety of damaged ship structure.

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.

scholarly journals Reliability Estimation for Highway Bridges

2020 ◽  
Author(s):  
Nafiseh Kiani
Keyword(s):  
Reliability Index ◽  
Structural Reliability ◽  
Limit State ◽  
Highway Bridges ◽  
Reliability Estimation ◽  
State Function ◽  
Limit States ◽  
Resistance Factors ◽  
Load And Resistance Factors ◽  
Reliability Methods

Structural reliability analysis is necessary to predict the uncertainties which may endanger the safety of structures during their lifetime. Structural uncertainties are associated with design, construction and operation stages. In design of structures, different limit states or failure functions are suggested to be considered by design specifications. Load and resistance factors are two essential parameters which have significant impact on evaluating the uncertainties. These load and resistance factors are commonly determined using structural reliability methods. The purpose of this study is to determine the reliability index for a typical highway bridge by considering the maximum moment generated by vehicle live loads on the bridge as a random variable. The limit state function was formulated and reliability index was determined using the First Order Reliability Methods (FORM) method.

scholarly journals Reliability of Buried Pipes in Heterogeneous Soil Subjected to Seismic Loads

2021 ◽  
Vol 11 (1) ◽  
pp. 6708-6713
Author(s):  
H. Benzeguir ◽  
S. M. Elachachi ◽  
D. Nedjar ◽  
M. Bensafi
Keyword(s):  
Structural Reliability ◽  
Limit State ◽  
Bending Moment ◽  
Longitudinal Direction ◽  
Point Of View ◽  
Ultimate Limit State ◽  
Buried Pipe ◽  
Limit States ◽  
Ground Acceleration ◽  
Buried Pipes

Dysfunctions and failures of buried pipe networks, like sewer networks, are studied in this paper from the point of view of structural reliability and heterogeneity of geotechnical conditions in the longitudinal direction. Combined soil spatial variability and Peak Ground Acceleration (PGA) induce stresses and displacements. A model has been developed within the frame of geostatistics and a mechanical description of the soil–structure interaction of a set of buried pipes with connections resting on the soil by a two-parameter model (Pasternak model). Structural reliability analysis is performed considering two limit states: Serviceability Limit State (SLS), related to large "counter slope" in a given pipe, and Ultimate Limit State (ULS), corresponding to bending moment.

scholarly journals Strengthening of Concrete Column by Using the Wrapper Layer of Fibre Reinforced Concrete

Materials ◽  
2020 ◽  
Vol 13 (23) ◽  
pp. 5432
Author(s):  
Peter Koteš ◽  
Martin Vavruš ◽  
Jozef Jošt ◽  
Jozef Prokop
Keyword(s):  
Reinforced Concrete ◽  
Cross Section ◽  
Limit State ◽  
Fibre Reinforced Concrete ◽  
Limit States ◽  
Load Bearing Capacity ◽  
Concrete Core ◽  
Fibre Concrete ◽  
Special Cases ◽  
Ultimate Limit

Structures and bridges are being designed on the proposed and requested design lifetime of 50 to 100 years. In practice, one can see that the real lifetime of structures and bridges is shorter in many cases, in some special cases extremely shorter. The reasons for the lifetime shortening can be increased of the load cases (e.g., due to traffic on bridges, or due to other uses of a structure), using the material of lower quality, implementation of new standards and codes according to Eurocode replacing older ones. During the whole lifetime the structures must be maintained to fulfil the code requests. If the constructions are not able to fulfil the Ultimate Limit States (ULS) and the Serviceability Limit State (SLS), the structures or bridges have to be strengthened (whole or its elements). The purpose of the paper is the presentation of using a layer of the fibre concrete for a columns’ strengthening. Using the fibre reinforced concrete (FRC) of higher tensile strength makes it possible to increase the load-bearing capacity of the cross-section the column. The contact between the old concrete (core of column) and newly added layer (around column) is very important for using that method of strengthening. In the article, there is also a comparison of the surface modification methods.

scholarly journals PROBABILISTIC AND STATISTICAL METHODS FOR DESIGNING AND ANALYZING LIMIT STATES/TIKIMYBINIS IR STATISTINIS RIBINŲ BŪVIŲ PROJEKTAVIMO IR ANALIZĖS METODAI

2001 ◽  
Vol 7 (5) ◽  
pp. 413-418
Author(s):  
Benediktas Užpolevičius
Keyword(s):  
Statistical Methods ◽  
Cross Sections ◽  
Limit State ◽  
Multidimensional Data ◽  
Limit States ◽  
Reliability Factor ◽  
Additional Information ◽  
Design Values ◽  
Construction Operation ◽  
Effective Use

Errors of partial reliability factor (PRF) method, being used in operating codes to provide required reliability of construction work (foundations, structures and their systems), are discussed. It is pointed out that additional resistance (strength, stiffness, etc) of the members to compensate these errors is required, and it makes much more than 10%. The main cause of these shortcomings is that in the PRF method, for the sake of simplicity, independent partial coefficients and limited number of these coefficients are applied. Direct probabilistic and statistical methods (without application of partial coefficients and design values) are proposed. It is demonstrated that these methods are free of systematic errors which are characteristic of the known codified (standardized) probability calculations. The proposed methods make up a unified method used for foundations and structures, uniformly based on theoretical conclusions of probability theory and mathematical statistics. These economy seeking methods are intended for effective use (without change of codes) of available additional information, which is made of different amount of data of statistical measurements or statistical observations on minimal values of soils and building material mechanical characteristics of structures and maximum values of loads, actions and their combinations during the operation period, geometrical dimensions of critical cross-sections, errors of algorithms for calculation of resistance and action effects, control errors made by people during design, construction, operation of construction works, etc. In case of a limited amount of information the proposed statistical model is to be used. In addition, the proposed method is adjusted for effective use of the known reliability solutions of economical and social optimisation (in relation to economical and social damage caused by the limit state, human safety and other factors) co-ordinating them with application experience of PRF code method and statistical multidimensional data of limit state frequency. Areas of application and economy of the proposed probabilistic and statistical methods are presented in Table 1. National and established specifications prepared for probabilistic and statistical calculation design and tests of foundations, structures and their systems are discussed. Practical application and economical comparison of calculation of construction members by PRF, probabilistic and statistical methods (area of the cross-section, foundation pad base A % in relation to that determined by SNiP codes)

scholarly journals Reliability on timber columns under fire situation

Fire Research ◽  
2018 ◽  
Author(s):  
Auro Cândido Marcolan Júnior ◽  
Poliana Dias de Moraes
Keyword(s):  
Reliability Analysis ◽  
Cross Section ◽  
Structural Reliability ◽  
Rectangular Cross Section ◽  
Limit State ◽  
Random Variable ◽  
State Equations ◽  
Reduced Cross Section ◽  
Reliability Method ◽  
In Fire

Timber structures in fire situation are subject to intrinsic uncertainties from the material and the actions on the structure and their probabilistic behavior has not being studied exhaustively. In this paper, four limit state equations using the reduced cross-section method are developed for timber columns in fire situation. The security criteria taken into account in these equations are the compression, the lateral stability and the combined bending and compression, according to the NBR 7190:1997 standard. The structural reliability analysis of five simply supported timber columns with rectangular cross-section in fire situation and different base and height ratios where performed using the first order reliability method. The overall probability of failure of the column was obtained by associating the failure criteria in a series system. The reliability behavior of the different base to height ratios was evaluated, leading to different results for the distinct ratios and the criteria used. Also, a sensitivity analysis was performed indicating the timber charring rate as the most important random variable in the reliability analysis for these limit state equations.

scholarly journals Structural reliability-based assessment of Nigerian Anogeissus schimperi timber bridge beam in shear and bearing forces

2021 ◽  
Vol 39 (4) ◽  
pp. 1011-1020
Author(s):  
P. Abubakar ◽  
A. Iorkar ◽  
A.A. Adedeji ◽  
J.I. Aguwa ◽  
U.N. Wilson
Keyword(s):  
Sensitivity Analysis ◽  
Reliability Analysis ◽  
Structural Reliability ◽  
Limit State ◽  
Safety Margin ◽  
Physical And Mechanical Properties ◽  
Ultimate Limit State ◽  
Safety Level ◽  
Ultimate Limit ◽  
North Western

This research investigates the reliability of Anogeissus schimperi timber specie grown in North Western Nigeria as a bridge beam in shear and bearing forces. Specimens for laboratory tests were prepared using the timber specie in accordance with BS 373 (1957). Tests were carried out to determine the physical and mechanical properties at 12% moisture content in line with BS 5268 (2002). Statistical analysis was carried out using strength properties obtained and the specie was classified to strength class D60, confirmed to be Hardwood. Anogeissus schimperi timber bridge beam was designed in accordance to BS5268 (2002), using deterministicapproach. While, reliability analysis to confirm the safety level of the timber bridge beam designed was carried out using constant failure rate model in accordance with Jimoh, (2018). Sensitivity analysis to ascertain the safety margin of a simply supported timber bridge beam subjected to Shear and bearing by varying the span, depth, width and live load was carried out. Results of reliability analysis showed that Anogeissus schimperi met the minimum reliability index of 0.5 under ultimate state of loading in Shear and bearing. Safety index was found to be directly proportional to the depth and width but inversely proportional to the span and live loadof the timber bridge beam during Sensitivity Analysis. The result confirmed that Anogeissus schimperi specie from north western Nigeria at 400mm depth, 150mm breadth and 5000mm span under ultimate limit state loading in Shear and bearing can be used as a reliable timber bridge beam material. Keywords: Bridge Beam, Nigerian Anogeissus schimperi Reliability, Structural Material, Timber, Ultimate Limit State.

scholarly journals RELIABILITY OF IMPERFECT STRUCTURES (SIMPLE NON-LINEAR MODELS)

2002 ◽  
Vol 8 (2) ◽  
pp. 83-87
Author(s):  
Eugeniusz Bielewicz ◽  
Jarosłlaw Goórski
Keyword(s):  
Monte Carlo ◽  
Applied Load ◽  
Structural Reliability ◽  
Linear Models ◽  
Limit State ◽  
Random Variables ◽  
Limit States ◽  
Non Linear ◽  
Non Linear Operator ◽  
Imperfect Structures

Limit states of simple, spatial, non-linear models of structures with two degrees of freedom are considered. Geometric and material imperfections are taken in the form of random variables. The simulation of these random variables and the Monte Carlo technique are employed. Two possibilities in the assessment of the reliability of structures are presented: 1) Simulation of random imperfections and the Monte Carlo operation give as a result a histogram of the limit loads. Assuming that the probability distribution of the applied load is known, the structural reliability can be obtained according to the exact formula. 2) In order to obtain the histogram of the limit state of the structure, the values of the applied load are also simulated at every Monte Carlo step. The factor which amplifies the load responsible for the structure failure is derived. The set of all these factors leads to the model reliability calculation. The estimation of the limit state of an imperfect structures can be described as a transformation of random input data into random output results. In the transformation operation the non-linear operator of the model under considerations is of the greatest significance. The effects of stable and unstable operators are discussed.

Influence of Material Toughness on Fracture Reliability in Steel Bridges

2021 ◽  
pp. 036119812110566
Author(s):  
Frank A. Artmont ◽  
Thomas P. Murphy
Keyword(s):  
Fracture Toughness ◽  
Brittle Fracture ◽  
Structural Reliability ◽  
Limit State ◽  
Base Material ◽  
Steel Bridges ◽  
Steel Bridge ◽  
Limit States ◽  
Control Approach ◽  
Probabilistic Distribution

The fracture limit state of the AASHTO LRFD Bridge Design Specifications is addressed by requiring minimum impact toughness values for base material and mitigating potential fracture initiators through proper structural detailing. This fracture control approach has been successful in minimizing the number of fractures in steel bridges designed since its inception; however, it is not a calibrated limit state and the structural reliability against sudden brittle fracture has not been previously established. Accordingly, the objective of this study was to quantify the relationship between material toughness and fracture reliability in steel bridge members, considering the probabilistic distribution of fracture toughness and applied stress for a variety of structural steels and assumed crack sizes. The master curve approach is used to account for the probabilistic distribution of fracture toughness, and reliabilities are determined using Monte Carlo simulation and the Hasofer-Lind approach. The results indicate that the fracture reliability for modern bridge steels is consistent with the reliability of AASHTO strength limit states, and that certain steels currently available on the market can provide enough reliability against fracture to essentially eliminate brittle fracture as a limit state of concern. This finding holds the potential for a new way of approaching the design of fracture-critical members.

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