Reliability Evaluation of Structural Safety Factor Using a Global Resistance Approach

2019 ◽  
Author(s):  
Sergio Santos ◽  
Marcio Tacques R. Monteiro Junior ◽  
Luiz Fernando Martha ◽  
Claudia Interlandi
Keyword(s):  
Limit State ◽  
Point Of View ◽  
Structural Safety ◽  
Structural Behaviour ◽  
Limit States ◽  
Average Value ◽  
Model Code ◽  
Resistance Approach ◽  
Model Code 2010 ◽  
Ultimate Limit

<p>This paper presents a discussion on different ways of assessing the safety of concrete structures applying Reliability Analyses. The usual design approach based on the Ultimate Limit States (ULS) is confronted with the Global Resistance Format, as defined in <i>fi</i>b Model Code 2010. The Global Format considers the several uncertainties present in the structural behaviour through a pre-defined limit state in which one or more loading variables are increased by a <i>λ </i>factor, until a collapse situation is attained. In this evaluation, the variables related to the actions and to the resistances are taken with their average value. The obtained values for the <i>λ </i>factor shall be compatible, in the safety point-of- view, with the β reliability factors corresponding to the required safety levels. A conventional building is analyzed, and the obtained reliability factors corresponding to the two approaches are presented. It is shown that the application of the Global Resistance Format can lead to more economical structures.</p>

Applications of Vector Evaluated Genetic Algorithms (VEGA) in Ultimate Limit State Based Ship Structural Design

2014 ◽  
Author(s):  
Owen Hughes ◽  
Ming Ma ◽  
Jeom Kee Paik
Keyword(s):  
Genetic Algorithms ◽  
Structural Design ◽  
Limit State ◽  
Structural Safety ◽  
Wall Structure ◽  
Ultimate Limit State ◽  
Thin Wall ◽  
Limit States ◽  
Multi Objective ◽  
Ultimate Limit

Ship structural design often deals with multiple objectives such as weight, safety, and cost. These objectives usually conflict with each other, and optimizing a particular solution with respect to a single objective can result in unacceptable results with respect to the other objectives. A reasonable solution to a multi-objective problem is to investigate a set of solutions, each of which satisfies the objectives at an acceptable level without being dominated by any other solution. Genetic algorithms have been demonstrated to be particularly effective to determine excellent solutions to these problems. In this paper a multi-objective GA, called Vector Evaluated Genetic Algorithm (VEGA) is formulated and used to optimize a large and complex thin-wall structure (a complete cargo hold of a 200,000 ton oil tanker) on the basis of weight, safety and cost. The structure weight and cost and all of the stresses are calculated using a realistic finite element model. The structure adequacy is then evaluated using the ALPS/ULSAP computer program (Paik and Thayamballi, 2003) which can efficiently evaluate all six ultimate limit states for stiffened panels and grillages. This example was chosen because the initial design is severely inadequate. The results show that the proposed method can perform ultimate strength based structural optimization with multi-objectives, namely minimization of the structural weight and cost and maximization of structural safety, and also that the method is very robust.

scholarly journals Probabilistic Approach to Limit States of a Steel Dome

Materials ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 5528
Author(s):  
Paweł Zabojszcza ◽  
Urszula Radoń ◽  
Waldemar Szaniec
Keyword(s):  
Normal Distribution ◽  
Limit State ◽  
Probabilistic Approach ◽  
Random Variables ◽  
Structural Safety ◽  
Ultimate Limit State ◽  
Limit States ◽  
Serviceability Limit State ◽  
First Case ◽  
Ultimate Limit

In this paper, Numpress Explore software, developed at the Institute of Fundamental Technological Research of the Polish Academy of Sciences (IPPT PAN), was used to conduct reliability analyses. For static-strength calculations, the MES3D module, designed by the authors, was employed. Ultimate limit state was defined as condition of non-exceedance of the capacity value, resulting from the stability criterion of the bent and compressed element. The serviceability limit state was defined as the condition of non-exceedance of allowable vertical displacement. The above conditions constitute implicit forms of random variable functions; therefore, it was necessary to build an interface between the Numpress Explore and MES3D programs. In the study, a comparative analysis of two cases was carried out. As regards the first case, all adopted random variables had a normal distribution. The second case involved a more accurate description of the quantities mentioned. A normal distribution can be adopted for the description of, e.g., the randomness in the location of the structure nodes, and also the randomness of the multiplier of permanent loads. In actual systems, the distribution of certain loads deviates substantially from the Gaussian distribution. Consequently, adopting the assumption that the loads have a normal distribution can lead to gross errors in the assessment of structural safety. The distribution of loads resulting from atmospheric conditions is decidedly non-Gaussian in character. The Gumbel distribution was used in this study to describe snow and wind loads. The modulus of elasticity and cross-sectional area were described by means of a log-normal distribution. The adopted random variables were independent. Additionally, based on an analysis of the elasticity index, the random variables most affect the failure probability in the ultimate limit state and serviceability limit state were estimated.

OPERATIONAL ASSESSMENT OF THE LIMIT STATE OF TRACTOR UNITS WITH THE USE OF INDICATOR COUNTERS

2021 ◽  
Vol 3 (144) ◽  
pp. 12-21
Author(s):  
Nikolay A. Petrishchev ◽  
◽  
Mikhail N. Kostomakhin ◽  
Aleksandr S. Sayapin ◽  
Igor’ M. Makarkin ◽  
...  
Keyword(s):  
Limit State ◽  
Technical Condition ◽  
Point Of View ◽  
Research Purpose ◽  
Diagnostic Tools ◽  
Diagnostic Process ◽  
Technical Documentation ◽  
Limit States ◽  
Limit Condition ◽  
Reliability Indicators

In accordance with GOST 20793-2009, the tractor and its components are subjected to resource diagnostics before maintenance. The technical condition of the components of the tractor or machine should be checked with the use of control and diagnostic equipment. Currently, the criteria for the limit state are significantly outdated and require revision from the point of view of tightening modern requirements for operational and economic characteristics and reliability indicators. (Research purpose) The research purpose is in analyzing the state of the issue and the current regulatory documentation and making proposals for remote monitoring of the criteria for the limit states of individual components and aggregates. (Materials and methods) The article presents an analysis of scientific and technical documentation, State standards of the Russian Federation and scientific papers on the problems of minimizing technological risks, diagnostics and control suitability for determining the maximum technical condition, and staged studies on the possibility of monitoring the operation of individual components and units online. The article notes the need to adjust the criteria for the maximum technical condition in accordance with the new designs of resource-determining units, aggregates and existing technical regulations. (Results and discussion). The article presents the justification of the diagnostic process and identified contradictions in the design of tractors and existing scientific and technical documentation and standards, and proposed option of using meters-identifiers when upgrading tractors as a system of built-in online diagnostic tools. (Conclusions) Timely, automated monitoring of the technical condition of tractors, which is based on comparing data with the criteria of the limit condition, serves as a justification for the effective operation of equipment with built-in devices for diagnostics, which allows minimizing agrotechnological risks.

Spatial Effects in Risk-Based Design and Maintenance of Pipelines

2007 ◽  
Author(s):  
Marc A. Maes ◽  
Michael Havbro Faber
Keyword(s):  
Spatial Correlation ◽  
Unit Length ◽  
Limit State ◽  
Point Of View ◽  
Spatial Extent ◽  
System Component ◽  
Continuous Systems ◽  
Spatial Effects ◽  
Limit States

Pipelines are to a large extent spatially continuous systems having a system-component relationship that is not as clearly articulated as for other structural systems. Reliability-based design methods for pipelines often provide conflicting views about the spatial extent of limit states, the effect of spatial correlation, the applicability of target risks and target reliabilities (for instance on a per unit length basis), the link with lifecycle cost methods, and risk acceptability in general. The present paper first reviews probabilistic design and assessment approaches for pipelines, ranging from partial factors and limit state design, to reliability based and consequence-based methods. Subsequently we identify the various types of limit states from the point of view of their spatial characteristics. The paper also reviews the possible approaches to target risks and target reliabilities in view of the different spatial extent of the limit states. The role of spatial correlation as it impacts on different kind of pipeline limit states and on the risk acceptance process is discussed. The role of inspection, repair and maintenance can easily be included in many of the reliability-based pipeline design and assessment approaches as the lifetime costs of mitigative actions are fairly well defined, together with the spatially distributed consequences of failure, but they do add some additional challenges to the spatial modeling of the system.

Seismic Test Methods for Architectural Glazing Systems

1996 ◽  
Vol 12 (1) ◽  
pp. 129-143 ◽  
Author(s):  
Richard A. Behr ◽  
Abdeldjelil Belarbi
Keyword(s):  
Rational Design ◽  
Limit State ◽  
Test Methods ◽  
Test Method ◽  
Ultimate Limit State ◽  
Limit States ◽  
State Data ◽  
Design Procedures ◽  
Seismic Loadings ◽  
Ultimate Limit

An ongoing effort is being made at the University of Missouri-Rolla to develop standard laboratory test methods and codified design procedures for architectural glass under seismic loadings. Recent laboratory work has yielded some promising results regarding the development of an appropriate seismic test method for architectural glass, as well as identifying ultimate limit states that quantify the seismic performance and damage thresholds of various glass types. Specifically, a straightforward “crescendo-like” in-plane dynamic racking test, performed at a constant frequency, has been employed successfully. Two ultimate limit states for architectural glass have been defined: (1) a lower ultimate limit state corresponding to major glass crack pattern formation; and (2) an upper limit state corresponding to significant glass fallout. Early crescendo tests have yielded distinct and repeatable ultimate limit state data for various storefront glass types tested under dynamic racking motions. Crescendo tests will also be used to identify and quantify serviceability limit states for architectural glass and associated glazing components under dynamic loadings. These limit state data will support the development of rational design procedures for architectural glass under seismic loadings.

An Automated Approach for Designing Monopiles Subjected to Lateral Loads

2017 ◽  
Author(s):  
James P. Doherty ◽  
Barry M. Lehane
Keyword(s):  
Limit State ◽  
Ultimate Limit State ◽  
Lateral Loads ◽  
Limit States ◽  
Laterally Loaded Piles ◽  
Improve Design ◽  
Design Procedures ◽  
Automated Algorithm ◽  
Laterally Loaded ◽  
Ultimate Limit

This paper describes an automated algorithm for determining the length and diameter of monopile foundations subject to lateral loads with the aim of minimising the pile weight, whilst satisfying both ultimate and serviceability limit states. The algorithm works by wrapping an optimisation routine around a finite element p - y model for laterally loaded piles. The objective function is expressed as a function representing the pile volume, while the ultimate limit state and serviceability limit states are expressed as optimisation constraints. The approach was found to be accurate and near instantaneous when compared to manual design procedures and may improve design outcomes and reduce design time and costs.

Investigation of Ultimate Limit State Safety Margins in the Structural Design Rules

2017 ◽  
Author(s):  
Kristoffer Lofthaug ◽  
Lars Brubak ◽  
Åge Bøe ◽  
Eivind Steen
Keyword(s):  
Finite Elements ◽  
Safety Factor ◽  
Limit State ◽  
Load Level ◽  
Structural Safety ◽  
Ultimate Limit State ◽  
Structural Members ◽  
Safety Margins ◽  
Non Linear ◽  
Ultimate Limit

A study to document the Ultimate Limit State (ULS) safety margins built into the DNV GL rules for Bulk and Tanker is presented. Critical structural members were identified together with the load level at which these members start to develop permanent buckling sets exceeding normal fabrication tolerances. These critical load levels are then compared with the local ULS rule strength limits in order to have a measure for the structural safety margins and hull redundancy. Non-linear finite element (NFLE) analyses were performed to estimate the structural response for different focus areas (critical structural members). Typically, critical members in bottom, deck, transverse bulkhead and hopper were chosen. Cargo hold models were developed both with linear finite elements, [1,2] and non-linear finite elements, [3]. In the non-linear FE analysis, the structural safety factor for ULS was defined as the load level giving permanent plastic deformation equal to the permissible distortion (production tolerances) for structural members. The non-linear FE results were compared with the maximum permissible load level with respect to buckling and yielding according to DNV GL Ship rules [1] inclusive Common Structural Rules for BC&OT (CSR) [4]. The structural safety factor shows a typical value of 1.2–1.4, and for most cases the plate is governing dimensioning structural member. This study has identified significant structural safety margins, typically 20–40% above rule acceptance level for typical highly utilized local areas in Bulk and Tanker hulls. It is to be noted that global Hull Girder Capacity is not addressed in present paper.

Advances of a FEM for the Failure Probability Evaluation of Masonry Vehicular Bridge Support Piers

2012 ◽  
Vol 538-541 ◽  
pp. 580-585
Author(s):  
Luis Horacio Martínez-Mártinez ◽  
Gustavo Mendoza-Chavez ◽  
David Joaquin Delgado-Hernandez ◽  
David De León Escobedo ◽  
Elia Mercedes Alonso Guzmán ◽  
...  
Keyword(s):  
Risk Analysis ◽  
Structural Engineering ◽  
Limit State ◽  
Element Model ◽  
Failure Criteria ◽  
Point Of View ◽  
Structural Safety ◽  
State Function ◽  
Limit State Function ◽  
Risk Magnitude

One of the responsibilities of a Civil Engineer is to make decisions regarding preservation of infrastructure; therefore, there have been established concepts such as risk and risk analysis. Risk analysis, is a methodology applied to determine and evaluate the risk magnitude. From the structural engineering point of view, it is required that any structure become secure, this means that the capacity to withstand external actions (strength) will be higher than these actions (loads). In order to determine the structural safety, it is required to define the failure of the structure that it is not strongly related with the collapse of the structure; the failure criteria needs to be fixed depending on the use of the building and the consequences associated with the interruption of services provided by the facility. The failure then, is calculated by means of a limit state function in where it is established the failure criteria; failure is reached when a specific condition (strength) is surpassed by the actions over the structure. The present work aims to propose a preliminary Finite Element Model (FEM) that represents a pier used as support for vehicular bridges. This FEM is required for the assessment of mechanical behavior of the structure that will be used for the determination of the limit state function needed for risk assessment. Most of the simulations with FEM presented in literature are very used for modeling of masonry walls, but it is not usual to model structures such as bridge piers.

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 Secondary Moments due to Prestressing with Different Bond at the Ultimate Limit State

2018 ◽  
Vol 26 (1) ◽  
pp. 10-18
Author(s):  
Jaroslav Halvoník ◽  
Peter Pažma ◽  
Radoslav Vida
Keyword(s):  
Limit State ◽  
Plastic Hinge ◽  
Ultimate Limit State ◽  
Critical Cross Section ◽  
Structural System ◽  
Secondary Effects ◽  
Limit States ◽  
Internal Forces ◽  
Ultimate Limit ◽  
Kinematic Mechanism

Abstract Secondary effects of prestressing develop in statically indeterminate structures (e.g., continuous beams) due to the restraint of deformations imposed by hyperstatic restraints. These effects may significantly influence internal forces and stresses in prestressed structures. Secondary effects are influenced by the redundancy of a structural system, which raises the question of whether they will remain constant after a change in the structural system, e.g., due to the development of plastic hinge(s) in a critical cross-section(s) or after the development of a kinematic mechanism, or if they will disappear when the structure changes into a sequence of simply supported beams. The paper deals with an investigation of the behavior of continuous post-tensioned beams subjected to an ultimate load with significant secondary effects from prestressing. A total of 6 two-span beams prestressed by tendons with different bonds were tested in a laboratory with a load that changed their structural system into a kinematic mechanism. The internal forces and secondary effects of the prestressing were controlled through measurements of the reactions in all the supports. The results revealed that the secondary effects remained as a permanent part of the action on the experimental beams, even after the development of the kinematic mechanism. The results obtained confirmed that secondary effects should be included in all combinations of actions for verifications of ultimate limit states (ULS).

Sign in / Sign up

Export Citation Format

Share Document