Dealing With Knowledge Uncertainties in Pipeline Reliability Based Design and Assessment

2008 ◽  
Author(s):  
Maher Nessim ◽  
Joe Zhou ◽  
Mark Fuglem
Keyword(s):  
Epistemic Uncertainty ◽  
Probability Distributions ◽  
Limit State ◽  
Reliability Estimate ◽  
Formal Approach ◽  
Minimum Requirement ◽  
Reliability Based Design ◽  
Other Information ◽  
Input Variables ◽  
Knowledge Uncertainty

Knowledge uncertainties result from limitations of the data and other information required to define parameters that are used in estimating reliability with respect to a given failure threat. The parameters affected typically represent distribution parameters of input random variables used in the calculation; for example, the mean corrosion growth rate for a given pipeline segment. Knowledge uncertainties are distinct from randomness, which is typically manifested in variations in the basic input parameters affecting a given limit state; for example, variations in the excavator force applied to the pipeline in different impact events. Randomness is reflected in the probability distributions used to model the input variables affected and is automatically built into the reliability estimate. However, the reliability estimate is conditional on the values used for parameters affected by knowledge uncertainty. Since these parameters can take a range of values with different probabilities, knowledge uncertainty is best represented as a distribution or confidence interval on the calculated failure probability. Two approaches are proposed to deal with knowledge uncertainties in Reliability Based Design and Assessment (RBDA) applications in which design and operational choices are accepted if they meet a specified reliability target. The first is a formal approach in which reliability targets must be met with a specified level of confidence (e.g. meet the reliability targets with 90% confidence). The second approach is an informal one in which a single conservative value is used for each parameter affected by knowledge uncertainties. Although this approach relies on the judgment of the user, it has the advantage of being simple. In the context of standardizing RBDA, it is recommended that epistemic uncertainty be identified as an important issue that must be considered in demonstrating compliance. It is also recommended that both formal and informal approaches be permitted as viable means of accounting for epistemic uncertainty. The informal approach should be included as a minimum requirement, whereas the formal approach should be presented as an option. This recommended strategy addresses epistemic uncertainty without creating a significant obstacle to the application of RBDA.

scholarly journals Statistics of model factors in reliability-based design of axially loaded driven piles in sand

2018 ◽  
Vol 55 (11) ◽  
pp. 1592-1610 ◽  
Author(s):  
Chong Tang ◽  
Kok-Kwang Phoon
Keyword(s):  
Probability Distributions ◽  
Limit State ◽  
Hyperbolic Model ◽  
Driven Piles ◽  
Copula Theory ◽  
Resistance Factors ◽  
Reliability Based Design ◽  
Measured Resistance ◽  
Axially Loaded ◽  
Two Parameters

This paper compiles 162 reliable field load tests for axially loaded driven piles in sand from previous studies. The L1–L2 method is adopted to interpret the measured resistance from the load–settlement data. The accuracy of resistance calculations with the ICP-05 and UWA-05 methods based on cone penetration test profile is evaluated by the ratio (bias or model factor) of the measured resistance to the calculated resistance. A hyperbolic model with two parameters, where the load component is normalized by the measured resistance, is utilized to fit the measured load–settlement curves. The means, coefficients of variation, and probability distributions for the resistance model factor and the hyperbolic parameters are established from the database. Copula theory is employed to characterize the correlation structure within the hyperbolic parameters. The statistical properties of the model factors are applied to calibrate the resistance factors in simplified reliability-based designs of closed-end piles driven into sand at the ultimate and serviceability limit state by Monte-Carlo simulations. A simple example is provided to illustrate the application of the proposed resistance factors to estimate the allowable load for an allowable settlement at the desired serviceability limit probability.

Reliability Based Design Optimization Modeling Future Redesign With Different Epistemic Uncertainty Treatments

2013 ◽  
Vol 135 (9) ◽  
Author(s):  
Taiki Matsumura ◽  
Raphael T. Haftka
Keyword(s):  
Design Optimization ◽  
Thermal Protection ◽  
Epistemic Uncertainty ◽  
Probability Distributions ◽  
Aleatory Uncertainty ◽  
Reliability Based Design Optimization ◽  
Worst Case ◽  
Reliability Based Design ◽  
The Future ◽  
Integrated Thermal Protection System

Design under uncertainty needs to account for aleatory uncertainty, such as variability in material properties, and epistemic uncertainty including errors due to imperfect analysis tools. While there is a consensus that aleatory uncertainty be described by probability distributions, for epistemic uncertainty there is a tendency to be more conservative by taking worst case scenarios or 95th percentiles. This conservativeness may result in substantial performance penalties. Epistemic uncertainty, however, is usually reduced by additional knowledge typically provided by tests. Then, redesign may take place if tests show that the design is not acceptable. This paper proposes a reliability based design optimization (RBDO) method that takes into account the effects of future tests possibly followed by redesign. We consider each realization of epistemic uncertainty to correspond to a different design outcome. Then, the future scenario, i.e., test and redesign, of each possible design outcome is simulated. For an integrated thermal protection system (ITPS) design, we show that the proposed method reduces the mass penalty associated with a 95th percentile of the epistemic uncertainty from 2.7% to 1.2% compared to standard RBDO, which does not account for the future. We also show that the proposed approach allows trading off mass against development costs as measured by probability of needing redesign. Finally, we demonstrate that the tradeoff can be achieved even with the traditional safety factor based design.

An Efficient Response Surface Method Using Givens Transformation for Structural Reliability Analysis

2012 ◽  
Vol 532-533 ◽  
pp. 408-411
Author(s):  
Wei Tao Zhao ◽  
Yi Yang ◽  
Tian Jun Yu
Keyword(s):  
Response Surface ◽  
Response Surface Method ◽  
Structural Reliability ◽  
Limit State ◽  
State Function ◽  
Limit State Function ◽  
Surface Method ◽  
Mathematical Techniques ◽  
Input Variables ◽  
Improved Accuracy

The response surface method was proposed as a collection of statistical and mathematical techniques that are useful for modeling and analyzing a system which is influenced by several input variables. This method gives an explicit approximation of the implicit limit state function of the structure through a number of deterministic structural analyses. However, the position of the experimental points is very important to improve the accuracy of the evaluation of failure probability. In the paper, the experimental points are obtained by using Givens transformation in such way these experimental points nearly close to limit state function. A Numerical example is presented to demonstrate the improved accuracy and computational efficiency of the proposed method compared to the classical response surface method. As seen from the result of the example, the proposed method leads to a better approximation of the limit state function over a large region of the design space, and the number of experimental points using the proposed method is less than that of classical response surface method.

scholarly journals Information Analysis of Catchment Hydrologic Patterns across Temporal Scales

2016 ◽  
Vol 2016 ◽  
pp. 1-11 ◽  
Author(s):  
Baoxiang Pan ◽  
Zhentao Cong
Keyword(s):  
Epistemic Uncertainty ◽  
Temporal Scale ◽  
Information Analysis ◽  
Energy Correlation ◽  
Temporal Scales ◽  
Correlation Pattern ◽  
Event Scale ◽  
Information Contents ◽  
Input Variables ◽  
Annual Water

Catchment hydrologic cycle takes on different patterns across temporal scales. The interim between event-scale hydrologic process and mean annual water-energy correlation pattern requires further examination to justify self-consistent understanding. In this paper, the temporal scale transition revealed by observation and simulation was evaluated in an information theoretical framework namedAleatory Epistemic Uncertainty Estimation. The Aleatory Uncertainty refers to posterior uncertainty of runoff given the input variables’ observations. The Epistemic Uncertainty refers to the posterior uncertainty increase due to the imperfect observationdecodingin models. Daily hydrometeorological observations in 24 catchments were aggregated from 10 days to 1 year before implementing the information analysis. Estimations of information contents and flows of hydrologic terms across temporal scales were related with the catchments’ seasonality type. It also showed that information distilled by the monthly and annual water balance models applied here did not correspond to that provided by observations around temporal scale from two months to half a year. This calls for a better understanding of seasonal hydrologic mechanism.

scholarly journals Epistemic uncertainties and natural hazard risk assessment – Part 2: Different natural hazard areas

2016 ◽  
Author(s):  
K. J. Beven ◽  
S. Almeida ◽  
W. P. Aspinall ◽  
P. D. Bates ◽  
S. Blazkova ◽  
...  
Keyword(s):  
Debris Flows ◽  
Volcanic Ash ◽  
Natural Hazard ◽  
Epistemic Uncertainty ◽  
Probability Distributions ◽  
Good Practice ◽  
Pyroclastic Flows ◽  
Dam Safety ◽  
Landslides And Debris Flows ◽  
Hazard Risk Assessment

Abstract. This paper discusses how epistemic uncertainties are considered in a number of different natural hazard areas including floods, landslides and debris flows, dam safety, droughts, earthquakes, tsunamis, volcanic ash clouds and pyroclastic flows, and wind storms. In each case it is common practice to treat most uncertainties in the form of aleatory probability distributions but this may lead to an underestimation of the resulting uncertainties in assessing the hazard, consequences and risk. It is suggested that such analyses might be usefully extended by looking at different scenarios of assumptions about sources of epistemic uncertainty, with a view to reducing the element of surprise in future hazard occurrences. Since every analysis is necessarily conditional on the assumptions made about the nature of sources of epistemic uncertainty it is also important to follow the guidelines for good practice suggested in the companion Part 1 by setting out those assumptions in a condition tree.

scholarly journals Seismic Reliability-Based Design Approach for Base-Isolated Systems in Different Sites

2020 ◽  
Vol 12 (6) ◽  
pp. 2400
Author(s):  
Paolo Castaldo ◽  
Tatiana Ferrentino
Keyword(s):  
Seismic Hazard ◽  
Structural Properties ◽  
Limit State ◽  
Large Data ◽  
Design Approach ◽  
Data Set ◽  
Ductility Demand ◽  
Seismic Reliability ◽  
Reliability Based Design ◽  
Inelastic Structures

This study employs the seismic reliability-based design approach for inelastic structures isolated by friction pendulum isolators, considering two different highly seismic Italian sites to provide useful design recommendations. Incremental dynamic analyses are carried out to estimate the seismic fragility of the superstructure and of devices, assuming different structural properties and limit state thresholds. Finally, considering seismic hazard curves of the investigated sites, seismic reliability-based design curves are proposed to derive the dimensions in plan of devices and the ductility demand of the superstructure as a function of both the structural properties and the reliability level expected. The proposed results confirm the possibility of using seismic reliability-based design as a sustainable and applicable approach and represent a large data set to adopt this design methodology in any site with a similar seismic hazard.

scholarly journals Interpreting and propagating the uncertainty of the standard atomic weights (IUPAC Technical Report)

2018 ◽  
Vol 90 (2) ◽  
pp. 395-424 ◽  
Author(s):  
Antonio Possolo ◽  
Adriaan M. H. van der Veen ◽  
Juris Meija ◽  
D. Brynn Hibbert
Keyword(s):  
Probability Distribution ◽  
Isotopic Composition ◽  
Probability Distributions ◽  
Atomic Weight ◽  
Relative Molecular Mass ◽  
Detailed Knowledge ◽  
Technical Report ◽  
Other Information ◽  
Isotopic Abundances ◽  
Molecular Masses

AbstractIn 2009, the Commission on Isotopic Abundances and Atomic Weights (CIAAW) of the International Union of Pure and Applied Chemistry (IUPAC) introduced the interval notation to express the standard atomic weights of elements whose isotopic composition varies significantly in nature. However, it has become apparent that additional guidance would be helpful on how representative values should be derived from these intervals, and on how the associated uncertainty should be characterized and propagated to cognate quantities, such as relative molecular masses. The assignment of suitable probability distributions to the atomic weight intervals is consistent with the CIAAW’s goal of emphasizing the variability of the atomic weight values in nature. These distributions, however, are not intended to reflect the natural variability of the abundances of the different isotopes in the earth’s crust or in any other environment. Rather, they convey states of knowledge about the elemental composition of “normal” materials generally, or about specific classes of such materials. In the absence of detailed knowledge about the isotopic composition of a material, or when such details may safely be ignored, the probability distribution assigned to the standard atomic weight intervals may be taken as rectangular (or, uniform). This modeling choice is a reasonable and convenient default choice when a representative value of the atomic weight, and associated uncertainty, are needed in calculations involving atomic and relative molecular masses. When information about the provenance of the material, or other information about the isotopic composition needs to be taken into account, then this distribution may be non-uniform. We present several examples of how the probability distribution of an atomic weight or relative molecular mass may be characterized, and also how it may be used to evaluate the associated uncertainty.

APPLICATION OF UNCERTAINTY ANALYSIS TO STABILITY PROBLEMS OF STEEL-CONCRETE STRUCTURAL MEMBERS

2009 ◽  
Vol 1 (1) ◽  
pp. 44-49 ◽  
Author(s):  
Libor Puklický ◽  
Zdeněk Kala
Keyword(s):  
Epistemic Uncertainty ◽  
Limit State ◽  
Ultimate Limit State ◽  
Load Carrying Capacity ◽  
Structural Members ◽  
Load Carrying ◽  
Steel Sections ◽  
Limit Stress ◽  
Ultimate Limit

The paper deals with the fuzzy analysis of the ultimate limit state of a steel strut with an encased web in compression. The first part of the paper lists presumptions required for the determination of the theoretical load carrying capacity for the column. Stresses in the concrete and steel sections are determined according to the principles of elasticity. The ultimate limit state is given as the limit stress attained in the most stressed section of either the steel or concrete section. A general extended principle, which takes into account the epistemic uncertainty of input parameters, was utilized for the conducted analysis.

Practical Reliability-Based Design Approach for Foundation Engineering

1996 ◽  
Vol 1546 (1) ◽  
pp. 94-99 ◽  
Author(s):  
Kok Kwang Phoon ◽  
Fred H. Kulhawy
Keyword(s):  
Research Study ◽  
Limit State ◽  
Drilled Shafts ◽  
Ultimate Limit State ◽  
Foundation Engineering ◽  
Reliability Level ◽  
Reliability Based Design ◽  
Ultimate Limit State Design ◽  
Ultimate Limit ◽  
Selection Of

A research study was completed recently that was directed toward the development of practical, reliability-based design (RBD) equations specifically for foundation engineering. Some of the key RBD principles used in the study are presented. The important considerations involved in the development of practical and robust RBD criteria are emphasized. In particular, the selection of an appropriate reliability assessment technique and the careful characterization and compilation of geotechnical variabilities are important because of their central role in the calculation of the probability of failure and the assessment of the target reliability level. An overview of a simplified RBD approach is given, and an application of this approach to the ultimate limit state design of drilled shafts under undrained uplift loading is discussed.

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