Partial safety factors for designing and assessing flexible pavement performance

2004 ◽  
Vol 31 (3) ◽  
pp. 397-406 ◽  
Author(s):  
S S Wang ◽  
H P Hong
Keyword(s):  
Safety Factor ◽  
Load Resistance ◽  
Flexible Pavement ◽  
Pavement Performance ◽  
Single Factor ◽  
Safety Factors ◽  
State Highway ◽  
Partial Safety Factor ◽  
Reliability Method ◽  
Partial Safety Factors

In designing and assessing pavement performance, the uncertainty in material properties and geometrical variables of pavement and in traffic and environmental actions should be considered. A single factor is employed to deal with these uncertainties in the current American Association of State Highway and Transportation Officials (AASHTO) guide for design of pavements. However, use of this single factor may not ensure reliability-consistent pavement design and assessment because different random variables that may have different degrees of uncertainty affect the safety and performance of pavement differently. Similar problems associated with structural design have been recognized by code writers and dealt with using partial safety factors or load resistance factors. The present study is focused on evaluating a set of partial safety factors to be used in conjunction with the flexible pavement deterioration model in the Ontario pavement analysis of cost and the model in the AASHTO guide for evaluating the flexible pavement performance or serviceability. Evaluation and probabilistic analyses are carried out using the first-order reliability method and simple simulation technique. The results of the analysis were used to suggest factors that could be used, in a partial safety factor format, for designing or assessing flexible pavement conditions to achieve a specified target safety level.Key words: deterioration, reliability, pavement, serviceability, stochastic process, performance, partial safety factor.

Reliability-Based Derivation of Partial Safety Factor for Structural Integrity Assessment

2008 ◽  
Author(s):  
Shuo Pan ◽  
Jianping Zhao
Keyword(s):  
Safety Factor ◽  
Fracture Mode ◽  
Structural Integrity ◽  
Research Work ◽  
Random Variables ◽  
Assessment Procedure ◽  
Safety Factors ◽  
Integrity Assessment ◽  
Partial Safety Factor ◽  
Partial Safety Factors

When there are uncertainties in the input random variables, or scatter in the material properties, probabilistic assessment is a useful tool for decision making in the field of safety analysis. The partial safety factor (PSF) method was aimed on ensuring that the failure probability did not exceed a target value. In order to be conservative the input value for each random variable during the assessment procedure should be multiplied by the partial safety factors. So it is essentially a deterministic assessment using conservative values of the input random variables and a relatively simple and independent method of assessing failure probabilities using R6 failure assessment diagram. The application of partial safety factors is an important breakthrough of assessment in structures containing defects. In recent years, sets of PSFs for load, defect size, fracture toughness and yield stress had been given in two standards, BS7910 and API579. However, the recommended PSFs in both standards were larger than the original PSFs in PD6493 which was replaced by BS7910. It is therefore a new method of calculating PSFs should be found to prove which is more appropriate and convenient for engineering application. In the case of the partial safety factor method target reliabilities in the range from 0.001 to 0.00001 were considered and new series of PSFs were derived from the results of reliability analysis for the linear elastic fracture mode and elastic-plastic fracture mode. After comparing with the PSFs in BS7910 and API 579, it is concluded that the partial safety factors were generally conservative compared to our research work.

Applying Partial Safety Factors in Mooring System Design

2005 ◽  
Author(s):  
Siril Okkenhaug ◽  
Bjo̸rn Sogstad ◽  
Jan Mathisen
Keyword(s):  
Safety Factor ◽  
Low Frequency ◽  
Offshore Structures ◽  
Mooring Line ◽  
Safety Factors ◽  
Safety Level ◽  
Partial Safety Factor ◽  
Account Due ◽  
Almost All ◽  
Partial Factor

The DNV offshore standard for position mooring, DNV-OS-E301 [1], was issued June 2001 based on the result from a joint industry project. A new revision was issued in October 2004. The consequences for mobile units when applying the new standard, compared to the old class rules, have been a major concern for operators of mobile units. A comparison study has therefore been initiated, where four relevant units are considered. We have applied the mooring design for existing mobile units that operate in Norwegian waters. Two different water depths are covered. The new standard, DNV-OS-E301, applies a partial safety factor format. However, the main difference when applying DNV-OS-E301 compared to the old POSMOOR [2] rules is that low frequency (LF) motions will have to be taken into account when calculating the line tensions. The results for the four mobile units are compared also to other relevant codes, i.e. the Draft International Standard ISO 19901-7 [4] and the present Norwegian regulations for offshore structures, NMD [5 & 6]. It should be noted that the present NMD regulations still do not require that LF motions are taken into account. Due to the partial safety factor format in DNV-OS-E301, more or less all of the units fulfill the requirements even though LF motion is accounted for. However, when comparing the results to the NMD regulations, the introduction of LF motion is crucial for almost all of the mobile units studied, as they have problems in fulfilling the requirements when this response is accounted for. Simply including LF motion in design would tend to increase the required strength of the resulting mooring line designs, and thereby raise the safety level if nothing else is done with the NMD regulations. Thus, provided that the present safety level for mobile units is sound, the present NMD safety factors could either be reduced or the partial factor format in DNV-OS-E301 could be adopted in order to maintain the safety level for mobile units when LF motion is taken into account.

Analysis of the Partial Safety Factor Method Using Probabilistic Techniques

2010 ◽  
Author(s):  
B. A. Lindley ◽  
P. M. James
Keyword(s):  
Probabilistic Method ◽  
Probability Of Failure ◽  
Safety Factors ◽  
First Order Reliability Method ◽  
First Order ◽  
Target Probability ◽  
Reliability Method ◽  
Input Parameters ◽  
Partial Safety Factors ◽  
Hand Calculation

Partial Safety Factors (PSFs) are scaling factors which are used to modify the input parameters to a deterministic fracture mechanics assessment in order to consider the effects of variability or uncertainty in the values of the input parameters. BS7910 and SINTAP have adopted the technique, both of which use the First Order Reliability Method (FORM) to derive values for PSFs. The PSFs are tabulated, varying with the target probability of failure, p(F), and the Coefficient of Variance (COV) of the variable. An accurate assessment of p(F) requires a probabilistic method with enough simulations. This has previously been found to be time consuming, due to the large number of simulations required. The PSF method has been seen as a quick way of calculating an approximate, conservative value of p(F). This paper contains a review of the PSF method, conducted using an efficient probabilistic method called the Hybrid probabilistic method. The Hybrid probabilistic method is used to find p(F) at a large number of assessment points, for a range of different PSFs. These p(F) values are compared to those obtained using the PSF method. It is found that the PSF method was usually, and often extremely, conservative. However there are also cases where the PSF method was non-conservative. This result is verified by a hand calculation. Modifications to the PSF method are suggested, including the establishment of a minimum PSF on each variable to reduce non-conservatisms. In light of the existence of efficient probabilistic techniques, the non-conservatisms that have been found in the PSF method, coupled with the impracticality of completely removing these non-conservatisms, it is recommended that a full probabilistic assessment should generally be performed.

A Partial Safety Factor Method for System Reliability Prediction With Outsourced Components

2019 ◽  
Vol 5 (2) ◽  
Author(s):  
Zhengwei Hu ◽  
Xiaoping Du
Keyword(s):  
System Reliability ◽  
Joint Probability ◽  
System Level ◽  
Safety Factors ◽  
Component Reliability ◽  
Reliability Method ◽  
Component Supplier ◽  
Partial Safety Factors ◽  
Joint Probability Density ◽  
Probability Density Function Pdf

System reliability is usually predicted with the assumption that all component states are independent. This assumption may not accurate for systems with outsourced components since their states are strongly dependent and component details may be unknown. The purpose of this study is to develop an accurate system reliability method that can produce complete joint probability density function (PDF) of all the component states, thereby leading to accurate system reliability predictions. The proposed method works for systems whose failures are caused by excessive loading. In addition to the component reliability, system designers also ask for partial safety factors for shared loadings from component suppliers. The information is then sufficient for building a system-level joint PDF. Algorithms are designed for a component supplier to generate partial safety factors. The method enables accurate system reliability predictions without requiring proprietary information from component suppliers.

scholarly journals Probabilistic Assessment Approach of the Aerostatic Instability of Long-Span Symmetry Cable-Stayed Bridges

Symmetry ◽  
2021 ◽  
Vol 13 (12) ◽  
pp. 2413
Author(s):  
Fenghui Dong ◽  
Feng Shi ◽  
Libin Wang ◽  
Yang Wei ◽  
Kaiqi Zheng
Keyword(s):  
Finite Element ◽  
Safety Factor ◽  
Random Variables ◽  
Safety Analysis ◽  
Safety Factors ◽  
Long Span ◽  
Reliability Method ◽  
Sutong Bridge ◽  
Cable Stayed Bridges ◽  
Probabilistic Safety

The existing safety analysis methods for the assessment of the aerostatic stability of long-span symmetry cable-stayed bridges have difficulties in meeting the requirements of engineering applications. Based on the finite element method and the inverse reliability theory, an approach for the probabilistic safety analysis of the aerostatic instability of long-span symmetry cable-stayed bridges is proposed here. The probabilistic safety factor of aerostatic instability of long-span symmetry cable-stayed bridges was estimated using the proposed method, with Sutong Bridge as an example. The probabilistic safety factors for the aerostatic instability of Sutong Bridge were calculated using the finite element inverse reliability method, based on the FORM approach. The influences of the mean value and the coefficient of variation of random variables, as well as the iterative step length of finite difference, on the probabilistic safety factors of aerostatic instability of Sutong Bridge were analyzed. The results indicated that it is necessary to consider the uncertainties of random variables in probabilistic safety factor assessments of aerostatic instability in cable-stayed bridges using the proposed method, which could be recommended for the assessment of safety factors involved in the aerostatic instability of long-span symmetry cable-stayed bridges. The randomness of the parameters had an important influence on the probabilistic safety factor of the aerostatic stability of Sutong Bridge. Neglecting the randomness of these parameters may result in instability of the structure.

Application of Partial Safety Factors for Fitness-for-Service Assessment of Pressure Equipment With Local Metal Loss

2017 ◽  
Author(s):  
Takuyo Kaida ◽  
Shinsuke Sakai
Keyword(s):  
Reliability Analysis ◽  
Limit State ◽  
Probability Of Failure ◽  
Pressure Vessels ◽  
Metal Loss ◽  
State Function ◽  
Safety Factors ◽  
Loss Assessment ◽  
Reliability Method ◽  
Partial Safety Factors

Reliability analysis considering data uncertainties can be used to make a rational decision as to whether to run or repair a pressure equipment that contains a flaw. Especially, partial safety factors (PSF) method is one of the most useful reliability analysis procedure and considered in a Level 3 assessment of a crack-like flaw in API 579-1/ASME FFS-1:2016. High Pressure Institute of Japan (HPI) formed a committee to develop a HPI FFS standard including PSF method. To apply the PSF method effectively, the safety factors for each dominant variable should be prepared before the assessment. In this paper, PSF for metal loss assessment of typical pressure vessels are derived based on first order reliability method (FORM). First, a limit state function and stochastic properties of random variables are defined. The properties of a typical pressure vessel are based on actual data of towers in petroleum and petrochemical plants. Second, probability of failure in several cases are studied by Hasofer-Lind method. Finally, PSF’s in each target probability of failure are proposed. HPI published a new technical report, HPIS Z 109 TR:2016, that provide metal loss assessment procedures based on FORM and the proposed PSF’s described in this paper.

Reliability Assessments of Concrete Filled FRP Tube Columns

2013 ◽  
Vol 405-408 ◽  
pp. 731-734
Author(s):  
Ying Wu Zhou ◽  
Feng Xing ◽  
Li Li Sui
Keyword(s):  
Safety Factor ◽  
Coefficient Of Variation ◽  
Reliability Index ◽  
Concrete Strength ◽  
Reliability Design ◽  
Partial Safety Factor ◽  
Highly Sensitive ◽  
Partial Safety Factors ◽  
Reliability Assessments ◽  
Frp Tube

This paper has investigated the reliability of concrete filled FRP tube columns using the FRP confined concrete theory developed recently by the authors. The reliability index of the column is assessed by Monte Carlo method. The importance of the use of partial safety factors of FRP and concrete in the reliability design of concrete filled FRP tube columns is studied. The results indicate that the reliability index of concrete filled FRP tube columns increases remarkably as the FRP partial safety factor increased. It is concluded that the FRP partial safety factor is independent on the coefficient of variation of FRP strength but is highly sensitive to the coefficient of variation of concrete strength especially in the case of low confinement ratio. Considering the actual situation in engineering applications, to reach a target reliability index of 3.5, a partial safety factor of 1.4 is finally recommend for both FRP and concrete.

Investigation of Partial Safety Factor Approach for Flaw Assessment Procedure in Chinese FFS Code

2017 ◽  
Author(s):  
Zhiyuan Han ◽  
Guoshan Xie ◽  
Shanshan Shao ◽  
Zhifeng Li
Keyword(s):  
Safety Factor ◽  
Limit State ◽  
Assessment Procedure ◽  
State Equations ◽  
First Order ◽  
Partial Safety Factor ◽  
Reliability Method ◽  
Failure Assessment ◽  
Derivation Method ◽  
Level 2

Partial safety factor (PSF) is a reliability approach for considering the variance of parameters in flaw assessment procedure in major fitness-for-service (FFS) codes, such as recent API579 and BS7910 codes, but is still not adopted in Chinese FFS code GB/T 19624-2005. This study investigated the derivation method for PSFs based on GB/T 19624 procedure. The limit state equations for PSFs calculation were proposed based on GB/T 19624 level 2 failure assessment diagram (FAD). The distribution of random variables was determined according to China’s domestic features. The first order reliability method (FORM) and second order reliability method (SORM) were employed as reliability analysis methods, and the calculated results were both compared with that simulated using Monte Carlo method. The PSFs at different target reliability levels were established and compared with that in API 579 and BS 7910. The method proposed in this study provides a basis for introducing PSF approach into Chinese FFS code.

PROBABILISTIC OPTIMIZATION OF PARTIAL SAFETY FACTORS FOR THE DESIGN OF INDUSTRIAL BUILDINGS

2008 ◽  
Vol 15 (05) ◽  
pp. 411-424 ◽  
Author(s):  
ZOLTÁN SADOVSKÝ ◽  
DUŠAN PÁLEŠ
Keyword(s):  
Probabilistic Models ◽  
Limit State ◽  
Optimization Procedure ◽  
Ultimate Limit State ◽  
Safety Factors ◽  
Probabilistic Optimization ◽  
Industrial Buildings ◽  
Reliability Method ◽  
Partial Safety Factors ◽  
Ultimate Limit State Design

By probabilistic optimization of partial safety factors for a class of structures a more uniform reliability of practical design of individual cases within the class is aimed at. The paper deals with an ultimate limit state design of a class of low rise industrial buildings subject to climatic loads and permanent loads. The optimization is carried out on selected representative structures, the reliability of which is calculated by the level II reliability method FORM. Probabilistic models of cross section resistance and of climatic loads pertinent to a continental climate are based on measurements. Peculiarities of the optimization procedure, particularly optimization stages in conjunction with the choice and possible differentiation of partial factors are discussed.

Structural Reliability Analysis Applied on Steel Ships for Rule Partial Safety Factors Calibration

2017 ◽  
Author(s):  
Alexis Benhamou ◽  
Quentin Derbanne ◽  
Jérôme de Lauzon
Keyword(s):  
Reliability Analysis ◽  
Ultimate Strength ◽  
Structural Reliability ◽  
Bending Moment ◽  
Safety Factors ◽  
Structural Rules ◽  
Structural Reliability Analysis ◽  
Reliability Method ◽  
Partial Safety Factors ◽  
Common Structural Rules

Ultimate strength assessments in current IACS Common Structural Rules (CSR) are determined by a limited number of constant partial safety factors (PSF). These coefficients are inherited from the previous Common Structural Rules for Oil Tankers, and were determined using a structural reliability analysis (SRA) based on a limited number ship. The authors decided to lead a more comprehensive structural reliability analysis to propose and discuss a new set of rule formulations. A literature review is carried out in order to determine an extensive database of virtual ships covering the whole range of existing ships with a few representative parameters. SRA is applied for ultimate strength assessment on this database. Uncertainties are modeled by a set of probability distributions applied to each characteristic quantity (still water bending moment, wave bending moment and capacity) and a Second Order Reliability Method (SORM) is used to target the ultimate capacity corresponding to a given failure probability for each ship. A set of several PSF formulations are then derived from these results using both Working Stress Design (WSD) and Load and Resistance Factor Design (LRFD) approaches. These formulations are then discussed to get an optimum between simplicity and accuracy of the results.

Sign in / Sign up

Export Citation Format

Share Document