Load and Resistance Factor Design (LRFD) of Nuclear Straight Pipes for Loads That Cause Primary Stress

2010 ◽  
Vol 132 (2) ◽  
Author(s):  
Kleio Avrithi ◽  
Bilal M. Ayyub
Keyword(s):  
Resistance Factor ◽  
Safety Factors ◽  
Primary Stress ◽  
Safety Margins ◽  
Division 1 ◽  
Partial Safety Factors ◽  
Factor Design ◽  
Load And Resistance Factor ◽  
Different Levels ◽  
Allowable Stress Design

Class 2 and 3 nuclear piping is designed according to the allowable stress design (ASD) method used in the ASME Boiler and Pressure Vessel (B&PV) code, Sec. III, Division 1, NC and ND-3600 according to which safety factors applied to the strength of steel (resistance) provide acceptable safety margins for the piping design. This paper describes the development of design equations according to the load and resistance factor design (LRFD) method for loads that cause primary stress such as sustained weight, internal pressure, and earthquake for different levels of piping operation. The LRFD method differs from the ASD since multiple factors, applied separately to each load and the strength of steel, provide safety margins that correspond to a known and acceptable probability of failure for the piping. Load combinations are provided, statistical properties for the variables under consideration are presented and the partial safety factors are moreover illustrated for different values of the target reliability index.

Development of load and resistance factor design format for flexible pavements

1998 ◽  
Vol 25 (5) ◽  
pp. 880-885 ◽  
Author(s):  
Hyung Bae Kim ◽  
Ronald S Harichandran ◽  
Neeraj Buch
Keyword(s):  
Flexible Pavements ◽  
The United States ◽  
Resistance Factor ◽  
Pavement Design ◽  
Fatigue Design ◽  
Reliability Methods ◽  
Partial Safety Factors ◽  
Factor Design ◽  
Load And Resistance Factor ◽  
Different Levels

The objective of pavement design, just as with the design of other structures, is to provide economical designs at specified levels of reliability. Methods that yield designs with different levels of reliability are undesirable, and over the course of time design approaches in the United States have converged toward the load and resistance factor design (LRFD) format in order to assure uniform reliability. At present the LRFD format has been implemented in concrete, steel, wood, and bridge design specifications. In this paper, reliability concepts are used to illustrate the development of an LRFD format for fatigue design of flexible pavements. It is shown that 10 candidate pavement sections designed against premature fatigue failure according to standard practice using the DNPS86 software do not have uniform reliability. It is demonstrated that uniform reliability can be achieved by using the LRFD format. The work reported is based on assumed variations of pavement layer properties and on analytical formulation; field verification was not attempted.Key words: LRFD, reliability index, fatigue, partial safety factors, flexible pavement design.

Target Reliability Index for Load and Resistance Factor Design of Class 2 Carbon Steel Pipes

2017 ◽  
Author(s):  
Kleio Avrithi ◽  
Ramiro Mendoza
Keyword(s):  
Carbon Steel ◽  
Internal Pressure ◽  
Reliability Index ◽  
Safety Margin ◽  
Resistance Factor ◽  
Safety Factors ◽  
Target Reliability Index ◽  
Partial Safety Factors ◽  
Factor Design ◽  
Load And Resistance Factor

The use of the Load and Resistance Factor Design (LRFD) for Class 2 nuclear piping can be an alternative of the traditional Allowable Stress Design (ASD) method currently used in the ASME Boiler Pressure Vessel Code, Section III, Div. 1 providing the benefit of a known and consistent reliability for the designed piping. The design uncertainties and the necessary safety margin are evaluated for each equation for all service levels by considering the applied loads (e.g., earthquake, deadweight, internal pressure, etc.) and the resistance of steel, in the form of either the yield or ultimate strength, as separate variables described by their mean value, distribution, and coefficient of variation. The procedure yields different partial safety factors for each load and the resistance in opposition to the one safety factor used in each of the ASD equations of the Code. Although LRFD equations have been developed in the past, a range of possible partial safety factors were assigned to the variables, corresponding to different levels of reliability. This paper discusses the method used, namely calibration, for achieving same reliability as in the Code equations, and the progress made to assess a minimum target reliability index or else acceptable probability of failure for the LRFD equations that consider the earthquake load for pressurized pipes as well as the design for internal pressure for Class 2 nuclear pipes made of carbon steel.

A Reliability-Based Approach for the Design of Nuclear Piping for Internal Pressure

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Kleio Avrithi ◽  
Bilal M. Ayyub
Keyword(s):  
Internal Pressure ◽  
Allowable Stress ◽  
Safety Factors ◽  
Limit States ◽  
Present Design ◽  
Partial Safety Factors ◽  
Factor Design ◽  
American Society ◽  
Load And Resistance Factor ◽  
Allowable Stress Design

Nuclear pipes are designed to withstand primary membrane stresses generated by internal pressure according to the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (B&PV) Code, Section III, Parts NB-3641, NC-3641, and ND-3641, which uses the allowable stress design (ASD) method. This paper presents limit states and equations for the design of nuclear pipes for internal pressure based on the load and resistance factor design (LRFD) method. The LRFD method is shown and explained to be more consistent than the ASD method. The paper presents the procedure for the derivation of the partial safety factors. Moreover, these factors are evaluated, example calculations are provided, and comparisons with the present design are made.

Assessing the Target Reliability Index for Nuclear Piping

2016 ◽  
Author(s):  
Kleio Avrithi
Keyword(s):  
Reliability Index ◽  
Historical Data ◽  
Allowable Stress ◽  
Safety Factors ◽  
Code Calibration ◽  
Target Reliability Index ◽  
Consistent Manner ◽  
Factor Design ◽  
Load And Resistance Factor ◽  
Allowable Stress Design

Previous research developed Load and Resistance Factor Design (LRFD) equations for Class 2 and 3 nuclear piping for different reliability levels and load combinations. The LRFD equations consider separate safety factors for each load and for the strength of steel in opposition to the Allowable Stress Design (ASD) equations used in the ASME Boiler and Pressure Vessel (B&PV) Code, Section III, Div. 1, where only one safety factor is considered. In order to use the developed LRFD equations for the design of nuclear piping, specific reliability levels or else acceptable probabilities of failure need to be assigned to each Code equation. The paper discusses the available methods for evaluating the target reliability index, such as historical data of piping failures, expert-opinion elicitation, and Code calibration. Code calibration is the method of determining the existing level of reliability in the Code equations and assigning the same reliability to the developed LRFD equations in a consistent manner. Code Calibration is explained to be the more appropriate method of assigning reliability levels to the LRFD equations. The other methods can supplement the analysis results.

Risk-Informed Load and Resistance Factor Design (LRFD) Methods for Piping

2005 ◽  
Author(s):  
Bilal M. Ayyub ◽  
Ibrahim A. Assakkaf ◽  
Klieo Avrithi ◽  
Abinav Gupta ◽  
Nitin Shah ◽  
...  
Keyword(s):  
Resistance Factor ◽  
Future Research ◽  
Performance Requirements ◽  
Reliability Method ◽  
Load Effects ◽  
Partial Safety Factors ◽  
Factor Design ◽  
And Performance ◽  
Load And Resistance Factor ◽  
Technical Basis

The main objective of structural design is to insure safety, functional, and performance requirements of a structural system for selected target reliability levels, for specified period of time and for a specified environment. As this must be accomplished under conditions of uncertainty, risk and reliability analyses are deemed necessary in the development of such methods as risk-informed load and resistance factor design for piping. This paper provides a summary of the methodology and technical basis for reliability-based, load and resistance factor design suitable for the ASME Section III, Class 2/3 piping for primary loading, i.e., pressure, deadweight and seismic. The methodology includes analytical procedures, such as the First-Order Reliability Method (FORM) for calculating the LRFD-based partial safety factors for piping. These factors were developed in this paper for demonstration purposes, and they can be used ultimately in LRFD design formats to account for the uncertainties in strength and in the load effects. The technical basis provided in the paper is suitable for a proof-of-concept in that LRFD can be used in the design of piping with consistent reliability levels. Also, the results from additional projects in this area, including future research for piping secondary loads, will form the basis for future code cases.

Reliability-Based LRFD Criteria for Unstiffened Panel of Ship Structures

2013 ◽  
Author(s):  
Yong Bai ◽  
Miao-hua Qian
Keyword(s):  
Limit State ◽  
State Equation ◽  
Safety Factors ◽  
Ship Structures ◽  
Future Design ◽  
Practical Project ◽  
Safety And Reliability ◽  
Partial Safety Factors ◽  
Factor Design ◽  
Load And Resistance Factor

It is of significance to do the research of safety and reliability for ship structures, especially for marine structures because of the poor conditions and high risks, future design for ship structures will move toward a more rational and probability-based design. This paper chooses the unstiffened panel of ship structures as the research subject. Based on the MATLAB software, this paper develops the procedures and calculates one limit state equation of the panel, derives partial safety factors (PSF) for the Load and Resistance Factor Design (LRFD) of the panel under different reliability index levels. The PSF may provide a reference for the practical project design.

Structural Integrity for Nuclear Power Plant Against Excessive Load on Design Extension Condition

2013 ◽  
Author(s):  
Daigo Watanabe ◽  
Kiminobu Hojo
Keyword(s):  
Nuclear Power ◽  
Structural Integrity ◽  
Safety Factors ◽  
Design Code ◽  
Acceptance Criteria ◽  
Integrity Assessment ◽  
Current Design ◽  
Factor Design ◽  
Excessive Load ◽  
Load And Resistance Factor

This paper introduces an example of structural integrity evaluation for Light Water Reactor (LWR) against excessive loads on the Design Extension Condition (DEC). In order to assess the design acceptance level of DEC, three acceptance criteria which are the stress basis limit of the current design code, the strain basis limit of the current design code and the strain basis limit by using Load and Resistance Factor Design (LRFD) method were applied. As a result the allowable stress was increased by changing the acceptance criteria from the stress basis limit to the strain basis limit. It is shown that the practical margin of the LWR’s components still keeps even on DEC by introducing an appropriate criterion for integrity assessment and safety factors.

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