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

Abstract

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.