Reliability Bases of Structural Safety and Design

Principal probability concepts are presented and developed for the proper modeling and analysis of uncertainty, and for evaluating the associated effects on safety and design. Under conditions of uncertainty, safety and serviceability of structures can be assured only in terms of the probability of survival (or conversely of failure); accordingly, the level of safety is expressed explicitly as a function of the degree of uncertainty. The assumptions necessary to implement probability concepts in the development of practical design criteria and code provisions are explained and delineated. Uncertainty (including uncertainty associated with errors in estimation and imperfection in mathematical models) is expressed in terms of the coefficient of variation; in this term, its effect on safety and design can be assessed systematically and logically through first-order statistical analysis. Specific proposals for evaluating safety level and for developing safety and load factors for design are developed.