Reliability-Based Structural Design

Safety is described in terms of reliability or probability of survival for multimember multiload condition structures with loads and strengths as random variables. These include weakest link structures which fail if any member fails and fail-safe structures which survive even after the failure or yielding of some members. A proposed design method is to proportion member sizes with a mathematical programming approach to minimize weight subject to an overall probability of failure constraint. Examples presented include trusses designed by weakest link failure analysis and limit designed redundant or fail safe rigid frames. A sequence of numerical integrations evaluates the failure probability for any form of load and strength frequency distribution. Results show the optimum design versus allowable failure probability, coefficients of variation and frequency distribution for load and strength and the effect of failure mode correlation which is due to different members being affected by the same loading.