Quantifying Quality Improvement Programs

by Joseph F. Murphy, Structural Reliability Consultants, United States,

Document Type: Proceeding Paper

Part of: Probabilistic Methods in Civil Engineering


Structural codes are evolving to a limit state design basis in which the safety checks are derived from the underlying probability distributions of strength and loads. An example safety checking equation is: φ Rn≥1.2 Dn+1.6 Ln where 1.2 and l.6 are load factors on nominal dead and live loads, Dn and Ln, and φ is a resistance factor on nominal resistance, Rn. For specific probability distributions of dead and live loads, D and L, and resistance R, a reliability index β can be calculated as a function of the resistance factor φ. If φ is held constant, the increase in β quantifies the increase in reliability. If β is held constant, the increase in φ quantifies the increase that can be taken on the nominal resistance, Rn, of the original distribution. Two processes are presented: a process which selectively removes material (with a specified or measured removal efficiency) from the lower tail (below a specific strength); a process which removes material based on a correlated variable. Material is removed with 100% efficiency on the correlated variable below a specific set point.

Subject Headings: Structural safety | Load factors | Limit states | Probability | Probability distribution

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