Reliability-Based Calibration of Design Code for Concrete Structures (ACI 318)

Calibration was performed to determine the resistance factors corresponding to a new set of load and load combination factors. The study involved the development of calibration procedure, development of statistical models for load and resistance, reliability analysis for selected representative structural components and materials, selection of the target reliability indices, and finally selection of the recommended resistance factors. Structural resistance is considered as a product of three factors: material properties, fabrication (dimensions), and professional (analysis factor). The major focus of this study is the analysis of material properties. Test results were provided by the industry for three groups of material: concrete, reinforcing steel bars and prestressing steel strands. It was observed that the quality of materials has been improved over the last 30 years and this is reflected in reduced coefficients of variation and increased bias factors. The reliability is expressed in terms of reliability index calculated as a function of the load and resistance parameters. The results served as a basis for the selection of the target reliability indices. The final step in calibration is the selection of resistance factors. keyword: Concrete, Resistance factor, Cumulative distribution function, Statistical parameters,