NORTHUMBERLAND STRAIT CROSSING: VERIFICATION OF THE TARGET RELIABILITY INDEX USED AS A BASIS FOR DESIGN

The Project Requirements for the Northumberland Strait Crossing specified that the bridge was to be designed to a target reliability index of 4.0 for multiple load path structures and greater than 4.0 for single load path structures, based on a design service life of 100 years. As part of its concurrence that the design and design criteria met the Project Requirements, an Independent Engineer made an independent assessment of ice loads, and of distributions of lifetime maximum values. A distribution for the sliding resistance of the soil was developed based on information provided by the Contractor's geotechnical consultants. With limited availability of historical data on ice characteristics of the region, and in the absence of a proven theory to predict ice forces on the structure, an analysis was made of uncertainty as opposed to variability. It was concluded that a probable range of values for a target reliability index could be calculated, and the study resulted in a set of load and resistance factors used to check the design.