CALIBRATION OF THE ONTARIO HIGHWAY BRIDGE DESIGN CODE 1991 EDITION

The paper describes the calculation of load and resistance factors for the Ontario Highway Bridge Design Code (OHBDC) 1991 edition. The work involved the development of load and resistance models, the selection of the reliability analysis method, and the calculation of the reliab ility indices. The statistical models for load and resistance are revi ewed. The considered load components include dead load, live load, and dynamic load. Resistance models are developed for girder bridges (ste el, reinforced concrete, and prestressed concrete). A reliability anal ysis is performed for selected representative structures. Reliability indices are calculated using an iterative procedure. The calculations are performed for bridge girders designed using OHBDC 1983 edition. Th e resulting reliability indices are between 3 and 4 for steel girders and reinforced concrete T-beams, and between 3.5 and 5 for prestressed concrete girders. Lower values are observed for shorter spans (up to 30-40 m). The acceptance criterion in the selection of load and resist ance factors is closeness to the target reliability level. The analysi s confirmed the need to increase the design live load for shorter span s. Partial resistance factors are considered for steel and concrete. T he criteria for the evaluation of existing bridges are based on the re liability analysis and economic considerations.