Determination of the Target Reliability Index of the Concrete Main Girder of Long-Span Structures Based on Structural Design Service Life

Abstract

This article studies the quantitative relationship between the target reliability index and the design service life for concrete main girders of cable-stayed bridges. A resistance degradation model of the concrete components is established by quantifying the effects of concrete carbonation and steel corrosion. It is assumed that the dead load and the live load are time-invariant with the distributions of normal and extreme type I, respectively, while the resistance is considered as time-variant with the distribution of lognormal. The standard values of the most unfavorable moment under dead and live loads are calculated by ANSYS, its mean value and standard deviation are further obtained using the statistical parameters suggested by the Unified Standard for Structural Reliability Design of Highway Engineering. The mean and standard deviation of resistance are obtained using the target reliability index value provided in the code above. The resistance value and reliability index at different times in a certain design service life can be obtained through the resistance degradation model. The result shows the reliability index decreases exponentially during the service life of the structure. For different design service years, different initial resistance values and initial reliability indexes can be deduced. Based on this, the target reliability index values considering the design service life are suggested. In the example analysis, the target reliability index of the concrete main girder of a cable-stayed bridge with a design service life of 100 years is suggested as 6.24. This research provides references for the design of concrete main girders of cable-stayed bridges.

Keywords

• long-span concrete girder
• target reliability index
• design service life
• concrete carbonation
• steel corrosion