Research for Calibration and Resistant Factors of LRFD Design of Steel Bridge in China

Abstract

The coming Chinese specification for the steel highway bridge will adopt the design method of probability limit state on the basis of the structure reliability theory. The limit-state equation with load and resistance factors plays a key role in this method, so determining the reasonable value of the factors is the foremost work in load and resistance factor design (LRFD). The primary objective of this paper is to calibrate the target reliability index of the steel highway bridge according to current specification by the first-order secondary-moment method (JC method) and to calculate the recommended resistance factors of Q235q and Q345qD (two commonly used steels for bridges in China) by means of an optimization method. The primary and adjunctive load combinations of the steel highway bridge are taken into account, respectively. The calibrated reliability index is used to calculate the five types of loading members’ factors, which are axial tensile, axial compressive, eccentric compressive, flexural, and shear member. Then the results are compared with the relative parameters in the “Unified Standard for Reliability Design of Highway Engineering Structures” (Ministry of Transport of China GB/J50283-1999). It is demonstrated that the value put forward in this study shows precision and application well. Hence, the recommended resistance factors of the steel highway bridge can be a reference for the new specification of the steel highway bridge.