RELIABILITY ASSESSMENT OF REINFORCED CONCRETE GRILLAGE GIRDER BRIDGE

Structural reliability analysis provides a rational framework to assess bridge performance. The generally adopted component-level reliability assessment cannot concern load redistribution after some components fail. Bridge reliability index calculated from component reliability indices will thus underestimate structural potential to resist loads. In this study, a system-level reliability assessment procedure based on bridge system limit state analysis is conducted to assess the reliability of a typical simply-supported reinforced concrete grillage girder bridge. The bridge is composed of 5 main girders and 3 diaphragms with T-shape cross section. A finite element model of the bridge is firstly established by modeling all girders and diaphragms as grid elements. Thousands of samples of random variables associated with resistance and loads are generated according to their probability distributions and then are substituted into the FEM model. For limit state analysis of each structure sample, the traffic loads are gradually increased till the bridge collapse, which means enough plastic hinges emerge in the structure. The load factor (LF), a ratio between ultimate loads and design loads, is computed to show the redundancy of bridge load carrying capacity. Based on the probability distribution of LF, the reliability index of the grillage girder bridge is calculated. The results can be used for bridge design and assessment process with a reasonable concern of uncertainties associated with resistance and load effect.