Reliability evaluation of twin steel box girder bridges using a simplified method

Abstract

The objective of this study is to comprehend the performance of twin steel box girder (TSBG) bridges after complete fracture of one girder and to establish an outline of an approach for reliability analysis required for assessing their levels of structural redundancy. The earlier work has concluded that the main mode of failure for the bridge in such case is a failure in the deck. This conclusion obtained through a series of experimental and numerical studies significantly reduces the efforts for assessing the safety of TSBG bridges. For the purpose of developing an approach for reliability analysis, a simply-supported single-span bridge tested at the University of Texas (UT) at Austin was selected as a baseline model. The results of the current study through an extensive finite element analysis confirmed the earlier findings that concrete deck failure is the dominant failure mode of the bridge after the occurrence of a fracture in one of the girders. Building on the work at UT, an improved simple and unified yield line analysis method was developed to determine the bridge deck capacity. For the first time, a comprehensive and coherent reliability approach was used to assess the safety of TSBG bridges after the complete fracture of one steel girder. Though the developed safety assessment approach was applied to one example bridge, nevertheless, the method described in this paper could easily be extended to evaluate other TSBG bridges. Although the results of this study cannot readily be generalized for all TSBG bridges without further evaluation, this study shows that simply supported twin steel box girder bridges could indeed be safe and potentially removed from the fracture critical list.