United States Department of Transportation
i
Redundancy of Twin Steel Box Girder Bridges
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2021-01-01
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[PDF-11.64 MB]
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Edition:Final Report, January 2018-January 2021
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Abstract:Currently, twin steel box girder bridges (TSGB) are classified as bridges with fracture critical members. Recent research results, however, demonstrated a high level of internal redundancy. The main question as to what load levels and performance measures established on a scientific basis should be used still remains unanswered. The objective of this project is to establish a design target performance and safety level for TSGB, and outline an approach for assessing the redundancy. For the purpose of this study, a simply supported single-span bridge tested at the University of Texas with a span length of 120 ft was selected as a baseline model. Weigh-in-motion data in the state of Florida was used to develop a live load model. A detailed finite element model was developed and validated to investigate the failure mode and capacity. The results showed that concrete deck bending is the dominant failure mode after a fracture occurs in one girder in the bridge. Using these results, a simple and unified yield line analysis method was developed to determine the bridge deck capacity. Furthermore, a simplified reliability analysis approach was developed to estimate the minimum criteria that the deck and intact girder should satisfy in order to ensure redundancy; that is, the bridge can carry safely a minimum level of load after a fracture in one girder until the next inspection. This analysis developed and tabulated a set of reliability indexes that could be translated to redundancy expectation based on the various levels of live load expected on the bridge between inspection intervals
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