Date

2013

Document Type

Thesis

Degree

Master of Science

Department

Civil Engineering

First Adviser

Roy, Sougata

Abstract

Recently, there has been an interest in to enhancing the longevity of temporary bridge structures. These structures have successfully survived up to five years in-service in rural areas and secondary roads. However, the decks develop significant fatigue cracking within eight months when subjected to heavy truck traffic. A pilot study of the existing deck design including 3D Finite Element Analyses and static and fatigue testing of three full size specimens showed that the stringer-to-tube connections were the most fatigue critical deck details. To improve the fatigue performance, the deck design was enhanced with a thicker deck plate, thicker transverse tubes, and rearrangement of the stringer-to-deck plate welds. Grillage analyses of the deck designs, validated against the 3D FEA results, were performed to assess the global behavior of the decks under load. In general, the grillage analysis results were accurate along the deck stringers. Two full size enhanced bridge decks were tested under static and fatigue loading. The enhanced deck deflected less than the existing deck, and had some reduction in stresses. Both decks had fatigue cracking at the stringer-to-tube fillet welded connections after about 9 million cycles; this was less than the target lifespan. Post-mortem evaluations revealed that the sub par fatigue performance of the decks was due to poor weld quality. The fatigue life of the connection detail was found to be on the AASHTO Category D design curve, in the finite life regime.Quality weld fabrication at the stringer-to-tube connections is recommended for improved fatigue performance of the enhanced deck design. In addition, asymmetric rearrangement of the stringer-to-tube welds may be investigated to increase the flexibility of the stringer web and reduce the out-of-plane bending stresses

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