Date of Award

8-2012

Level of Access

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Civil Engineering

Advisor

William G. Davids

Second Committee Member

Roberto A. Lopez-Anido

Third Committee Member

Eric Landis

Abstract

The Maine Department of Transportation (MaineDoT) is responsible for 2,723 bridges and minor spans, of which 271 are in poor condition and 226 are structurally deficient. The MaineDoT estimates that 288 bridges are at risk of closure or weight restrictions in the next decade. A MaineDoT report titled "Keeping Our Bridges Safe" estimates that funding for bridge replacement and rehabilitation needs to be increased from 70 million per year to 130 million per year to ensure bridge safety and minimize bridge restrictions or closures. Current AASHTO provisions for the conventional load rating of flat slab bridges rely on the equivalent strip method of analysis for determining live load effects, this is generally regarded as overly conservative by many professional engineers. As a result there are a significant number of slab bridges in Maine that are (or will be) posted for reduced truck weights, when in reality such postings may not be necessary. The objective of this study is to verify a program called SlabRate which was created using MATLAB, a numerical computing tool and explore the potential benefits of using it over the conventional strip width method. SlabRate computes the rating factors for simply-supported, continuous flat slab bridges using finite element analysis (FEA). The program allows for the definition of a variety of bridge configurations such as span length and width, skew angle, slab thickness etc. A user-friendly graphical user interface has been developed for SlabRate to allow rapid model creation and the review of load rating results. The verification includes creating parallel models of identical bridges in both SlabRate and the commercial software, and comparing the maximum moments and locations of those moments due to a variety of live and dead loads. These models were used to assess SlabRate's finite-element implementation and verify the assumptions that are used in SlabRate. In addition to using commercial software to verify SlabRate, live load testing of a reinforced flat-slab concrete bridge was done, these results were then compared with the predictions of SlabRate. To explore the potential benefits of using SlabRate over the conventional strip width, twenty existing bridges were load rated using both. Twenty one different truck configurations were analyzed, these include AASHTO's design and legal trucks, along with AASHTO's specialized hauling vehicles and MaineDoT's rating trucks. The results from comparing SlabRate to commercial models and the live load test showed that its finite element implementation is correct for evaluating simply-supported and continuous flat slab bridges. It was also found that the assumptions inherent in SlabRate were also verified, these assumptions were pinned supports, linear elasticity, and small deformations. It was also concluded that SlabRate can be reliably used to load rate flat slab bridges having skew angles of 20° or less. Only fourteen bridges of the original twenty bridges met this criteria, of which seven would have rating factors above one using SlabRate while below one using the conventional strip width method.

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