Date of Award

Spring 5-3-2024

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Civil Engineering

Advisor

William Davids

Second Committee Member

Andrew Schanck

Third Committee Member

Roberto Lopez-Anido

Abstract

Bridges are vital nodes in the national transportation network and are essential for the movement of people and goods. With aging infrastructure new replacements are required, and increasing the longevity of these new structures is beneficial to future generations. This has opened the door to the use of new materials including fiber reinforced polymers (FRPs) that are light weight and non-corroding, offering longer life spans compared to currently used materials such as steel and concrete. At the University of Maine, a novel FRP composite tub (CT) girder has been developed and used in the construction of four bridges to-date. While laboratory experimentation and limited field tests have been completed to further understanding of its strength and behavior, live load distribution in the structures has yet to be studied in detail.

This study focuses on quantifying of the percentage of live load moment and shear apportioned to a single girder for design purposes. The American Association of State Highway and Transportation Officials (AASHTO) provides guidance on live load distribution in bridges constructed with steel, concrete, and wood girders, but not for FRP girders, and current CT girder design assumes the applicability of AASHTO’s guidance for concrete spread box girders live load distribution. This research addresses this current lack of guidance for CT girder design both experimentally and computationally. First, live load distribution in CT girder bridges is assessed using four diagnostic field live load tests performed on two different, in-service CT girder bridges. Test results are then compared to existing AASHTO provisions to critically assess their applicability to CT girders. Subsequently, finite element (FE) models employing various levels of discretization were assessed for their ability to predict test results. Ultimately, two different FE discretizations that are computationally tractable and broadly applicable to CT girder bridges were implemented for predicting live load distribution, one for moment and another for shear. These models were used for a suite of parametric studies that provided insight into the effects of realistic ranges of significant bridge geometric design parameters such as girder spacing, span length and skew angle on live load distribution factors (DFs). The results show that current AASHTO provisions for concrete box girders consistently predict higher DFs for both moment and shear carried by interior CT girders. New, CT-girder specific DF expressions for moment were then developed and proposed for use in future designs. For shear, initial parametric studies were completed to explore the limitations of current AASHTO expressions, and future work is proposed that includes expanding the shear parametric study to develop shear DF expressions tailored to CT girders.

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