Date of Award

6-2026

Degree Name

Doctor of Philosophy

Department

Civil and Construction Engineering

First Advisor

Upul Attanayake, Ph.D., P.E.

Second Advisor

Yufeng Hu, Ph.D.

Third Advisor

Jinseok Kim, Ph.D.

Fourth Advisor

Purushotham Pakala, Ph.D.

Keywords

Beam end cracking, bridge preservation and repair, capacity-based condition assessment, prestressed concrete beams, service life extension, Strut-and-Tie Method (STM)

Abstract

Prestressed concrete (PSC) I-shaped beams are widely used in bridge construction because of their structural efficiency and durability. The service life of these beams is reduced and the maintenance frequency is increased due to the distress during fabrication and subsequent deterioration. Although several mitigation strategies have been proposed and implemented, beam end cracking during fabrication remains a major concern. The causes and mitigation strategies for beam end cracking have been studied for decades, but there have been no comprehensive studies utilizing beam end strains during fabrication and lifting at prefabrication plants under normal operational conditions. Moreover, existing maintenance and repair decisions are vaguely tied to beam end conditions rather than correlating beam end conditions and repair options to the capacity. This dissertation presents an integrated framework for extending the service life of PSC I-shaped beams by combining mitigation strategies for beam end cracking during fabrication, capacity-based condition assessment of in-service beam ends, and guidelines for selecting preservation and repair strategies suitable for each condition state.

Sixteen (16) PSC I-shaped beam ends were instrumented using vibrating wire strain gauges to monitor strain during fabrication (including the change in strain during the release of each strand), lifting off of the casting bed, and storage. The strain data indicated that the cracking initiated within the bottom flange and at the bottom flange-web interface during strand release. These cracks were further developed, while the new cracks along the beam height developed when the beams lifted off the casting beds. The strand configuration, release sequence, and lifting details were identified as the primary contributors to beam end cracking. Finite element simulation results showed the development of strain and the locations of critical strain during strand release and beam lifting off the casting bed. To mitigate beam end cracking, alternatives to strand layout, release sequence, and lifting device details were proposed after evaluating monitoring data and FE results.

The capacity impacts of beam end deterioration were assessed using the Strut-and-Tie Method. Sensitivity analyses showed that reductions in beam end capacity were proportional to the percentage of exposed prestressing strands, whereas section loss and bearing area loss without strand exposure had limited influence on shear capacity. Deterioration thresholds corresponding to 15% capacity reduction have been established for various I-shaped beam types. Preservation and repair strategies were evaluated using analytical modeling, experimental data from literature, and accelerated corrosion testing. Full-depth reinforced concrete overcast repairs were identified as the most effective method for restoring beam end capacity, while integrated preservation techniques, such as zinc-rich epoxy reinforcement coatings with concrete surface treatments, significantly reduced corrosion activity compared with conventional patch repairs alone.

Overall, this study establishes strategies to extend the service life for PSC I-shaped beams by integrating crack mitigation strategies during fabrication, capacity-based condition assessment, and improved preservation and repair decision-making to enhance long-term structural performance.

Access Setting

Dissertation-Open Access

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