Date of Award
5-2026
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Civil Engineering
Committee Chair/Advisor
Dr. Brandon E. Ross
Committee Member
Dr. Tommy E. Cousins
Committee Member
Dr. Michael W. Stoner
Abstract
The South Carolina Department of Transportation manages approximately 2,300 “flat-slab” bridges statewide, with an average age of 58 years, according to the National Bridge Inventory (NBI 2024). Many of these structures were originally designed for H10 or H15 truck loadings, which are significantly below current design standards. As a result, numerous bridges have been load-posted, restricting freight movement, emergency response, and local connectivity. While full replacement provides a long-term solution, it is often cost-prohibitive and disruptive. Accordingly, the South Carolina Department of Transportation is seeking cost-effective retrofit strategies that improve performance and extend the service life of these bridges. Implementing retrofit methods could reduce load postings, preserve critical infrastructure, mitigate disruptions to the natural environment, and deliver lifecycle cost savings to the state. The Horseford Road bridge, originally built in 1967, crossing Four Hole Swamp, is a 375 ft. long bridge consisting of twenty-five 15 ft. spans, and is one of 590 flat-slab bridges in South Carolina that is posted for load. The Horseford Road Bridge was closed to the public in July 2023 due to a timber pile failure on its southwest edge and is scheduled for replacement. While it awaits replacement, the SCDOT allocated the bridge for testing of potential retrofits. The objectives of the research in this thesis are first, to evaluate V2 Composites T-Biscuits (Biscuits) for improving load distribution between adjacent slabs, and second, to evaluate near-surface-mounted (NSM) bars for creating continuity between adjacent spans. Both the biscuits and the NSM bars have the potential to improve the structural performance of flat-slab bridges, thereby mitigating the direct costs of bridge replacement and the indirect costs of load postings. Live load field testing was conducted to evaluate the retrofit methods. The testing revealed that the biscuits improved the service-level performance of the retrofitted slabs and curb. Using biscuits to attach the curb member to the slabs engaged the curb in carrying truck loads, even though it was not directly loaded. The estimated force in the curb member from the post-retrofit test was seven times greater than that in the baseline test. Additionally, the biscuits improved load distribution in retrofit slabs by 35% to 45%. Results of the live load field testing also demonstrated the benefits of the NSM bars, specifically increased stiffness, resulting in lower deflections of the attached slab members. The improved performance was observed even without cleaning and grouting the joints between the connected slabs. The NSM bars reduced the maximum live load displacement of the end span by 36% relative to the baseline retrofit condition and reduced the maximum displacement of the inner span by 68%. The difference between span 1 and span 2 displacement changes was attributed to the fact that span 2 had NSM installed on both the east and west sides of the span, whereas span 1 had only NSM installed on the west side. The field testing conducted in this study demonstrated proof of concept under service-level loading conditions. Both the NSM and biscuit retrofit techniques showed promising performance; however, additional testing is needed to address remaining uncertainties regarding their structural behavior. Cyclic loading tests are recommended to evaluate the fatigue response of each retrofit system, while ultimate-strength testing is needed to determine the individual capacity of a single biscuit and an NSM bar. Quantifying these capacities will support the development of design procedures and improve confidence in practical applications.
Recommended Citation
Bowers, Jacob, "Field Testing of Retrofits to Improve the Structural Behavior of South Carolina Flat-Slab Bridges" (2026). All Theses. 4710.
https://open.clemson.edu/all_theses/4710