Project Overview
A state Department of Transportation in the Southeast faced a critical infrastructure challenge: eight reinforced concrete bridges along a major freight corridor had been load-posted due to deterioration-related capacity deficiencies. These bridges, constructed between 1965 and 1978, carried an average of 12,000 vehicles per day including significant heavy truck traffic serving regional distribution centers and manufacturing facilities. The load postings had forced overweight vehicles onto lengthy detour routes, adding an estimated $2.3 million annually in increased transportation costs for regional freight operators.
The DOT's bridge management system had flagged all eight structures for either replacement or major rehabilitation within a five-year planning window. However, the estimated cost of replacing all eight bridges exceeded $48 million, far beyond the available budget allocation for the corridor. The DOT needed a solution that could restore full legal load capacity to all eight bridges within a single construction season, at a fraction of the replacement cost.
The Challenge
Each of the eight bridges presented a unique combination of deterioration mechanisms and structural deficiencies, though they shared common themes typical of aging concrete bridges in the Southeast. Decades of deicing salt application had caused chloride penetration into the concrete, initiating corrosion of the reinforcing steel in the bridge beams. The resulting section loss in the tension reinforcement had reduced the flexural capacity of the beams below the threshold required for unrestricted HL-93 loading.
Spalling and delamination of the concrete cover had exposed reinforcing steel on multiple beams across all eight bridges. In several cases, the loss of concrete section had also reduced the shear capacity of the beams, creating a dual deficiency that required both flexural and shear strengthening. Several bridges had been designed for HS-20 loading, which is less demanding than the current HL-93 design loading standard, meaning even without deterioration they would have required strengthening.
The DOT's engineering team evaluated several repair alternatives including steel plate bonding, external post-tensioning, and full superstructure replacement. Each alternative presented significant drawbacks in terms of cost, construction duration, or long-term maintenance requirements. The corridor's importance to regional freight movement made extended lane closures or bridge closures commercially and politically unacceptable.
The CFRP Solution
CFRP Repair proposed a comprehensive CFRP strengthening program that would address all eight bridges in a single construction season. The solution was designed to restore full HL-93 load rating to every bridge while maintaining traffic flow throughout the construction period. The approach included both flexural strengthening using CFRP laminates bonded to the tension face of the beams and shear strengthening using CFRP fabric U-wraps on beams with identified shear deficiencies.
Our engineering team performed detailed load rating analyses for each bridge using the AASHTO LRFD Bridge Design Specifications and the Manual for Bridge Evaluation (MBE). The analyses identified the specific capacity deficiencies for each beam and determined the required CFRP reinforcement to achieve the target HL-93 load rating. The CFRP system was designed in accordance with ACI 440.2R and NCHRP Report 655, with appropriate strength reduction factors and environmental reduction factors for the exterior bridge environment.
The construction program was organized to minimize traffic disruption while maintaining an efficient production schedule. The eight bridges were grouped into four pairs based on geographic proximity, with two mobile crews working simultaneously on paired bridges. Each bridge required approximately two weeks of active construction time, including surface preparation, concrete repair, CFRP installation, and protective coating application. Traffic was maintained on all bridges throughout construction using lane closures and flagging operations.
Results
8
Bridges Strengthened
HL-93
Full Load Rating Restored
70%
Cost Savings vs Replacement
Post-construction load rating analyses confirmed that all eight bridges achieved the target HL-93 load rating, allowing the DOT to remove all load postings and restore unrestricted freight access to the corridor. The total project cost was approximately $14.4 million, representing a 70% savings compared to the $48 million estimated cost of replacing all eight bridges. The 16-week construction timeline compared favorably to the estimated 3-4 year replacement program.
Pull-off adhesion testing performed on every bridge confirmed bond strengths exceeding the 200 psi minimum specification, with an average bond strength of 340 psi. All test failures occurred in the concrete substrate, indicating that the CFRP-to-concrete bond exceeded the tensile strength of the concrete itself.
Key Takeaways
This project demonstrates the transformative potential of CFRP strengthening for DOT bridge programs. By treating eight bridges as a single corridor-level project, the DOT achieved economies of scale in mobilization, engineering, and construction management that further reduced per-bridge costs. The program approach also allowed the DOT to address an entire freight corridor in a single construction season, delivering immediate economic benefits to the regional transportation network.
For state DOTs and government agencies facing similar challenges with posted bridges and constrained budgets, CFRP strengthening offers a proven, cost-effective path to restoring full load capacity. Visit our Load Capacity Upgrade page to learn more, or contact us for a free assessment of your bridge inventory.