Approximately 25 percent of bridges in the United States have been classified as structurally deficient or functionally obsolete. Although the number of deficient bridges has gradually declined over the past 10 years, much work remains to be done, especially with many state transportation agencies that have limited funds to allocate to repairing or replacing bridges that are quickly aging beyond their planned service lives. KTC’s Structures group is dedicated to evaluating and monitoring bridges and other structures with the most sophisticated technology and modeling techniques, and strengthening new and existing structures with novel, high-performance materials, thus playing a critical role in helping to preserve the nation’s infrastructure. The group’s researchers have developed the CatStrong family of products, including CatStrong CRP-XXX, a lightweight carbon fiber reinforced polymer rod panel used to repair deficient bridges, and several varieties of carbon fiber reinforced polymer fabrics and wraps. CatStrong products are designed for quick application, which reduces the cost and labor necessary to complete bridge maintenance projects. The Structures group has worked extensively with the Kentucky Transportation Cabinet, completing over 85 projects on issues ranging from bridge retrofit and bridge replacement, to instrumenting bridges and performing structural health monitoring. Researchers also collaborate with KTC’s Bridge Preservation and Pavements, Materials, Geotechnology, and Infrastructure Assessment groups to devise holistic solutions to challenging bridge structure problems.
Structures – News & Research
Rapid Retrofit & Strengthening of Bridge Components
Rapid repair of damaged or deteriorated concrete bridge components prevents irreversible damage to the bridge’s structural integrity. KTC used newly developed spliced carbon fiber reinforced polymer rod panels (CatStrong CRP) and CatStrong Unidirectional and Triaxial Carbon Fabric (UCF and TCF) to rapidly repair seven selected bridges in Kentucky. Ease of application is the advantage of CRP, requiring only a single worker without the need of heavy construction equipment or tools. Although high performance materials are higher in cost, they reduce overall repair costs compared to other retrofit measures. This is due to the reduction of work days. As a part of this study, KYTC will implement CatStrong Triaxial Carbon Wrap (TCW) and TCF for timber pile repair and strengthening.
Bridge Load Testing and Bridge Load Rating
The AASHTO load rating method, which is the standard for rating bridges, is based on simple calculation procedures that underestimate the actual load rating for bridges. Numerous field studies conducted in other states show that field test data provides a more accurate representation of the bridge and better predicts the load rating. KTC evaluated several types of strain gauges and wireless data acquisition systems to load test the KY 1068 bridge over Laurel Fork in Lewis County and the KY 220 bridge over Martins Branch Creek in Hardin County. The load posting on the bridges were increased due to the results of the load rating, calculated based on the NCHRP Manual for Bridge Rating through Load Testing. This method of load rating can be used on many single span steel girder bridges throughout Kentucky.
Retrofit of Pier Impact Damage using CatStrong UCF and TCF
A semi tractor-trailer truck traveling south on William H. Natcher Parkway veered off the road and impacted a pier-column of the overpass bridge on Elrod Road in Warren County, KY. The impact caused cracking and spalling of concrete in the column as well as cracking on the pier cap. Requiring a rapid retrofit due to the approaching winter weather, KYTC, in cooperation with KTC, proposed the use of CatStrong Uniaxial and Triaxial Carbon Fabric (UCF and TCF) to retrofit the impacted bridge pier-column and pier cap. KTC designed the retrofit, performed analysis, and oversaw the retrofit construction, which was carried out within six work days. Additionally, the bridge remained open to vehicle travel during the repair work.
Adjacent PPC Bulb Tee Beam Bridge Prestressed with CFRP Strands and Reinforced with Stainless Steel Rebars
Public expectation of an efficient transportation infrastructure and minimized congestion during construction has prompted the Kentucky Transportation Cabinet (KYTC) to widely implement the use of Accelerated Bridge Construction (ABC). KYTC proposed the use of adjacent Precast Prestressed Concrete (PPC) Bulb Tee beams pretensioned with carbon fiber reinforced polymer (CFRP) tendons and stainless steel rebar. KTC assisted KYTC with the installation of a CFRP PPC Bulb Tee beam bridge, which replaced a functionally obsolete bridge on KY70 over Stoner Creek in Taylor County. Researchers collaborated on the design, carbon fiber material specifications, girder fabrication, and overall construction. This bridge project represents the first time CFRP pretensioned beams have been used by KYTC. Performance will be evaluated for future application on bridges in Kentucky.
Load Rating of Bridge Size Culverts
The Kentucky Transportation Cabinet (KYTC) is responsible for load rating all bridge size culverts for their safe load carrying capacity. KTC researchers used culvert rating software to assist the Cabinet with determining the load rating of 1400 bridge size concrete box culverts in Kentucky. Special culverts (circular, concrete and steel arch, etc.) required finite element modeling and evaluation. The result of the study was characterization of the Allowable Stress Rating (ASR), Load Factor Rating (LFR) and Load and Resistance Factor Rating (LRFR) for all types of bridge sized culverts.