Bridge Load Testing Versus Bridge Load Rating

The current method of load rating bridges according to AASHTO specifications can underestimate the capacity and behavior of bridges. Analytical equations do not account for the degree of rigidity of the supports, unintended composite action due to friction between girders and the slab, and other factors. Load testing of individual bridges can produce a load rating that much more accurately reflects the capacity of a non-composite bridge. However, current methods of load testing require significant time commitments to instrument a bridge profile to record data, rendering it impractical in many cases. But there are new commercially available strain gauges that greatly reduce the time required to instrument a location. This study evaluated the accuracy and efficiency of set up of the magnetic Sensormate QE-1010 strain gauge and reusable BDI ST350 strain gauge. Both gauge types were interfaced with wireless data transmission capabilities, tested in laboratories alongside the more traditional foil-type strain gauges, and deployed on two Kentucky bridges to test their overall efficacy. Although magnetic strain gauges performed well in the field and reduced installation time, due to the rugged requirements of field testing, they will not be considered for future deployments given the current status of the technology. Reusable strain gauges coupled with wireless transmitters balance rugged performance with short installation times. The field-tested bridges were load posted due to the load rating factor for several truck types being less than one. Field load tests revealed the load rating factor for strength was adequate for the KY 220 Bridge in Hardin County while the load rating for the KY 1068 Bridge in Lewis County could be increased by 68%

Rapid Retrofit and Strengthening of Bridge Components

Rapid repair of damaged or deteriorated concrete bridge components will prevent the entire bridge from suffering irreversible damage in the future due to gradual spalling of concrete or corrosion of exposed steel. CFRP laminates and fabrics have become popular for repairing and strengthening of concrete girders. A series of CFRP materials — branded CatStrong — specifically designed for the repair and retrofit of bridges was developed at the Kentucky Transportation Center and the University of Kentucky. These materials include the CFRP Rod Panels (CatStrong CRPs), Unidirectional and Triaxial Carbon Fabric (CatStrong UCF and TCF), and Triaxial Carbon Wrap (CatStrong TCW). This study documented the implementation of CFRP materials to rapidly repair/strengthen six bridges in Kentucky. Three of the retrofit projects utilized CatStrong CRPs for strengthening reinforced concrete bridge girders. Because the CRPs have modular construction, they can easily be applied by a by a single worker, eliminating the need for extensive scaffolding/access equipment and a large work force. As such, the construction costs related to panel application is less than those for other retrofit measures. CatStrong TCW, combined with CatStrong TCF, was deployed for the repair and strengthening of deteriorated timber piles. The remaining two projects involved the use of CatStrong UCF and TCF for strengthening cracked prestressed concrete girder ends and strengthening a cracked bridge pier cap. Each bridge retrofit project was carried out by Kentucky Transportation Cabinet bridge maintenance crews. The crews were trained on the use and application of the new material. Design and construction specifications for the CatStrong CRPs were also developed as part of the study. This study will implement these new CFRP materials to rapidly repair/strengthen six selected bridges in Kentucky. Three of the retrofit projects utilized CatStrong CRPs for strengthening Reinforced Concrete (RC) bridge girders. The modular construction of the CRPs allows for easy application by a single worker without the need for extensive scaffolding/access equipment and a large work force. Consequently, application of the panels reduces construction costs when compared with other FRP retrofit measures. The CatStrong TCW, combined with CatStrong TCF, was deployed for the repair and strengthening of deteriorated timber piles. The remaining two projects involved the use of CatStrong UCF and TCF for strengthening cracked Prestressed Concrete (PC) girder ends and strengthening a cracked bridge pier cap. Each bridge retrofit project was carried out by the Kentucky Transportation Cabinet (KYTC) bridge maintenance crew of the respective KYTC district. The crews were trained on the use and application of the new material. Design and Construction Specifications for the CatStrong CRPs were also developed as part of the study

Truss Bridge Rehabilitation Prioritization

Kentucky’s inventory of historic steel truss bridges is declining rapidly. There are more than 150 historic truss bridges in the Kentucky Transportation Cabinet’s (KYTC) bridge inventory. Most of these bridges require maintenance to avoid replacement. However, prioritizing the rehabilitation of these bridges based on their historic importance is challenging. While AASHTO’s Guidelines for Historic Bridge Rehabilitation and Replacement contain guidance on selecting bridges for preservation, currently there is no guidance on how to prioritize those historic bridges selected for rehabilitation. Building on a previous study that identified historic truss bridges in Kentucky meriting preservation, the Kentucky Transportation Center (KTC) developed a truss bridge database listing the historic, geometric and other key features of the bridges. 108 candidate bridges were selected as being historically significant for preservation. Fourteen of the bridges were replaced during the course of the study, leaving 94 bridges for evaluation. KTC developed a ranking system for rehabilitation prioritization. Two levels of prioritization were considered in this study. The first level, Historical Importance, is the primary and most important level of prioritization. A historical importance factor, HIF, was calculated for each bridge based on its uniqueness, year of construction, and other factors. Bridges were then sorted based on their HIF to identify the ones for rehabilitation prioritization. When a number of bridges have the same HIF, a second level of prioritization, P2F, which accounts for Bridge Condition and Rehabilitation Potential, is deployed. A bridge condition factor, BCF, and rehabilitation potential factor, RPF, are calculated for each bridge. Eight of the bridges were identified as being of significant historical importance, receiving an HIF greater than 100. Of the remaining bridges, 30 had an HIF between 10 and 100, and the rest (56 bridges) earned an HIF less than 10

CFRP Strengthening of KY 583 Over the Bluegrass Parkway Bridge in Hardin Country

The report details the planning, design, and construction of the retrofit measure on the KY 583 Bridge (047B00072N), which traverses the Bluegrass Parkway in Hardin County, Kentucky. Reinforced concrete girders within the span over the eastbound Bluegrass Parkway of the bridge had cracks that led to concrete delamination and deterioration of the girders. To remedy the problem, triaxial carbon fiber reinforced polymer (CFRP) fabric sheets were selected to perform a retrofit due to their strength, conformability, and flexibility. The concrete surface, over which the fabric sheets were applied, were first prepared by removing all spalling and deteriorated concrete, which exposed corroded rebars within the region. The rebars were cleaned and coated with a zinc primer. Soon after, formwork was built around the damaged area. A bonding agent was applied and repair mortar placed within the formwork to return beams to their original shape. The area targeted for strengthening was then sandblasted, and triaxial CFRP fabric was applied using a two-part saturating epoxy. The retrofit was completed in May of 2014, and the bridge was monitored over a three-year period. No defects were observed in the retrofit during this time. Eighteen months after the retrofit, inspectors found an additional crack location causing concrete delamination, away from the retrofit locations

Rapid Repair of Bridge Decks in Cold Weather

Using regular concrete or mortar to repair potholes in concrete bridge decks is typically infeasible in cold weather due to extended set and curing times. However, several commercially available rapid-set repair materials can be used at temperatures near or below freezing. This study evaluated five such materials to assess their properties and determine which are most suited to executing pothole repairs in cold weather. For each material, laboratory testing evaluated set times, compressive strength gains, and bond strength to existing concrete at three temperatures: 35°F, 15°F, and 0°F (1.7°C, -9.4°C, and -17.8°C, respectively). Testing identified Phoscrete as the repair material best suited to cold weather partial-depth deck patching. It consistently had the highest compressive strength (more than 2,500 psi within three hours at all three test temperatures), while its bond strength with existing concrete was adequate (between 250 psi and 760 psi at 28 days). Phoscrete, aided by its fast-set accelerant, set up within 40 minutes at all three test temperatures. Subsequent field testing evaluated the use of Phoscrete to repair a pothole on the deck of the US 27 Bridge over the Kentucky River (040B00028L). As expected, the material set up rapidly and the lane was reopened to traffic within two hours. Maintenance personnel found the low workability of Phoscrete, compared to a typical cement-based repair mortar, to be an issue. Before maintenance crews repair bridge decks in the field using Phoscrete they should perform a trial pothole repair in order to ensure their familiarity with Phoscrete’s workability. Field inspections conducted one year after the US 27 Bridge was mended found no distress on the Phoscrete-repaired patch

Concentrically Loaded Circular RC Columns Partially Confined with FRP

Wrapping reinforced concrete (RC) columns with fiber reinforced polymer (FRP) composites is effective in increasing their capacity. The current state of the art concentrates primarily on fully wrapped columns and few studies dealt with partially wrapped ones. The objective herein is to evaluate the effectiveness of partial wraps (or strips) and to develop a confined concrete compressive stress–strain (fc − εc) model that accounts for partial wrapping. Three-dimensional finite element (FE) models are generated to evaluate the influence of different parameters on the behavior of concentrically loaded RC circular columns that are partially and fully wrapped with FRP. The results indicated an increase in ductility as the number of FRP strips is increased, and revealed that longitudinal steel had little influence on the confined fc − εc relationship. The proposed fc − εc model, derived from the parametric study, accounts for the effect of partial and full confinement, the unconfined concrete strength f c, and yielding of transverse steel. Comparison of the results generated using the proposed model with FE and experimental results are in good agreement

Inspection and Evaluation of a Bridge Deck Reinforced with Carbon Fiber Reinforced Polymer (CFRP) Bars

Cracking in reinforced concrete decks is inevitable. It leads to the corrosion and eventual deterioration of the deck system. The use of non-corrosive reinforcement is one alternative to steel in reinforced concrete construction. This report deals with the field evaluation and performance of a concrete bridge deck reinforced with carbon fiber reinforced polymer (CFRP) bars. The bridge is identified as the Elkin Station Road Bridge on route CR1210 over the Two Mile Creek in Clark County, KY. The CFRP bars were placed in the top and bottom mats of the bridge deck in both the transverse and longitudinal directions. The results of the laboratory tensile tests of the CFRP bars used in the deck are presented in this report. The bridge was opened to traffic in May 2002. Monitoring of crack formation and location, and maximum crack width and length in the deck initiated in June 2002and continued until September 2005. The cracks in the deck were not measurable since the maximum observed crack width was less than the smallest unit (1/100 inch) on the crack comparator. This indicates that the cracks are well below the maximum allowed crack width of 0.013 inch per AASHTO Standard Specification for exterior exposure

Structural Evaluation of the John A. Roebling Suspension Bridge

The primary objective of the structural evaluation of the John A. Roebling Bridge is to determine the maximum allowable gross vehicle weight (GWV) that can be carried by the bridge deck structural elements such as the open steel grid deck, channels, standard sections, or built-up sections. To achieve this objective, four levels of analysis are carried out: Element Level , Sectional level 1 , Sectional level II , and Global level analysis. The four levels of analysis yield a load envelope that encapsulates the maximum and minimum allowable loads. The maximum allowable gross vehicle weight (GWV) for different truck and bus types are presented for different levels of structural elements sectional loss. The loss or reduction in element sectional properties is due to rust, cracks, etc. The Element Level Analysis is the most critical and yielded the maximum allowable gross vehicle weights. The critical member in the bridge deck is the built-up 36 inch deep section. Its allowable bending strength controls the maximum Gross Vehicle Weight (GVW) that can be permitted on the bridge. Results are presented for different levels of sectional losses (10% to 40%, in 10% increments). In the event that replacement of the open grid deck will take place in the future, results are presented for different deck weights (10 psf to 50 psf in 10 psf increments). The current open grid deck weight is 20 psf