Featured Project: Identification of Bridges with Fracture-Prone Details
Of the 1,100 steel bridges in Kentucky, several make use of steel girders with weld details that, once exposed to service stresses, are prone to constraint-induced fractures (CIFs). Once a crack initiates, a brittle fracture can develop and severely damage or sever parts of the girders. KTC researchers evaluated welded girder bridges across the state by first reviewing KYTC’s bridge inventory. Based on this work, KTC found 45 bridges that have potentially problematic CIF details and another 55 steel span bridges labeled as being of a different material type, warranting up-close inspection. Researchers developed arm’s length inspection criteria which KYTC inspectors can use to determine whether the 55 steel span bridges have CIF details and if they are problematic enough to require repairs. Additionally, KTC devised a prioritization method for bridges, including specifics about fatigue and fracturing along with the recommended retrofit or mitigation action.
Bridge Preservation – News & Research
Longer Service Life Bridge Coatings
In Kentucky, there are roughly 1,100 steel bridges maintained by The Kentucky Transportation Cabinet (KYTC). Extending the service lives of both new construction and painting projects would help alleviate the current backlog of maintenance projects and result in life cycle cost savings. Researchers in KTC’s Bridge Preservation group identified coating methods for extending the service life of Kentucky bridges and developed technical guidance to assist KYTC with implementation. They focused efforts on analyzing a range of protective coatings., including surface preparation activities that would maximize the service lives of any coatings. The team examined the practices used in KYTC welding shops, as well as industry standards that ensure high quality galvanized welded girders. KTC developed procedures for metallizing and applying duplex coatings on girders, monitored an experimental field application, and identified causes of any coatings failures. The study found that using hot-dip galvanized (HDG) and/or metalized steel will substantially extend the service life of bridges. Metallic coatings (HDG or metalized spray) are preferred over the current liquid applied to structural steel, based on their ability to prevent corrosion of the underlying steel and resist weathering.
Technology for Bridge Evaluation
KYTC steel bridges are aging and require sophisticated testing and evaluation to ensure their integrity and continued safe performance. New or untried nondestructive test procedures are available to address these inspection needs and provide necessary information for proper decision‐making. The need for nondestructive testing was demonstrated in the in‐depth testing on the I‐275 Combs‐Hehl (2008) and the I‐64 Sherman Minton Bridges (2011). Proper testing includes the use of qualified personnel/test methods, a viable approach to the testing and the ability to translate test results to management decisions. The need exists to evaluate all of the available NDE tools in relation to anticipated KYTC inspection requirements. NDE of bridge steel typically requires spot removal of existing protective coatings. Repair of those areas is problematic in terms of inspection costs and motorist inconvenience.
Faculty & Staff
Deterioration Modelling of Bridges on BrM 5.2.3
Bridge deterioration and cost models use data on bridge elements, structure age and condition, and traffic volumes to forecast future trends in condition and service. The Kentucky Transportation Cabinet (KYTC) relies on AASHTOWare Bridge Management software (BrM) to predict the future performance of structures, thereby informing future cost and resource allocation. KYTC asked KTC researchers to assist with the transition to BrM version 5.2.3 and adapt its deterioration and cost modeling features in accordance with the Cabinet’s specifications. Researchers reviewed literature for available mathematical modelling options, honed those strategies to forecast bridge and culvert element condition and performance, and verified the model’s accuracy through statistical analysis. KTC continues to work with the Cabinet to collect enough field data to continuously calibrate and validate BrM 5.2.3.
Bridge Overcoating Materials
From 1990 until 2000, the Kentucky Transportation Cabinet (KYTC) exclusively employed overcoating for maintenance painting of steel bridges. From 2000 to 2003 overcoating and removal/replacement practices were employed. For the last decade, the cost of total removal/replacement was competitive with overcoating from a life-cycle cost standpoint and subsequently supplanted overcoating as the predominant KYTC maintenance painting practice. Over recent years, the costs of total removal/replacement have increased significantly compared to overcoating, making the latter coating option more economically feasible. KYTC is planning to conduct more bridge maintenance painting projects utilizing overcoating. However, prior to the start of this research project, KYTC had not updated its qualified products list for overcoating systems in the past seven years and many of the coatings on that list were no longer available.
Determination of Steels in Kentucky Bridges
Over 200 bridges across Kentucky have steel superstructures of unknown composition and strength. Included among these are older bridges nearing the end of their design life. The team researched identification methods and developed a minimally invasive field test to identify steel strength and composition, making bridges easier to rehab and repair. KTC validated the test procedures and documented them for KYTC’s use. The end product was a database that classifies steels by weldability, mechanical (tensile) properties, ASTM or AASHTO steel type, and weathering properties.
Chloride Contamination Remediation on Steel Bridges
Painting is the primary means of corrosion prevention for most existing KYTC steel bridges. It is a very expensive operation and KYTC strives to limit its life‐cycle costs by obtaining the maximum service lives of maintenance painting projects. Prior to painting, the steel surfaces of those bridges become contaminated with chlorides from leaking deck joints or aerosols kicked up by traffic during inclement weather. Conventional maintenance painting practice begins with abrasive blasting to remove soils and existing paint. Recent research has shown that this practice retains residual chlorides trapped in high concentrations in microscopic pits. This leftover contamination serves as “hot spots” for follow‐on corrosion after the new coating is applied and has the effect of reducing the service lives of coatings.
Waterproofing Options in Bridge Decks
The increased use of deicing chemicals requires that bridge decks be waterproofed for protection. Because bridge decks are such a high maintenance item for KYTC, the Center investigated waterproofing membranes that protect and create a renewable deck surface. Researchers developed laboratory procedures to prequalify products to be tested in the field, including waterproofing membranes, polymer asphalts and laminates. Not only did the team look at the application requirements, but analyzed cost, best locations for use, and how the Cabinet would be able to adopt any candidate waterproofing systems.