ABSTRACT
Of the three components of a highway bridge, the deck is the most vulnerable to climate effects including freeze-thaw transitions, load and vibration from truck traffic, corrosive salts from deicing agents or coastal environments, and the interactions between these deterioration agents. Also, compared to the other components, poor deck condition has the greatest effect on user costs associated with the bridge operations. For this reason, highway agencies are interested in establishing programs to monitor the condition of their bridge decks so that they can identify the right time to carry out deck repair or replacement. However, system-wide programs are costly, and therefore agencies seek to evaluate the cost-effectiveness of such programs. In this study, various NDT technologies were evaluated for the cost, reliability, and operational conditions, and an optimal combination of specific technologies was identified for implementation at a system-wide level consisting of 5,500 bridges. For different monitoring scenarios, the life-cycle cost was calculated as the sum of inspection costs and repair costs, and the most cost-effective scenario was identified. The study also investigated the sensitivity of the optimal solution to the different analysis factors.
Coordination and planning of repair actions for bridge decks can be vastly improved with better knowledge of condition. The main objective of this study was to ascertain if implementing NDT methods will save INDOT money compared to current practices through better allocation of funds.
Based on findings from research papers and reports, it was found that the NDT methods investigated in this study are much better at locating corrosion and delaminations than visual inspection. Several studies also showed the value of using complementary NDTs to locate and better understand the different types of deterioration occurring in the deck.
Cost estimates for NDT inspection and repair were provided by INDOT personnel and vendors. The deterioration curve used in the simulations was based on factored chain drag data collected by INDOT; it was factored to account for incipient delaminations typically not found using chain drag. For the simulations that examine the economic impact of NDT inspection, it was initially assumed that INDOT would perform data collection and analysis in-house. An assumed decision matrix relied on probability and percent delamination to determine when and what type of repairs are performed.
The first project level analysis involved comparing costs amongst the NDT methods being considered. Of these, infrared thermography was the least expensive. The best combination was CIP, IR, and ground-coupled GPR from a cost perspective. The second project level analysis involved simulations that inspected and repaired random decks for their lifetime. Five sets of thirty bridge decks were investigated. The combination of CIP, IR, and groundcoupled GPR was used to inspect these decks. The net present value (NPV) and equivalent uniform annual cost (EUAC) were calculated for the condition-based NDT inspection program, and then the NPV and EUAC were for the current INDOT program-matic schedules. The least expensive programmatic schedule was 23% more costly than the NDT alter-native, and the most expensive schedule increased the EUAC by 54%.
The analysis was expanded to network level inspection and maintenance for the entire bridge inventory in Indiana, and similar results are seen. Using NDT methods led to a decrease in the EUAC by at least 45% when compared to the programmatic schedules. Average percent delamination is lower when the programmatic schedules are in place; however, this is achieved by performing more work actions and spending much more money.
The in-house network level NDT usage was compared to the alternative of contracting a consultant. The break-even point was found to be 22ȼ based on cost estimates from two consultants. If a consultant provides services for less than this, it would be economically beneficial to utilize their services instead of performing in-house data collection and analysis.
It is concluded that using nondestructive testing methods enables inspectors to more accurately determine condition of the deck by seeing deteriorations that were previously undetectable by visual inspection.
