Reliability and Accuracy of In-Depth Inspection of Highway Bridges

In-depth inspection is one of the two most common types of bridge inspection. In contrast with routine inspection, in-depth inspection is a close-up, hands-on inspection that generally covers only a portion of a bridge. The Federal Highway Administration’s Nondestructive Evaluation Validation Center recently completed a study of the reliability of visual inspection of highway bridges. Part of this study focused on the accuracy and reliability of in-depth inspections as completed by state bridge inspectors from across the United States. Three in-depth inspection tasks were completed, two focusing on the inspection of steel superstructures and one focusing on the inspection of concrete bridge decks. Visual inspection techniques were used, with the possible use of simple inspection tools. Results show that many in-depth inspections completed by state bridge inspectors do not accurately represent the condition of the structure. In-depth inspections of the steel superstructures revealed that certain deficiencies for which this type of inspection is frequently prescribed were rarely detected. Specifically, only a small minority of state bridge inspectors located the presence of any of the existing crack indications. The delamination survey of a concrete bridge deck indicated that the accuracy of this type of inspection is relatively poor. Very few state bridge inspection teams provided results that could be considered to portray the condition of the deck accurately.