Ground-Penetrating Radar Investigation of Salvaged Timber Girders from Bridges Along Route 66 in California

This study describes assessment of the internal conditions of timber bridge structural members along Route 66 in California. These timber bridges were exposed to desert climate conditions for several decades, which can lead to a variety of deterioration. Overtime, the deterioration may cause loss of structural integrity within the bridges and lead to potentially hazardous conditions for the motoring public. Members from dismantled bridges were brought to the Forest Products Laboratory in Madison, WI. Strength-reducing features including decay, splits and cracks insect attack, and corrosion of metal components were initially identified using visual inspection. Further assessment was then performed using several nondestructive testing technologies including ground=penetrating radar (GPR). GPR was used, among other nondestructive techniques, to identify and locate internal features and defects within the timbers. The tomographic output of the GPR known as radargrams, revealed deterioration. Based on the information contained within the radargrams, it was possible to classify some internal features and defects with a high degree of certainty, whereas others remained less clear. In this study, the potential of using GPR for inspection of bridge timbers is discussed and supported through interpretation of the radargrams.