Nondestructive Testing Of Arch Bridges

Nondestructive sonic/ultrasonic and ground penetrating radar (GPR) measurements were made on 80 to 100 year old arch bridges to determine the location and spacing of internal reinforcing and to assess the strength, thickness and condition of the arch concrete. GPR data were acquired on longitudinal and transverse lines of coverage on the roadway over the bridge and on the underside of the arch. Sonic/ultrasonic data are acquired along parallel transverse lines on the underside of the arch. The sonic/ultrasonic measurements determine the characteristics of concrete by measurements of compressional and shear wave transmission velocities as well as reflected compressional waves (pulse-echoes). The transmission velocity values determine the elastic deformational characteristics of the concrete, including Young's, bulk, and shear moduli, as well as Poisson's ratio, and calculated strength values which are principally controlled by the amount of cracking. The reflected (pulse-echo) signals resonate at a frequency that is related to the concrete thickness and compressional velocity (strength). These reflections are used to identify delamination and determine the concrete thickness. GPR data are acquired using a digital system coupled with a 400 MHz antenna. The GPR method uses a pulsed electromagnetic signal that is transmitted to and reflected by, a target back to the point of transmission. The wave transmission and reflection is dependent on the dielectric constant and conductivity (electrical properties) of the host and target material(s). Metal reinforcing produce strong reflections of radar signals. Nondestructive testing results are presented with visual observations on a bridge plan.

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