TDR Monitoring for Integrity of Structural Systems

Abstract

Most infrastructures are made up of large number of parts, such as truss members and bridge decks. Relative movement of the connections between members causes load redistribution or even failure. Monitoring the integrity of the structural system can assure its performance and safety. TDR (time domain reflectometry) is proposed here as a multiple-points smart monitoring system using only one coaxial cable as the sensing and conducting medium all the way through the monitored structure. The cable is fixed at both ends of each pair of adjacent members to be the sensing device along itself. Relative movements between the members at the connecting points are monitored simultaneously by sending a fast-rise impulse into the cable. When lateral movement occurs, the cable will deform, having the effect of adding an equivalent capacitance at that point and causing the signature to jump up. When two adjacent blocks move apart from each other, the cable will be extended and cause its characteristic impedance change. The most important ability for a TDR system to have is to locate the relative movement along the cable that is very clearly shown in the time domain signature. The pulse of a TDR tester can go a few thousand feet, which gives enough monitoring range for most infrastructure.