Monitoring of Manhattan Bridge for Vertical and Torsional Performance with GPS and Interferometric Radar Systems

Abstract

This paper describes monitoring of the vertical and torsional displacements of the midspan of the Manhattan Bridge using Interferometric Radar and Global Positioning Systems (GPS). The Manhattan Bridge is a particularly interesting case study due to its immense size, unique loadings, high traffic volume, age, and recent multimillion dollar rehabilitation and stiffening program. The Interferometric radar system is an non-contacting, innovative microwave radar sensor (IBIS-S) used to simultaneously measure the displacement response of multiple locations of a structure from distances up to 0.5 kilometer. GPS systems use triangulation from satellite signals to accurately locate the absolute position of a receiver and are routinely used in a variety of applications. The systems were employed to measure the midspan deflections of the bridge under normal automobile and train traffic loadings. The GPS data characterizes the maximum deflections as well as deflection time histories of the outer roadway edges at midspan. The data acquired using the Interferometric Radar system characterized the maximum deflections as well as deflection time histories simultaneous at 80 points along the midspan with a set-up and test time of about 3 to 4 hours. Both measurement systems compared well with one another and are promising technologies in the area of bridge deflection and vibration measurements.