Fiber Optic Monitoring of the Masonry Arch Approach Spans in the Brooklyn Bridge

The Brooklyn Bridge was constructed before the turn of the century and opened for use in 1883. The bridge has been a major transportation artery for New York City ever since, while undergoing numerous rehabilitation projects. The most recent of these will address the masonry arch spans in the Manhattan approach where cracks are present. Over the two years before work could begin, two of the arches were monitored by a system of fiber optic sensors installed under an FHWA initiative. The monitoring system provides real time data over the internet. Crack opening, thermal fluctuations, related structural movements and vibrations are monitored by fiber optic deflection sensors, accelerometers and tiltmeters. The monitoring program is intended to provide feedback to the bridge owner (NYCDOT) on the activity of the crack opening and the implications to the structural safety. Data has been collected for a year and a half. Correlations are observed between the tilt and settlement of the walls, the temperature changes and the crack openings. Such findings also provide more accurate estimates of the global behavior of the masonry structure which leads to more accurate calculations and finite element modeling. This in turn provides guidance for the proposed structural repairs.

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