Current inspection procedures of suspension bridge main cables mainly consist of visually inspecting the exterior covering of the cable every two years.  An in-depth inspection is usually scheduled when necessary to assess the condition of the interior wires by wedging the cable at selected locations along the cable.

In this project, a corrosion monitoring system for main cables of suspension bridges has been developed.  This project, sponsored by FHWA, involves a research team that includes Columbia University, Parsons Transportation Group, and Physical Acoustics Corporation. The goal of the project is to develop an integrated methodology that uses state-of-the-art sensing capabilities and NDT direct and indirect technologies to assess the cable condition. A smart sensor network that can monitor the external and internal environment, integrated with NDE that would map the entire length of the cable, is the only accurate method for reliably assessing the condition of suspension bridge cables. Some promising NDT technologies for direct detection of the corrosion damage (Main Flux method, Magnetostrictive technology together with Acoustic Emission technology) have been implemented and validated and their applicability to large suspension bridge cables has been tested.

To recreate conditions as close as possible to real operating conditions, a cable mock-up, 20 in diameter and 20 ft long subjected to 1,200 kips and fully instrumented, has been built at Columbia University and is currently under testing inside an accelerated corrosion chamber.  In this 6 × 5 × 16 ft chamber, raining/heating/cooling cycles are induced through a sprinkler system, heating lamps and an air conditioning unit that operate on a 4-hour cycle. During this test measurements of environmental variables such as temperature, relative humidity, pH and corrosion rate of zinc and steel are collected by 76 sensors embedded inside the cable.  These measurements will be processed on line to estimate the actual value of the remaining strength of the cable.

Once the cable mockup test has been concluded and the sensors performances have been evaluated, the sensor network will be installed on a panel of one of the main cables of the Manhattan bridge. The sensor will be collecting information that will be transmitted on real time to a central unit that will provide an up-to-date evaluation of the cable strength.

For further information contact Raimondo Betti at +1.212.854.6388 or Adrian Brügger at +1.212.854.8782.