Publication Number: FHWA-HRT-07-008
Date: November 2006

A New Approach to Monitoring Bridge Substructure Health

Better data resulting in better bridge management is the goal of a new Federal Highway Administration (FHWA) field project under way at the Woodrow Wilson Bridge construction site outside of Washington, DC. As States inspect their bridge inventory to determine maintenance and rehabilitation needs, the nonquantitative and highly variable data obtained from current visual inspection programs often prove to be inadequate for making comprehensive long-term life-cycle and bridge management decisions.

"The bridge management systems of the future must be based upon better information, better knowledge, better technology, and improved decision support tools," says Carl Ealy of FHWA. "These systems must provide decisionmakers with the ability to select the optimal course of action for a bridge or population of bridges at any point in their life and for any planning horizon."

One of the improved tools for assessing the condition of highway bridges that has emerged in recent years is a structural health-monitoring (SHM) approach that uses sensing technology. Until now, however, much of the emphasis has been on using this approach for the bridge superstructure and not the entire bridge system. FHWA's project at the Woodrow Wilson Bridge is using SHM for substructure monitoring, with the goal of developing a comprehensive research plan for substructure SHM needs and guidelines for a "smart bridge" monitoring system.

In cooperation with the Virginia Department of Transportation (VDOT), the field project is evaluating whether an off-the-shelf instrumentation system designed for pile installation monitoring can also be used for long-term substructure health monitoring. Known as SmartPile, the monitoring system was developed by researchers at the University of Florida. It has been installed on prestressed concrete foundation piles that are approximately 17 m (57 ft) long. The system consists of two strain gauges and two accelerometers that are placed two diameters below the top of the pile and at the tip of the pile, respectively. Strain and acceleration data is collected in the concrete piles and caps. Signals are transmitted by cable to a receiver and transmitter and then wirelessly to a workstation, where data reduction and analysis are performed in real time. An Internet-based interactive structural monitoring application allows for programming of the sensors to set data thresholds.

Installation and data collection began 3 months ago, with positive results reported to date. The monitoring is expected to continue for the next 25 to 30 years. Several other foundation piles will also have SmartPile gauges installed, which will be monitored by VDOT personnel.

An instrumented concrete pile and cap at the Woodrow Wilson Bridge outside of Washington, DC. The instrumentation system is collecting strain and acceleration data.

A companion project is planned for a drilled shaft in Clearwater, Florida, to test a substructure SHM system that can detect and report the consequences of extreme events. This study and other future ones will be used to develop guidance on selecting instrumentation, monitoring, and analysis systems and using the data for bridge management. The shaft was donated and constructed by Harris Construction in Clearwater. It will be loaded several ways and monitored remotely by researchers at the University of South Florida to evaluate the acquisition and data reduction of randomly generated data under controlled conditions. Load testing will simulate transient loadings caused by extreme events. A self-powering load measurement system that can be embedded in concrete will also be evaluated. This system is entirely wireless and is designed to transmit through concrete and soil.

For more information on the FHWA field projects or to learn more about substructure SHM, contact Carl Ealy at FHWA, 202-493-3039 (email: carl.ealy@fhwa.dot.gov). For more information on the Woodrow Wilson Bridge project, contact Fawaz Saraf at VDOT, 703-329-3429 (email: Fawaz.Saraf@VDOT.Virginia.gov).

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