Monitoring Bridge Substructure Health

Emerging in recent years as one of the improved tools for highway bridge assessment is a structural health-monitoring (SHM) system that uses sensing technology.

Emerging in recent years as one of the improved tools for highway bridge assessment is a structural health-monitoring (SHM) system that uses sensing technology. To date, this approach has been applied primarily to monitoring bridge superstructure rather than the entire bridge system. Using SHM for substructure assessment, by contrast, the Federal Highway Administration (FHWA) has undertaken field research at the Woodrow Wilson Bridge construction site outside Washington, D.C.

Obtaining better data for more effective bridge management is the aim of the Woodrow Wilson Bridge project, whose goal is development of a comprehensive research plan for substructure SHM needs and guidelines for a smart bridge monitoring system. 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 inadequate for making comprehensive long-term life-cycle and bridge management decisions.

Bridge management systems of the future must be based upon better information, better knowledge, better technology, and improved decision support tools, says FHWA’s Carl Ealy. These systems must provide decision makers 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.

By means of the field study, FHWA in cooperation with the Virginia Department of Transportation (VDOT) seeks to evaluate whether an off-the-shelf instrumentation system designed for pile installation monitoring can also provide long-term substructure health assessment. Accordingly, SmartPile Û a monitoring system developed by University of Florida researchers Û has been installed on 57-ft.-long prestressed concrete foundation piles. The system comprises two strain gauges and two accelerometers placed two diameters below the top of the pile and at its tip, respectively, to collect strain and acceleration data in the concrete piles and caps. Signals sent by cable to a receiver and transmitter are then transmitted wirelessly to a workstation, where data reduction and analysis are performed in real time. An Internet-based interactive structural monitoring application allows programming of the sensors to set data thresholds.

Since installation and data collection began last year at the Woodrow Wilson Bridge site (Interstate 95/495 and the Potomac River), positive results have been reported. Monitoring is expected to continue for 25 to 30 years. Several additional foundation piles will be instrumented with SmartPile gauges to be monitored by VDOT personnel.

A companion project planned for a drilled shaft in Clearwater, Fla., will test a substructure SHM system engineered to detect and report the consequences of extreme events. This and further studies will provide the basis for developing guidance on selection of instrumentation, monitoring, and analysis systems and applying the data for bridge management. The shaft, donated and constructed by Harris Construction in Clearwater, will be loaded various ways and monitored remotely by University of South Florida researchers to evaluate the acquisition and reduction of randomly generated data under controlled conditions. Load testing will simulate transient loadings caused by extreme events. Also evaluated will be a self-powering load measurement system that can be embedded in concrete. Completely wireless, it is designed to transmit through concrete and soil.

More information on FHWA field projects or substructure SHM can be obtained by contacting Carl Ealy at FHWA, 202/493-3039; [email protected]; or, for Woodrow Wilson Bridge project, VDOT’s Fawaz Saraf, 703/329-3429; [email protected]

This article was adapted from a report in the Federal Highway Administration’s November 2006 Focus, also available online at