Steven B. Chase

Smarter bridges, why and how?

Abstract Bridge safety, especially during extreme events, is enhanced by measurement and monitoring of critical bridge components. Enhanced safety, reliability and efficient maintenance can result from improved incident detection and assessment enabled by ‘smarter’ bridges. This article considers the problems, and discusses some solutions being investigated by the US Federal Highway Administration.

The Role of Sensing and Measurement in Achieving FHWA’S Strategic Vision for Highway Infrastructure

Like many countries, the United States has implemented a bridge inspection program to collect information on bridges. In the US, the Federal Highway Administration’s (FHWA) National Bridge Inventory database is one of the most comprehensive sources of long-term bridge information in the world. In the US the majority of the States have implemented element level inspection programs to support State and local level bridge management programs. A basic limitation of both the NBI and element level approach is that the data collected relies almost totally upon visual inspection techniques. Visual inspection is not quantitative and hidden or otherwise invisible deterioration damage is missed. The non-quantitative, subjective, highly variable, and nonspecific nature of this data makes it inadequate for comprehensive long-term decision support. Essential research necessary to support the information needs for bridge management for the future is a Long-Term Bridge Performance (LTBP) program. Sensing and measurement technologies play an essential role in this program.

Evaluation of dual-band infrared thermography system for bridge deck delamination surveys

This paper describes the evaluation and improvement of a Dual Band Infrared (DBIR) thermal imaging system developed by Lawrence Livermore National Laboratory (LLNL), under the sponsorship of Federal Highway Administration (FHWA). DBIR thermal imaging system is a nondestructive evaluation technique which has the potential of detecting delaminations in concrete bridge decks, with and without asphalt overlays. The system consist of two infrared scanners, one operating at a wavelength of 3 - 5 micrometer and the other at a wavelength of 8 - 12 micrometers. The scanners are mounted in front of a vehicle and are microprocessor controlled from inside the vehicle. The vehicle is driven at a speed of 40 km/hr and a typical bridge deck can be scanned in less than 5 minutes, with a low level of traffic control.

A long-term bridge performance monitoring program

The state of the practice of bridge inspection and bridge management in the United States is briefly discussed. This practice has many limitations. The most significant limitation is that the data collected is based solely upon visual inspection, augmented with limited mechanical methods such as hammer sounding or prying. Visual inspection is highly variable, subjective and inherently unable to detect invisible deterioration, damage or distress. There are many types of damage and deterioration that need to be detected and measured that are beyond the capabilities of visual inspection. Bridge performance also needs to be measured. The FHWA and many others have conducted research and development in technologies that can help meet these needs. Several examples illustrating the application of this technology for the long term monitoring of bridges are described. While the summary is not comprehensive it demonstrates that technology exists to meet the needs identified. Future directions and further application of bridge monitoring technology are also briefly discussed.

Radar tomography of bridge decks

This paper presents the development of ground-penetrating radar bridge deck inspection systems sponsored by the Federal Highway Administration. Two radar systems have been designed and built by Lawrence Livermore National Laboratory. The HERMES bridge inspector (High-speed Electromagnetic Roadway Mapping and Evaluation System) is designed to survey the deck condition during normal traffic flow. Thus the need for traffic control during inspection is eliminated. This system employs a 64 channel antenna array covering 1.9 m in width with a sampling density of 3 cm. To investigate areas of a bridge deck that are of particular interest and require detailed inspection a slower, cart mounted radar has been produced. This system is named PERES (Precision Electromagnetic Roadway Evaluation System). The density of data coverage with PERES is 1 cm and an average or 100 samples is taken at each location to improve the signal to noise ratio. Images of the deck interior are reconstructed from the original data using synthetic aperture tomography. The target of these systems is the location of steel reinforcement, corrosion related delaminations, voids and disbonds. The final objective is for these, and other non-destructive technologies, to provide information on the condition of the nations bridges so that funds will be spent on the structures in most need of repair.

Determination of bridge foundation type from structural response measurements

Evaluation of bridge substructures for vulnerability to scour or other potential sources of damage requires knowledge of foundation conditions beneath piers and abutments that are often unknown. This paper presents a potential method for determining unknown foundation conditions which is simple and inexpensive. The method is based on strain and rotation measurements which are used to compute a stiffness matrix for the unknown foundation. The stiffness coefficients in the matrix are then matched with values previously determined for known foundations. The objective of the reported work has been to demonstrate the feasibility of this method. Finite element models for representing pile and spread footing conditions have been used to characterize the difference in stiffness properties between the two foundation types. Field measurements of strains, displacements, and rotations have been taken on two bridges in Massachusetts: one with a spread footing and the other with a pile foundation. Parameter estimation models have been developed and used in conjunction with this field data to calculate the foundation stiffness properties. The paper describes the models, the numerical results, and the results of field testing.

Advanced fatigue-crack detection system in steel bridges

The Federal Highway Administration has sponsored the development of a new system for fatigue crack detection and quantification of fatigue cracks in steel bridges. The NDE technology selected for the new system is based on earlier studies that have identified the best methods for this task. The new system that has been developed is based on previous work which produced two portable instruments that were field tested but were not widely accepted. The best characteristics from these systems have been integrated into a single instrument, using portable computer technology and adapted to the bridge inspection environment. The new system, which has come to be known as the New Ultrasonic-Magnetic Detection System (NUMAC), is configured as a backpack with a heads-up display that leaves the inspectors hands free to climb the structure and to view the inspection site simultaneously while viewing the ultrasonic or magnetic signals. The operation of the system controlled with a mouse or a keyboard. Importantly, the accuracy and repeatability of the NUMAC is combined with the ability to store inspection data. The stored data can be used to document condition, demonstrate and identity important trends, and efficiently channel resources. The flexibility of the portable computer based NDE system is intended to provide a basic, reliable and cost- effective instrument for steel bridge inspection.

Instrumentation for load rating of bridges

A large percentage of the nations bridges are classified as structurally deficient or functionally obsolete. Many bridges are classified as such due to the bridges load rating. However, the vast majority of bridges are not actually tested to determine their load capacity. In general, actually testing a structure to determine the load rating is time consuming and expensive. As a result only a low number of bridges can be tested. A main time consuming portion of the load test is the setup of conventional instrumentation to monitor the status of the bridge under test. Typically strain gages and LVDT (or similar) deflection transducers are used. Instrumentation which would allow rapid load testing of bridges is currently being developed and tested at the Federal Highway Administration. This instrumentation includes wireless data acquisition systems interfaced with clamp-on strain gages, which can be placed at a measurement location in a matter of minutes. Also, the instrumentation includes a remote laser- based deflection measurement system. The combination of the two types of instrumentation, wireless data acquisition and laser-based deflection measurements, has the potential to allow a greater number of structures to be load rated giving a more accurate picture of the health of the nations bridges.