The objective of this paper is to present a 'straw-person' framework that appears to be a practical first step towards a
more transparent, objective, quantitative and risk-based approach to bridge assessment and prioritization. While the
framework presented is qualitative in nature it has distinct advantages over the current approach in that (a) it explicitly
recognizes key performance limit states, (b) directly addresses bridge hazards, vulnerabilities, and exposures, (c)
incorporates the uncertainty associated with various assessment techniques and provides flexibility for their
implementation, and (d) provides a means to capture (in a useable format) expert knowledge and heuristics from top
bridge engineers. In addition to the straw-person framework, the paper presents a rudimentary classification system to
illustrate one approach to implementation. A series of case studies are then presented to demonstrate the potential value
of this approach in distinguishing between bridges that are essentially "equivalent" based on the current assessment
procedure. In addition, these case studies also serve to illustrate that the proposed approach may be utilized with existing
inspection data. The paper concludes with some observations and comments regarding the straw-person framework
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.
Since early 1995 the Federal Highway Administration (FHWA) has been sponsoring the development of ground-penetrating radar technology to produce a tool for the non-destructive evaluation of bridge decks. Under contract with the FHWA, Lawrence Livermore National Laboratory designed and built a system capable of recording data over a 2 meter width during normal traffic flow. The derived system is called `The HERMES Bridge Inspector' (High-speed Electromagnetic Roadway Measurement and Evaluation System) and includes a 64 channel antenna array within a 30 ft trailer. For detailed investigation of portions of a bridge deck, a robotic cart mounted radar has been developed. This cart system is named `The PERES Bridge Inspector' (Precision Electromagnetic Roadway Evaluation System). PERES records data over the chosen area by rastering a single transceiver over the road. Images of the deck interior are reconstructed from the original synthetic aperture data using diffraction tomography. The work presented herein describes the findings of initial experiments conducted to determine the inspection capabilities of these systems. Internal defects such as delaminations, voids and disbonds; and construction details including deck thickness, asphalt overlay thickness and reinforcement layout were the features targeted. The final goal is for these systems, and other non-destructive technologies, to provide information on the condition of the nation's bridges for input to bridge management systems.
A large percentage of the nation's bridges are classified as structurally deficient or functionally obsolete. Many bridges are classified as such due to the bridge's 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 nation's bridges.
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 nation's bridges so that funds will be spent on the structures in most need of repair.
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.
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.
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.