Daniel N. Farhey

Bridge Instrumentation and Monitoring for Structural Diagnostics

Diagnostic instrumentation and monitoring of bridges are essential for reliable structural condition assessment and performance evaluation. This management step applies particularly to structurally deficient bridges that cannot be accurately evaluated by inspection and/or analysis alone. Reliable evaluation is an economic and engineering requirement before any decision-making for preventive action. Thus, field diagnostic capabilities are indispensable tools to enable evaluation and support field-calibrated modeling, analysis, identification, and load rating. The reliability of structural evaluation for objective bridge management is determined by the dependable performance of all the system components. Although instrumentation and monitoring procedures appear to be well established, some misconceptions still keep recurring critically in practice. To improve the state-of-practice of structural diagnostics, available field systems and methods need re-evaluation of their instrumentation and monitoring performance under real-world conditions. Subsequently, dedicated field capabilities can be formulated and developed to have advanced and practical characteristics. This article discusses various less-emphasized critical aspects of multidisciplinary research experience on bridge structural health monitoring, to explore dependable evaluation methods, compile practical data on actual bridge monitoring for immediate implementation, and generate focused insight for the development of advanced, reliable, and practical research methods in the future. To reach a systematic conceptualization for a better methodology, various diagnostic components are criticized. The resulting discussions on the various bridge evaluation aspects are practical for transportation agencies, bridge officials, and researchers. The detailed aspects are intended to help select appropriate implementation practices in field applications of bridge instrumentation and monitoring. These help focus bridge management policies, re-orient evaluation strategies, and reconsider diagnostic methods.

Integrated Virtual Instrumentation and Wireless Monitoring for Infrastructure Diagnostics

This article presents the research, development, and field testing of a computer-controlled integrated instrumentation and monitoring system for rapid-response infrastructure testing and evaluation. The system eliminates both stand-alone laboratory benchtop equipment sets and cable-based, hard-wired, on-site networking for individual sensors. A software-based virtual instrumentation program package is developed to replace conventional data acquisition and monitoring equipment and control all system components through a user-friendly graphical user interface. In addition, a multiple-channel wireless site network throughout the structure is developed to substitute cable networking and integrated in the modular system. Concept and design characterizations, validation testing, and practical field use for experimental live-load bridge test monitoring are also presented. The tests verify the computer-controlled operation of the system integrating virtual instrumentation with multiple-channel wireless site network. The results are compared with conventional instrumentation system and found to be consistent.

Performance of Bridge Materials by Structural Deficiency Analysis

The diagnostic concept of the structural deficiency of bridges is an essential engineering and management consideration with implications of performance. The structural deficiency analysis reflects the constructed system performance at the serviceability limit states. This paper analyzes trends in the structural deficiency of bridge inventory on the basis of material kind. A multiple-criteria diagnostic approach defines measures for condition, durability, and longevity performances and determines the overall equivalent performance. Thus, the structural performance levels reflect the structural reliability and vulnerability indices for bridge serviceability. The application of the approach analyzes the raw database of the entire bridge inventory in the United States. This comprehensive operational experience provides a national network-level comparative basis. The comparison suggests a relative need for improvements in one or more areas, such as design details or maintenance level, to increase the desirability of bridge construction materials. The results support more objective bridge management and decision making on distribution of funds, updating of policies, perfection of practices, and trade-off analyses for design, construction, maintenance, and replacement.

Operational Structural Performances of Bridge Types

This paper analyzes the raw database of the entire bridge inventory in the United States and derives distinctive bridge type-specific structural performances. The distributions, 15-year histories, and average ages of bridges and structurally deficient bridges of the various structural design and construction types are determined to study typical trends of structural deficiency. Based on the concept of structural deficiency and the objective of life-cycle expectancy, the multiple-criteria diagnostic approach of the analysis determines and compares the condition, durability, longevity, and equivalent performances. The comprehensive results provide a national network-level comparative basis for the operational performances of all coded bridge types. The approach characterizes the probability of bridge structural system deficiency, consequences attributable to deficiency, and time to renewal. Thus, the structural performance levels reflect structural reliability and vulnerability indexes for bridge serviceability. The concept presents an objective comparison source for the long-term overall utility and value of bridge type alternatives and helps to identify life-cycle issues and the need for improvements to increase desirability of bridge types.

Instrumentation System Performance for Long-term Bridge Health Monitoring:

The instrumented long-term continuous health-monitoring system installed on the Tech 21 Bridge during its fabrication is used to evaluate the performance of the instrumentation system itself. The bridge has been continuously monitored for nearly four years to demonstrate its performance. Field monitored results are studied to evaluate the behavior and durability of the bridge structure, components, and material. This evaluation is also studied to determine the level of long-term performance of the instrumented monitoring system in the harsh infrastructure environment. The measured readings of the bridge include the hidden additive of the system’s performance. In addition to the structural behavior, results measured also demonstrate the ambient effects on the system. Time, temperature, and humidity dependence of the system are recorded and characterized.

Quantitative Assessment and Forecast for Structurally Deficient Bridge Diagnostics

Diagnostic instrumentation and monitoring of bridges are essential for reliable structural condition assessment and performance evaluation. Particularly, structurally deficient bridges cannot be accurately evaluated by inspection and/or analysis alone. Reliable evaluation is an economic and engineering requirement before any decision-making for preventive action. Although structural health monitoring for bridge diagnostics appears to be accepted, it is not yet a typical field practice. This article assesses quantitatively the future needs for bridge diagnostics of structurally deficient bridges through structural health monitoring. Logistic components of bridge diagnostics are also discussed. The detailed aspects are intended to help, plan, and manage financial resources and implementation practices for bridge evaluation.

Operational Structural Performances of Bridge Materials by Deterioration Trends

This paper demonstrates the analysis of the deterioration trends of bridges to evaluate the operational structural performances of the various kinds of bridge construction materials and/or structural designs. The goal of this study is to improve the performance of structural materials used to construct bridges, based on rigorous population-based analysis of the performance of those materials in service. The analysis uses the raw database of the entire National Bridge Inventory in the United States and derives material deterioration aspects at the serviceability limit states. The study develops measures of deterioration to consider the trends in the accumulation of structural deficiency versus service life cycle by material. The approach defines the criteria of rate and pattern performances to analyze the comparative deterioration trends. A multiple-criteria diagnostic approach determines the overall equivalent structural performances integrating the rate and pattern performances with the measures of condition, durability, and longevity. The national network-level operational experience by categorical deterioration trends produces the most comprehensive comparative basis of structural performance of bridge materials. Overall for all bridges, the average increase of structural deficiency is 0.51%/year, adding to the already existing 12.35% and consisting of an average annual increase of structurally deficient bridges by 4.10%. The accumulation of structurally deficient bridges begins only after 10 years for most materials. The rate and pattern performances of almost all of the materials are quite poor. Thus, the equivalent performances integrating the deterioration trends are lower. The results provide a more objective indication and comparison of structural performances under the actual circumstances and help predict future performance. The approach supports the development of improvements necessary to increase the relative performances of distinct bridge materials for more sustainable service.

Operational Structural Performance of Bridge Types by Areas

This paper demonstrates trends in bridge structural deficiency and evaluates the operational structural performance of various types of bridge structural design and/or construction. The study analyzes the database of the National Bridge Inventory and derives data based on actual bridge deck areas, rather than discrete bridge counts. Based on the concept of structural deficiency and the objective of life-cycle expectancy for uninterrupted service life, the multiple-criteria diagnostic analysis determines condition, durability, longevity, and equivalent performance. For some bridge types, the results reflect limited remaining service life before structural deficiency is reached. Average service life is only 56% of life-cycle expectancy. The relatively higher condition performance contrasts with the significantly poor performance of durability and the relatively lower longevity. The equivalent structural performance of some bridge types is low. Overall, the study provides an indication of the current average potential, which serves as a basis for predicting future performance under similar operational conditions. The systems approach supports more objective design, maintenance, and decision-making practices, leading to more effective operation and management and more sustainable infrastructure solutions.

Operational Structural Performances of Bridge Materials by Areas

AbstractThis paper evaluates the operational structural performances of the various kinds of bridge construction materials and/or structural designs, considering the deck areas of bridges, rather than their discrete counts. Deck areas represent more objectively the actual constructed capacity in the inventory and the traffic mobility. The study compiles and analyzes the entire bridge inventory in the United States. The analysis uses multiple-criteria diagnostic measures to determine the condition, durability, longevity, and overall equivalent performances. The results provide a comprehensive national network-level comparative basis for bridge material performances at the serviceability limit states. Nearly 99% of all the bridge areas in the inventory have average structural deficiency ages significantly lower than the official life-cycle expectancy. The durability performances indicate that the average service life before structural deficiency is only 42xa0years. The relatively high condition contrasts with...

In-Service Analytical Investigation of Precast-Concrete, Short-Span, Skewed Bridges with Integral Abutment Walls

Precast-concrete, skewed bridges with integral abutment walls are typically designed as simplified two-dimensional rigid portal frames, neglecting the degrading effects of the skew angle and laterally unsymmetrical vertical loading. This practice produces under-designed bridges for certain aspect ratios, causing cracking and local deterioration near the obtuse corners of the deck. To evaluate the limitations of this practice, an analytical study was carried out for the live load response at the linear service level. Three-dimensional finite-element models of precast-concrete, short-span, skewed bridges with integral abutment walls were developed and analyzed. For some bridge configurations, both the positive and negative moment stresses are higher than the stresses given by simplified two-dimensional frame analysis. In other cases, the two-dimensional frame method results in over-designed bridges. The results were presented in correlation diagrams, enabling simple comparison and quantification. The correlation diagrams also provide modification factors to amend the simplified two-dimensional frame design.