John T. DeWolf

Long-term Structural Health Monitoring of a Multi-girder Steel Composite Bridge Using Strain Data

This paper presents an approach to use strain data from a multi-girder, composite steel bridge for long-term Structural Health Monitoring (SHM). The bridge being studied is part of a research project at the University of Connecticut in which long-term SHM systems are being installed on a series of bridges throughout the State of Connecticut. Strain data is collected from normal truck traffic to determine live load stresses, load distribution factors, and the location of the neutral axis in each girder. Known weight trucks were used along with a finite element analysis for verification of the behavior. The long-term monitoring approach is based on determining the live load distribution factors, peak strains, and the neutral axis locations. The goal is to use existing, readily applied technology for SHM for long-term use on bridges that have raised concerns, due to corrosion noted in routine visual inspections, overloading, or fatigue sensitive details. The SHM system proposed can be used on a continuous basis to determine if there are significant changes in the structural behavior that would be indicative of major damage to either the girders or the concrete deck.

Monitoring Bridge Performance

Researchers and engineers at the University of Connecticut and the Connecticut Department of Transportation have been using non-destructive field monitoring to evaluate a variety of bridges in the State. This has been done to answer questions on the performance of existing bridges, refine techniques needed to evaluate different bridge components, and develop approaches that can be used to provide a continuous picture of a bridges structural integrity. This paper reports on some of the lessons learned in this continuing research. The field monitoring studies have supplemented the regularly scheduled visual inspection program. Without field data, it would be necessary to use simplified, conservative assumptions to define the actual behavior. The field monitoring efforts have resulted in savings to the state by eliminating or reducing the scope of planned renovations and replacements. This paper shows the need and benefits in using non-destructive evaluation to determine structural health.

Effect of Differential Temperature on a Curved Post-Tensioned Concrete Bridge

This paper presents the results of an experimental and analytical study of a continuous three-span curved post-tensioned concrete bridge. This bridge is being studied in a long-term project that involves the placement of continuous monitoring systems on a number of bridges that are critical to the bridge infrastructure in the State of Connecticut. The bridge has been monitored using tiltmeters, thermocouples and accelerometers. The experimental data has been used to develop a three-dimensional finite element analysis model to describe the overall behavior. The model has been used to explore the effect of the differential temperatures on the overall behavior.

The Long-term Structural Health Monitoring of Bridges in the State of Connecticut

The University Of Connecticut and the Division of Research in the Connecticut Department of Transportation have been involved in monitoring both steel and concrete bridges during the past two decades. This paper will report on the operation of permanent monitoring systems on four different bridges in the State of Connecticut during the past decade. The monitoring systems have been tailored to each bridge, using sensors for strain, temperature, tilt and vibration. Monitoring is conducted on a continuous basis, with excitation provided by normal traffic loading. The bridges are monitored remotely from the University of Connecticut and the Connecticut Department of Transportation. The extensive data has been used to characterize the performance of each bridge and to provide information for long-term structural health monitoring. This has required significant data management, based on what has been learned in previous research at the University of Connecticut.

Development of Computer‐Based System for the Temperature Monitoring of a Post‐Tensioned Segmental Concrete Box‐Girder Bridge

This paper describes the development and implementation of a computer-based remote monitoring system for temperature monitoring of an 11-span segmental, post-tensioned concrete box-girder bridge. Monitoring was carried out for 5 years. The extensive data collected is analyzed using software developed to provide engineers with information that can be used in the evaluation of the long-term behavior and performance of the bridge. The software was used to determine the maximum and minimum bridge temperatures, vertical temperature differences through the bridge cross section, and horizontal temperature differences in the transverse directions. Comparisons are made with design specification provisions and with recommendations proposed by previous researchers. In addition, software has been developed to determine the relationship between the daily maximum temperature differences and the air temperatures inside the box-girder. This approach is also used to develop the relationship between the maximum stresses due to temperature differences and the air temperature inside the box-girder. This paper shows the benefits from using a computer-based monitoring system to provide a continuous evaluation of data collected on the bridge.

Effect of temperature on modal variability for a curved concrete bridge

This paper presents the results of a study to determine the effect of temperature on modal variability on a curved post-tensioned box girder bridge with three continuous spans. The bridge has been monitored during the past 6 years using 16 accelerometers, 12 thermocouples and 6 tilt meters. Monitoring is based on normal vehicle loading. There is concern that changes due to temperature variations may mask changes due to structural damage. A thorough understanding of this uncertainty is necessary so that changes in vibration response resulting from damage can be discriminated from changes that are due to temperature variability. This paper presents the results of a study to evaluate the ambient vibration information over a full year period in which data was collected continuously. The effects of temperature change on the bridges modal frequencies are analyzed and interpreted. This correlation between the natural frequencies and temperature is essential to establishing a structural health monitoring approach that can provide for indications that damage has occurred.

Implementation of a Probabilistic Structural Health Monitoring Method on a Highway Bridge

This paper describes the application of a probabilistic structural health monitoring (SHM) method to detect global damage in a highway bridge in Connecticut. The proposed method accounts for the variability associated with environmental and operational conditions. The bridge is a curved three-span steel dual-box girder bridge located in Hartford, Connecticut. The bridge, monitored since Fall 2001, experienced a period of settling in the Winter of 2002-2003. While this change was not associated with structural damage, it was observed in a permanent rotation of the bridge superstructure. Three damage measures are identified in this study: the value of fundamental natural frequency determined from peak picking of autospectral density functions of the bridge acceleration measurements; the magnitude of the peak acceleration measured during a truck crossing; the magnitude of the tilt measured at 10-minute intervals. These damage measures, including thermal effects, are shown to be random variables and associated P values are calculated to determine if the current probability distributions are the same as the distributions of the baseline bridge data from 2001. Historical data measured during the settling of the bridge is used to verify the performance of the bridge, and the field implementation of the proposed method is described.

Proposed Data Specifications for Bridge Structural Health Monitoring Sensor Data

Bridge structural health monitoring involves the collection and analysis of systematic measurements obtained from installed sensors on the bridge. While there are many quality certification systems available for civil engineering systems, e.g. American Society for Testing and Materials (ASTM), typical bridge monitoring specifications do not explicitly address performance requirements. As the applications of bridge structural health monitoring becomes more varied and advanced it will become necessary to ascertain the quality of measured data in order to check its suitability for new and varied applications. The quality of measured data has a direct impact on the results obtained from data analysis in structural health monitoring. The quality of measured data for a bridge monitoring system should meet three basic criteria: First, measured data should be devoid of anomalies such as signal clipping, intermittent noise spikes, temporary signal dropouts, and spurious trends. Second, the errors, including aliasing and quantization, and system noise should be within an acceptable range. Lastly, the measured data should satisfy required assumptions, such as stationarity and normality. Data qualification is defined as validating the quality of measured data and quantifying errors and noise to ensure the measured data sufficiently satisfies the above mentioned criteria. Despite the tremendous impact the quality of measured data has on bridge structural health monitoring, data qualification has not been formalized for bridge monitoring to provide a basis for bridge monitoring data specifications. This paper proposes measures of data qualification that can be used as a foundation for data specifications in bridge structural health monitoring. This paper will use data collected from monitored bridges in the Connecticut Long Term Bridge Monitoring program as examples of issues faced when using long term bridge monitoring data acquisition systems.

Development and implementation of a nondestructive monitoring system on a composite steel box-girder bridge in Connecticut

The University Of Connecticut, with support and assistance from the Connecticut Department of Transportation, has been involved in the design and implementation of long-term monitoring systems on a network of bridges critical to the State of Connecticuts highway infrastructure. This paper presents a report on the development, implementation and evaluation of the monitoring of a steel box-girder bridge. The bridge is a multi-span, continuous, box girder bridge made up of two steel box-sections that are composite with the deck slab. The bridge is supported on a series of tall concrete columns, one per support. Field investigations have shown that the columns have been subject to cracks that are thought to be due to torsion. Two spans in a three-span continuous segment are currently being monitored using 8 accelerometers, 8 temperature sensors and 6 tilt meters. An extensive analysis has been conducted to evaluate the test data. There have been large temperature gradients due to both annual climate changes and due to the position of the sun with respect to the bridge. The data has also been used to develop a basis for long-term nondestructive evaluation. This is based primarily on the development of a vibration signature. The field data has also been compared with results from an extensive finite element analysis. The longterm goal of this project has been to characterize the bridge behavior and then to use this in the nondestructive evaluation of the performance over multi-year periods.

Nondestructive Evaluation with Vibrational Analysis

A full-scale highway bridge, in the process of being demolished and replaced, was monitored using vibrational techniques. The bottom of the flange and web of one fascia girder were incrementally cut. Vibrational monitoring during the passage of a test vehicle was used to demonstrate that the vibrational signature of a bridge will change when a major defect occurs. Included in this paper is a discussion of how vibrational studies have been used in the evaluation of bridges.