NDT.net • Jan 2006 • Vol. 11 No.1

Abstracts of NDT Sessions of the 6th International Bridge Engineering Conference

Reliability, Security, and Sustainability in Bridge Engineering
The Westin Copley Place Boston
Boston, Massachusetts
July 17-20, 2005
Internet

Technical Session 5: Non-destructive Evaluation (NDE) of Bridges

Monday, July 18, 2005, 3:30 p.m.-5:00 p.m.
Richard A. Walther, Wiss Janney Elstner & Associates, presiding

Void Detection in Post-Tensioning Ducts Using Time-Domain Reflectometry
Laura Akl, Robert G. Hunsperger, Michael Chajes, Jian Li and Wei Liu, University of Delaware; Eric Kunz, Vetek Systems Corp.
When post-tensioned ducts are not completely grouted, resulting in voids, the steel strands are left vulnerable to premature corrosion. This paper describes a nondestructive evaluation (NDE) procedure that will allow bridge owners to ensure that post-tensioned ducts are properly grouted (i.e., have no voids). The NDE procedure utilizes Time Domain Reflectometry (TDR), a technique developed by electrical engineers for locating discontinuities in transmission lines. The technique involves sending a signal through a transmission line using a step-pulse generator, seeing whether or not the signal is reflected back, and, if it is reflected back, using the elapsed time to determine the location of the discontinuity. Prior research funded by the Delaware Department of Transportation and the NSF has shown that TDR can be used to detect corrosion on strands, and can be implemented in the field. In order to detect and evaluate voids, the transmission line is placed either in, or adjacent to, the region in which a void is suspected. The presence of a void affects the electric field surrounding the transmission line and causes a distinct reflection. Data is presented to show the measurement of both the relative size and the position of voids. The effects of environmental conditions, such as moisture content, temperature, and material contained in the void (e.g. corrosion products) also is reported.



Fast Location of Prestressing Steel Fractures in Parking Lots and Bridge Decks
Horst Scheel, Technische Universitaet Berlin
The Remanent Magnetism Method (RM-Method) allows identification of potentially unsafe conditions in pre-tensioned and post-tensioned concrete structures by locating fractures of single wires, even if they are bundled with intact wires. Once the tendons have been pre-magnetized with an electromagnet, the magnetic field of tendons is measured at the concrete surface. Fractures produce characteristic leakage fields, which can be measured with appropriate sensors at the concrete surface.
The measuring speed of the RM-Method can be enhanced significantly by replacing the time-consuming multi-step-magnetization by a single-step-magnetization. Large yoke-shaped magnets have been constructed to magnetize transverse tendons in bridge decks over lengths of up to 3.5 m ( 3.8 yd) in a single process. Measuring the magnetic flux density of an entire bridge deck simplifies the comparison of data from measurements at different times, which would be helpful for monitoring the long time behavior of the structure.


Critical Evaluation and Condition Assessment of Post-Tensioned Bridges in Texas
Mohsen A. Shahawy, SDR Engineering Consultants, Inc.; William R. Cox, Texas Department of Transportation
The recent findings of corrosion in longitudinally post-tensioned (PT) tendons in several bridges in Florida and other states raised an alarm with respect to the conditions of PT bridges in Texas. Texas Department of Transportation (TXDOT) Bridge Division in Austin initiated an investigation to assess the actual conditions of three major PT bridges within their area of operation. The three bridges are:
• US-183 segmental Bridge in Austin
• San Antonio “Y” segmental Bridge in San Antonio
• Veterans Memorial Cable Stay Bridge in Port Arthur
This investigation consists of two phases. Phase I included the preliminary evaluation of construction and design details and conducting a detailed walkthrough inspection to visually evaluate the existing conditions. The walkthrough inspection was designed to identify any existing potential problems and their locations. The information collected from Phase I was used in developing the testing plan for the in-depth evaluation carried out under Phase II.
This paper covers the work performed under Phase II for all three bridges. The objectives of this investigation are to closely examine these bridges in order to identify any PT related deficiencies. Observed deficiencies are analyzed to determine their effects on the structural performance and long-term durability of the bridges. The findings from Phase II are presented herein along with recommendations for future actions.


Non-destructive Evaluation of Bridges (presentation w/out paper)
Mark Moore, Wiss, Janney, Elstner Associates; Travis Green, Wiss Janney Elstner & Associates; Hamid Ghasemi, Federal Highway Administration
The aging highway and bridge infrastructure presents a significant challenge to effectively maintain the operational status and safety of the highway system. Effective and reliable condition assessment tools are an important part of the ongoing efforts to evaluate and maintain the nations bridge structures. Nondestructive evaluation technologies have played an increasingly important role in the inspection and assessment process. Recent advances in NDE techniques have improved the functional characteristics of many NDE methods and have led to systems that are more reliable. Increased use of NDE methods will depend on several factors including the ability of the systems to accurately detect deteriorated conditions, the ease of use and field portability of the systems, and the total cost of completing the NDE based inspections. A review of NDE systems for bridges has been completed. The capabilities of selected NDE techniques and systems have been evaluated and will be presented.

Technical Session 11: Bridge Health Monitoring

Tuesday, July 19, 2005, 1:30 p.m.-3:00 p.m.
James E. Roberts, Consultant, presiding

Continuous Monitoring for the Management, Safety and Reliability of Connecticut’s Bridge Infrastructure
John T. DeWolf, University of Connecticut
Researchers at the University of Connecticut have been working with researchers in the Connecticut Department of Transportation to develop and implement continuous bridge monitoring systems on a series of bridges in Connecticut. The monitoring systems are designed to evaluate the long-term behavior of the bridges and to evaluate safety and reliability, assuring that there have not been any major structural changes that can lead to significant problems. This paper reports on the approach used to organize the large amount of data that is collected from the first three bridges in the project. The goal of this work is to facilitate the continuous evaluation of the bridge network, assisting those responsible for the management and safety of Connecticut’s bridge infrastructure.
Virtual Wireless Infrastructure Evaluation System
Daniel Farhey, University of Dayton
System identification through nondestructive experimental testing and analysis is essential for reliable structural evaluation. Experimental testing and monitoring of full-scale structures in the field is complicated, time consuming, and labor intensive. The lack of practical field experimental technology impedes further research and development of bridges. This issue critically conflicts with public needs to preserve existing bridges and upgrade substandard bridges. Thus, it is imperative to develop a particularly efficient field-testing and monitoring system for identification, condition assessment, and performance evaluation. A study considering system intelligence characterizations conceptualized an effective upgrade. A virtual Wireless InfraStructure Evaluation (WISE) system was designed and developed. The system is devised for structural field experimentation through static or moving loads, utilizing various types of electronic sensors. The system integrates a computer-controlled site network of multiple-channel wireless transmission. A software-based virtual instrumentation program was developed to control the system, collect data, and monitor the results through a user-friendly graphical user interface. The results of successfully testing two bridges in the field under real-world conditions are presented.
Bridge Inspections Using Electronic Data Collectors
Kevin Hartford Hahn-Keith, Parsons Brinckerhoff; James L. Stump, Pennsylvania Turnpike Commission; Dave Charters, Parsons Brinckerhoff; Lance Andrews, Michael Baker Corporation
To monitor reliability, ensure security, and maintain sustainability accurate, efficient data collection is required for condition assessment of an owner’s assets. Replacing cumbersome clipboards, pencils and paper with an electronic data collection system is a way to streamline the data collection process, improve the accuracy of data collection, and enhance management of all asset data. At the request of the Pennsylvania Turnpike Commission (PTC), a consultant developed and utilized a handheld data collection system for the National Bridge Inspection Standards (NBIS) inspections for over 800 bridges on the Pennsylvania Turnpike. In addition to developing the data collection system, the same consultant was chosen to perform a second two-year cycle of routine inspections, this time using the electronic data collection system, instead of handwritten reports. Since many of the same personnel worked on both inspection cycles, this provided a unique opportunity to compare the two ways of collecting inspection data and preparing bridge inspection reports.
This paper describes in detail the hardware and software used for the PTC Inspection Program and the report preparation processes for both cycles (handwritten and electronic). Feedback from inspectors and the PTC is used to show the resulting benefits of using an electronic reporting system: reduced costs, better quality assurance and quality control, and easier access to inspection information. Finally, lessons learned and possible future developments are discussed. The conclusion of the authors is that handheld data collection units will continue to replace the handwritten reporting system and improve the reports prepared for NBIS bridge inspections.




Thermally Induced Superstructure Stress in Prestressed Girder Integral Abutment Bridges
Daniel G. Linzell, Pennsylvania State University; Michael Paul, Wilbur Smith Associates
This parametric study investigates forces and stresses that develop in the superstructure of prestressed concrete, integral abutment (IA) bridges as a result of thermal load. Applied loading consists of uniform temperature changes in the superstructure. This study investigated the influence of bridge length, number of spans, abutment height, and pile orientation on thermally-induced superstructure forces. The largest thermally induced superstructure forces and stresses occurred near the abutment. It was determined that bridge length and abutment height most strongly influence thermally-induced superstructure forces. The number of spans has the largest influence on thermally-induced superstructure stress and pile orientation influences thermally-induced superstructure forces and stresses to a smaller degree. The results also indicate that thermally-induced superstructure stresses and shear forces are comparable in magnitude to those caused by live load.

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