C. J. Naito Main

Pennsylvania Department of Transportation Project:
Inspection Methods & Techniques to Determine Non Visible Corrosion of Prestressing Strands in Concrete Bridge Components

Figure 1: Bottom flange of PS box beam with heavy strand corrosion

Laboratory Invitation Letter to NDE Colleagues by Professor Pessiki
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Executive Summary
Recent catastrophic failures of prestressed precast box beam bridges have occurred in a number of states in the north east region of the United States. The most recent involved the failure of the Lake View Drive Bridge over Interstate 70 near Pittsburgh Pennsylvania. On December 27, 2005 the east-side fascia beam failed near midspan and fell to the highway below. No impact from traffic on the highway below or overload of the bridge itself was reported. Inspection of the failed member revealed heavy concrete spalling and corrosion of the strands on the bottom flange of the non-composite prestressed concrete box beam. Additional corrosion was revealed on other box beams and the bridge was subsequently removed from service.

Forensic investigation of the beams conducted by Lehigh University revealed a significant level of damage that would otherwise not have been uncovered in a traditional inspection. Conventional bridge inspection consists of rating the extent of damage present based on a visual inspection. This is dependent on the type and amount of signs on the surface of the member. In some cases the significant internal damage can be present with minimal indicators.

In response to the collapse of that bridge, PennDOT has revised the NBIS inspection and rating requirement and procedures for this type of bridges and has put this type of bridges on high alert list for inspection and evaluation. However, the current inspection procedures are still based on visual inspection on the pavement and the bottom of the beams. Although some strand corrosion/deterioration symptoms can be identified from the cracks on the beams, loss of camber, and exposed strands, exact strand conditions cannot be quantified for evaluations and ratings for most bridges. Considering more than 140 bridges of the same construction type are in service in Pennsylvania alone, an efficient nondestructive (ND) method needs to be used to determine the condition of those bridges, so as to prioritize the repair/replacement.

Pennsylvania owns more than 900 prestressed concrete box-beam bridges. Most of them are composite construction with concrete deck on top. Although they are not as critical as non-composite box-beam bridges, condition of the prestressed strands is still a controlling element of the bridges’ load carrying capacity. The ND method developed for the non-composite bridges may also be used for the composite bridges, thus providing enhanced inspection techniques for a wider variety of bridges. The purpose of the proposed research is to develop inspection methods, techniques, and equipment to detect and evaluate corrosion in reinforcing steel in concrete bridge structures. The focus of the proposed research is the detection and evaluation of corrosion in prestressing steel in prestressed concrete bridge beams. The work will seek to: (1) develop inspection methods, techniques and equipment to detect and evaluate corrosion that is otherwise undetectable by visible inspection methods; and (2) seek to further refine visual inspection methods that correlate external observation and simple materials testing (e.g. chloride content, depth of carbonation, etc.) with the extent of corrosion.

Research Team
Associate Professor Clay Naito (PI)
Professor Stephen Pessiki
Professor Richard Sause
Research Engineer Ian Hodgson
Student Researcher Jordan Warnke

Sponsors
PennDOT Bureau of Planning and Research

Publications
Naito, C., Sause, R., Hodgson, I., Pessiki, S., Desai, C., "Forensic Evaluation of Prestressed Box Beams from the Lake View Drive Bridge over I-70: Final Report," ATLSS Report No.06-13, ATLSS Center, Lehigh University, September, 2006, 62 pages. (Available Via PennDOT)

Page Last Updated Monday, 22-Sep-2008 10:11:01 EDT