U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590

Skip to content
Facebook iconYouTube iconTwitter iconFlickr iconLinkedInInstagram

Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations

This report is an archived publication and may contain dated technical, contact, and link information
Publication Number: FHWA-HRT-07-024
Date: February 2007

Flexural Capacity of Fire-Damaged Prestressed Concrete Box Beams

View Table of Contents

PDF Version (332 KB)

PDF files can be viewed with the Acrobat® Reader®


The Federal Highway Administration, at the request of the Connecticut Department of Transportation, has investigated the flexural capacity of a set of prestressed concrete adjacent box beams that were damaged in a fire. The U.S. Route 7 bridge over the Norwalk River near Ridgefield, CT was damaged when a gasoline tanker crashed and caught fire on the bridge. During the replacement of the superstructure of this bridge, four beams were saved and transported to the Turner-Fairbank Highway Research Center. Full-scale structural tests were completed on the beams to determine their flexural behavior through ultimate failure. Additional visual and petrographic examinations were also completed. In summary, the investigation found that the flexural capacity of the beams had not been degraded significantly as compared to their anticipated capacity; however, their long-term durability may have been degraded by the fire. This report presents the results of this experimental investigation.

Gary L. Henderson

Director, Office of Infrastructure

Research and Development


This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document.

The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers' names appear in this report only because they are considered essential to the objective of the document.

Quality Assurance Statement

The Federal Highway Administration (FHWA) provides high-quality information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement.

Technical Report Documentation Page

1. Report No.


2. Government Accession No. 3 Recipient's Catalog No.
4. Title and Subtitle

Flexural Capacity of Fire-Damaged Prestressed Concrete Box Beams

5. Report Date

February 2007

6. Performing Organization Code
7. Author(s)

Benjamin A. Graybeal

8. Performing Organization Report No.


9. Performing Organization Name and Address

PSI, Inc.
2930 Eskridge Road
Fairfax, VA 22031

10. Work Unit No. (TRAIS)

11. Contract or Grant No.
12. Sponsoring Agency Name and Address

Office of Research and Technology Service
Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296

13. Type of Report and Period Covered

Final Report, December 2005 - July 2006

14. Sponsoring Agency Code


15. Supplementary Notes

Additional FHWA Contacts - William Wright, Contract Officer's Technical Representative

16. Abstract

A gasoline tanker truck fire caused significant damage to an adjacent member box-beam bridge in southwestern Connecticut. It was unclear whether the type of damage that these box beams experienced was sufficient to critically impair the structure's ability to serve its intended purpose. Four of the beams were removed from the bridge and were loaded in flexure to failure. These tests indicated that each of the beams retained sufficient flexural capacity to resist a 1,572 kilonewton-meter (kN-m) (1,160 kip-feet (kip-ft)) moment prior to ultimate flexural failure. This value is greater than the rated ultimate flexural capacity of each beam. As such, it seems that these beams had sufficient remaining flexural capacity to serve their intended purpose in the immediate aftermath of the fire. The long-term viability of these beams is more questionable. The visual and petrographic examinations indicated that the damage to the bottom flange concrete was sufficient to allow pathways through the concrete to the depth of the bottom strands. Therefore, it is possible that fire may have acted to allow for the accelerated deterioration of the superstructure and thus decreased the long-term flexural capacity of the bridge.

17. Key Words

Fire Damage, Prestressed Concrete, Adjacent Box Beam Bridge, Flexural Capacity

18. Distribution Statement


19. Security Classification
(of this report)


20. Security Classification
(of this page)


21. No. of Pages


22. Price
Form DOT F 1700.7 Reproduction of completed page authorized

SI (Modern Metric) Conversion Factors





  1. Photo. Remains of tanker truck after fire.
  2. Photo. Bridge fascia immediately after fire.
  3. Photo. Flexural loading of a box beam.
  4. Illustration. Standard cross section of voided box beam.
  5. Graph. Compressive stress-strain behavior of core from Beam 3.
  6. Photo. Bottom face of Beam 4.
  7. Photo. Photomicrograph of a crack near the exposed surface of the concrete.
  8. Graph. Applied load versus midspan vertical deflection for Beam 3.
  9. Graph. Deflected shape of Beam 3.
  10. Graph. Midspan neutral axis depth from top of Beam 3.
  11. Photo. Failure of Beam 3.
  12. Graph. Applied load versus midspan vertical deflection for Beam 4.
  13. Graph. Deflected shape of Beam 4.
  14. Graph. Midspan neutral axis depth from top of Beam 4
  15. Photo. Deflection of Beam 4 at maximum applied load.
  16. Photo. Failed Beam 4.
  17. Graph. Applied load versus midspan vertical deflection for Beam 7.
  18. Graph. Deflected shape of Beam 7.
  19. Graph. Midspan neutral axis depth from top of Beam 7.
  20. Photo. Failure of Beam 7.
  21. Graph. Applied load versus midspan vertical deflection for Beam 14.
  22. Graph. Deflected shape of Beam 14.
  23. Graph. Midspan neutral axis depth from top of Beam 14.
  24. Photo. Failed Beam 14
  25. Graph. Applied load versus midspan vertical deflection backbone curves.
  26. Graph. Applied moment versus average compression flange strain backbone curve.


  1. Compressive strength, modulus of elasticity, and density.




Federal Highway Administration | 1200 New Jersey Avenue, SE | Washington, DC 20590 | 202-366-4000
Turner-Fairbank Highway Research Center | 6300 Georgetown Pike | McLean, VA | 22101