This report summarizes the results of a project to establish limits, based on fatigue and fracture performance, on the number of damage and repair cycles to which damaged steel bridge girders may be subjected using the heat-straightening procedure. A key product presented here are suggested revisions to the Federal Highway Administration (FHWA) http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_604.pdfmanual of practice for heat straightening. The report will be of particular interest to engineers in state highway agencies and industry responsible for bridge maintenance and repair. Heat straightening refers to the in-place application of heat and jacking forces to remove bends and distortion in steel bridge girders damaged by the impact of over-height vehicles. This report may be accessed by Internet users at The procedure is often described as combining art with engineering, and is principally conducted by specialized firms in the private sector. Since 1999, however, the FHWA has presented workshops intended to acquaint state forces and consultants with the use of heat straightening. The syllabus for this workshop is based on the 1998 report FHWA-IF-99-004, “Heat-Straightening Repairs of Damaged Steel Bridges: A Manual of Practice and Technical Guide,” prepared by R. Avent and D. Mukai. Key questions in heat-straightening technology are the procedure’s effect on the fatigue and fracture of repaired steel girders and the degree to which the damage and heat-straightening history of the steel influence that performance. These questions have been prompted by situations in which field-repaired girders subsequently fractured. Under NCHRP Project 10-63, “Heat-Straightening Repair of Damaged Steel Bridge Girders: Fatigue and Fracture Performance,” the ATLSS Engineering Research Center of Lehigh University was assigned the tasks of (1) determining the relative effects of damage and subsequent heat-straightening on the fatigue and fracture performance of steel girders; (2) identifying and quantifying the material and process parameters that may affect the fatigue and fracture performance of heat-straightened steel girders; and (3) establishing guidelines, including limits on initial damage and critical process parameters, to minimize the potential for fracture and fatigue problems in heat-straightened steel girders. The research team designed and conducted a major program of large-scale laboratory experiments to accomplish these tasks. Multiple steel girders were dynamically damaged using a large-scale, purpose-built drop-weight machine, repaired using the heat-straightening procedure, and fatigue tested. Up to three damage and repair cycles were made at the same position on a girder. Based on the results of this testing program, the report concludes that the number of repairs should be limited to two for subsequent impact damage within the geometric limits of the first impact repair (i.e., the region where the most severe initial damage was focused). The research also reviewed and developed (as needed) techniques for evaluation, repair, and inspection of damaged steel girders to assist the owner, engineer, and heat-straightening contractor during the repair process. Finally, the research team suggested changes to the FHWA manual of practice that reflect the findings and conclusions of the project. This report presents the full text of the contractor’s final report of the project and four appendices, which present (1) drawings of purpose-built test equipment and specimen gages (Appendix A), (2) fatigue test results (Appendix B), (3) material properties of the damaged and repaired steel girders (Appendix C), and (4) suggested revisions to 1998 report FHWAIF- 99-004, “Heat-Straightening Repairs of Damaged Steel Bridges: A Manual of Practice and Technical Guide,” (Appendix D). (Author/publisher)
Samenvatting