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FHWA >
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Steel >
Heat Straightening
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The Bridge Office
Ministry of Transportation, Ontario Workshop
In Ontario, the Ministry of Transportation is responsible for the construction, operation, maintenance and repair of many bridges with superstructures having girders fabricated out of structural steel. The Ministry is also responsible for other steel structures including sign supports and high mast lighting poles. These structures may suffer damage during their fabrication, transportation or erection as well as during their service life. Because of this, heat straightening may be an economical and practical way of repairing certain damaged steel components.
Heat straightening is a process where a limited amount of heat from a torch is used to heat a damaged section of steel using a specific pattern. While the heat would normally cause the steel to expand; during the heat straightening process restraining forces are applied to prevent this. After the application of heat has been completed, the steel is allowed to cool. As it cools, it contracts. Since expansion has been restrained, the only possible deformation in the steel is from contraction. It is this contraction that straightens the damaged steel.
The use of heat straightening to repair damaged steel dates back to the early days of welding. Steel fabricators observed how the heat from welding caused distortion in regular patterns. Some of the fabricators began experimenting with ways to counteract the initial distortion by heating the steel in specific patterns. With experience, some of them developed skills in both removing the weld distortion and repairing other damage. Back then, however, heat straightening was more of an art than a science. There was no quantitative analysis of the process, and the techniques were merely passed from one practitioner to the next.
Over the past 15 years, technicians, engineers, and researchers have made significant efforts in providing a rational engineering basis to heat straightening repairs. The highlights of this research and development are presented in the Demonstration Project on Heat-Straightening Repair of Damaged Steel Bridge Members offered by the Federal Highway Administration. FHWA has been increasing awareness of heat straightening as a means to repair of damaged steel and propagating expertise in the heat straightening process. This two day workshop will be held at the Travelodge Hotel in Downsview and at the Ministry's Reservoir building on November 16th and 17th, 2004.
The purpose of the workshop is to provide the fundamental principles upon which heat straightening is based, and to show how these principles can be implemented in practice. These include damage assessment, heating temperatures, the application of restraining forces during heat straightening, heating patterns, the effects of heat straightening on material properties and the classification of heating damage.
The workshop will be comprised of a presentation and a hands-on laboratory demonstration. Subjects covered will include:
In terms of practical applications, the presentation will focus on how to heat straighten the typical types of damage to steel. Particular emphasis will be placed on:
Each participant will receive a copy of the FHWA publication Heat-Straightening Repairs of Damaged Steel Bridges, a student's notebook and a set of two interactive CDs.
In addition to heat straightening, the workshop will include a demonstration and short introduction to ultrasonic impact treatment, which can be used to arrest fatigue cracks in steel and improve fatigue life. This is a relatively new technique that was invented by Dr. Efim Statnikov in the Soviet Union, and has recently been the subject of further research at Lehigh University. The technique has implications for both new fabrication and for maintenance and repair procedures.
Professor Avent holds the C.W. Armstrong distinguished professorship in the department of Civil and Environmental Engineering at LSU. He has over 30 years of teaching and research experience in structural engineering. He has focused his research efforts on structural repair and rehabilitation. He received the 1991 Wellington Prize from ASCE for his work on heat straightening, and the ASCE Innovation in Civil Engineering Award in 1995 for his work in developing epoxy repair methods for timber structures.
Mr. Verma is the Principal Bridge Engineer - Structural Fabrication in the Office of Bridge Technology, Federal Highway Administration Headquarters in Washington DC. He received a Master's Degree (Material Engineering) from Rensselaer Polytechnic Institute, a Master's Degree (Civil Engineering Structures) from the University of Calgary, and a BSCE Degree from Benaras Hindu University, India. He has coordinated FHWA's efforts to implement heat straightening for the repair of bridge structures.
Ministry staff:
The Ministry's partners in bridge construction and design:
