|FHWA > Infrastructure > Bridge > Steel > Heat Straightening|
FHWA Demonstration Project
Heat Straightening Repair for Damaged Steel Bridges
Army Corps of Engineers Workshop
The U.S. Army Corps of Engineers are responsible for the maintenance, operation, and repair of many hydraulic steel structures in its civil works projects. Many of these steel structures have been in service for over fifty years. Many of these structures have suffered extensive deterioration and damage to them. Dents, racking, and yielding of steel members caused by impact, boat mishandling, and accidents are quite common in USACE hydraulic steel structures. Until recently, the only repair alternative open to USACE was to remove the damaged member and replacing it with a new one. Now there is a alternative method - Heat Straightening.
Heat Straightening Quiz:
How do you heat straighten a dent in steel?
- Heat the steel cherry red and beat it back into place with a hammer.
- Heat the steel moderately and bend it back into place with a jack.
- Heat the steel moderately and restrain its expansion, allowing its contraction to straighten the steel.
Answer a) is called hot working. Answer b) is called hot mechanical straightening. Neither procedure should be used to repair damaged steel as the secondary effects to the material properties (yield strength, fracture toughness, etc.) are quite unpredictable.
Heat straightening is a process where a technician, using a limited amount of heat from a torch, heats a damaged section of steel using a specific pattern. The heat will normally cause the steel to expand; however, the technician applies restraining forces to prevent the expansion. After the technician finishes the first heat, the steel cools. As it cools, it contracts. Since the technician restrained the expansion, the only deformation in the steel is from the 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 these fabricators began to experiment with ways to reverse this distortion by heating the steel in specific patterns to counteract the initial distortion. With experience, some of these fabricators developed skills at not only removing the weld distortion, but repairing other damage also. 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 to provide a rational engineering basis behind heat straightening repairs. The highlights of this research and development are taught in the Demonstration Project on Heat-Straightening Repair of Damaged Steel Bridge Members offered by the Federal Highways Administration. FHWA has been increasing awareness and expertise in heat straightening repairs of steel bridge members damaged by high load impacts. This same two day workshop will be held at the Sam Rayburn Dam and Reservoir on February 9th and 10th, 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 include both a presentation and a hands-on laboratory demonstration. Subjects covered will include:
- An overview of heat straightening and how to avoid potentially damaging mistakes.
- Determination as to what damage is heat straightening is suitable for.
- Heating patterns and how to use them to use them to repair different damage types.
- Heat straightening design.
- The behavior of rolled and built-up shapes during and after heat straightening, including effects on material properties
- Estimation of the time required to straighten a bent piece of steel.
- Technical specifications, inspection, and supervision of repairs.
- Case studies, including a detailed repair using an interactive computer program.
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:
- Flexural damage about both the major and minor axis.
- Localized bulges in plate elements.
- Twisting damage.
- Specialty items such as tubular members and connections.
Each student 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 to arrest fatigue crack 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. This technique has implications for both new fabrication and for maintenance and repair procedures.
Dr. Richard Avent
Department of Civil and Environmental Engineering, Louisiana State University, Baton Rouge, LouisianaProfessor 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.
Krishna K. Verma
Federal Highway Administration, Washington, DC.Mr. Verma is the Senior Welding Engineer 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.
Who Should Attend?
This workshop is ideal for engineers, operations and maintenance personnel, and construction quality assurance representatives. CESWF would like to have a good mix from all three disciplines attend.
As a special bonus, Dr. John Jaeger from LRH, Huntington, is likely attend. He is the Corps of Engineers' leading expert in the subject of heat straightening repairs and one of the authors of the Corps' HSS regulations and manuals.
We hope to see you there!