National Bridge Company

Address: 4556 Arrowhead Rd. Okemos, MI 48864
Tel: (517) 347-6167
E-Mail:dgarijo@nationalbridge.com
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WHAT IS HEAT STRAIGHTENING?

The practice of heat straightening steel has been used for decades. Early ironworkers and welders discovered that when heat was applied to small areas of a steel member, the member was distorted. Taking this observation further, they began to experiment on their own, trying to discover how to use this concept on their jobs. Over the years, the practice was used to camber beams, when mechanical cambering was insufficient for the task. Since then, the process has been applied to steel beams and girders, trusses and columns, in an effort to repair damaged members.

Scientifically, heat straightening is a relatively simple process to understand. When a steel member is heated, the heated area expands. Upon cooling, the area will contract. This is the principle upon which heat straightening is based. However, it is the application of this principle which produces the desired results, and which requires experience and expertise to be successful.

Over the years, true heat straighteners have learned the proper application of heat and restraining forces necessary to conduct real heat straightening repairs. Some "heat straighteners" believe all that is necessary to conduct these repairs is to heat the damaged area and push it back into place. In order to do this, the steel must be heated above the phase transformation temperature, thus changing the steel's molecular structure and it's strength and ductility characteristics. This is known as mechanical or "hot" working. It used to be known as blacksmithing. Call it what you will, IT IS NOT HEAT STRAIGHTENING. During proper repairs, the repeated heating and cooling of the damaged area will move the member back to it's original shape. It is never forced back into position. The heat is controlled and kept below the phase transformation temperature, thus retaining the steel's original molecular characteristics. Only by carefully controlling the amount and location of the heat and restraining forces can true heat straightening repairs be accomplished.

WHAT TYPES OF MEMBERS CAN BE HEAT STRAIGHTENED?

Any steel member can be repaired by heat straightening. The most common repairs are to highway bridge beams that have been impacted by over-height loads. However, repairs have also been performed on columns of multi-level bridges, crane rails in steel plants and trusses and columns in automotive plants. In addition, many different sizes of members have been repaired, from a 12' deep crane rail with a 4" flange, down to a 3x3x5/16 angle.

WHAT ARE THE ADVANTAGES OF HEAT STRAIGHTENING?

There are several advantages to using heat straightening, but as we all know, it all comes down to money. This is the biggest advantage of heat straightening. IT COSTS LESS. An average repair of a highway bridge beam takes just FOUR DAYS. Even the most severe damage can usually be repaired in two weeks or less. In addition, traffic on the bridge does not have to be detoured (unless the damage is extremely severe). Also, lane closures under the structure can be removed at the end of each day, no permanent closures are necessary. Finally, repairs can be conducted during night and weekend hours, whenever traffic volumes are at their lowest, thus significantly reducing the impact to the public. Compare this to the long and expensive process of replacing a beam; long traffic closures, both on and under the bridge, cost of materials and labor, public frustration, it all adds up, quickly. Over the years, heat straightening costs have generally been about 25% OR LESS of the cost of replacement. It's easy to see why heat straightening is an attractive alternative.

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