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Posted by Jennifer Jernigan on May 28, 2010 at 9:40 AM.
Heating the flange of a steel girder has predictable effects that can be used to introduce curvature in a very controlled way. Temperature-indicating materials show when enough heat has been applied to the area.
Heat curving is a common process used on bridge girders to obtain a specified curvature needed for construction. Two common methods of curving are Continuous and V-type heating. Heat is applied to both the top and bottom flanges of the girder to achieve uniform curvatures.
Special temperature-indicating materials are used to insure the steel is not heated to a temperature above the maximum allowable. One option is to use crayons that have a calibrated melting point and only leave a mark when that temperature has been reached. Another option is to apply a swatch of a lacquer-like liquid, that is similarly calibrated. Once the specific temperature is reached, its appearance changes from dull and chalky to a shiny wet-look.
To learn more about using heat on steel members consult Section 5 of the Steel Bridge Fabrication Guide Specifications, a standard developed by the AASHTO/NSBA Steel Bridge Collaboration. The standard is available as a free PDF download from the National Steel Bridge Alliance website, www.steelbridges.org, in the Collaboration area. To go straight to the Guide, click here.
A program offered on the Steel Detailers Inc. website can be helpful in planning V-heat locations and temperatures to obtain a desired curvature.
One source of temperature-indicating materials and information about the technology is www.tempil.com.