Residual stresses in heat-straightened steel members

Various forms of heat straightening have been used by fabricators and erectors for many years. However, it has only been in the last 15 years that heat-straightening procedures have begun to be quantified in engineering terms. There has been a general lack of information on the type and distribution of residual stresses that occur in heat-straightened rolled shapes. The purpose of this paper is to report on an experimental study in which residual stresses were measured in heat-straightened plates and rolled shapes. Residual stress patterns were measured for members in which various heat-straightening parameters were varied. It was found that the most reliable data should be obtained from tests on damaged members that have been completely heat straightened. The residual stresses in heat-straightened plates were fairly consistent, having maximum compression stresses of about 159 MPa (20 ksi) at the edges and tension stresses of about one-half that value at the center of the plate. Residual stresses in heat-straightened angles tended to have maximum values approaching yield in compression at the toes and heel. Relatively high tension stresses were found near the middle of each leg. Maximum residual stresses in wide flange beams tended toward the yield stress for both major and minor axes heating patterns. High residual stresses may help or hinder heat straightening. Since jacking forces are usually applied as part of the heat-straightening process, movement could be hindered by the distribution of residual stresses. In addition, overstress may occur due to the combination of residual stresses and jacking stresses. Finally, large compression residual stresses may produce bulges in the compression elements of a cross section. Special heating patterns and sequences may be required to prevent this effect.