Christian, Lee Conner (2006-05). Thru-thickness bending stress distribution at elevated temperatures. Master's Thesis. Thesis uri icon

abstract

  • During the bending of flange plate used for dapped girders some highway bridge fabricators are experiencing cracking of the flange plate particularly when heat is used in assisting the bending process. Due to the extreme strains experienced during the fabrication process, investigating this problem requires the use of a finite element analysis. The fabrication process was broken down into two parts, first the heating of the plate through the use of either a furnace or an acetylene torch (thermal), and the second was the bending process (structural). The five different temperatures collected during the thermal analysis were a uniform temperature of 75oF, a 1100oF uniform temperature as a result of furnace heating, both five and ten minutes of air-cooling after the plate had reached a uniform temperature of 1100oF, and the temperature gradient after heating the flange plate to a surface temperature of 1200oF though the use of an acetylene torch. After the thermal analysis was completed, the resulting temperatures were imported into the structural model. The plate thicknesses analyzed were one, one and a half, and two inches, assuming both 50 and 70 ksi yield strengths. To achieve a 90 degree six-inch radius bend the plate was bent in five separate locations. The result of this analysis showed that with the introduction of temperature gradients into thefabrication process, the strains along the plate??s extreme fibers increased. The model further showed that for both a one and a half and two-inch thick plate the extreme fiber strains exceeded ten percent, which further adds to the increased risk of the flange plate cracking during fabrication. The highest residual stresses through the plate??s thickness occurred during cold bending. The residual stresses through the plate??s thickness decreased when the fabrication process was carried out at elevated temperatures. When steel exceeds a strain of 10 to 16 percent during the fabrication process, the plate becomes susceptible to cracking. This strain limit was exceeded for plate thicknesses of one and a half and two inches.
  • During the bending of flange plate used for dapped girders some highway bridge
    fabricators are experiencing cracking of the flange plate particularly when heat is used in
    assisting the bending process. Due to the extreme strains experienced during the
    fabrication process, investigating this problem requires the use of a finite element
    analysis. The fabrication process was broken down into two parts, first the heating of
    the plate through the use of either a furnace or an acetylene torch (thermal), and the
    second was the bending process (structural). The five different temperatures collected
    during the thermal analysis were a uniform temperature of 75oF, a 1100oF uniform
    temperature as a result of furnace heating, both five and ten minutes of air-cooling after
    the plate had reached a uniform temperature of 1100oF, and the temperature gradient
    after heating the flange plate to a surface temperature of 1200oF though the use of an
    acetylene torch. After the thermal analysis was completed, the resulting temperatures
    were imported into the structural model. The plate thicknesses analyzed were one, one
    and a half, and two inches, assuming both 50 and 70 ksi yield strengths. To achieve a 90
    degree six-inch radius bend the plate was bent in five separate locations. The result of
    this analysis showed that with the introduction of temperature gradients into thefabrication process, the strains along the plate??s extreme fibers increased. The model
    further showed that for both a one and a half and two-inch thick plate the extreme fiber
    strains exceeded ten percent, which further adds to the increased risk of the flange plate
    cracking during fabrication. The highest residual stresses through the plate??s thickness
    occurred during cold bending. The residual stresses through the plate??s thickness
    decreased when the fabrication process was carried out at elevated temperatures. When
    steel exceeds a strain of 10 to 16 percent during the fabrication process, the plate
    becomes susceptible to cracking. This strain limit was exceeded for plate thicknesses of
    one and a half and two inches.

publication date

  • May 2006