Structural Steel

k-Area Cracking

Wide flange sections are typically straightened as part of the mill production process. Often a rotary straightening process is used, although some heavier members may be straightened in a gag press. Some reports in recent years have indicated a potential for crack initiation at or near connections in the ‘‘k’’ area of wide flange sections that have been rotary straightened.
The k area is the region extending from approximately the mid-point of the web-toflange fillet, into the web for a distance approximately 1 to 11⁄2 in beyond the point of tangency. Apparently, in some cases, this limited region had a reduced notch toughness due to cold working and strain hardening. Most of the incidents reported occurred at highly restrained joints with welds in the k area. However, the number of examples reported has been limited and these have occurred during construction or laboratory tests, with no evidence of difficulties with steel members in service.
Research sponsored by AISC is underway to define the extent of the problem and make appropriate recommendations. Until further information is available, AISC has issued the following recommendations concerning fabrication and design practices for rolled wide flange shapes:
• Welds should be stopped short of the ‘‘k’’ area for transverse stiffeners (continuity plates).
• For continuity plates, fillet welds and/or partial joint penetration welds, proportioned to transfer the calculated stresses to the column web, should be considered instead of complete joint penetration welds. Weld volume should be minimized.
• Residual stresses in highly restrained joints may be decreased by increased preheat and proper weld sequencing.
• Magnetic particle or dye penetrant inspection should be considered for weld areas in or near the k area of highly restrained connections after the final welding has completely cooled.
• When possible, eliminate the need for column web doubler plates by increasing column size.
Good fabrication and quality control practices, such as inspection for cracks and gouges at flame-cut access holes or copes, should continue to be followed and any defects repaired and ground smooth. All structural wide flange members for normal service use in building construction should continue to be designed per AISC Specifications and the material furnished per ASTM standards.’’
(AISC Advisory Statement, Modern Steel Construction, February 1997.)

Related Articles

Close