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The warning message has been introduced in STAAD.Pro SS6 build 20.07.11.82. The is related to cl.4.4.2 where it is mentioned that if the Ky and Kz values calculated in cl.9.3.2.2 is greater than 1.4, then a second order analysis is required. For any member for each bending + compression load case, program calculates the Ky and KZ values according to cl.9.3.2 and check it against 1.4. For any load case for which linear analysis has been performed, if the Ky or Kz value is greater than 1.4, program reports the warning message in the output file. A second order analysis (for example, P-Delta analysis in place of perform analysis) is required for those load cases.
Also, for second order analysis Repeat load case is required in place of load combination cases.
This warning message is related to the minimum web thickness check according to cl.8.6.1. For each member, program performs the web thickness check according to cl.8.6.1.1 - Serviceability requirement and cl.8.6.1.2 - Compression Flange buckling requirement. If any of the criteria mentioned in the above mentioned clause is not satisfied, a warning message is reported in the output file informing the exact clause number. It is required to modify the web dimension (increase the web thickness or decrease the depth).