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.126.96.36.199 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.
For second order analysis, it is mandatory to use Repeat load case instead of load combination case. If load combination case is used, program considers the analysis results for that combination case as linear analysis results and second order effect is not considered. So the warning message will be reported. Using REPEAT LOAD case will remove those warnings.
Check this video for more details and how to remove the warning -- https://youtu.be/5Jy0XoefyXA
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.188.8.131.52 - Serviceability requirement and cl.184.108.40.206 - 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).
If any user defined section is specified using the Create User Table > General option or imported from the Section wizard, program requires the section dimension of the equivalent i section (D, TD, B, TB) to design the section according to IS800:2007 code. These equivalent i section dimensions are required to check the section class of the section. If any of these dimensions is missing, program is unable perform the design and a warning message is reported in the output file. All the section dimensions along with the property values should be provided to design the section as general I section.
The meaning of the warning message is – same load case cannot be present in two separate types of load envelopes. If same load case is specified in different load envelopes, program considers the last envelope type for those load cases present in both the load envelopes. For example, consider the following load envelopes --
DEFINE ENVELOPE100 110 120 121 ENVELOPE 1 TYPE STRENGTH100 110 125 126 ENVELOPE 2 TYPE SERVICEABILITY
For these load envelopes, load case 100 and 110 is present in both the load envelopes. So these load cases will be treated as service load cases considering the load envelope type of the last load envelope.
It is required to define separate load cases in separate load envelopes.
***WARNING : MEMBER - XXX IS SLENDER AND CANNOT BE CHECKED FOR MOMENT FORCES. IF THERE IS ANY BENDING, THEN BE AWARE THAT THERE IS NO CAPACITY FOR THOSE FORCES. ***NOTE : ONLY WIDE FLANGE SHAPES WITH SLENDER WEBS CAN BE CHECKED FOR BENDING.
As mentioned in cl.3.7.2(d), slender section should be designed either according to IS801 code or with reduced section property. For wide flange section, the option to design slender section is implemented if only the web is slender, flange is non-slender. If the flange class of any section is slender, the design of that section is incomplete. Program calculates the axial and shear capacity only. If there is any bending, capacity is not calculated and the section is not checked against bending and interaction. A warning message is displayed for this and the overall design ratio is set to infinity.
In summary, following the recommendation if IS800:2007 code, STAAD.Pro doesn’t allow flange slender section design. Since STAAD.Pro 11.82 version, if the flange class is slender, the warning message is displayed in all TRACK output and the critical design ratio is set to infinity so that member fails in design check. This will intimate the user about the fact that the member design is incomplete. The section size needs to be increased so that the section class is non-slender.
**WARNING- Deflection check of member # xx will not be performed as service envelope not provided.
Check the following post for more details --