When performing a response spectrum analysis, I'm getting a warning that says, "The period is larger than the maximum input period, so the analysis is performed using the maximum input period value." What is the reason for this warning?
This warning appears when conducting a response spectrum analysis, and it signifies that the periods of modes obtained through eigenvalue analysis are longer than the maximum input period specified in the response spectrum data.
For instance, if the period specified in the response spectrum data (Response Spectrum Function) goes up to 6 seconds, and the period of the first mode obtained through eigenvalue analysis is 10.467 seconds, MIDAS will use the spectral data value at 6 seconds for analysis, triggering the warning message mentioned.
In such cases, upon examining the mode shapes in the analysis results, you might find that there are poorly connected members or cantilevered members, or there could be instances where excessive deformations occur at arbitrary locations.
Many times, it's necessary to review the modeling and make modifications before conducting a reanalysis.