For my platform model, I have performed Dynamic Analysis using the response spectra tab. Since there is no diaphragm, I have manually calculated the COM and applied the same as nodal loads.I have reviewed my results and am satisfied with the model in terms of reviewing the mass participation, period, drifts etc. My only concern is the end reactions. the reactions in the X & Z directions look fine, but I am concerned about the reactions in the Y-Direction. The total Dead load (including the self weight is 170 kips), but my end reactions are being published greater than the dead load (about 300 kips.) I have attached the model here too for your review. I would appreciate if some one can catch my mistake and advise me.
Thanks,2475.FCC-SCR STRUCTURE_DYNAMIC ANALYSIS_12-20-2019.std
If you are talking about support reactions, the maximum I see is about 86Kip at support node 14 for load case 1. On a different note, you do not need to use the second PERFORM ANALYSIS command.
Correct, but if you sum up reactions at Nodes 1, 4, 11, 14 & 131, wouldn't the reaction be equal to the overall Dead Load of the structure, which is about 170 kips? Should this be compared or not in the response spectra analysis? If not, please can you provide an explanation too.
You should not sum up the reactions in a response spectrum analysis as these are the individual maximums. These do not occur at the same instant of time.
Understood. But based on the load combinations I have defined in the model, I can determine the beam/column forces and perform a design check on the beams, columns and connections based on the response spectrum analysis? Is this approach correct?
Yes you can use these forces for design