Results of Response Spectrum

I am doing a case study comparing the fundamental period of a 20-story reinforced concrete building with dual system in both directions and compared the results from SAP 2000 and Midas Gen. The reference building is from the book of SK Ghosh Seismic Design using Structural Dynamics. here is the link of the book http://secure.skghoshassociates.com/product/show_book.php?isbn=9781580017485.

The example problem in the book is solve by the author manually and the modal analysis was done using SAP 2000 and I wanted to verify the accuracy of the result by comparing them with midas gen and staadpro, Midas Gen result is very close with the book's output within 1 to 2 % difference however, staadpro output is way off, Here is the tabulated result,

                                          

                            
         SAP 2000 3D MODEL                                     MIDAS GEN 3D MODEL                            STAADPRO 3D MODEL

MODE  PERIOD   MASS PARTICIPATION   PERIOD   MASS PARTICIPATION     PERIOD     MASS PARTICIPATION
1              2.485                71.2%                        2.418                     72.19%                  2.738                        22.62%
2              0.659                14.8%                        0.658                     14.19%                  2.386                        36.85%
3              0.300                6.1%                          0.307                       5.98%                   2.034                       14.22%
4              0.178                3.1%                          0.184                       3.16%                   0.779                          3.98%
I have tried analyzing the staadpro model with and without P-delta but still way off. Both SAP 2000 and Midas Gen were using P-delta analysis with Response Spectrum analysis.


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