Also I must thank Eng.kareem Elmuslim behalf of Civilax team for sending us this video tutorial.
Download
Code
Seismic Analysis by Response Spectrum Method Part 1
https://www.youtube.com/watch?v=l3v62RGwB1c
Part 2
https://www.youtube.com/watch?v=5J1K3nGJs6s
Part 3
https://www.youtube.com/watch?v=r9HCHF777ng
Spreadsheet
http://www.4shared.com/office/I3ACPLLO/response_spectrum_curve.html