Mass of a story, Center of mass, Center of Gravity

You have to check the seismic base shear formula used in your country with the codes available in Staad. Im pretty sure it would be similar to to that of the US since most codes are derived from the UBC or  ASCE, etc. If it is really entirely different then you have no choice but to calculate the base shear as per your country's code and distribute it on each storey manually. You will then have to compute manually the center of mass at every floor. If you already located the center of mass, you use this as the master node for the floor.you will apply the seismic load of the story at this node. The master node should always coincide with the center of mass. When you do this you will automatically consider the torsion caused by the eccentricity between the center of rigidity and the center of mass. IBC requires that the eccentricity be increased by 5% of the building's least dimension to account for accidental torsion.Check if this is required by your code. I hope you get what I am trying to tell you. Regards.

You have to check the seismic base shear formula used in your country with the codes available in Staad. Im pretty sure it would be similar to to that of the US since most codes are derived from the UBC or  ASCE, etc. If it is really entirely different then you have no choice but to calculate the base shear as per your country's code and distribute it on each storey manually. You will then have to compute manually the center of mass at every floor. If you already located the center of mass, you use this as the master node for the floor.you will apply the seismic load of the story at this node. The master node should always coincide with the center of mass. When you do this you will automatically consider the torsion caused by the eccentricity between the center of rigidity and the center of mass. IBC requires that the eccentricity be increased by 5% of the building's least dimension to account for accidental torsion.Check if this is required by your code. I hope you get what I am trying to tell you. Regards.

 Hi,

Thank you all for your help.

Actually  I have to make the caculation sheet for the Seismic Load as per my country's code step by step.

I already caculated the the base shear manually.  I just wonder that does Staad.Pro can caculated the mass & center of mass for each storey so that I can distribute it on each storey. But unfortunately,Staad doesn't  as you tell.

Maybe I will run an email to Bentley Service to let them know for futher version of Staad. 

Anyway, Many thanks for helping me. 

Best regards. 

Eng. Nguyen Tuong Hai

Toyo Vietnam Corporation

Email: eng.hainguyen@gmail.com or hai.nt@toyo-vn.com