Mass of a story, Center of mass, Center of Gravity - Structural Analysis and Design - Forum - Structural Analysis and Design - Bentley Communities

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

## Structural Analysis and Design

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

•  Dear all,

I'm using Staad.Pro for design building with Seismic Load but this Load is defined as per my country's codes.

My concern is does Staad.Pro can caculate the Mass ,the Center of mass, center of Gravity  for each Storey?

As my knowledge, Etabs sofware can solve this problem.

Your reply is much appreciated.

Best regards,

Eng.HaiNguyen

• Staad does calculate the mass of the structure to be used in the detemination of the seismic base shear.That is if you mean the seismic mass. But this mass is dependent on the seismic weights which you will input after you define the seismic load parameters. After you define the parameters you will be prompted to specify the seismic weights.You can do this in this sequence. Go to Commands>Loading>Define Load>Seismic Load then choose code. Note that Staad will not use the any dead load which you input in the "Load" tab under the "General" page. You can have Staad print the location of the Cg by adding "Print CG" command after the "Perform analysis" command in the staad editor. After analysis, staad will give you the location of the Cg.

• Hi

yes of course Staad will calculate the mass as its reference to seismic base shear. I use Robot Millenium, Staad and Etabs every software calculate the mass of the structure for seismic of course there is quite difference in vertical and horizontal distribution because of methods they use compare to hand calculation

•  Hi mark112, engineerX.

Many thanks for your reply.

I knew that Staad can caculate the mass of the structure.

However as I say in previous. I have to define the Seismic load as per my country's code, but this one is not available in Staad pro. So I should define it manually. My concern is If I define the Seismic Weight, Will Staad can caculate the Mass of a Storey? The center of mass for each Storey. And how can I define the Seismic Weight if my Country's code is not available in Staad?

When I use Etabs, this problems is solved very easy, Just define the weight. Run it and go to  the report. All the Weight & Center of mass for each storey will be caculate automatically.

But my present company use Staad.Pro. So I try to figure out this one but haven't had the result.

Anyone can help me?

Your reply is much appriciated.

Thanks

Regards.

Eng.HaiNguyen

Civil Engineer.

Toyo VietNam Corporation.

Email: eng.hainguyen@gmail.com

• i think u need to contact the staad service provider for the great problem u have: no country code was available

• You have to check what is the formula used in your code, if they are similar to US or british standard you can easily apply the parameters as per you country's code.

In staad you have to input the mass in terms of loads (i.e. weight) staad will compute automatically the mass based on the loads you input.

• 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

• HaiNguyen,

Your request for calculating the Center of Mass of individual storeys has been passed along to the STAAD software development group.

Thanks for your suggestion.