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## Autodesk Robot Structural Analysis

Valued Contributor
Posts: 55
Registered: ‎02-07-2012

# Incorrect masses ?

238 Views, 3 Replies
11-12-2012 03:57 AM

Hello,
I'm having trouble with the masses participating to modal analysis.
In order to avoid any other errors i defined a single load (33 Masses) specialy for load to mass conversion.
I set the Direction -z, coef. = 1.00 , ->global masses

The 33Masses load is uniformly distributed at the roof level.

After i run the calculation, in the Dynamic Analysis Results table i get the Total Mass = 14442 Kg.
The mass participation for the first mode (UY direction) is only 65%.
BUT, the total UZ reactions for 33Masses load is 61kN;

Q1: Why is the toatal weight from 33Masses (=61kN) converted in 14442 Kg mass? Shouldn't it be ~6100 Kg ?

Q2: The roof elements are the only ones loaded with 33Masses. I also added a ridgid diaphragm at the roof level. Why is only 65% of the total mass participating in the first 3 modes?

I couldn't attach my model but you can find it here. http://dl.transfer.ro/transfer_ro-12nov-10a5ae9b2b8744cd.zip

Product Support
Posts: 2,519
Registered: ‎04-26-2010

# Re: Incorrect masses ?

11-12-2012 04:07 AM in reply to: jo2ny

Q1: Why is the toatal weight from 33Masses (=61kN) converted in 14442 Kg mass? Shouldn't it be ~6100 Kg ?

It is like that - see below:

Rafal Gaweda
Product Support
Autodesk, Inc.
Product Support
Posts: 2,519
Registered: ‎04-26-2010

# Re: Incorrect masses ?

11-12-2012 04:09 AM in reply to: jo2ny

Q2: The roof elements are the only ones loaded with 33Masses. I also added a ridgid diaphragm at the roof level. Why is only 65% of the total mass participating in the first 3 modes?

Take a look at screen shot above - 98/100 % after first 2 modes without considering selfweight.

Rafal Gaweda
Product Support
Autodesk, Inc.