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Robot Structural Analysis

Distinguished Contributor
Posts: 120
Registered: ‎09-17-2012

Load to mass conversion

902 Views, 23 Replies
10-04-2012 12:02 AM

Dear Sir

-  Which mass type (global mass & dynamic mass ) shall I use it for my model (concrete tower 21 floor )?

Shall I activate the mass in three directions (X,Y,Z) or only (X,Y) Because my building height = 75m ?

Refaat

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Valued Mentor
Posts: 626
Registered: ‎09-07-2011

Re: Load to mass conversion

10-04-2012 12:09 AM in reply to: refaat

Most accurate is consistent I believe.  But we normally use lumped with rotations.

If you disregard density there will be no mass participating in the modal analysis. Unless you add it back in via load to mass conversion.

I would NOT disregard density, and also add 30% live load (or whatever percentage) to the load to mass conversion.  Normally can ignore Z direction.  If you add mass to global or dynamic the mass will be added to all dynamic cases.  If you specify the modal case only, it will only be added to that case.

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Product Support
Posts: 4,188
Registered: ‎04-26-2010

Re: Load to mass conversion

10-04-2012 12:10 AM in reply to: refaat
Refaat

-  Which mass type (global mass & dynamic mass ) shall I use it for my model (concrete tower 21 floor )?

http://forums.autodesk.com/t5/Autodesk-Robot-Structural/Conversion-load-to-mass/m-p/3050232/highligh... - message 3

Rafal Gaweda
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Distinguished Contributor
Posts: 120
Registered: ‎09-17-2012

Re: Load to mass conversion

10-04-2012 02:28 AM in reply to: Rafal.Gaweda

Dear Sir

I got confused about base shear coeff. ( as i see in the attached capture 01) you got this coeff. (1.74) by dividing (automatic / inactive ). Did you mean that the inactive case is the static linear case ?? (because as we know that the base shear scale is the ratio (0.85Vstatic/Vdyanmic) . as I used it in the capture 02 ,is it true or not ?

Thanks

Refaat

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Distinguished Contributor
Posts: 120
Registered: ‎09-17-2012

Re: Load to mass conversion

10-04-2012 02:29 AM in reply to: Rafal.Gaweda

Dear Sir

Pls , give me more explanation (  3 Selecting Global mass - converted masses will be applied to all dynamic cases and also can be used in inertia   forces (of course if such forces are applied on model)

In my case , I will use (global mass ) in my model is Keya ?

Thanks

Refaat

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Product Support
Posts: 4,188
Registered: ‎04-26-2010

Re: Load to mass conversion

10-04-2012 03:32 AM in reply to: refaat

Pls , give me more explanation (  3 Selecting Global mass - converted masses will be applied to all dynamic cases

Example:

Rafal Gaweda
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Product Support
Posts: 4,188
Registered: ‎04-26-2010

Re: Load to mass conversion

10-04-2012 03:39 AM in reply to: refaat
Refaat,

I got confused about base shear coeff. ( as i see in the attached capture 01) you got this coeff. (1.74) by dividing (automatic / inactive ). Did you mean that the inactive case is the static linear case ??

Inactive means that results come directly from seismic calculation without base shear.

as I used it in the capture 02 ,is it true or not ?

Yes, true.

One more remark: do not use "Use normalized values" checkbox.

Rafal Gaweda
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Distinguished Contributor
Posts: 120
Registered: ‎09-17-2012

Re: Load to mass conversion

10-04-2012 04:23 AM in reply to: Rafal.Gaweda

Dear Sir

Do you mean that ( Dynamic = globle + modal ) ? , and i have to use dynamic

Thanks

Rrfaat

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Distinguished Contributor
Posts: 120
Registered: ‎09-17-2012

Re: Load to mass conversion

10-04-2012 04:35 AM in reply to: Rafal.Gaweda

Dear Sir

As appears in the attached capture

As I understand (T= structure period ) and what  about (reduction coeff.)?

Thanks

Refaat

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Product Support
Posts: 4,188
Registered: ‎04-26-2010

Re: Load to mass conversion

10-04-2012 04:35 AM in reply to: refaat
Do you mean that ( Dynamic = globle + modal ) ? , and i have to use dynamic

Global means that converted masses will be considered in ALL dynamic cases in model (modal and footfall ones; other dynamic cases need to be run after modal case so they consider masses from precedent modal).

My advise: use dynamic.

Rafal Gaweda
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