Load to mass conversion

[Refaat]

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 ?

 Thanks in advance

Refaat

[Anonymous]

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. 

[Rafal.Gaweda]

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

[Refaat]

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

[Refaat]

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

[Rafal.Gaweda]

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

Example:

[Rafal.Gaweda]

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.

[Refaat]

Dear Sir

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

Thanks

Rrfaat

[Refaat]

Dear Sir

As appears in the attached capture

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

Thanks

Refaat

[Rafal.Gaweda]

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.

[Refaat]

Dear sir

Confirmation  >>>>>> ((seismic pseudo model(ritz)) with dynamic mass is okay ?

Thanks  a lot

Refaat

[Refaat]

Dear Sir

As appears in the attached capture

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

Thanks

Refaat

[Rafal.Gaweda · Accepted solution]

 

Confirmation  >>>>>> ((seismic pseudo model(ritz)) with dynamic mass is okay ?

Okay

[Refaat]

Dear Sir

As appears in the attached capture

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

Thanks

Refaat

[Rafal.Gaweda]

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

I need to check the codebook. Wait.

[Refaat]

Dear Sir

Could i know if you have checked the code book ? I am waiting .

(UBC97)

Thanks alot

Refaat

[Rafal.Gaweda]

Could i know if you have checked the code book ? I am waiting .

(UBC97)

It is just a factor to multiply calculated base shear by it.

[Refaat]

Dear Sir

Pls , Could u give me more explanation ?. From where can i get it  and how to calculate it?

Thanks

Refaat

[Refaat]

Dear Sir

Pls , Could u give me more explanation ?. From where can i get it  and how to calculate it?

Thanks for your help

Refaat

[Rafal.Gaweda]

1631.5.4 Reduction of Elastic Response Parameters for design.