How does ETABS calculate effective seismic weight?

[engtipline]

ASCE 7/IBC requires that the "effective seismic weight" include dead load plus, say, 25% live load. My question is: will ETABS be smart enough to automatically calculate DL+0.25LL for the "effective seismic weight"? If not, how can I tell ETABS to include that 25% live load when calculating the "effective seismic weight"? Thank you.

 

[slickdeals]

You do that in the mass source (DEFINE --> MASS SOURCE)

 

[amadeus]

I would add: Define Menu -> Mass Source. On the emerging form select the "From Loads" Radio Button. On the "Define Mass Multiplier For Loads" section, write 1 on the Multiplier cell for Dead Load. Click Add and then write 0.25 (or whatever percentage is required in your code) for Live Load. Click OK and you are done.

 

[johnbridge231]

You can click DEFINE --> MASS SOURCE as slickdeals suggests and then select ANY from the available methods and not compulsory the "From Loads" option.

Analysis and Design of arbitrary cross sections
Reinforcement design to all major codes
Moment Curvature analysis

http://www.engissol.com/cross-section-analysis-design.html

 

[stressed]

The "From Loads" option is the one generally recommended by people familiar with ETABS. The reason is because the default "From self and specified mass" option means that additional mass has to be manually assigned, and that involves unit conversions for mass assignments.. the 3rd option "from self and specified mass and loads" is dangerous because many users tend to include the DEAD selfweight in that list, thereby double-counting selfweight in the mass model.

From loads is the most straightforward option.

 

[dadomago75]

Hi engtipline,
in ETABS there are 3 ways to define seismic masses:

1 - from self and specified mass
2 - from loads
3 - from self, specified mass, and loads

I usually prefer the 3rd because it is faster and more precise....as long as you use DL load case only for the self weight, otherwise you account twice the self weight.
I think it is specified as well in ETABS user guide or in some other ETABS manuals.