Use Of Mass Source Command In Etabs

[haro0n]

In etabs we define mass source frm there we select from load and then we define differnt loads like dead , live etc my question is that what is use of this "mass souce" we donot apply it in the structue then where we need it?? and which loads are defined here means dead, live and which are not defined??

Thanks

[WR1]

its the seismic weight according to code. The load you put here will be used for Seismic calculations. This is W in IBC, UBC or other american codes...

Select "From Loads" option and put all dead loads with factor = 1 and all live loads with factor = 0.25

this is to consider 100%dead loads + 25%live loads for seismic calculations....

[haro0n]

thanks rana bro its cleared now u defined it in simple way

[UmarMakhzumi]

Like Rana said, I will just add one more thing. I remember that Live Load only needs to be considered in Mass Source if its a warehouse, or LL=100psf or more. See UBC, for clarification, there is something about the warehouse or 100 psf requirement.

[Waqar Saleem]

it means for noraml building where we are not considering seismic loads there is no need of defining "mass sorce"

[WR1]

yes....no need for mass source where there is no EQ

[Waqar Saleem]

thanx RAna bro

[WR1]

Just to correct you here (and my self too) that mass source command is used for calculating Center of Mass of the diaphgram. So this option is used even for wind load or any other load where we need these two centers. Pardon for my old post which was a mistake

[haro0n]

okz rana bro and what about the loads we should take them same as u mentioned earlier..

[WR1]

Yes 25% is for warehouse, Usually only 100%D is enough for normal buildings, but you need to consider all the Live Loads and Dead Loads that are permanent. For example if you have permanent mechanical equipment as Live Load then consider then in mass source too. If a portion of live load is assumed to be sustained for example where LL is heavy like in malls, a portion (~25%) of LL should also be considered. In summary, any load that is deemed to be permanent...consider that in seismic weight calculations.

[Lemuel Al Fernandez]

Can anybody site where we can find that in the code please?I mean that 25% Live load for seismic

 

[EngrUzair]

See Section 12.7.2 of ASCE 7-10.

Regards.

[Beenay Shahi]

If i analyze my model with default mass source I.e. element mass and additional mass it will be incorrect?

Because it won't include the live load and other loads like floor finish and wall load in the calculation of earthquake load.

So I must define the mass source as specified load pattern and define load patters as 1 DL+1 floor finish+1 wall load+0.25 live load.

And I must select the options: include lateral mass and

                                                lump lateral mass at story level

Please tell me whether I am right or wrong?

But I have some doubts and questions too.

what does etabs consider as "additional mass"?

does additional mass include the loads we define as live load, wall load, and floor finish?

I know that etabs refer to "element mass" as the mass of the structural elements we used to model the structure like beam, column, slab for which we define the material and section properties.

What does the option include lateral mass do"

what is lateral mass?

Is lateral mass something we define of is it something etabs calculate from our model?

 

 

 

[EngrUzair]

6 hours ago, Beenay Shahi said:

If i analyze my model with default mass source I.e. element mass and additional mass it will be incorrect?

Because it won't include the live load and other loads like floor finish and wall load in the calculation of earthquake load.

No, in case the inclusion of live load in Mass Source is not required as per your applicable design code, and other parameters including 'Additional masses' have been correctly applied. Otherwise, yes.

Replies to your other questions and doubts are available at the following link:

http://docs.csiamerica.com/help-files/etabs/Menus/Define/Mass_Source.htm

Regards.

 

[muneeb1213]

Hello i have seen many designer who take into effect the EQ loads however they dont alter the mass source option. is this approach ok?? the results still gives base shear values

[Waqar Saleem]

Muneeb, if mass source is not defined properly, seismic forces will not be calculated correctly and so the base shear value will also be incorrect. Selecting different options in mass source menu is quite fine if loads has been taken in consideration as mentioned above 100% dead and 25% live in case of warehouses or permanent live loads. 

Regards

[WR1]

They might be using "mass" option that is by default.

[Hamza Ahmad]

so please can any one clarify me... if we have dead load and also finishing load define in load pattern... so in mass source we have to add both dead load and finishing load as 1 ?? or will use only dead or finishing load...

[EngrUzair]

4 hours ago, Hamza Ahmad said:

so in mass source we have to add both dead load and finishing load as 1 ??

Yes.

[Hamza Ahmad]

Thankyou...

i have another question ..can we tick all three option present in mass source i.e element self mass , additional mass, specified load pattern ..as it will give max mass source is it correct ot not??

[Waqar Saleem]

Dear Hamza 

you have to tick the specified load pattern and specify load patterns Dead, Super dead or Live with their multiplier factor or tick the other two, you do not have to tick all three.

 

Regards

 

[Hamza Ahmad]

okay sir thankyou... sir can i have your email ? 

 

[NMN]

On 6/5/2016 at 1:57 PM, EngrUzair said:

See Section 12.7.2 of ASCE 7-10.

Regards.

Hi,

How about for Canadian code. and what if I have snow load, do I need to consider as well for mass source.

[Ahsan Kazmi]

Sorry in advance but what i haven't understood from the above discussion is that how we differentiate between the the options that etabs provide us in Mass source  tab?

If we check the " From self and specified mass" would this be incorrect?

If we check the " From self and specified mass and loads" would it double the effect of Mass?

Is specified mass is the the one what we have applied as area, point and line loads ?

[Ayesha]

On 9/27/2017 at 2:29 PM, NMN said:

Hi,

How about for Canadian code. and what if I have snow load, do I need to consider as well for mass source.

@NMN ASCE 7 says to use 20% of any snow load greater than 30psf as seismic weight. For Canadian Code, you will need to see your local jurisdiction code. If the code doesn't says anything about it, you can use ASCE 7 clause and include the snow load.

On 10/5/2018 at 3:45 AM, Ahsan Kazmi said:

If we check the " From self and specified mass" would this be incorrect?

If we check the " From self and specified mass and loads" would it double the effect of Mass?

Is specified mass is the the one what we have applied as area, point and line loads ?

This all depends how you have defined the loads. Some people differentiate between dead loads by creating a dead load case and a super dead load case. Other don't. So go with the option based on your loads definitions.