NBCC Seismic (Equivalent Static Method)

[CameronEC]

I have been trying to use the new NBCC 2010 Equivalent Static Method in ROBOT 2014. I have a few questions/suggestions.

See the attached picture for reference to my points.

1. The S(Ta) given seems to be incorrect. It should =Fv*Sa(Ta) =0.1 see NBCC2010 CL4.1.8.4 (7).

2. The base of my structure is at 461.2m (defined at z=461.2), The results of the force distribution come up wrong because the 1st storey is cacluated to be at 4.57m+461.2m above the base level. Is there any way to make 461.2m be the "base level" so static forces are distributed correctly (using the formula V*Wi*hi/(sumWh)

3. I was wondering if there is any way to neglect the selfweight of the structure for this analysis? Currently the selfweight has been accounted for twice since I input the DL load case into the "load to mass conversion".

[Anonymous]

remove DL from the load to mass conversion?

[Anonymous]

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@Anonymous wrote:
remove DL from the load to mass conversion?

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Yes, if you want automatic self-weight calculations for all elements. And for sure you can adjust all your material densities and panel thicknesses and do it this way. But if you choose to have only selected self-weights calculated automatically and define loads manually for others, then you're out of luck. In modal analysis this is solved by having a checkbox "Disregard density".

[Anonymous]

Yes I understand.  I was thinking of regular spectral analysis, where you can exclude self weight, then add self weight as necessary by using a secondary load case that is added to mass via "load to mass conversion". 

It seems with equivalent static there is no way to avoid self weight, other than setting material density to Zero.  This is not very difficult in reality, but it is a pain, and you probably end up with two analysis models which is never nice.   

Maybe this feature needs to be on the wishlist for next service pack ?

Tony

[Artur.Kosakowski · Accepted solution]

 

1. The S(Ta) given seems to be incorrect. It should =Fv*Sa(Ta) =0.1 see NBCC2010 CL4.1.8.4 (7).

Actually the value that is used in calculations is correct but as you noticed the one displayed in the calculation note is wrong.

2. The base of my structure is at 461.2m (defined at z=461.2), The results of the force distribution come up wrong because the 1st storey is cacluated to be at 4.57m+461.2m above the base level. Is there any way to make 461.2m be the "base level" so static forces are distributed correctly (using the formula V*Wi*hi/(sumWh)

No, this is currently not possible. You may try to move the structure downwards so that its base is at Z=0m

3. I was wondering if there is any way to neglect the selfweight of the structure for this analysis? Currently the selfweight has been accounted for twice since I input the DL load case into the "load to mass conversion".

I have added the request for the neglect density option similar to the one available for the modal analysis to the wish list.

Thank you for focusing our attention to these points. 

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

[CameronEC]

Thanks for the response.

[Artur.Kosakowski]

2. The base of my structure is at 461.2m (defined at z=461.2), The results of the force distribution come up wrong because the 1st storey is cacluated to be at 4.57m+461.2m above the base level. Is there any way to make 461.2m be the "base level" so static forces are distributed correctly (using the formula V*Wi*hi/(sumWh)

The recognition of the definition of the base of the model has been introduced in SP2 for Robot 2014.

[Artur.Kosakowski]

Hi @CameronEC 

3. I was wondering if there is any way to neglect the selfweight of the structure for this analysis? Currently the selfweight has been accounted for twice since I input the DL load case into the "load to mass conversion".

Introduced in RSA 2020.

If I managed to answer your question(s) press the Accept as Solution button please. This will help other users to find solution(s) much faster. Thank you.