Problem with DAM analysis

[mustafahesenow]

Hi Guys,

Since that there is no option in Robot to reduce the moment of inertia of steel members .I was wondering how the DAM analysis operation is done for this particular issue .

I did 2D frame analysis and with Vertical and lateral load and and I made 2 combinations similar one static linear and one with considering P-delta analysis then I Activated DAM analysis without generating notional loads only with reducing the stiffness then after comparing the results I found out that there is additional vertical displacement for Dam combination  shouldn't be exist  partially this came because the operation Of DAM analysis is fallowing the Reducing E modulus of steel members not the inertia .

See the pictures attached and model as well .

Kindly confirm these Results and this is happened because of Reducing E.

Thanks.

[Artur.Kosakowski]

HI Mustafa,

For steel elements there is the reduction of E.

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.

[mustafahesenow]

1

[Artur.Kosakowski]

Hi @mustafahesenow

I'm not very familiar with DAM and the required level of the accuracy however bearing in mind that SLS conditions are to be checked for non DAM model my initial assumption is that such assumption should not cause any significant issues.

If one or more of these posts answered your question, please click Accept as Solution on the posts that helped you so others in the community can find them easily.

[mustafahesenow]

1

[Artur.Kosakowski · Accepted solution]

Hi Mustafa,

If your question was is reduction of E 100% the same as reduction of IY/IZ then the answer is NO

If the question is if such difference in the displacements due to the above matter is important for the DAM analysis accuracy then I don't know as I'm not familiar with and I can't tell how it influences the further design (column buckling check). On the other hand if I remember correctly from the discussion with the US designers at the time it was being implemented in Robot (I hope my memory still serves me well) the same principle is also applied in other design programs.

Looking at some sources I'm also not sure this is actually that wrong bearing in mind that EA should also be reduced:

http://howtoengineer.com/stability-aiscs-direct-analysis-method/

https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/10606/dire...

If one or more of these posts answered your question, please click Accept as Solution on the posts that helped you so others in the community can find them easily.

[mustafahesenow]

Hi @Artur.Kosakowski

Many thanks to you my friend for the grate support. You are the best.

I was carious about that because base on AISC code there is 3 different methods of checking the stability the other 2 are more simplified and easy but limited (should be 2nd order drift to first order drift < or = 1.5 )