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ETABS has various options i.e., Diaphragm Max over Avg Drifts, Story Max over Avg Displacements, Story Max over Avg drifts (Go to display tables> analysis results> joint output> displacement> the options area available here) I noticed some people do this torsional sensitivity check and calculation of torsional amplification factor (Ax and Ay) based on story drift and not on story displacements... the results from each approach gets different ??? also there is another option with Diaphragm  so what's the correct approach ??? and how do we know actually what points ETABS has considered for calculation of max/min displacement or drifts.  

I am working on a high rise building (overall 69 stories, 10 stories of carpark, transfer slab at level 12) located in a very low seismic zone (PGA 5%g). The building first mode is translational (i considered Ux, Uy and Uz tables for this classification) and 2nd mode is torsional followed by 3rd mode again in translational.  The modal mass participation ration as shown below. I considered the default 12 modes and getting the required overall 90 percent mass participation both in X and Y direction (Sum Ux and also Sum Uy) but didnt consider the SumUz or ther SUm Rx,Ry and Rz. Is this important ??? I understand that ideally the first 2 modes should be translational followed by torsional mode and this can be achieved with proper structural distribution of elements on the floor plans however for this building the design was freeze and the design team want to proceed. After the response spectrum analysis, i showed them that the higher reinforcement in column and shear walls are resulting from this torsional behavior in 2nd mode. My question is that we have incorporated additional reinforcement tin these shear walls and columns however the slab diaphragm needs any attention ??? or any other element like designing diaphragm particularly at the transfer level to ensure that it receives this torsion and transfer safely to shear walls and columns ??    

I am working on a multi tower building with a common podium (Fig 1). The initial ETABS model  wasn't built using multiple tower option however during the seismic design incorporation, i activated this "Multiple tower" option in ETABS and accordingly set podium to T1 and T2 and T3 for the remaining two towers (Fig 2). Afterwards i partially exported the towers and performed the analysis to get story forces from individual tower models. These forces were finally added as user defined seismic load in the full complete model (Fig3) As mentioned above that not to use ELF base shear, i initially thought it shouldn't be an issue. However later after analyzing the complete full model with multiple towers i realized, that it  almost showed double base shear from ELF in case we go for automatic seismic load (based on code) compared to manually applying the story forces on the towers (Fig 4). I am not sure if its some modelling mistake and trying to figure out why there is much different in static load case however the response spectrum from both models show minor difference         

Yes, as the approximate period is simplified and often conservative compared to more accurate one obtained from modal analysis which reflects actual stiffness, mass distribution, and geometry of structure

@Wajahat Latif Can you further elaborate on the above point 

Can share and elaborate the different load combos required for the towers which are resting on a common podium and how these are different in case a seismic joint is there ?? Also what design consideration have to be taken for the diaphragm at top of podium where the towers are resting ??As i believe that out of phase movement for the 2 towers will generate high internal forces at the podium diaphragm. Does ETABS automatically considers them or we need to manually define some combinations for such scenarios ???

what is our ultimate goal by making reduction in members stiffnesses in softwares ?? i know the concept but i do not know the sense behind this in terms of the practical advantages will get after doing this and what will happen if we did not .

hi engineers , May i know why we have to rely on meshing to govern our programe results and hence the design , if result is going to be affected by meshing how colud we get the accurate result for safe design ??? and to what limit can we depend on meshing ?

Just use excel. Make a simple worksheet listing bar dia, number, length for each element. Bar weight tables are available online.  OR If its a building and you have the Etabs model. Run the detailer, it will give weight of steel required for each floor or member wise. Staad Pro also gives total steel weight and concrete volume for the model