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update: 19.02.2014 Read about equilibrium nd compatibility torsion. You have to determine which case you have, if it is equilibrium torsion you cannot releaee torsion so your modifier will be 1.0 like in a cantilever slab or hollow core slab supporting beams because if you will release torsion it will redistribute to slab and as in equilibrium torsion there is no redistribution possible so you cant release torsion. But in case of compatibility torsion you can release torsion and it will redistribute. Si you can make its modifier equal to 0.35 but uf you make it 0.01 make sure there is no excess cracking in slab and you design slab for increased moments...thats why code does not explicitly tells u abt torsion modifier because it depends on case to case. Value of equilibrium torsion is not affected by the modifier so always apply 0.1 or 0.35 or whatever for torsion modifier whatever the case is.

Seismic engg is based on human exp from previous damage done to buildings....they studied abt collapse and improved codes so not study the latest one. All the basics are also given in IBC but u r rite too..i my self started with ubc....

im still waiting for some to ask about over-strength factor..omega in seismic combinations..lets see when our curious young minds...raise this question...(as i said..im waiting for you )

1) goto File>Print Summary and ETABS will report you V = 0.05W something like this....means base shear V = 5% of W where W = effective seismic weight which is equal to the weight you put in mass source in etabs to check W ...after analysis...goto Display>Show Tables...Select all load cases you put in mass source and show Story Shears in tables> goto last story of model....you will see top and bottom of each story just add all load cases P (axial load) at the bottom most story (bottom)...this is equal to your effective seismic weight you put in mass source dialogue box note it down..lets say 1000 kip now similarly show tables and see EQx and EQy in tables at the bottom most story..both values should be equal if your time period and R are same in both load cases..this is your total base shear in x and y...you can see this value from the graph by Display>Show Story Response Plots.. lets say 100 kip So it means your V = 100 kips, W = 1000 kip which means your base shear = 10% of your effective building seismic weight 2) study UBC chapter on seismic design or IBC or ASCE ...you will find what is R...R is response modficication factor of building system...... values of displacements or drifts in ETABS are elastic....but earthquake design goes into in-elastic range...so to convert your elastic displacement value you should first convert it into in-elastic values before checking drifts...(this applies only for seismic design...as wind displacements remain in elastic region) in ASCE or IBC this 0.7R is equal to Cd/I where Cd is amplification factor for drifts in these codes..and I is the importance category... UBC is obselete now....start studying IBC 2006 or 2010...or if possible 2012...you are young generation...follow the latest codes..with background of old codes..I will upload here the 2012 code soon

I think, you may be right. But this term is used by the one, formulating a constitutive model to simulate the behaviour of a material under specific loading conditions. For me, who do not and cannot(limited ability) go into such details, makes no difference: both terms define the behaviour of a particular 'node' of a 'finite element' in a mathematical model. raised a good point!