Base Shear, Eccentricity And Checks In Etabs

[abdulqadeer29]

Kindly inform me few things about Etabs!.
how we can check eccentricity of our bldg after analysis in etab?
What is the purpose of base shear's calculation during design of RC struct.?
WHat are the parameters we have to check after completing our design in Etabs?

[Badar (BAZ)]

You can use summary of results for the eccentricity between center of mass and stiffness.

I did not get ur second query. I am also not sure about third query.

If you want to validate ur model after running analysis in ETABS; perform some manual checks, such as equation of statics,see if moment diagrams of the members look what they should look like or you can check one of the frames through moment distribution method.

[WR1]

1) What do you mean by eccentricity of the building? you mean the deflection of the building from lateral loads or you are talking specifically about seismic design?

2) Base shear is the shear force of the building from lateral loads. This shear is produces moments and other forecs in shear walls, columns and beams...when transferred to them by the diaphragm such as slab.

3) Check the total axial force or reaction of the building under dead load and live load..See if this is what you applied in your assignments?

Calculate the ditributary area of a column and multiply by its loading and check the axial force in that column.

Export the displacement tables under a combination or load case to excel and check the maximum deformation.

Goto last analysis run log..it should never show you that the building is unstable and ill-conditioned..

Goto response plots in display menu to see the base shear plot of lateral loads..if there is strange shape it means you have supports in intermediate levels..

Check if there is tension in the walls under wind load..etc..

there are many checks to be performed to feel confident about the building. this level varies with each building and its importance and the level of knowledge you have...

i hope it will help

[abdulqadeer29]

sir i was basically asking about eccentricity due to difference in center of mass and center of rigidity?----

and sir whch code and whch chapter of tht code describe load combinations for shear wall?

[abdulqadeer29]

sir .........what kind of meshing we should prefer...manual or auto????

[WR1]

it depends..if its very regular use auto..otherwise ur in trouble lolx

[abdulqadeer29]

sir one more thng i have to ask...

sir , for foundation design , i export file 4rm etab and did analysy in safe for foundation...sir my reinforcement in x and y strip near shear wall is quite different ( kafi zayada aa raha hai steel area) from other locations where there iz no shear wall, so nw if i have to determine actual reinf. in column strip and middle strip at the location of shear wall, wht should i do?

either design same model removing shear walls then export tht file...gve me option.?

and sir whch kind of meshing u prefer ...manual or auto and whch gve more precise rezlt?

[WR1]

yar both will give you precise results....but do automatic meshing if and only if..you have regular building or floor or part of floor...

otherwise do it manually in large chunks and you can mix both the techniques...make slabs regular by manual meshing then do it auto mesh...its ur choice...

when you make automesh..just goto view options and turn on meshing option....you will see yourself..where the automeshing is causing problem....

for foundation...how can you remove shear walls....and design the foundation....ofcouse there will be much more reinforcement under your shear wall....its a lateral resisting element.....but there are some areas of higher concentration of stress...you dont need to take this in design...you can average it on a relatively bigger area....

[abdulqadeer29]

sir , when we are doing p delta analysis in etab ,

when we select p delta parameters, and select option....iterative based on load combinations....sir in whch code these parameters are defined or tht load combination z difined whch we normally put there??/