ETABS Pier Output

[4dmodeller]

Hi all,

Can anyone explain to me if torsional shear is included into shear V2 output if you were to assign each individual wall as a pier? I want to be able to extract the right load for manual spreadsheet design...

to give a background -

I have designed the core as a 3D pier, using P/M2/M3 to work out stresses at each location using P/A+My/I....however, I realise that I can't break down the torsional moment into shear force on each wall for in-plane shear wall design (due to part of core creating an open section + door opening) I plan to add the torsion induced shear on top of shear demand in each wall in proportion of its length along the shear force direction.....with this, i feel that i cant design manually the shear using a 3D pier..

so then, my next approach is to assign each wall as its own pier label..and design the shear on each wall...however, i found that on small nib wall (next to opening)..the shear attracted to it can be a lot higher than longer wall element..this does not make sense to me...I thus im not certain how i can design for shear using etabs pier output

can anyone help?

I have attached the etabs model here. Note this is a simple model where there is no vertical load transfer from slab...dummy beam with load is added ontop of each wall to simulate the load from the slab. this is from loadrundown

 

[4dmodeller]

I also found that if you are to grab the P/A +My/I of the individual wall...the resultant stress that you get can be no where near what S22 spits out when you display shell stresses..or when you do a manual calc assuming a 3D core works as 3D pier
e.g
assume thickness = 200 mm, length = 700 mm, height = 3m
Story Pier Load Case/Combo Location P V2 M3
L5 C1W1A DL Bottom -149.6701 4.6486 6.8321
L5 C1W1A SDL Bottom -229.4344 3.292 5.1115
L5 C1W1A LLR Bottom -87.0659 5.1952 8 .0331
L5 C1W1A LSWY Bottom -364.6715 104.6142 168.1043
For load combination 1.2(DL+SDL)+0.4*LLR+LSWY
I got P/A+My/I of 26.19 MPa
I got P/A-My/I of -16.27 MPa
This is crazy load.
However, when I check in the S22 output from shell stresses, it is only 6.4 MPa

 

[Enrique2015]

When designing a composite piers (i.e C shape or L-shape, etc) the program internally divides the wall in legs , and torsion is decomposed into shear for ondividaiul legs (i.e Shear flow)The problem I find with EATBS, is that it has so many parameters and variables for preferences and overwrites , and not all intermediate calculations results are displayed, hence it makes difficult for the engineer to check design. I have worked for companies that used both approaches, the one you mentioned to use ETABS only for lateral loads and then use a spreadsheet to combine loads and design walls using full iteration diagrams, and others that design everything in ETABS. The issue I find with the second approach is that errors during modeling are overseen, since the program will not check your structure for you to make sure things make sense, for sure I wouldn't trust anyone without a great experience in ETABS design to do this, whereas the first approach lets you have a feeling of the structure and realize if your results make sense. Lately I been using a program from

http://www.structuralaps.com

caled EZ-Shear wall, which lest you check results easily, it also allows for individual pier results to be imported from ETABS and checked.