Doing ETABS dynamic analysis, we ge 1

[niravshah1964]

Doing ETABS dynamic analysis, we get building modes with values of UX, UY, UZ RX RY RZ.

What is unit of RZ??

 

[PicoStruc]

Mode shape have no unit in any direction... including translation and torsional mode of vibration..

Mode Shape are only amplitude normalized to the mass matrix.

 

[niravshah1964]

Thanks PicoStruc.

ETABS:

I find many times issue with Print/Tables/Input/Auto Seismic loads. It does not create output. With Display tables I find them blank, though I have made input.
Any idea why??

Thanks in Advance

 

[PicoStruc]

Cannot help for that, never use Auto Load.

 

[niravshah1964]

Thanks any way.

 

[MrHershey]

Regarding printing, make sure you select your seismic loads for display. 'Select Loads...' over on the right of the dialog box.

 

[niravshah1964]

Thanks, I shall try the same.

 

[niravshah1964]

ETABS user:

Can anybody suggest best way to optimize RC design of multi-storey buildings, particularly columns & shear wall??

Can virtual work done help??

Thanks in advance

 

[PicoStruc]

New Postniravshah1964

For column design and shear wall... the best way is do it by hand (or using homemade spreadsheet or sectional analyse software like spColumn, Response2000) using force from the software !

I never trust design module of these softwares !don't forget minimum moment in the weak axis of columns !

 

[MrHershey]

I prefer to use my own spreadsheets for walls where possible.

When there's too many walls to export forces and sections into spreadsheets, I'll use ETABS' own design module and verify problem locations with spColumn. Usually works well but occasionally I've had problems with light axial loads in walls with lots of moment.

Columns I'll generally design in ETABS and confirm with SPColumn or spreadsheets. Especially confirming prescriptive requirements for special moment frames, I generally don't trust ETABS to do everything. Will use spreadsheets to go through and make sure all requirements are met.

 

[niravshah1964]

Thanks PicoStruc & MarkHirschi:

I agree with you.

What is Virtual work facility in ETABS, do you use it??

Mark your suggestion on Auto seismic loads did work.

 

[wannabeSE]

For information on virtual work in ETABS, see

http://docs.csiberkeley.com/help-files/etabs/Menus/Display/Show_Energy_Virtual_Work_Diagram.htm

 

[niravshah1964]

Thanks.

Can we extract the design forces of any element into an excel sheet??
If yes, can anybody explain how?? This would be extremely handy to optimize design manually using spread sheets.

 

[MrHershey]

There are a couple ways.

1. Display>Show Tables... Then select your design load cases/combos (hold down CTRL to add combos to selection, SHIFT to add all combos between previous and present clicks to selection) and choose to show Analysis Results>Frame Output>Frame Forces. You can do the same for shell elements if you've assigned piers/spandrels. After displaying these tables you can copy (Ctrl-C) and paste the whole thing into an Excel spreadsheet.

2. For large files you can also export to an Access Database (*.mdb) using File>Export>Save input/output as Access data file... (then select tables and combos just like you would to show tables in 1 above) and then run a query to or link the data from the mdb file from within Excel. This method is a little more complex, but works better especially for large models with lots of elements.

 

[niravshah1964]

I tried to do the first method you suggested yesterday. Pasted into excel spread sheet. I am developing a small algorithm to choose max & min forces for P M2 & M3.

I can then use these to check same with manual design spreadsheet.

Appears to be a long task!!