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Pl. Down load the attachment " ColumnDesign.zip" in the fallowing link
//www.buonovino.com/forum/viewtopic.php?t=14930

[logeshcivil]

Dear sirs
I have attached a column design done in STAAD Pro as well its analysis results. I would like to know how guiding load case is determined in STAAD Pro. for column design.

1.
In this case, if we assume moment is the guiding factor in design, then moment (Mz) of 1474 kNm should be the critical one. If My is considered as guiding factor , there is a value of 194kNm but only the value of 187 is taken for design. So how does STAAD determines critical load case?
How should I go about designing the column manually?

2.
If we take a single column from Footing top to terrace floor top, should i design the column for maximum load and maximum moments which may occur in different floors for different load combinations

or

Should I take the load combination which has maximum moment and use the Pu and moment of the combination for design.

Thank you

[vikram.jeet]

Column design, Critical forces

It is better to design the Column with one column sec taking care of for two floors in low rise building and three floors in high rise,,
The Load of lower floor,, is higher and to be taken in design s

The moments from gravity loading may not differ much if str arrangement is nearly ssme on floors,, and higher ones gravity moments may be taken in manual analysis, but seismic moments will be higher at lower floor and to be taken.

However one sec must be checked at terrace since P is minimum but gravity moments are appreciable, though seismic moments are also least.

For design of each column sec, Column data to be taken for three different cades viz
CASE 1 - NORMAL CASE (NON SEISMIC)
CASE 2- EQx (SEISMIC Along X DIR ))
CASE 3 - EQy ( SEISMIC Along Y DIR)

Manual Design of Column section :
A Hypothetical data for illustration purpose only,,
Floor to floor clr ht = H
Col dimension Dx * Dy

CASE 1 NORMAL CADE

P = 200 tonne
Mx :
Applied - 15 tm (from gravity analysis)
Minimum - say 5.0tm (based on IS 456 , H/500+Dx/30 but min 20mm to be taken)
Slenderness - say Nil due to Dx/H <12
Hence Mx for design = 15 tm

My :
给出= 1.5 tm (fm重力分析、interior col on y dir)
Minimum = 3.5 tm
Slenderness = 6.5 tm ( based on cl 38.7.1 of IS 456 Dy/H = 15 ,, Slenderness moment = 200* Dy /2000 *(1/15) ^2 say =6.5 tm
Hence My for design = 3.5 + 6.5 = 10 tm

Design the column for Gravity Loading, that is Normal case ( Non seismic)

(To be continued)

[vikram.jeet]

(Continuing fm previous post)
Column design, Critical forces


Manual Design of Column section :
SEISMIC CASES

CASE 2 SEISMIC ALONG X DIR



A Hypothetical data for illustration purpose only,,
Floor to floor clr ht =
Col dimension Dx * Dy
P = 185 * tonne
Mx :
Applied - 15 tm (from gravity analysis) PLUS 25 tm from seismic Hence applied mox = 15+25= 40 tm
Minimum - say 4.5 tm (based on IS 456 , H/500+Dc/30 but min 20mm to be taken)
Slenderness - say Nil due to Dx/H <12
Hence Mx for design = 40 tm

My :
给出= 1.5 tm (fm重力分析、interior col on y dir)
Minimum = 3..2 tm
Slenderness = 6.1 tm ( based on cl 38.7.1 of IS 456 Dy/H = 15 ,, Slenderness moment = 185 * Dy /2000 *(1/15) ^2 say =6.51tm
Hence My for design = 3.2+ 6.1= 9.3 tm

Design the column for Appropriate Gravity Loading plus seismiic in X dir that is Seismic Case X dir

(To be continued)

[vikram.jeet]

(Continuing fm previous post)
Column design, Critical forces


Manual Design of Column section :
SEISMIC CASES

CASE 3 SEISMIC ALONG Y DIR



A Hypothetical data for illustration purpose only,,
Floor to floor clr ht =
Col dimension Dx * Dy
P = 185 * tonne
Mx :
Applied - 15 tm (from gravity analysis)

Minimum - say 4.5 tm (based on IS 456 , H/500+Dc/30 but min 20mm to be taken)
Slenderness - say Nil due to Dx/H <12
Hence Mx for design = 15 tm

My :
给出= 1.5 tm (fm重力分析、interior col on y dir) PLUS 25 tm EQ Mo y
Hence My = 1.5 + 25 = 26.5 tm
Minimum = 3..2 tm
Slenderness = 6.1 tm ( based on cl 38.7.1 of IS 456 Dy/H = 15 ,, Slenderness moment = 185 * Dy /2000 *(1/15) ^2 say =6.51tm
Hence My for design = 26.5+ 6.1= 32.6tm

Design the column for Appropriate Gravity Loading plus seismiic in Ydir that is Seismic Case Y dir

(To be continued for manual design procedure after comilinb data on column sec for three cases viz Case1 NORMAL,, CASE2 - EQx and CASE3 -EQ y)

[va]

Hello,In STAADpro column design is checked for all listed load combinations with PU, Muz and Muy as per interaction ratio provided in IS456. It reports the critical load case in the design output. One has to consider respective value of axial�load and biaxial moments in respective load combinations while doing hand calculations.
Regards.
Hemant Vadalkar
Consulting Engineer Mumbai


On Tue, Apr 11, 2023 at 10:37 PM logeshcivil forum@www.buonovino.com) > wrote:

[R_Shenoy]

Dear Logesh,

The correct approach would be to identify four load combinations at each end of a column in the lowest storey.
1. Pmax with concurrent Mx & My
2. Pmin with concurrent Mx & My
3. Mxmax with concurrent P & My
4. Mymax with concirrent P & Mx
See which of the above 4 yields the highest requirement of reinforcement at each end of the column.
Similarly, repeat thee exercise at both ends of columns at all other storey levels.
Once you have a vertical listing of reinfircement percentage required at all storeys of the column, review and rationalise the same to achieve a practical and easy to construct scheme for possible curtailment of reinforcement along the height of the building.
Please note that the top storey column often requires more reinforcement than some immediately lower storeys and this will often require provision of more reinforcement than theoretically needed at some levels. This will have to be accepted for practical�purposes and to have a constructable detail.


This may look like a lot of work, but is more reliable than assuming that all columns are governed, either solely by axial load or by moment.
The governing load case can be different at different storey levels of the same column.


Some time and effort could be saved by sensible sizing and grouping of columns at the preliminary design stage.


I hope the above explanationbis sufficiently clear.


Regards.


Ramnath


On Tue, 11 Apr, 2023, 22:39 logeshcivil, forum@www.buonovino.com) > wrote: