For columns located in non-seismic region is there any limit on the normalized axial load(Ned/(fcd*b*h), Ned-design axial load, b and h are column cross section and fcd is design axial load) to insure ductile behavior?
Dear Ephrem:
There are no specific limits on this quantity. However, it is easy to suggest some guidelines for design. In general, a ductile column is one in which the normalized axial load is less than 0.25, a moderately ductile column is one in which it is approximately 0.3, and a non-ductile column is one in which it is larger than 0.35. I am normalizing the axial load by the product of the gross area (b*h) and the 28-day compressive strength of concrete as defined in the US (f'c). Please see the attached document to see how the guidelines are defined.
Axial load of column will depend upon the % of reinforcement and column size for various mixes and steel.
For steel grade fy 415
CONCRETE GRADE &Axial Load carrying Capacity in KN (P)
M15 ,P= (2.7205 p + 6) b D/1500
M20, P= (2.7005 p + 8) b D/1500
M25 ,P= (2.6805 p + 10) b D/1500
M30, P= (2.6605 p + 12) b D/1500
M35, P= (2.6405 p + 14) b D/1500
M40, P= (2.6205 p + 16) b D/1500
For steel grade fy 500
CONCRETE GRADE &Axial Load carrying Capacity in KN (P)
M15 ,P= (3.29 p + 6) b D/1500
M20, P= (3.27 p + 8) b D/1500
M25, P= (3.25 p + 10) b D/1500
M30, P= (3.23 p + 12) b D/1500
M35, P= (3.21 p + 14) b D/1500
M40, P= (3.19 p + 16) b D/1500
For steel grade fy 550
CONCRETE GRADE& Axial Load carrying Capacity in KN (P)
M15, P= (3.625 p + 6) b D/1500
M20, P= (3.605 p + 8) b D/1500
M25, P= (3.585 p + 10) b D/1500
M30, P= (3.565 p + 12) b D/1500
M35, P= (3.545 p + 14) b D/1500
M40, P= (3.525 p + 16) b D/1500
Note :-
1. The axial Load carrying capacity column is arrived based on the formula
Pu =0.4 fck Ac + 0.67 fy Asc as per IS 456-2000.
2. Here in the Table P is Axial Load Carrying capacity of column in KN.
p is steel in percentage say percentage as 1
b is breadth of column in mm
D is depth of column in mm.
For preliminary design use square columns.
If the building height is 3 stories or less:
If beam span < 6000mm, h (mm) = 300
If 6000 < beam span < 9000, h = 350
If 9000 < beam span < 12000, h = 400
If the building height is 4 to 9 stories:
If beam span < 6000mm, h (mm) = 400
If 6000 < beam span < 9000, h = 500
If 9000 < beam span < 12000, h = 600
I hope it will give you clear idea about column axial load.
Ductility can be defined as the “ability of material to undergo large deformations without rupture before failure”. Ductility in concrete is defined by the percentage of steel reinforcement with in it. Mild steel is an example of a ductile material that can be bent and twisted without rupture. it has been discuses in the below attachment.
There is a thesis titled:
Ductility of rectangular reinforced concrete columns with axial load
I hope it be helpful.
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