So If a column isn't casted exactly in the intended location according to the structural drawings, and the centre of this column is moved 3 cm away from it's original location.now in the ACI code, accidental eccentricity is taken into account in the column design equation,so the question is how to check If that eccentricity is within the allowable range? According to the ACI?
If column is not casted exactly in the intended location or some other accidental reason the minimum eccentricity as per IS 456 is e min = Leff/500 + D/30 or 20mm which is not greater than 0.05D in case of axial loaded column.
For more details please refer IS 456
As per ACI
For nonprestressed members with spiral reinforcement conforming to 7.10.4 or composite members conforming to 10.16:
φPn,max = 0.85φ[0.85fc′(Ag – Ast) + fy Ast ]
For nonprestressed members with tie
reinforcement conforming to 7.10.5:
φPn,max = 0.80φ[0.85fc′(Ag – Ast) + fy Ast ]
The primary purpose of the minimum eccentricity requirement was to limit the maximum design axial load strength of a compression mem- ber. This is now accomplished directly in above equations by limiting the design axial strength of a section in pure compression to 85 or 80 percent of the nominal strength. These percentage values approximate the axial strengths at eccentricity to depth ratios of 0.05 and 0.10, specified in the earlier codes for the spirally reinforced and tied members, respectively. The same axial load limitation applies to both cast-in-place and precast compression members.
For more details you may go through ACI code.
minimum eccentricity = 12D/500 + D/30 = 0.057D
maximum amount of eccentricity of a short column = 0.05D or 0.05B
we can write the minimum eccentricity = 12D/500 + D/30 = 0.057D, which has been taken as 0.05D or 0.05b as the maximum amount of eccentricity of a short column.
Design Criteria For Reinforced Concrete Columns Under Seismic ...
It seems to me that in such a case you would need to assess the axial load - moment interaction at an eccentricity equal to the actual eccentricity due to misalignment plus the required accidental eccentricity.
I think it depends on the country code,But according EURO CODE the greatest of following is recommended (ea):
-Le/400
-h/30
-20mm
where Le is effective length of column and h is greater dimension of column.
Ali Al-rubiay
ACI already recognizes a minimum eccentricity in the column strength equation. That is why if you draw out the interaction diagram it starts off with a horizontal line from the vertical axis (P). The point where the horizontal line is no longer horizontal is the minimum eccentricity (emin=M/P). This is obviously slightly different for each section given the variables (f'c, section dimensions, rebar pattern, etc), but is considered nonetheless. That is the only "minimum eccentricity" that I'm aware of for short columns.
Slender columns do require a minimum eccentricity of 0.6" + 0.03h from ACI 318, but that is only for determining if a column is slender or not and to use with a slender column. It's not to use with a short column.
I hope, I have answered your question.
Regards,
Pravin Kumar
Please, see the following helpful link:
https://www.eurocode.us/concrete-structures-eurocode-2/ie.html
Compare eccentricity which is calculated by ACI code and the shifted eccentricity.If the code provision is greater than the shifted eccentricity it is okay because the moment which is greater than the shifted is considered in the design but for the opposite the column should be redesigned by considering for excess moment which is axial times the difference of shifted eccentricity and eccentricity of code provided.
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