Bi-axial bending chart - concrete column 29

[Pretty Girl]

This is from "Reinforced concrete design to eurocodes" by prab bhat, page 371 and 372.
It has mentioned the it's for My/ (hb^2) = 2.

But I don't know how to reproduce with that ratio kept constant. So, I tried to create it with making the alpha and beta values at a constant ratio of 0.8 (beta = 0.8 alpha). Then I produced a chart.

Since I didn't reproduce the exact chart in the book, now I have another problem. I have got no reference chart to compare my chart with. Can anyone kindly help me find out if my chart is correct for the column dimensions and data I provided.

Are there any free software/ excel sheet to enter the column details mentioned below and compare it with my chart?

I'm concerned that my chart may not be correct as I don't see the part the book's chart have I have shown in the green rectangle below, when I produce my chart. I understand it cannot be the same chart, but if my chart is correct that "nose" like curve should also be in my chart isn't it.

1. Chart from the book






2. The chart I produced

This is a rectangular column, h = 2000 mm, b = 1000 mm. I maintained "beta/ alpha ratio = 0.8".
4 reinforcement bars, 1 bar each corner. Steel percentage 4% (So, 1% bh area for each bar).
40 mm distance from column surface to the centroid of r/f for each bar.
fck = 30 MPa, fcd = 20 MPa, fyk = 500 MPa, fyd = 434.7 MPa.

 

[IDS]

Thank you for the response.

Now I get it.
What I still don't get is, how their chart is almost horizontal after the pure compression occurs. If they followed Eurocodes, there should be a drop as it caps at 0.00175 or 0.002. If their line is perfectly horizontal, we could have guessed they have just ignored the concentric behaviour. But it's not perfectly horizontal, that means they have not ignored concentric behaviour. But they get almost horizontal line and i get a drop after pure compression. So, they are following different type of calculation after the pure compression. Wonder what is more precise.

Have another look at Fig. 6.1 in the code:
- When the bottom face is in tension the top face strain stays constant at 0.0035
- When the NA reaches the bottom face the top face strain is still 0.0035, the bottom face is zero, and point C is 0.00175 (or 0.002 for the parabolic stress block).
- For any further increase in axial load the strain at C stays constant, the top face strain gradually reduces and the bottom face strain continues to increase.
- Under uniform compression the strain across the full section is constant at 0.00175 or 0.002.
- There is never a step change in the strain at any point, so there is never a step change in the moment capacity.

I am not sure what you mean by ignoring concentric behaviour. The short straight section at the top left end of the lines on the chart looks perfectly horizontal to me. It might be associated with the minimum eccentricity of the load, but the values don't match my calculations, so I'm not sure.