Neutral Axis Calculation for Concrete Columns Under Biaxial Bending

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Discussion Overview

The discussion centers on determining the location and orientation of the neutral axis (N.A.) in concrete columns subjected to biaxial bending, particularly when given a load and eccentricities. The scope includes numerical methods, programming approaches, and theoretical references related to structural engineering.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant inquires about the method to compute the N.A. location and orientation under given loading conditions.
  • Another participant suggests that due to the non-linear nature of concrete and steel, numerical methods using trial and error are the most accurate approach.
  • A participant expresses willingness to develop a program in Mathematica or Excel to create the interaction curve of the column and seeks clarification on the initial assumptions for the N.A. position.
  • It is proposed that starting with an initial N.A. and checking the computations against this assumption is a valid approach.
  • A later reply mentions that finding capacities for an interaction curve may simplify the process and references a specific text for further guidance.

Areas of Agreement / Disagreement

Participants generally agree on the necessity of numerical methods for accurate calculations, but there is no consensus on the specific approach or assumptions to be made regarding the initial N.A. position.

Contextual Notes

Limitations include the non-linear behavior of materials and the dependence on the initial assumptions made regarding the N.A. position, which remain unresolved in the discussion.

Who May Find This Useful

Structural engineers, students in civil engineering, and professionals interested in concrete design and analysis under complex loading conditions may find this discussion relevant.

mohamadh95
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How can the neutral axis of a concrete column under biaxial bending be determined. I mean if the load P is given along with the eccentricities ex and ey, how could the N.A. location and orientation be computed?
Thank you.
 
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Since concrete and steel are both non-linear materials the only accurate way to do it is numerically using trial and error.
 
Well I'm willing to make a program using Mathematica or a spreadsheet in excel in order to create the interaction curve of a column,so trial and error is no problem. Can you explain how shall I do it? Should I assume an initial N.A and then do the computations, and after that check if the computation check with the N.A assumed position?
 
That's pretty much it. Generally you have the vertical value of c and the rotation angle θ to locate it.

Now if you are doing an interaction curve that is a little different because now you are finding capacities which I think will turn out to be a little easier to do. A good reference is Collins & Mitchell's "Prestressed Concrete Structures".
 
Thank you for your help.
 

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