Column Compression Stress
Computes compression stress on a column from axial load and section area.
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Compression stress in a short column
When a short column carries an axial load, the normal compression stress comes out to σ = P/A. Here P is the axial load and A the cross-sectional area. You check it against σ_max ≤ σ_allowable, and because the column is short there's no buckling reduction to worry about. Take P = 300 kN and A = 400 cm². That gives σ = 300·10³ / (400·10⁻⁴) = 7.5 MPa. With concrete f_ck = 25 MPa, the admissible stress lands around 18 MPa (roughly 0.85·f_ck/γ_c, taking γ_c = 1.4).
A column counts as short when its slenderness λ = K·L/r stays below the limit set by NBR 6118 §15 (for unbraced concrete columns that's usually λ < 35). Once you go past that, second-order effects and buckling need their own separate check. Keep the units lined up: P in N, A in m², σ in Pa.
Applications
Use it to dimension short reinforced-concrete columns under NBR 6118, to size pedestals and short steel posts, and to verify precast slab supports and bearing walls. It also works for a quick axial-load check before you bring in moment and slenderness effects.
FAQ
When is a column considered short? When λ = K·L/r stays below the code limit. NBR 6118 §15.8 puts that around 35 for typical concrete columns. Go past it and you have to add the second-order moment.
Does this include the rebar contribution? No. The full capacity of an RC column is N_d = 0.85·f_cd·A_c + f_yd·A_s. What this tool reports is the gross-concrete stress, meant as a quick check.
Why is the admissible stress so much lower than f_ck? NBR 6118 applies γ_c = 1.4 and then a 0.85 factor for sustained loading (the Rüsch effect). So σ_allow works out to roughly 0.85·f_ck/1.4 ≈ 0.6·f_ck, and that's before any safety margin on the load side.
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The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.