Structural Load Capacity Calculator
ANA›Life Services Authority›National Calculator Authority›Structural Load Capacity Calculator
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Structural Load Capacity Calculator
Calculate the axial compressive load capacity of steel or concrete columns using standard structural engineering formulas (AISC / ACI 318).
Material Type
Steel (AISC) Concrete (ACI 318)
Yield Strength, Fy (MPa)
Cross-Sectional Area, A (mm²)
Modulus of Elasticity, E (MPa)
Radius of Gyration, r (mm)
Effective Length, KL (mm)
Compressive Strength, f'c (MPa)
Gross Cross-Sectional Area, Ag (mm²)
Total Steel Area, Ast (mm²)
Steel Yield Strength, fyt (MPa)
Calculate Results will appear here.
function slcUpdateMaterial() { var mat = document.getElementById('slc_material').value; document.getElementById('slc_steel_inputs').style.display = (mat === 'steel') ? '' : 'none'; document.getElementById('slc_concrete_inputs').style.display = (mat === 'concrete') ? '' : 'none'; document.getElementById('slc_result').innerHTML = 'Results will appear here.'; }
function slcCalc() { var res = document.getElementById('slc_result'); var mat = document.getElementById('slc_material').value;
if (mat === 'steel') { var Fy = parseFloat(document.getElementById('slc_fy').value); var A = parseFloat(document.getElementById('slc_area').value); var E = parseFloat(document.getElementById('slc_E').value); var r = parseFloat(document.getElementById('slc_r').value); var KL = parseFloat(document.getElementById('slc_L').value);
if ([Fy, A, E, r, KL].some(isNaN) || Fy ⚠ Please enter valid positive values for all steel inputs.'; return; }
// AISC LRFD Chapter E — Steel Column Capacity // Slenderness ratio var slenderness = KL / r;
// Elastic buckling stress (Euler) var Fe = (Math.PI * Math.PI * E) / (slenderness * slenderness);
// Critical stress Fcr var Fcr; var limit = 4.71 * Math.sqrt(E / Fy); var mode; if (slenderness ' + 'Slenderness Ratio (KL/r): ' + slenderness.toFixed(2) + '' + 'Elastic Buckling Stress Fe: ' + Fe.toFixed(2) + ' MPa' + 'Buckling Mode: ' + mode + '' + 'Critical Stress Fcr: ' + Fcr.toFixed(2) + ' MPa' + 'Nominal Capacity Pn: ' + (Pn / 1000).toFixed(2) + ' kN' + 'Design Capacity φPn (φ=0.90): ' + (phiPn / 1000).toFixed(2) + ' kN';
} else { // Concrete — ACI 318-19 Section 22.4.2 var fc = parseFloat(document.getElementById('slc_fc').value); var Ag = parseFloat(document.getElementById('slc_Ag').value); var Ast = parseFloat(document.getElementById('slc_Ast').value); var fyst = parseFloat(document.getElementById('slc_fyst').value);
if ([fc, Ag, Ast, fyst].some(isNaN) || fc ⚠ Please enter valid positive values for all concrete inputs.'; return; } if (Ast >= Ag) { res.innerHTML = '⚠ Steel area Ast must be less than gross area Ag.'; return; }
// Steel ratio check (ACI 318 limits: 1% to 8%) var rho = Ast / Ag; var rhoWarning = ''; if (rho 0.08) { rhoWarning = '⚠ Steel ratio ρ = ' + (rho * 100).toFixed(2) + '% is outside ACI 318 limits (1%–8%).'; }
// ACI 318-19 Eq. 22.4.2.2 — Tied column // Pn = 0.80 * [0.85 * f'c * (Ag - Ast) + fy * Ast] var Pn_tied = 0.80 * (0.85 * fc * (Ag - Ast) + fyst * Ast);
// ACI 318-19 Eq. 22.4.2.1 — Spiral column // Pn = 0.85 * [0.85 * f'c * (Ag - Ast) + fy * Ast] var Pn_spiral = 0.85 * (0.85 * fc * (Ag - Ast) + fyst * Ast);
// Design capacity phi = 0.65 (tied), 0.75 (spiral) var phiPn_tied = 0.65 * Pn_tied; var phiPn_spiral = 0.75 * Pn_spiral;
res.innerHTML = 'Concrete Column Results (ACI 318-19)' + 'Steel Ratio ρ: ' + (rho * 100).toFixed(3) + '%' + rhoWarning + '' + 'Tied Column (φ = 0.65):' + 'Nominal Capacity Pn: ' + (Pn_tied / 1000).toFixed(2) + ' kN' + 'Design Capacity φPn: ' + (phiPn_tied / 1000).toFixed(2) + ' kN' + 'Spiral Column (φ = 0.75):' + 'Nominal Capacity Pn: ' + (Pn_spiral / 1000).toFixed(2) + ' kN' + 'Design Capacity φPn: ' + (phiPn_spiral / 1000).toFixed(2) + ' kN'; } }
#### Formulas Used
Steel Column — AISC LRFD (Chapter E):
- Elastic Buckling Stress: Fe = π²E / (KL/r)²
- Limit slenderness: 4.71√(E/Fy)
- Inelastic: Fcr = 0.658^(Fy/Fe) × Fy when KL/r ≤ 4.71√(E/Fy)
- Elastic: Fcr = 0.877 × Fe when KL/r > 4.71√(E/Fy)
- Nominal: Pn = Fcr × A
- Design: φPn = 0.90 × Pn
Concrete Column — ACI 318-19 (Section 22.4.2):
- Tied: Pn = 0.80 [0.85 f'c (Ag − Ast) + fyt Ast], φ = 0.65
- Spiral: Pn = 0.85 [0.85 f'c (Ag − Ast) + fyt Ast], φ = 0.75
#### Assumptions & References
- Steel calculations follow AISC 360-22 LRFD method, Chapter E (Compression Members).
- Concrete calculations follow ACI 318-19, Section 22.4.2 (Axial Strength).
- ACI 318-19 limits longitudinal steel ratio to 1% ≤ ρ ≤ 8%.
- All units: forces in N (inputs in MPa and mm²); results displayed in kN.
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