Foundation Settlement Differential Calculator

ANA›Life Services Authority›National Calculator Authority›Foundation Settlement Differential Calculator

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Foundation Settlement Differential Calculator

Calculate differential settlement between two foundation points, angular distortion, and evaluate against allowable limits per structural guidelines.

### Settlement Inputs

Settlement at Point A, S₁ (mm)

Settlement at Point B, S₂ (mm)

Distance Between Points, L (m)

### Structure Type & Limits

Structure Type

Steel Frame (1/300) Reinforced Concrete Frame (1/400) Load-Bearing Masonry (1/500) Sensitive Machinery / High-Rise (1/750) Custom Limit

Custom Angular Distortion Limit (1/N)

Maximum Allowable Differential Settlement (mm)

Calculate

(function() { const structSelect = document.getElementById('fou-struct'); const customInput = document.getElementById('fou-custom-limit');

structSelect.addEventListener('change', function() { customInput.disabled = (this.value !== 'custom'); if (customInput.disabled) customInput.value = ''; });

window.fouCalc = function() { const resultDiv = document.getElementById('fou-result'); resultDiv.style.display = 'none';

// --- Gather inputs --- const s1Raw = document.getElementById('fou-s1').value.trim(); const s2Raw = document.getElementById('fou-s2').value.trim(); const lRaw = document.getElementById('fou-dist').value.trim(); const maxDiff = document.getElementById('fou-max-diff').value.trim(); const struct = structSelect.value; const custRaw = customInput.value.trim();

// --- Validation --- const errors = []; if (s1Raw === '') errors.push('Settlement at Point A (S₁) is required.'); if (s2Raw === '') errors.push('Settlement at Point B (S₂) is required.'); if (lRaw === '') errors.push('Distance between points (L) is required.');

const s1 = parseFloat(s1Raw); const s2 = parseFloat(s2Raw); const L = parseFloat(lRaw);

if (!isNaN(s1) && s1 0 m.');

let limitDenom = null; if (struct === 'custom') { if (custRaw === '') { errors.push('Custom angular distortion limit (N) is required.'); } else { limitDenom = parseFloat(custRaw); if (isNaN(limitDenom) || limitDenom 0) { resultDiv.innerHTML = 'Please fix the following:' + errors.map(e => '').join('') + ''; resultDiv.style.display = 'block'; return; }

// --- Core Calculations --- // Differential settlement const deltaS = Math.abs(s1 - s2); // mm

// Angular distortion β = ΔS / L (convert L to mm) const L_mm = L * 1000; const beta = deltaS / L_mm; // dimensionless ratio

// Allowable angular distortion const betaAllow = 1 / limitDenom;

// Utilisation ratio const utilRatio = beta / betaAllow;

// Status flags const angOK = beta Overall Status: ' + statusText + '';

html += 'ParameterValueStatus';

html += 'Settlement at A (S₁)' + s1.toFixed(2) + ' mm—'; html += 'Settlement at B (S₂)' + s2.toFixed(2) + ' mm—'; html += 'Distance (L)' + L.toFixed(3) + ' m (' + L_mm.toFixed(0) + ' mm)—';

html += 'Differential Settlement (ΔS)' + '' + deltaS.toFixed(2) + ' mm' + '' + (diffOK === null ? '—' : (diffOK ? '✅ OK' : '⚠️ Exceeds ' + maxDiffVal.toFixed(1) + ' mm')) + '';

html += 'Angular Distortion (β = ΔS/L)' + '1/' + (1/beta).toFixed(0) + ' (' + beta.toExponential(3) + ')' + '' + (angOK ? '✅ OK' : '⚠️ Exceeds limit') + '';

html += 'Allowable Angular Distortion' + '1/' + limitDenom + ' (' + betaAllow.toExponential(3) + ')' + '(' + structLabels[struct] + ')';

html += 'Utilisation Ratio (β / β_allow)' + '' + (utilRatio * 100).toFixed(1) + '%' + '' + (angOK ? '✅ ≤ 100%' : '⚠️ > 100%') + '';

html += 'Tilt Angle' + tiltDeg.toFixed(4) + '°—';

html += '';

if (maxDiffVal !== null) { html += 'Allowable differential settlement checked against user-specified limit of ' + maxDiffVal.toFixed(1) + ' mm.

'; }

resultDiv.innerHTML = html; resultDiv.style.display = 'block'; }; })();

#### Formulas Used

Differential Settlement: ΔS = |S₁ − S₂|

Angular Distortion: β = ΔS / L where ΔS is in mm and L is in mm (consistent units).

Utilisation Ratio: U = β / βallow × 100%

Tilt Angle: θ = arctan(β) in degrees

#### Assumptions & References

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References

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