Glass Thickness Load Calculator

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Glass Thickness Load Calculator

Calculate the minimum glass thickness required to withstand a specified uniform load (wind pressure) based on pane dimensions, support conditions, and glass type using the glass stress formula per ASTM E1300.

Pane Width (mm)

Pane Height (mm)

Design Load (Pa)

Uniform lateral load (wind pressure). Typical: 500–3000 Pa

Support Condition

Four-sided simply supported Three-sided simply supported Two-sided (spanning short direction)

Glass Type

Annealed (AN) — 23.3 MPa Heat-Strengthened (HS) — 46.6 MPa Fully Tempered (FT) — 93.1 MPa

Safety Factor

Typical: 2.5 for wind load per ASTM E1300

Calculate

Enter pane dimensions, load, and conditions above, then click Calculate.

function gla_calc() { var resultDiv = document.getElementById("gla_result");

// --- Read inputs --- var W_mm = parseFloat(document.getElementById("gla_width").value); var H_mm = parseFloat(document.getElementById("gla_height").value); var q = parseFloat(document.getElementById("gla_load").value); var sup = parseInt(document.getElementById("gla_support").value); var gtype = document.getElementById("gla_type").value; var SF = parseFloat(document.getElementById("gla_sf").value);

// --- Validation --- var errors = []; if (isNaN(W_mm) || W_mm 10000) errors.push("Pane Width must be between 100 and 10,000 mm."); if (isNaN(H_mm) || H_mm 10000) errors.push("Pane Height must be between 100 and 10,000 mm."); if (isNaN(q) || q 20000) errors.push("Design Load must be between 50 and 20,000 Pa."); if (isNaN(SF) || SF 5.0) errors.push("Safety Factor must be between 1.0 and 5.0.");

if (errors.length > 0) { resultDiv.innerHTML = "Input Errors:" + errors.map(function(e){ return ""; }).join("") + ""; return; }

// --- Convert to SI (metres) --- var a = Math.min(W_mm, H_mm) / 1000.0; // short side (m) var b = Math.max(W_mm, H_mm) / 1000.0; // long side (m) var r = b / a; // aspect ratio

// --- Allowable stress (MPa → Pa) --- var sigma_allow_MPa; if (gtype === "annealed") sigma_allow_MPa = 23.3; else if (gtype === "heatstrengthened") sigma_allow_MPa = 46.6; else sigma_allow_MPa = 93.1;

var sigma_allow = (sigma_allow_MPa * 1e6) / SF; // Pa, design allowable

// --- Bending stress coefficient (beta) --- // For a rectangular plate under uniform load, simply supported: // sigma_max = beta * q * a^2 / t^2 // beta depends on aspect ratio and support condition. // Values from Roark's Formulas for Stress and Strain (Table 11.4) // Four-sided simply supported: beta interpolated from standard table // Three-sided: conservative increase factor ~1.33 // Two-sided (one-way spanning short): beta = 0.75 (beam strip)

var beta; if (sup === 4) { // Four-sided simply supported — Roark Table 11.4 beta values // r: 1.0 1.2 1.4 1.6 1.8 2.0 3.0 inf var r_tab = [1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 3.0, 100.0]; var beta_tab = [0.2874, 0.3762, 0.4530, 0.5172, 0.5688, 0.6102, 0.7134, 0.7500]; // Linear interpolation if (r = r_tab[r_tab.length-1]) { beta = beta_tab[beta_tab.length-1]; } else { for (var i = 0; i = r_tab[i] && r = r_tab[r_tab.length-1]) { beta4 = beta_tab[beta_tab.length-1]; } else { for (var i = 0; i = r_tab[i] && r = t_req_mm) { t_selected = std_thick[i]; break; } }

// --- Actual stress at selected thickness --- var sigma_actual_MPa = null; var util = null; if (t_selected !== null) { var t_sel_m = t_selected / 1000.0; sigma_actual_MPa = (beta * q * a * a) / (t_sel_m * t_sel_m) / 1e6; util = (sigma_actual_MPa * SF) / sigma_allow_MPa * 100; }

// --- Deflection check (serviceability) --- // Max deflection for four-sided plate: delta = alpha * q * a^4 / (E * t^3) // E_glass = 70 GPa, Poisson = 0.22 // alpha from Roark Table 11.4 (four-sided SS) var E_glass = 70e9; // Pa var alpha; if (sup === 4) { var r_tab2 = [1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 3.0, 100.0]; var alpha_tab = [0.04435, 0.06132, 0.07718, 0.09065, 0.10168, 0.11120, 0.13239, 0.13333]; if (r = r_tab2[r_tab2.length-1]) { alpha = alpha_tab[alpha_tab.length-1]; } else { for (var i = 0; i = r_tab2[i] && r "; html += "ParameterValue"; html += "Pane dimensions (W × H)" + W_mm.toFixed(0) + " × " + H_mm.toFixed(0) + " mm"; html += "Short side (a)" + (a1000).toFixed(0) + " mm"; html += "Aspect ratio (b/a)" + r.toFixed(3) + ""; html += "Design load (q)" + q.toFixed(0) + " Pa"; html += "Support condition" + supLabel + ""; html += "Glass type" + gtypeLabel + ""; html += "Allowable stress (σallow)" + sigma_allow_MPa.toFixed(1) + " MPa (before SF)"; html += "Safety factor" + SF.toFixed(1) + ""; html += "Design allowable stress" + (sigma_allow/1e6).toFixed(2) + " MPa"; html += "Stress coefficient (β)" + beta.toFixed(4) + ""; html += "Minimum required thickness*" + t_req_mm.toFixed(2) + " mm";

if (t_selected !== null) { html += "Selected standard thickness" + t_selected + " mm ✓"; html += "Actual bending stress" + sigma_actual_MPa.toFixed(2) + " MPa"; html += "Utilisation ratio" + util.toFixed(1) + "%"; html += "Max deflection" + defl_mm.toFixed(2) + " mm"; html += "Deflection limit (a/60)" + defl_limit_mm.toFixed(2) + " mm"; html += "Deflection check" + (defl_ok ? "✅ PASS" : "⚠️ FAIL — consider thicker glass") + ""; } else { html += "⚠️ Required thickness exceeds standard sizes (>25 mm). Consider laminated or insulated glass units."; }

html += "";

if (t_selected !== null && !defl_ok) { html += "Note: Although the selected thickness satisfies the stress criterion, the deflection exceeds the a/60 serviceability limit. Select the next standard thickness or consult a structural engineer.

"; }

resultDiv.innerHTML = html; }

#### Formulas Used

Maximum bending stress in a rectangular glass plate (Roark's Formulas for Stress and Strain, Table 11.4):

σmax = β · q · a² / t²

Where:

Required thickness:

treq = a · √(β · q / σallow)

Design allowable stress:

σallow = σglass / SF

Maximum deflection (four-sided simply supported):

δmax = α · q · a⁴ / (E · t³)

Where α is the deflection coefficient from Roark Table 11.4, E = 70 GPa (glass modulus of elasticity).

Serviceability deflection limit (ASTM E1300):

δlimit = a / 60

#### Assumptions & References

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