AS 1288:2021 Appendix B Example 2: Toughened glass, 2050 by 1500 mm, Pu 3.20 kPa, Ps 2.10 kPa

Find the thinnest toughened glass for a 2050 by 1500 mm pane on four edges, checking strength at 3.20 kPa and deflection at 2.10 kPa.

This page runs the 6 mm glass, the thickness that answers the example. The other thicknesses of the example are compared below.

Inputs

Glass lite

Support: Four edges supported
Long dimension, a: 2050.00 mm
Short dimension, b (the span B): 1500.00 mm
Construction: Monolithic
Glass type: Toughened (FT)
Nominal thickness: 6 mm
Glass thickness, t: 5.80 mm (Table 4.1 minimum)
Ultimate pressure, Pu: 3.20 kPa
Serviceability pressure, Ps: 2.10 kPa
Load: Wind, c3 = 1.00

Calculations

Glass area, A: 3.08 m²
Aspect ratio, AR: 1.37
Span, B: 1500.00 mm

Minimum thickness, t (Table 4.1): 5.80 mm
Glass type factor, c1 (Table 3.1): 2.50
Surface factor, c2 (Table 3.2): 1.00
Pressure in the formula, P = Pu / c2: 3.20 kPa
k1, k2, k3, k4 at AR 1.25 (Figure 4.13): 4599.7, 0.441394, −0.6071, −2.9
B at AR 1.25 = k1 (P + k2) to the power k3, plus k4: 2095.96 mm
k1, k2, k3, k4 at AR 1.50 (Figure 4.13): 4523.7, 0.441394, −0.6423, −46.98
B at AR 1.50 = k1 (P + k2) to the power k3, plus k4: 1925.40 mm
Interpolation in AR (Cl 4.4.2): 0.53 × 2095.96 + 0.47 × 1925.40 = 2016.37 mm
Allowable span, B_allow: 2016.37 mm
Capacity pressure, Pu,cap: 5.38 kPa
B / B_allow: 0.74
Span over thickness, B/t: 258.62
k1, k2, k3, k4 of Figure 4.35, span/60, at AR 1.25: 459.45, −0.1, −0.5022, 2.06
B/t at AR 1.25: 326.45
k1, k2, k3, k4 of Figure 4.35, span/60, at AR 1.50: 350.14, −0.15, −0.4503, 1.29
B/t at AR 1.50: 260.49
Interpolation in AR: 0.53 × 326.45 + 0.47 × 260.49 = 295.67
Allowable B/t at Ps (Figure 4.35, span/60): 295.67
Capacity pressure, Ps,cap: 2.74 kPa

Strength and deflection: AS 1288 Section 4 formulas (printed constants, Figures 4.1 to 4.35).

Section 3 plate solver: B_allow 2111.61 mm (4.7 percent higher), allowable B/t 291.50 (1.4 percent lower).

Allowable span, B_allow (strength). Section 3: peak stress S* = 41.30 MPa at Pu = 3.20 kPa, capacity φ c1 c2 c3 f′t = 72.39 MPa (φ 0.67, c1 2.50, c2 1.00, c3 1.00, f′t 43.22 MPa at the edge, t = 5.80 mm); S* / capacity = 0.57.

Allowable B/t at Ps (deflection). Section 3: deflection at the center of the glass w = 22.29 mm at Ps = 2.10 kPa, ≤ span/60 = 25.00 mm.

Outputs

Strength PASS. Deflection PASS.

Strength: B = 1500.00 mm ≤ B_allow = 2016.37 mm at Pu = 3.20 kPa; B/B_allow = 0.74.

Capacity: Pu,cap = 5.38 kPa.

Deflection: B/t = 258.62 ≤ allowable 295.67 at Ps = 2.10 kPa (span/60 basis).

Against the printed values

4 mm: GlassLoad.com B_allow 1376.27 mm, printed 1374 mm. Strength FAIL, printed FAIL. Deflection: B/t 394.74 against the allowable 295.67 (exceeds), Ps,cap 1.20 kPa.

5 mm: GlassLoad.com B_allow 1700.30 mm, printed 1698 mm. Strength PASS, printed PASS. Deflection: B/t 312.50 against the allowable 295.67 (exceeds), Ps,cap 1.88 kPa, printed B/t = 312.5 fails against the allowable 294.8.

6 mm: GlassLoad.com B_allow 2016.37 mm. Strength PASS, printed PASS. Deflection: B/t 258.62 against the allowable 295.67 (within), Ps,cap 2.74 kPa, printed B/t = 258.6 passes against the allowable 294.8.

The standard rounds the aspect ratio to 1.37 before interpolating; GlassLoad.com uses 1.3667, so its interpolated values differ by about 0.1 to 0.3 percent.

Notes

More examples are on the AS 1288:2021 page and on the examples page. Open the calculator to run your own check.

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