AS 1288:2021 Appendix B Example 1: Annealed glass, 1200 by 1200 mm, Pu 2.80 kPa
Find the thinnest annealed glass for a 1200 by 1200 mm pane on four edges under an ultimate pressure of 2.80 kPa.
This page runs the 5 mm glass, the thickness that answers the example. The other thicknesses of the example are compared below.
Inputs
- Support
- Four edges supported
- Long dimension, a
- 1200.00 mm
- Short dimension, b (the span B)
- 1200.00 mm
- Construction
- Monolithic
- Glass type
- Annealed (AN)
- Nominal thickness
- 5 mm
- Glass thickness, t
- 4.80 mm (Table 4.1 minimum)
- Ultimate pressure, Pu
- 2.80 kPa
- Serviceability pressure, Ps
- 2.80 kPa
- Load
- Wind, c3 = 1.00
Calculations
- Glass area, A
- 1.44 m²
- Aspect ratio, AR
- 1.00
- Span, B
- 1200.00 mm
- Minimum thickness, t (Table 4.1)
- 4.80 mm
- Glass type factor, c1 (Table 3.1)
- 1.00
- Surface factor, c2 (Table 3.2)
- 1.00
- Pressure in the formula, P = Pu / c2
- 2.80 kPa
- k1, k2, k3, k4 at AR 1.00 (Figure 4.3)
- 2527.1, 0.228312, −0.6124, 7.2
- B at AR 1.00 = k1 (P + k2) to the power k3, plus k4
- 1289.34 mm
- Allowable span, Ballow
- 1289.34 mm
- Capacity pressure, Pu,cap
- 3.18 kPa
- B / Ballow
- 0.93
- Span over thickness, B/t
- 250.00
- k1, k2, k3, k4 of Figure 4.35, span/60, at AR 1.00
- 603.79, −0.1, −0.5247, 1.64
- B/t at AR 1.00
- 360.19
- Allowable B/t at Ps (Figure 4.35, span/60)
- 360.19
- Capacity pressure, Ps,cap
- 5.54 kPa
Strength and deflection: AS 1288 Section 4 formulas (printed constants, Figures 4.1 to 4.35).
Section 3 plate solver: Ballow 1262.02 mm (2.1 percent lower), allowable B/t 361.13 (0.3 percent higher).
Allowable span, Ballow (strength). Section 3: peak stress S* = 27.80 MPa at Pu = 2.80 kPa, capacity φ c1 c2 c3 f′t = 29.96 MPa (φ 0.67, c1 1.00, c2 1.00, c3 1.00, f′t 44.71 MPa at the edge, t = 4.80 mm); S* / capacity = 0.93.
Allowable B/t at Ps (deflection). Section 3: deflection at the center of the glass w = 14.29 mm at Ps = 2.80 kPa, ≤ span/60 = 20.00 mm.
Outputs
Strength PASS. Deflection PASS.
Strength: B = 1200.00 mm ≤ Ballow = 1289.34 mm at Pu = 2.80 kPa; B/Ballow = 0.93.
Capacity: Pu,cap = 3.18 kPa.
Deflection: B/t = 250.00 ≤ allowable 360.19 at Ps = 2.80 kPa (span/60 basis).
Against the printed values
4 mm: GlassLoad.com Ballow 1044.16 mm, printed 1044 mm. Strength FAIL, printed FAIL. Deflection: B/t 315.79 against the allowable 360.19 (within), Ps,cap 3.57 kPa.
5 mm: GlassLoad.com Ballow 1289.34 mm, printed 1289 mm. Strength PASS, printed PASS. Deflection: B/t 250.00 against the allowable 360.19 (within), Ps,cap 5.54 kPa, printed B/t = 250 passes, the allowable Ps is about 5.6 kPa.
The standard prints whole millimeters and reads the allowable Ps of the deflection check from Figure 4.35. 3 mm is out by the area limit of 0.85 m².
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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