ASTM E1300 24 Example 4: Center of glass deflection, 37.99 by 75.98 in, 1/4 in
Find the approximate center of glass deflection of a vertical 37.99 by 75.98 by 1/4 in plate under a uniform load of 37.59 psf.
Inputs
- Long dimension, a
- 75.98 in
- Short dimension, b
- 37.99 in
- Nominal thickness
- 0.236 in
- Glass type
- Annealed (AN)
- Load duration
- Short (3 second)
- Design load, p
- 37.59 psf
- Allowable deflection, w_allow
- b/100
- Glass thickness, t
- 0.219 in
- Thickness source
- Table 4 minimum
Calculations
- Glass area, A
- 20.05 ft²
- Aspect ratio, AR
- 2.00
- Load times area squared, p·A²
- 15.11 kip·ft²
- Non factored load (NFL)
- 41.48 psf
- Glass type factor (GTF)
- 1.00
- Load resistance (LR)
- 41.48 psf
- Nondimensional load, p̂ = p·(a·b)²/(E·t⁴)
- 91.11
- Modulus of elasticity, E
- 10,400 ksi
- x = ln(ln p̂)
- 1.51
- r0 (X1, R capped at 5)
- −3.44
- r1 (X1, R capped at 5)
- 2.34
- r2 (X1, R capped at 5)
- 0.27
- Center of glass deflection, w
- 0.44 in
- Deflection before rounding (E1300 X1.1.1)
- 0.440 in
- Allowable deflection
- w_allow = b/100 = 37.99/100 = 0.38 in
- Deflection to thickness ratio, w/t
- 2.01
- Load duration in Annex A2 (td)
- 3 s, (td / 3 s)^(7/16) = 1.00
- B (Annex A2, Eq A2.2)
- 0.005
- Pb = 1 − exp(−B)
- 0.005
NFL and deflection: E1300 24 Fig A1.7 chart.
Contours: NFL in psf, labelled on the chart. 1/4 in glass, four sides simply supported, 3 second load.
Glass sizes where the NFL is above 315 psf, result outside the scope of ASTM E1300.
Curves: center of glass deflection w for aspect ratio (AR) 1 to 5; highlighted: this aspect ratio.
Redrawn by GlassLoad.com based on the ASTM E1300 24 Figure A1.7 printed chart; results vary by about 2.3 percent.
Outputs
Strength PASS. Deflection FAIL.
Probability of breakage at the design load: 5.0 per 1000 (1 in 200).
Strength: p = 37.59 psf ≤ LR = 41.48 psf; p/LR = 0.91.
Deflection at CoG: w = 0.44 in > w_allow = 0.38 in (b/100, four edges supported).
CoG: center of glass
GlassLoad.com 0.44 in, printed 0.43 in. The standard printed 11 mm.
Notes
- W7
- Deflection w is read from the E1300 deflection chart and is approximate. Where deflection governs, verify it by an independent method.
- W10
- w is greater than t, so it is rounded to the nearest 0.04 in as E1300 requires. Where the rounding affects the outcome, verify the unrounded w independently.
More examples are on the E1300 24 page and on the examples page. Open the calculator to run your own check.
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