ASTM E1300 24 Example 5: Center of glass deflection, 60 by 180 in, 3/8 in
Find the approximate center of glass deflection of a vertical 60 by 180 by 3/8 in plate under a uniform load of 20 psf.
Inputs
- Long dimension, a
- 180.00 in
- Short dimension, b
- 60.00 in
- Nominal thickness
- 0.394 in
- Glass type
- Annealed (AN)
- Load duration
- Short (3 second)
- Design load, p
- 20.00 psf
- Allowable deflection, w_allow
- b/100
- Glass thickness, t
- 0.355 in
- Thickness source
- Table 4 minimum
Calculations
- Glass area, A
- 75.00 ft²
- Aspect ratio, AR
- 3.00
- Load times area squared, p·A²
- 112.50 kip·ft²
- Non factored load (NFL)
- 25.38 psf
- Glass type factor (GTF)
- 1.00
- Load resistance (LR)
- 25.38 psf
- Nondimensional load, p̂ = p·(a·b)²/(E·t⁴)
- 97.95
- Modulus of elasticity, E
- 10,400 ksi
- x = ln(ln p̂)
- 1.52
- r0 (X1, R capped at 5)
- −3.56
- r1 (X1, R capped at 5)
- 1.25
- r2 (X1, R capped at 5)
- 0.88
- Center of glass deflection, w
- 0.52 in
- Deflection before rounding (E1300 X1.1.1)
- 0.512 in
- Allowable deflection
- w_allow = b/100 = 60.00/100 = 0.60 in
- Deflection to thickness ratio, w/t
- 1.44
- Load duration in Annex A2 (td)
- 3 s, (td / 3 s)^(7/16) = 1.00
- B (Annex A2, Eq A2.2)
- 0.002
- Pb = 1 − exp(−B)
- 0.002
NFL and deflection: E1300 24 Fig A1.9 chart.
Contours: NFL in psf, labelled on the chart. 3/8 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 A1.9 printed chart; results vary by about 0.0 percent.
Outputs
Strength PASS. Deflection PASS.
Probability of breakage at the design load: 1.6 per 1000 (1 in 610).
Strength: p = 20.00 psf ≤ LR = 25.38 psf; p/LR = 0.79.
Deflection at CoG: w = 0.52 in ≤ w_allow = 0.60 in (b/100, four edges supported).
CoG: center of glass
GlassLoad.com 0.52 in, printed 0.52 in.
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.
GlassLoad.com is an independent tool and is not affiliated with ASTM.