ASTM E1300 09a 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)
- 41.46 psf
- Glass type factor (GTF)
- 1.00
- Load resistance (LR)
- 41.46 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 (X2, R capped at 5)
- −3.44
- r1 (X2, R capped at 5)
- 2.34
- r2 (X2, R capped at 5)
- 0.27
- Center of glass deflection, w
- 0.45 in
- Allowable deflection
- w_allow = b/100 = 37.99/100 = 0.38 in
- Deflection to thickness ratio, w/t
- 2.04
- 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 09a Fig A1.6 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 210 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 09a Figure A1.6 printed chart; results vary by about 4.7 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 = 41.46 psf; p/LR = 0.91.
Deflection at CoG: w = 0.45 in > w_allow = 0.38 in (b/100, four edges supported).
CoG: center of glass
GlassLoad.com 0.45 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.
- W14
- Appendix X3 gives only an approximate method for Pb, for a 60 s load, so the value shown uses the failure model of E1300 24 Annex A2. Treat this Pb as approximate.
More examples are on the E1300 09a page and on the examples page. Open the calculator to run your own check.
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