IS 16231:2019 Annex D worked example: Annealed glass, 1200 by 1800 mm, Pnet 1.75 kPa

Find the thinnest annealed glass for a 1200 by 1800 mm pane on four edges under a net design wind pressure of 1.75 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 side, a: 1800.00 mm
Short side, b: 1200.00 mm
Construction: Monolithic
Glass type: Annealed (AN)
Nominal thickness, T: 6 mm Annealed (AN)
Pnet, net design wind pressure (clause 5.4): 1.75 kPa (1750 N/m²)
Serviceability pressure, Ps: 1.75 kPa (equal to Pnet)

Calculations

Glass area, A: 2.16 m²
Aspect ratio, AR: 1.50
Pnet in N/m²: 1750 N/m²

Strength (tables of clause 5.9)

Table and column: Table 6, annealed, four edges, column 6
Strength factor, Pf (Table 2): 1.00
Maximum aspect ratio, ARmax (Table 3): 6.3
Constant, c (fitted to Table 6): 4316.41 N
Allowable area from the table, A = c / Pnet: 2.47 m²
Area limit (clause 5.2 a): 15.00 m²
Allowable area, A_allow: 2.47 m²
A / A_allow: 0.88
Capacity pressure, Pcap: 2.00 kPa

Serviceability (Annex C, clause 7.6)

Thickness for Annex C, t (nominal thickness): 6.00 mm
Aspect ratio a / b in Annex C (capped at 5): 1.50
r0, r1, r2: −3.02154, 2.27011, 0.179325
q̄ = Ps (a b)² / (E t⁴): 87.87
X = ln ln q̄: 1.50
Deflection, w = t exp(r0 + r1 X + r2 X²): 13.13 mm
Limit, shortest span / 60 (clause 7.6.2 c): 20.00 mm
Limit, 19 mm (clause 7.6.2 c): 19.00 mm
Allowable deflection: 19.00 mm

Strength: IS 16231 (Part 3) Table 6 as one fitted constant per column (clauses 5.2 to 5.5, 5.9, 7.2 to 7.4).

Clause 5.3 relation: 2.70 m² (9.5 percent higher).

Plate solver with Table 15: 4.29 m² (74.0 percent higher).

Deflection: IS 16231 Annex C formula.

Allowable area, A_allow (strength). Table 15 (clause 7.7): face stress 20.38 MPa against 36.20 MPa away from the edge, edge stress 17.07 MPa against 28.96 MPa at the edge, at Pnet = 1.75 kPa; utilization 0.59.

Deflection, w (serviceability). Annex C at Ps = 1.75 kPa; limit ≤ 19.00 mm (shortest span / 60 or 19 mm, clause 7.6.2 c). Glass that complies with Tables 6 to 14 is deemed to meet the deflection limit (clause 7.6.1).

Outputs

Strength PASS. Deflection PASS.

Strength: A = 2.16 m² ≤ allowable A = 2.47 m² at Pnet = 1.75 kPa; A/A_allow = 0.88.

Capacity Pcap = 2.00 kPa.

Deflection: w = 13.1 mm ≤ allowable 19.0 mm at Ps = 1.75 kPa (shortest span/60 or 19 mm).

Glass that complies with Tables 6 to 14 is deemed to meet the deflection limit (clause 7.6.1).

Against the standard

5 mm: GlassLoad.com A_allow 1.72 m² against A 2.16 m². Strength FAIL, the relation of clause 5.3 gives T = 5.28 mm for A = 2.16 m², so 5 mm is too thin. Deflection: w 16.8 mm against the limit 19.0 mm (within).

6 mm: GlassLoad.com A_allow 2.47 m² against A 2.16 m². Strength PASS, the book chooses 6 mm. Deflection: w 13.1 mm against the limit 19.0 mm (within).

Annex D prints a deflection of 4 mm and compares it with 10.3 mm, the mullion limit of clause 7.6.2 a. The Annex C formula applied to the same inputs gives about 13 mm for 6 mm, and clause 7.6.2 c gives a limit of 19 mm, so GlassLoad.com reports the deflection against 19 mm and does not reproduce the printed 4 mm. AR is exactly 1.5, so the rule of clause 5.2 c does not apply.

Notes

⚠ Deflection is calculated with the Annex C formula at Ps, because IS 16231 (Part 3) gives no separate serviceability pressure. Check the serviceability load that the project requires.

⚠ IS 16231 (Part 3) does not say which governs when the tables of 5.9 and the relation of 5.3 disagree, and GlassLoad.com assumed the tables, which allow less. Check which of the two the project authority accepts.

⚠ IS 16231 (Part 3) 5.4 does not say whether Pnet carries a load factor, and GlassLoad.com applied none to the Pnet entered, as Annex D does. Check that the Pnet entered is the ultimate limit state net design wind pressure of 5.4, determined to IS 875 (Part 3).

⚠ IS 16231 (Part 3) 5.3 prints less than 6 mm and more than 6 mm and leaves 6 mm open, and GlassLoad.com used the branch up to 6 mm, as 5.3.1 and Annex D print. Check the relation value in the method panel only as a comparison.

⚠ IS 16231 (Part 3) 5.3 c and Table 15 give different design strengths, and GlassLoad.com used Table 15 for the plate solver row of the method panel. Use that row as a comparison only.

⚠ IS 16231 (Part 3) Annex D prints a deflection that the Annex C formula does not give, compares it with the mullion limit of 7.6.2 a, and names one thickness for Annex C, so GlassLoad.com used the Annex C formula as printed, the limit of 7.6.2 c, the sum of the sheets for laminated glass and the thinner pane for insulating glass. Check the deflection against the limit that the project requires.

Open the calculator to run a check.

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