Glass Deflection Calculator

The Glass Deflection Calculator is a structural engineering tool used to determine how much a glass panel will bend or sag under a given load. This calculation is essential in architecture, construction, and safety engineering because excessive deflection can lead to breakage, distortion, or reduced performance. By understanding the expected deflection, engineers can select the right glass thickness, type, and support design to ensure safety and durability.

This tool falls under the category of structural engineering and safety calculation tools.

formula

Main formula for a simply supported glass panel under uniform load

D = (P × L³) ÷ (48 × E × I)

Where:
D: Deflection of the glass panel
P: Load or pressure applied to the glass (in N/m² or Pa)
L: Length of the glass panel between supports (in meters)
E: Modulus of elasticity of the glass (approx. 70 GPa for most glass)
I: Moment of inertia of the glass panel’s cross-section (depends on glass thickness and width)

Moment of Inertia formula for rectangular glass cross-section

I = (b × h³) ÷ 12

Where:
b: Width of the glass panel (in meters)
h: Thickness of the glass panel (in meters)

How the Calculation Works

1. First, determine the dimensions and thickness of the glass.
2. Calculate the moment of inertia (I) using its formula.
3. Insert values for load (P), length (L), modulus of elasticity (E), and moment of inertia (I) into the main deflection formula.
4. The result shows how much the glass will bend under the given load.

General Glass Deflection Reference Table

Below is an approximate reference for deflection in millimeters for common glass sizes under a uniform load of 500 N/m², with E = 70 GPa.

Length (m) | Thickness (mm) | Deflection (mm)
1.0 | 6 | 0.62
1.0 | 8 | 0.26
1.5 | 6 | 2.09
1.5 | 8 | 0.87
2.0 | 6 | 4.97
2.0 | 8 | 2.07

Note: These are sample values for illustration. Exact results depend on actual load, dimensions, and support conditions.

Example

Suppose we have a glass panel with:

Length L = 1.5 m
Width b = 1 m
Thickness h = 0.008 m (8 mm)
Load P = 500 N/m²
E = 70 × 10⁹ Pa

Step 1: Calculate moment of inertia

I = (1 × 0.008³) ÷ 12 = 4.27 × 10⁻⁸ m⁴

Step 2: Apply main formula

D = (500 × 1.5³) ÷ (48 × 70 × 10⁹ × 4.27 × 10⁻⁸)
D ≈ 0.00087 m or 0.87 mm

Result: The glass will deflect approximately 0.87 mm under the given load.

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