Understanding Girders
Girders are primary horizontal support beams that carry loads from multiple floor joists, walls, or other structural elements.
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Types of Girders
- Solid Sawn: Traditional lumber beams
- Built-up: Multiple pieces fastened together
- Engineered: LVL, PSL, or Glulam beams
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Load Types
- Dead Loads: Permanent structural weight
- Live Loads: Occupancy and movable loads
- Point Loads: Concentrated forces
Technical Specifications
Wood Properties
- Douglas Fir: Fb = 1500 psi
- Southern Pine: Fb = 1350 psi
- Spruce-Pine-Fir: Fb = 1100 psi
Design Values
- Max Deflection: L/360
- Safety Factor: 2.0
- Load Duration: 1.0 (normal)
Design Formulas
Bending Moment
M = (w × L²) / 8
Where:
- M = Maximum bending moment
- w = Uniform load per unit length
- L = Span length
Deflection
Δ = (5 × w × L⁴) / (384 × E × I)
Where:
- Δ = Maximum deflection
- E = Modulus of elasticity
- I = Moment of inertia
Shear Force
V = (w × L) / 2
Where:
- V = Maximum shear force
- w = Uniform load
- L = Span length