Timber Span Basics
Bending: M = wL^2/8, S = bd^2/6, Fb = M/S
Deflection: d = 5wL^4 / (384EI), I = bd^3/12
Key Factors
- Species and grade determine allowable stress and stiffness
- Deeper members span farther - doubling depth doubles the span
- Closer spacing allows slightly longer spans
- Live load varies by occupancy type and jurisdiction