1. What is Wood Joist Deflection?

Wood joist deflection refers to the amount of bending or sagging that occurs in a wood joist under a uniform load. It is an important structural consideration in building design to ensure safety and serviceability.

2. How Does the Calculator Work?

The calculator uses the wood joist deflection formula:

Where:

• \( \delta_j \) — Deflection (mm)
• \( w \) — Uniform load (N/mm)
• \( L \) — Length of joist (mm)
• \( E \) — Modulus of elasticity (MPa)
• \( I \) — Moment of inertia (mm⁴)

Explanation: This formula calculates the maximum deflection at the center of a simply supported beam under uniform load.

3. Importance of Deflection Calculation

Details: Proper deflection calculation is crucial for structural integrity, preventing excessive sagging, and ensuring compliance with building codes and safety standards.

4. Using the Calculator

Tips: Enter uniform load in N/mm, length in mm, modulus of elasticity in MPa, and moment of inertia in mm⁴. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is acceptable deflection for wood joists?
A: Typically, deflection should not exceed L/360 for live loads and L/240 for total loads, where L is the span length.

Q2: How does moisture affect wood deflection?
A: Moisture can reduce wood's modulus of elasticity, potentially increasing deflection over time.

Q3: What are typical E values for wood?
A: Modulus of elasticity varies by wood species: Pine ~8,000-13,000 MPa, Oak ~10,000-12,000 MPa, Douglas Fir ~13,000 MPa.

Q4: How to calculate moment of inertia?
A: For rectangular sections, I = (b × h³)/12, where b is width and h is height/depth.

Q5: Does this formula work for other materials?
A: Yes, the formula applies to any homogeneous, isotropic material behaving elastically under load.