1. What is the Lag Screw Withdrawal Strength Formula?

The Lag Screw Withdrawal Strength formula calculates the force required to pull a lag screw out of wood. It estimates the screw's holding power based on diameter, length, and the specific gravity of the wood.

2. How Does the Calculator Work?

The calculator uses the withdrawal strength formula:

Where:

• \( D \) — Screw diameter (inches)
• \( L \) — Screw length (inches)
• \( SG \) — Specific gravity of wood (dimensionless)
• \( \pi \) — Mathematical constant (approximately 3.1416)
• 540 — Empirical constant for wood

Explanation: The formula accounts for the screw's dimensions and the density of the wood material to estimate withdrawal resistance.

3. Importance of Withdrawal Strength Calculation

Details: Accurate withdrawal strength estimation is crucial for structural design, ensuring screws provide adequate holding power for safety and performance.

4. Using the Calculator

Tips: Enter screw diameter and length in inches, and specific gravity value. All values must be valid positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is specific gravity in wood?
A: Specific gravity is the ratio of wood density to water density, indicating the wood's density and strength properties.

Q2: How accurate is this formula?
A: This provides an empirical estimate. Actual performance may vary based on wood species, moisture content, and installation quality.

Q3: What are typical SG values for common woods?
A: Softwoods: 0.3-0.5, Hardwoods: 0.5-0.7, Dense hardwoods: 0.7-0.9

Q4: Can this be used for other fastener types?
A: This formula is specifically designed for lag screws in wood. Other fasteners may require different calculations.

Q5: What safety factors should be applied?
A: Engineering applications typically apply safety factors of 2-4 depending on the criticality of the connection.