Enter the load, length, modulus of elasticity, and moment of inertia into the calculator to determine the deflection.

## 80/20 Deflection Formula

The following formula is used to calculate the deflection in an 80/20 beam.

D = (5 * W * L^4) / (384 * E * I)

Variables:

- D is the deflection of the beam (inches) W is the load applied to the beam (pounds) L is the length of the beam (inches) E is the modulus of elasticity of the material (psi) I is the moment of inertia of the beam’s cross-section (in^4)

To calculate the deflection of the beam, multiply the load applied to the beam by the fourth power of the length of the beam, then multiply the result by 5. Divide this result by the product of 384, the modulus of elasticity of the material, and the moment of inertia of the beam’s cross-section.

## What is an 80/20 Deflection?

An 80/20 deflection refers to a principle in structural engineering where a structure or material is designed to withstand up to 80% of its maximum load capacity, leaving a 20% margin for safety or unexpected additional stress. This principle ensures that structures are not operating at their maximum capacity, thereby reducing the risk of failure or collapse. The term “deflection” refers to the degree to which a structural element is displaced under a load.

## How to Calculate 80/20 Deflection?

The following steps outline how to calculate the 80/20 Deflection using the given formula.

- First, determine the load applied to the beam (W) in pounds.
- Next, determine the length of the beam (L) in inches.
- Next, determine the modulus of elasticity of the material (E) in psi.
- Next, determine the moment of inertia of the beam’s cross-section (I) in in^4.
- Next, gather the formula from above = D = (5 * W * L^4) / (384 * E * I).
- Finally, calculate the 80/20 Deflection.
- After inserting the variables and calculating the result, check your answer with the calculator above.

**Example Problem : **

Use the following variables as an example problem to test your knowledge.

load applied to the beam (W) = 100 pounds

length of the beam (L) = 50 inches

modulus of elasticity of the material (E) = 2000000 psi

moment of inertia of the beam’s cross-section (I) = 500 in^4