Floor Joist Capacity
Reference data and engineering information about floor joist capacity for piping systems applications.
Overview
Engineering reference data for Floor Joist Capacity in piping systems.
Key Formulas
Continuity
Mass conservation in pipe flow.
Pressure Drop
Darcy-Weisbach equation.
Pipe Area
Cross-sectional area of a pipe.
Variables
| Symbol | Description | Unit |
|---|---|---|
| Pipe diameter | m | |
| Flow velocity | m/s | |
| Pressure drop | Pa | |
| Friction factor | — |
Capacity Tables
The diagrams in the original document illustrate the maximum working loads for floor joists based on timber strength class (C18, C24, C30) and joist center spacing. The data for a working load of 3.0 kN/m² is summarized below.
Timber Grade | Capacity @ 300mm(kN/m²) | Capacity @ 400mm(kN/m²) | Capacity @ 450mm(kN/m²) | Capacity @ 600mm(kN/m²) |
|---|---|---|---|---|
| C18 | 3 | 2.7 | 2.4 | 2 |
| C24 | 3 | 3 | 2.8 | 2.4 |
| C30 | 3 | 3 | 3 | 2.8 |
Source: engineeringtoolbox.com
Design Considerations
The working load is the total load the joist is designed to carry under normal conditions, combining dead load (weight of structure) and imposed load (furniture, people, etc.).
Timber Strength Classes (C16, C18, C24, C30) are defined in Eurocode 5 (EN 1995-1-1) and British Standard BS 5268. They categorize softwood lumber based on characteristic values for bending strength, stiffness, and density.
- *C18 and *C24 are the most common structural grades.
- Higher class numbers indicate stronger, stiffer timber. For example, C24 has higher strength and stiffness properties than C18.
The allowable span or capacity for a given load is highly sensitive to the joist center spacing. Closer spacing (e.g., 300mm) distributes the load over more joists, increasing the total capacity per square meter compared to wider spacing (e.g., 600mm).