Understanding Load Capacity
Pallet rack load capacity is not a single number. A complete capacity assessment involves three separate calculations:
- Beam capacity: How much weight a pair of beams can support
- Upright capacity: How much total weight the frame can carry
- Bay capacity: Limited by the lesser of beam and upright capacities
Beam Capacity Calculation
Basic Formula
Beam capacity depends on three factors:
- Beam profile: Section modulus and moment of inertia
- Span: Distance between uprights
- Load distribution: Point load vs. uniform load
For a standard 2,700mm beam carrying two pallets:
- Each pallet applies a point load at approximately 1/3 and 2/3 of the span
- The manufacturer provides a load table based on testing per FEM or RMI standards
Deflection Check
Even if the beam is within its load capacity, check deflection:
- Maximum allowable deflection = Span / 200
- For a 2,700mm beam: 2,700 / 200 = 13.5mm maximum deflection
Upright Capacity Calculation
Factors Affecting Upright Capacity
- Section profile: Cross-section geometry and steel thickness
- Effective length: Distance between brace points (not floor to top)
- Axial load: Total weight from all beams connected to the upright
- Bending moments: From eccentric beam connections and potential seismic forces
- Number of levels: More levels means more bracing points but more load
Effective Length Calculation
The effective length (K x L) determines the buckling behavior:
- K = effective length factor (typically 1.0 for standard configurations)
- L = distance between consecutive bracing points
Safety Factors
Standards apply partial safety factors:
| Load Type | Safety Factor | Description |
|---|---|---|
| Dead load | 1.1-1.35 | Self-weight of racking structure |
| Pallet load | 1.15-1.5 | Variable depending on load type |
| Seismic | 1.0-1.3 | Reduced for seismic combination |
Practical Example
A 4-level selective rack, 2,700mm beam spans, storing 1,000kg pallets:
Per beam pair: 2 x 1,000kg = 2,000kg (verify against beam load table)
Per upright: 4 levels x 2 beam pairs x 1,000kg = 8,000kg total (verify against upright capacity table)
Per bay: Limited by whichever is lower (beam or upright capacity)
Always use the manufacturer's certified load tables. These calculations are simplified for understanding - actual design requires professional engineering assessment.