Typically, we require our customers' factory floors to have a load-bearing capacity of at least 5 tons per square meter. While most sites meet this requirement, many clients often ask how this value is calculated. Below, we present a real-world case study to explain the process.
Case Study
This project involves a new factory construction site that required the procurement of a 30-ton trackless transfer cart. The workshop floor had already been fully hardened. Since this was a state-owned enterprise project-which generally involves strict execution standards-several independent teams were commissioned to conduct a full structural stress analysis.
I. Technical Specifications of the Factory Workshop
Ground Foundation Structure:
A 150mm-thick crushed stone aggregate layer, grouted with M2.5 mortar and compacted by vibration.
A 0.6mm polyethylene film used as a moisture barrier.
A 20mm-thick 1:3 cement mortar protective layer.
A 150mm-thick C30 concrete slab, poured and leveled in one continuous operation. After reaching the required strength, the surface was ground smooth.
The slab is reinforced with double-layer, bi-directional Ø8 steel bars spaced at 200mm × 200mm intervals on both the top and bottom layers (with a characteristic foundation bearing capacity value, fak, of ≥100 kPa).
One coat of solvent-free epoxy primer.
A 2mm-thick self-leveling epoxy flooring layer.
Load-Bearing Capacity Analysis of the 150mm C30 Concrete Slab (Based on National Standards)
The standard compressive strength of C30 concrete is 30 MPa, meaning each square centimeter can withstand approximately 306 kg of compressive force.
For a concrete slab with a thickness of 15 cm (0.15 m), the load-bearing capacity per unit area is calculated as follows:
Theoretical Calculation:
30 MPa = 30 × 10⁶ N/m²
Converting force into mass units (1 N ≈ 0.102 kg):
30 × 10⁶ × 0.102 ≈ 3,060,000 kg/m² (≈ 306 tons/m²)
However, this value represents the ultimate compressive strength of the material. Therefore:
306 tons/m² × 0.15 m ≈ 46 tons/m²
II. Specifications for the Transfer Cart's Load-Bearing Wheels
Wheel Configuration of the Mobile Load-Bearing Platform:
Bottom wheel arrangement:
6 idler wheels (diameter 300 mm × width 240 mm)
2 drive wheels (diameter 450 mm × width 300 mm)
Load-bearing contact area calculation for idler wheels and drive wheels:
Theoretical Calculation Method 1 - Simplified Rectangular Contact Model
(based on the finite element analysis method of the steel platform)
The wheel-ground contact area is assumed to be rectangular, with a contact length L and contact width b.
The length L and the width b satisfy:
Contact Area:
Where:
k = tread coefficient (k = 1 for smooth surfaces; k = 0.7–0.9 for treaded surfaces)
E = elastic modulus of polyurethane (must be confirmed through material testing; typical range: 10–100 MPa)
Contact area for the 6 idler wheels (Φ300 mm × b 240 mm):
Contact area for the 2 drive wheels (Φ450 mm × b 300 mm):
Total wheel-ground contact area of the platform:
≈ 0.47 m² + 0.13 m² = 0.6 m²
Based on the foundation capacity (150mm C30 concrete ≈ 46 tons/m²), the overall load-bearing capacity supported by the wheel contact area is:
46 tons/m² × 0.6 m² = 27.6 tons
Conclusion for the Wheel Load-Bearing Design
The designed rated load capacity of the transfer cart is 20 tons. The calculated load-bearing capacity supported by the wheel contact area is approximately 27.6 tons.
Since the calculated value exceeds 1.3 times the rated load capacity, the wheel design of the mobile load-bearing platform meets the required load-bearing standards.
