Foundation beam introduction
A foundation beam on concrete piles are used when the soil can’t support direct foundations. The piles transfer the load to deeper, stronger soil layers.
In standard structural analysis, the beam is treated as continuous under an uniform load. This assumes all supports are infinitely stiff and has sufficient capacity. In reality, each pile’s capacity depends on soil conditions found in a geotechnical report.
This case is from a harbor project in Southwest Jutland, Denmark. Poor soil required pile foundations, but on-site tests showed lower capacity than first reported. Normally, more piles would be added — delaying the project and raising costs.
Instead, plastic analysis with PolyBeam was used to balance loads between piles without overloading them.
No extra piles were needed.
The result was a faster, cheaper, and more efficient solution.
Reaction Distribution - Elastic Analysis
In this project, the geotechnical report showed a compressive capacity of 635 kN per pile. The foundation beam carried a uniform line load of 135 kN/m, with piles spaced 4 m apart.
An elastic analysis, predicted maximum pile load of 617 kN — safely below the reported capacity.
However, on-site pile load tests told a different story: the maximum documented capacity was 595 kN.
Compounding the problem, the site’s location near the harbour placed it in an aggressive marine environment. Piles in an aggressive environment meant longer production time.
Adding more piles would have delayed the schedule significantly and driven up costs.
Reaction Distribution - Plastic Analysis
Instead of installing additional piles, the design team turned to a plastic analysis using PolyBeam. In this approach, a maximum compressive force of 580 kN was assigned to specific supports.
PolyBeam then automatically redistributed the excess load to the remaining piles, ensuring no pile exceeded its geotechnical capacity— without adding new piles.
Reaction Distribution on Piles -
Elastic vs Plastic Analysis
In the elastic analysis, several piles exceeded the field-tested capacity of 595 kN, with reactions reaching 617 kN.
In the plastic analysis, the reaction of some piles were limited to 580 kN, and the excess was redistributed to the other piles.
| Distance [m] | Elastic Analysis [kN] | Plastic Analysis [kN] | Comment |
|---|---|---|---|
| 0,0 | 212 | 224 | Slightly more load in plastic redistribution |
| 4,0 | 617 | 580 (max capacity) | Exceedance avoided |
| 8,0 | 501 | 552 | Slightly more load in plastic redistribution |
| 12,0 | 617 | 580 (max capacity) | Exceedance avoided |
| 16,0 | 212 | 224 | Slightly more load in plastic redistribution |
Conclusion
Plastic analysis with PolyBeam solved the foundation challenge. On-site test results were built into the design. Loads were redistributed so no pile was overloaded. No extra piles were needed. The project stayed on time and on budget.
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