Swap-Body Chassis Optimization

A 6.2 m steel swap-body flat, redesigned around a single guiding principle: remove mass only where it isn't carrying load, and never interrupt the structure's main load-bearing chain. The result was a custom interlocking cross-member architecture, fully welded rather than bolted, that let the chassis shed nearly half its mass while keeping its primary bending stiffness intact.

Every iteration of the design was validated by FEM against the same set of realistic pallet-loading scenarios, confirming that the lighter structure carried load just as predictably as the original.

The design philosophy centred on one rule above all others: the load chain must stay unbroken. Cross-members were designed to slot directly into precision-cut openings in the longitudinal beams and be fully welded in place, eliminating bolted connections entirely, reducing part count, and maximising structural continuity through every joint. Just as important was where material was not removed: no cut-outs were introduced in the high-inertia zones of the longitudinal beams themselves, so the chassis's primary bending load path stayed fully continuous throughout every mass-reduction step, and stiffness could be transmitted along the full length of the structure exactly as it was in the original design.

Starting from a 1091 kg baseline built largely from solid plate sections, the redesign proceeded through successive iterations. The first replaced solid plate with the interlocking welded cross-member architecture and upgraded the steel grade from S235 to S355, allowing thinner walls at equivalent strength and cutting mass to 612 kg. A further iteration removed additional material from regions identified as carrying genuinely low stress, while explicitly preserving full longitudinal beam continuity, and reduced the MDF deck panel thickness from 27 mm to 21–22 mm — bringing the final design down to 579 kg, a 46.9% reduction from the original baseline.

Each iteration was checked under three load cases run on a full FEM model: self-weight alone, as a baseline stiffness check; a symmetric working load of four 2,000 kg pallets distributed evenly across the flat; and a worst-case eccentric case with two 2,000 kg pallets concentrated at the corner furthest from the forklift support points, representing the governing tipping and bending scenario. Under self-weight, the optimised designs actually outperformed the heavier baseline. Under the eccentric case, deflection increased with each mass-saving step, but the overall pattern of deflection and stress distribution stayed consistent across all three designs rather than degrading structurally — direct evidence that the interlocking cross-member philosophy was doing its job of keeping stiffness distributed through the structure even as material came out.

High localised stress values did appear in the results under concentrated pallet loading, but were identified as mesh-singularity artefacts at weld and contact geometry rather than genuine bulk material failure — the stress contour maps showed the overwhelming majority of each structure remaining at low stress throughout every load case. Because the load path through the longitudinal beams had been kept deliberately continuous by design, that bulk structural response held steady across all three mass-reduction iterations, meaning any remaining local exceedances under concentrated loads could be managed through pallet placement guidance rather than requiring a structural rework.