What is a lattice girder slab with EPS infill?
This is a variant of the lattice girder (biscuit) slab: a precast soffit plank with blocks or strips of EPS — expanded polystyrene — set on top as void formers. In the Netherlands the system is sold as a polyplaatvloer (PPV).
The EPS blocks occupy the zone where concrete does little structural work. What remains is effectively a ribbed slab: concrete ribs between the void formers, with a continuous structural topping above. Self-weight drops as a result — depending on the arrangement, in the order of up to 30 per cent compared with a solid equivalent.
Build-up
- The precast plank is cast in the factory and contains the bottom reinforcement. On site it acts as permanent formwork.
- Lattice girders project from the plank. They provide the composite action between the precast plank and the concrete poured later, and stiffen the plank during transport and erection.
- EPS void formers sit between the lattice girders.
- On site the top reinforcement is placed and the structural topping is poured. Only then does the floor act as a composite section.
Advantages
- Lighter. Less self-weight means less reinforcement, lighter beams and a lighter foundation.
- Less concrete. That saves material, deliveries and embodied carbon.
- Greater span at the same weight, or a thinner floor at the same span.
- Fast erection and an immediately walkable working platform.
Points to watch
- Propping. Until the topping has gained strength, the plank does not span on its own. The supplier’s propping layout governs; striking props too early is a classic cause of damage.
- Reinforcement across the joints. In this floor type the reinforcement across the joints between planks is structurally critical. Following the 2017 collapse of a car park under construction in Eindhoven, this detail has been scrutinised far more closely. Leave it to the structural engineer.
- Drilling and fixing. There is not concrete everywhere in this floor. An anchor that lands in an EPS block holds nothing. Ask the supplier for a rib layout before installing heavy hangers or pipe brackets.
- Services. Openings and penetrations must be declared in advance; cutting into the ribs afterwards is not structurally acceptable as a matter of course.
- Soffit. The underside is the precast plank and therefore nicely flat, but the joints remain visible. For an exposed soffit that is a deliberate decision.
Related terms
- Lattice girder slab
- Precast floor
- EPS
- Structural topping
- Ribbed slab
- Polystyrene
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