Lattice Girder (Filigree) Slabs Explained

What Is a Lattice Girder (Filigree) Slab?

A lattice girder slab — known in German as Filigrandecke or Halbfertigdecke (semi-precast slab) — is a composite floor system consisting of two elements cast and assembled together:

• Precast concrete base slab (typically 50–80 mm thick): thin, factory-cast concrete panel containing the bottom mat of reinforcing steel. This panel is the permanent formwork for the structure.
• Lattice girders (Gitterträger): welded steel space trusses partially embedded in the precast base, projecting above its top surface. They stiffen the panel for transport and handling, and act as shear connectors between the precast and in-situ concrete.
• In-situ concrete topping: cast on site after the panels are placed and propped. The topping bonds monolithically with the precast base via the lattice girders, creating the full composite slab section.

The finished composite slab behaves as a monolithic reinforced concrete floor under service loads, with the structural advantages of controlled precast quality and the economy of site-cast flexibility.

Lattice Girder Geometry and Steel Specification

The lattice girder is the defining element. A standard Gitterträger consists of:

The diagonal wire geometry must ensure adequate shear transfer between the two concrete layers. The weld quality between diagonals and chords is governed by DIN EN ISO 17660 (welding of reinforcing steel). For export projects, girder dimensions and steel grades are confirmed on the Mill Test Certificate and project drawing package.

Construction Process: From Factory to Topping Pour

The construction sequence for a filigree slab is highly systematic:

1. Factory production: The precast panel is cast with the bottom reinforcement mat and lattice girders in a controlled environment. Concrete quality, reinforcement placement, and cover are all factory-controlled.
2. Transport and delivery: Panels are transported to site in stacks. Typical panel size is up to 6.0 × 2.3 m (limited by transport restrictions); larger floor areas use multiple panels butted together.
3. Erection and propping: Panels are crane-lifted into position and propped at regular intervals (typically every 1.5–2.0 m) until the topping concrete reaches sufficient strength. The lattice girders carry construction loads without excessive deflection.
4. Additional reinforcement placement: Top reinforcement mats, distribution bars, and any additional structural reinforcement are placed on top of the panels before the topping pour.
5. Topping pour: In-situ concrete is cast to complete the slab thickness. The lattice girders ensure monolithic composite action. Props are struck after the composite slab reaches design strength.

Structural Benefits and Design Considerations

Lattice girder slabs offer several structural and construction advantages compared to fully in-situ or fully precast alternatives:

• Permanent formwork: no temporary soffit formwork required, reducing site labour and crane time.
• Factory quality: controlled concrete curing and reinforcement placement in the tension zone, where quality is most critical.
• Composite action: the lattice girders provide reliable shear transfer, verified by design calculation under EN 1992-1-1 (Eurocode 2) composite slab provisions.
• Speed: multiple panels can be placed in a single crane cycle; topping can be poured floor-by-floor without waiting for full conventional formwork.
• Flexibility: slab thickness, span, and reinforcement can be varied panel by panel within a floor to suit loads and geometry.

For applications in precast concrete construction more broadly, see our precast concrete applications page and the lattice girder product page.

Related Resources