What is a lattice girder?
A lattice girder is a three-dimensional truss made of reinforcing steel or prestressing steel. It consists of at least two bottom chords, one top chord and zigzag diagonals that connect them, all spot-welded together. In section, a lattice girder is therefore triangular. In Dutch it is called a tralieligger.
Use in lattice girder slabs
The best-known application is the lattice girder slab, also called a filigree or half-slab floor. This is a precast concrete plank only a few centimetres thick, which is topped up on site with a layer of in-situ concrete.
- The bottom chords of the lattice girder are cast into the plank at the factory and count as bottom reinforcement.
- The top chord and the diagonals project above the plank.
- On site, supplementary and top reinforcement is laid on or between the girders, after which the structural topping is poured.
What it does
- Stiffness during transport and installation: without lattice girders the thin plank could hardly be lifted or span between supports.
- Bond between precast and in-situ concrete: the diagonals tie both layers together so they act as one slab.
- Spacer: the top chord supports the top reinforcement at the correct height.
The term is also used for flat steel or aluminium trusses in scaffolding and stage building, used to create larger spans under light loads.
Points to watch
- Lattice girders are part of the structural design of the floor. Never deviate from the layout and reinforcement drawings.
- During construction, the planks must be propped as specified by the supplier until the topping is strong enough.
- Do not walk on the diagonals or damage the welds; bent girders lose capacity.
- Only form openings for services where the structural engineer has allowed for them.
Related terms
- Filigree
- Supplementary reinforcement
- Top reinforcement
- Reinforcement
- Lattice girder slab with EPS infill
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