Lattice Girders Explained
Lattice girders (Gitterträger) are prefabricated steel reinforcement assemblies that combine structural efficiency with speed of construction. They are the backbone of filigree slab systems and precast-to-in-situ composite floor construction across Europe. This guide explains geometry, grades, applications, and procurement.
What Is a Lattice Girder?
A lattice girder (German: Gitterträger) is a prefabricated, three-dimensional reinforcement assembly comprising two or three longitudinal chord bars connected by a continuous diagonal (lattice) bar welded in a zigzag pattern. The resulting truss geometry provides substantial bending stiffness relative to the weight of steel used, making lattice girders ideal for spanning precast concrete elements over formwork or between walls during construction.
In the most common application — the filigree composite slab (Filigrandecke) — lattice girders are embedded in a thin precast concrete base plate (typically 50–80 mm thick) produced in a factory. On site, the girder tails projecting above the base plate are encased in cast-in-situ concrete to form a composite structural floor. The girder transfers shear between the two layers and ensures composite action per EN 1992-1-1 (Eurocode 2).
Lattice Girder Geometry and Key Dimensions
| Parameter | Typical Range | Notes |
|---|---|---|
| Overall height (H) | 60–400 mm | Governs composite slab depth and formwork span |
| Top chord diameter | 8–14 mm (B500B) | Primary compression/tension element |
| Bottom chord diameter(s) | 2 × 8–16 mm (B500B) | Two parallel bars; carry bottom flexural steel |
| Lattice (diagonal) bar | 5–8 mm (B500A) | Continuous welded zigzag; provides shear capacity |
| Width (centre-to-centre bottom chords) | 100–150 mm | Standard widths: 100, 110, 120, 150 mm |
| Standard delivery lengths | 1.0–12.0 m | Cut to order; 6 m and 12 m most common |
The two longitudinal chord bars are typically grade B500B (high ductility, minimum yield 500 MPa, k ≥ 1.08, Agt ≥ 5.0%). The diagonal bar is commonly B500A (normal ductility), which has adequate ductility for shear-transfer without requiring the more demanding B500B specification at that cross-section. Welded connections between the diagonal and chord bars comply with DIN EN ISO 17660 for welding of reinforcing steel.
Structural Role in Filigree and Precast Systems
Lattice girders serve three structural functions simultaneously:
- Construction-stage spanning: the girder stiffens the thin precast base plate so it can span between temporary props (or directly between walls/beams) during concrete pour without excessive deflection or cracking.
- Shear connection: the diagonal bar legs projecting above the precast plate transfer horizontal shear between the precast layer and cast-in-situ topping, enabling full composite action. Shear capacity is calculated per EN 1992-1-1 clause 6.2.5.
- Flexural reinforcement: the bottom chord bars contribute to the positive moment capacity of the finished composite slab, reducing the quantity of additional bottom bars required.
For precast concrete producers, lattice girders are a critical supply item. Standardised girder heights — commonly 60, 80, 100, 120, 150, 200 mm — map directly to finished slab depths. Selecting the wrong height results in inadequate concrete cover or constructional depth conflicts with services.
Grades, Standards, and Quality Assurance
Lattice girders produced in Germany are typically welded from bars conforming to DIN 488 (parts 1 and 2 for bar, part 4 for welded mesh — the welded connections follow equivalent principles) and EN 10080. The finished assemblies are not a standalone DIN product type, but are governed by general reinforcement fabrication standards and the relevant European Technical Assessment (ETA) or national technical approval document (allgemeine bauaufsichtliche Zulassung, abZ) that covers their use in filigree slabs.
Quality assurance documentation for exported lattice girders includes:
- Mill Test Certificates (EN 10204 3.1) for chord and diagonal bar coils/rods
- Weld inspection records (visual and, where specified, destructive peel/bend tests)
- Dimensional inspection reports (height H, width, chord diameters, weld spacing)
- Certificate of Origin for customs and preferential trade purposes
Procurement: What to Specify When Ordering
A complete lattice girder specification for procurement should state:
- Girder height H (mm) — select from standard range or specify custom
- Top chord and bottom chord bar diameters (mm)
- Diagonal bar diameter (mm)
- Width between bottom chord centrelines (mm)
- Delivery length (m) or cut-to-length schedule
- Steel grade: B500B chords / B500A diagonal (or all-B500B if project specification requires)
- Quantity in linear metres or pieces
- Applicable ETA or project technical approval reference
Steel Rebar Germany supplies lattice girders cut to the lengths specified in your project schedule, bundled and labelled for direct use in precast production or on-site slab pours. Export packing in seaworthy bundles with full documentation ensures compliance at destination ports. Contact us via the quote form with your schedule and we will confirm lead time and pricing.
Frequently Asked Questions: Lattice Girders
What is the difference between a lattice girder and a reinforcing mesh?
What concrete cover is required for lattice girder bottom chords?
Can lattice girders be used for walls and columns as well as slabs?
What standard governs the welding of lattice girders?
Are custom lattice girder heights available?
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