← All systems
Technical sheet
A.01A.02
SystemS-62

Timber-concrete composite floor

A floor in which timber boards or beams act together with a thin concrete slab, joined by shear connectors. The timber works in tension below, the concrete in compression above: together they make a section far stiffer and stronger than timber alone. It is the foremost technique for strengthening existing timber floors - more capacity, less vibration, a rigid diaphragm - without demolishing them.

SolaioComposite timber + collaborating slab floor
B.01
System build-up6 layers
piano superioreintradosso a vista1. Soletta collaborante (c.a.)2. Connettore a taglio3. Rete elettrosaldata4. Tavolato / interposto5. Trave di legno6. Pavimento + massetto

Technical section of the system, from inside (left) to outside (right).

Composite timber + collaborating slab floor
Soletta collaborante
5-6cm
Connettori
viti inclinate / pioli
Luce tipica
4-7m
Incremento rigidezza
3-4x (vs solo legno)
Peso aggiunto
120-180kg/m2
Piano rigido
si (diaframma)
Descriptive memo

A floor in which timber boards or beams act together with a thin concrete slab, joined by shear connectors. The timber works in tension below, the concrete in compression above: together they make a section far stiffer and stronger than timber alone. It is the foremost technique for strengthening existing timber floors - more capacity, less vibration, a rigid diaphragm - without demolishing them.

The timber-concrete composite floor couples a timber element - the beams or boards of an existing floor, or new members - to a concrete slab cast on top, made integral by connectors. It is not a simple superposition: the two materials act together as a single composite section.

Two materials, each in its place

Under load a floor bends: the bottom fibres go into tension, the top into compression. Timber is excellent in tension and light; concrete is excellent in compression. Putting the timber below and the slab above, each works where it performs best. The result is a much deeper, stiffer section that cuts deflection and vibration and greatly increases capacity.

The connector: it all happens there

For the two parts to act together, slip at the interface must be prevented: that is the job of the connectors - inclined screws, dowels, plates or trusses - that stitch timber and concrete. The stiffness of the connection decides how truly composite the section is: a stiff connection brings the behaviour close to theory, a soft one reduces the gain. It is the detail that makes or breaks the system.

Restoration, rigid diaphragm, seismic

Its chosen field is the strengthening of historic timber floors: the timber is kept exposed at the soffit and the slab is added above, gaining capacity and stiffness with a reversible and relatively light intervention. The reinforced slab, well tied to the walls, also creates a rigid diaphragm that distributes seismic actions - a decisive benefit in seismic upgrading. What remains to be managed is moisture on the timber and the added weight, to be checked on structure and foundations.

Systems architecture

Why it works

Composite section: timber below, concrete above
loadcompressiontensionconcretetimberlocked by the connectors, timber and concrete bend as one deep section: concrete takes the compression on top, timber the tension below — each where it is strongest

A timber floor is light and works well in tension, but on its own it is springy: it deflects and bounces underfoot, and there is a limit to the load it can carry. Casting a thin reinforced slab on top and — crucially — locking the two together with connectors, so they cannot slide over one another, turns them into a single, much deeper composite section. Now each material does what it does best: the concrete on top takes the compression, the timber below the tension, and the connectors at the interface carry the shear that makes them act as one. The gain is dramatic — several times the stiffness and capacity of the bare timber, far less deflection and vibration — which is exactly why it is the technique of choice for upgrading old timber floors. The reinforced slab, tied into the walls, doubles as a rigid diaphragm that holds the building together against earthquakes. The points to watch are the timber’s enemy, moisture (the slab must not trap damp against it), and the added weight, which the existing beams, walls and foundations must be checked to carry.

Stiffness and capacity of the floor

Comparison · insulants
Timber-concrete composite
stiff, strong
Full R.C. slab
stiffest, heavy
Timber + new boarding
a little stiffer
Bare timber floor
springy

Longer bar = the stiffer and stronger the floor for the same depth. Making the timber act together with a concrete slab turns a springy old floor into a stiff modern one — close to a full concrete slab, at a fraction of the weight and demolition.

Nodal details

Critical junctions · sections
123456
D.01
The shear connector

Everything hinges on this point. Under load the concrete slab on top wants to slide over the timber beam below; if it could, the two would behave as separate, weak members. An inclined screw (or a dowel, or a notched plate) driven across the interface stops that slip and carries the shear between them, so the slab and the beam bend together as one deep composite section. A mesh in the slab controls its shrinkage; the interface is often a separation layer so no damp is trapped against the timber.

  1. R.C. slab
  2. Inclined screw / connector
  3. Interface: no slip
  4. Timber beam
  5. Welded mesh
  6. Shear at the interface
123456
D.02
Ring beam and tie to the wall

For the new slab to act as a rigid floor diaphragm, it must be tied to the perimeter walls. A reinforced ring beam runs round the top of the masonry, and anchors hooked from the slab into that ring (or into the wall) stitch them together. Now the floor can gather the seismic forces and brace the walls against overturning - the decisive gain of the technique in old buildings - while the timber beam simply bears, free to be seen below.

  1. Perimeter masonry
  2. Slab (diaphragm)
  3. R.C. ring beam
  4. Anchor to the wall
  5. Beam end (bearing)
  6. Slab bearing

Installation controls

Specification · checklist

01 · Existing timber

Sound, dry timber
Capacity assessed
Surface prepared

02 · Connectors

Type and spacing
Fixed to depth
Shear flow covered

03 · Slab & mesh

Thickness to design
Mesh placed
Separation layer

04 · Cast & cure

Low-shrinkage mix
Compacted, no voids
No trapped water

05 · Diaphragm

Ring beam
Anchors to the walls
Tied at the perimeter

Recurring defects

Diagnostics · site
Meccanica
Slip at the shear connectors
CauseIf the connectors are too few, too soft or poorly fixed, the slab and the timber slide on one another at the interface and the composite action — the whole point of the system — is largely lost.
PreventionConnectors designed and spaced to the shear flow, stiff well-anchored fixings, an ETA-rated system, control of the slip in service.
Biologica
Rot of the timber from damp
CauseWet concrete cast straight onto the timber, or a later leak, keeps the wood damp under the slab where it cannot dry, and it rots — hidden and dangerous in the tension member.
PreventionA separation / vapour-control layer between timber and concrete, dry timber to start, no trapped water, ventilation and leak control.
Meccanica
Shrinkage cracking of the slab
CauseThe thin concrete slab shrinks as it cures; restrained by the connectors and the walls, it cracks on top if it is not reinforced and cured for it.
PreventionA shrinkage mesh, a low-shrinkage mix and curing, joints where needed, control of slab thickness and water content.
Adesione
Detachment of the slab from the timber
CauseWith weak connection and no bond, the slab can lift and debond from the timber under cycling loads and movements, sounding hollow and losing the composite action.
PreventionSufficient, stiff connectors that also hold down, a clean prepared interface, control of deflections, the connection checked in service.

Component materials

The network · materials
Linear element (beams)
Glued Laminated Timber (GLT)
Structural conglomerate
Reinforced Concrete
Structural alloy
Steel S235 / S355

Reference regulations

2 norms

Informational links to the regulatory framework. Always verify the current text on the official source.