What is distribution reinforcement?
Distribution reinforcement is the reinforcement laid at right angles to the main reinforcement, mainly in concrete slabs and floors that span in one direction. The main bars carry the tensile forces along the span; the distribution bars run across them and together they form a mesh. It is also called transverse or secondary reinforcement. In Dutch it is known as verdeelwapening.
What does it do?
- Spreads loads: a point load, such as a heavy cabinet or a column on the floor, is shared through the cross bars by several main bars instead of being carried by one.
- Holds bars in place: tied together, main and distribution bars form a stiff mesh that does not shift during pouring and vibrating.
- Limits cracking: concrete shrinks and moves with temperature, across the span too. Distribution bars keep cracks in that direction small.
How much, and where?
Eurocode 2 (EN 1992-1-1, clause 9.3.1.1) requires one-way slabs to have secondary transverse reinforcement of at least 20 per cent of the main reinforcement. The structural engineer sets the actual bar size and spacing; national annexes may add further rules.
In a one-way slab the distribution bars usually sit on the inside of the main bars. That gives the main bars the greatest effective depth, and so the most effect. In a slab spanning in two directions, there is effectively main reinforcement both ways.
Application
Distribution reinforcement is found in almost every reinforced floor, ground slab, basement slab and access balcony. On smaller jobs, such as a base for a garden building, you often use welded wire mesh, in which main and cross bars are already combined.
Tips and points of attention
- Follow the reinforcement drawing: which layer goes on top is a deliberate choice by the engineer. Swap the layers and the main bars lose capacity.
- Watch the concrete cover: the outermost bar sets the cover. Use spacers, under the mesh as well.
- Do not leave it out of narrow strips: a narrow slab still shrinks across its width and can crack.
- Tie it properly: loose cross bars move during the pour.
Related terms
- Main reinforcement
- Reinforcement
- Top reinforcement
- Supplementary reinforcement
- Concrete cover
- Welded wire mesh
Want to learn more about construction terms? Visit our knowledge base at fredsdiyplans.com.