Top reinforcement (Dutch: bovenwapening) is reinforcing steel placed in the upper zone of a concrete element — such as a beam, slab, or foundation — to resist tensile forces that occur at the top of the section. While bottom reinforcement handles sagging (positive) bending, top reinforcement handles hogging (negative) bending.
Why top reinforcement is needed
Concrete is strong in compression but weak in tension. When a structural element bends, one side is compressed and the other is stretched. In a simply supported beam, the bottom is in tension and the top is in compression. However, over supports — such as where a continuous slab passes over a wall or column — the bending reverses: the top of the slab is pulled apart (tension) and the bottom is compressed. Without top reinforcement at these locations, cracks would form and the structure could fail.
Where top reinforcement is placed
Common locations for top reinforcement include:
- Continuous slabs and beams — over intermediate supports where hogging moments occur.
- Cantilevers — the top of a cantilevered balcony or overhang is entirely in tension.
- Foundation slabs — top reinforcement resists upward soil pressure and uneven loading.
- Flat slab construction — a mesh of top reinforcement is placed over columns to resist punching shear and hogging moments.
The required amount and spacing of top reinforcement are calculated by a structural engineer based on the expected loads and span.
Application in construction
Top reinforcement bars are typically tied to spacers or chairs that hold them at the correct height within the formwork. Maintaining the right concrete cover above the steel is essential for durability and fire resistance. During a concrete pour, workers must take care not to step on or displace the top reinforcement, as even small deviations from the designed position can significantly reduce the structural capacity.
Related terms
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