The concept of a voided concrete slab involves a method where excess or non-working concrete in a structural slab is replaced with void formers. This innovative approach was pioneered by Jorgan Breuning of Denmark approximately two decades ago. The traditional solid slabs, burdened by their weight, create strain on the structure and foundation. The voided slab system addresses this by strategically incorporating void formers to reduce the overall weight, presenting significant advantages in terms of cost and environmental impact.
The voided slab system employs a grid of rigid void formers containing air, typically made from plastic or recycled materials. These voids, formed during concrete casting, create hollow boxes within the slab, supporting a flat surface and enabling load transfer in both directions. Common void formers include Bubble Deck, Cobiax, U-Boot Beton, Bee Plate System, and Airdeck, each developed in the last two decades with variations in shape, span limits, and material.
The conventional approach to constructing slabs faces challenges such as increased dead weight, leading to larger foundations and columns. This demands more concrete and steel, making the building process resource-intensive. Additionally, traditional slabs encounter span limitations due to their density, necessitating additional reinforcement. Voided slabs offer a solution by reducing weight without compromising structural strength, allowing for thicker slabs to support increased loads over longer spans.
The voided slab system exhibits shear strength ranging from 72-91% of solid deck capacity. Special attention is needed in high shear load areas, such as around columns, where void formers may be omitted to maintain full shear capacity.
Studies show that bending stress in a voided slab system is 6.43% less than in solid slabs.
Finite element analysis indicates that deflection in a voided slab system is 5.88% more than solid slabs due to reduced stiffness caused by hollow portions.
Voided slabs face punching shear concerns due to reduced weight. Design adjustments or additional shear reinforcement may be required based on the applied shear.
A case study on the Town Hall building in Den Hang demonstrated that the bubble deck variant was 5 to 16% less expensive than a solid concrete deck. The overall savings were estimated to be around 20%, making the voided slab system an economically viable option.
Voided slabs facilitate longer spans, lighter foundations, and smaller columns, reducing overall structural weight.
The system allows for open floor plates with fewer columns and beams, offering flexibility for future modifications.
Voided slabs decrease the consumption of concrete and steel, resulting in cost savings and reduced environmental impact.
The elimination of beams streamlines formwork, saving time and positively impacting project schedules.
Utilizing recycled materials for void formers aligns with sustainability goals and contributes towards LEED certification.
Voided slabs enhance building flexibility, meeting evolving demands and extending the useful life of structures. Integration with post-tensioning systems further reduces structural depth.