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I-sects (Voided Slab) System

In association with Daliform Group SRL, Italy, we present I-sects System / U-Boot Beton®, a voided slab technology that allows large spans, efficiently formed as flat plates without beams, for many types of buildings and other structures while using significantly less concrete than if solid. This is the most versatile voided slab system that allows builders to use less material and still maintain structural integrity.

The Concept

The concept is actually quite old. By using forming systems engineers have decreased the weight of floor slabs by creating voids through a variety of techniques for a very long time. But newer systems now make it possible to increase the efficiency of cast-in-place (CIP) concrete construction and reduce overall cost.

Traditional voided-slab forming systems that have been used include waffle slabs, single-and double-direction span forming systems, and hollow-core precast slabs. The guiding principle, is that building owners and designers can get the advantages of a thin two-way-spanning flat-plate structure while the structural engineer can lighten the floor by more efficiently using the concrete.


Take a tour through the timeline of Voided slab System

History of Concrete in the Twin Cities and Voided Slabs - Then and Now


I-sects / U-Boot Beton® is used in all applications that require a structural plate together with the need to use less concrete and therefore for a lighter structure. I-sects / U-Boot Beton® are the ideal solution for creating slabs with a large span and/or great load-bearing capacity:

  • It is particularly suited for structures that require considerable open spaces, such as executive, commercial and industrial buildings as well as public, civil and residential structures
  • It makes it possible to more irregularly distribute the pillars, as beams do not need to be created
  • In the case of yards that are difficult to access or restructuring work, U-Boot Beton®, due to its stackability, modularity, lightness and maneuverability, can be used to make horizontal structures without the help of handling and hoisting equipment


We are incorrectly led to estimate the advantage of a slab made lighter with I-sects / U-Boot Beton® limiting it to a mere comparison between savings in concrete and the cost of the formwork on the level of the slabs only. In this way however, as the analysis is immediate and intuitive, it does not account for the various economic, practical and operational advantages provided with U-Boot Beton® for the entire structure:

  • Less use of reinforcement in the slabs, columns and foundation up to a total of 15% (also in the case of variants)
  • Less concrete is used not only for the slabs but also for the columns and foundations
  • There are seismic advantages related to reduced building weight
  • Slimmer columns and foundations, lower costs related to excavation for foundations
  • Incorporates irregular arrangement of the columns to reflect the architectural freedom of the structure

  • Reduction of weight up to 40%
  • Reduced deformations (maximum loss of stiffness – 15%)
  • Reduction of the foundation load
  • Reduction of columns section or their number

  • Lower concrete cost with an equal thickness
  • Lower steel cost
  • Savings in useful height on each level as there are no emerging beams
  • Possibility to gain floors at the same building height (towers) and building volume
  • Quick and easy to implement
  • Possibility of large span at equal load or high load bearing capacity at an equal span
  • Economical and easy to transport, handle and store, also outdoors
  • The soffit has a flat surface that is ready to finish and does not require a false ceiling for aesthetic purpose
  • If a false ceiling is required, it can be created faster

  • Span up to 20m
  • No beams between columns
  • Reduction in the number of columns
  • Can be used together with prefabs
  • Does not require handling and/or hoisting equipment

  • Lower seismic mass
  • Fewer dimensional limitations for the elements
  • Double slab - upper and lower

  • Larger spaces
  • Greater architectural freedom
  • Simplified changes to the purpose of use

  • Considerable fire resistance with a concrete cover of only 35mm

  • Thanks to the increased stiffness of the lower and upper slab, acoustic transmittance is reduced
  • Characteristics of a I-sects / U-Boot Beton® slab and comparison with a conventional solid slab

    A factual comparison of void slab with solid slab with same depth is evident based on the criteria of flat plate configuration for various column grids.


    The quality of the used mixture, the innovative shape, the thicknesses and dimensions of the product, the fire safety and strict working techniques make it a product of excellence. U-Boot Beton®, is not subject to deformations, either during or after the casting, either due to the weight of the concrete or the dynamic effect connected to the work operations: it is able to support before casting the workers and fresh concrete, the pressure created during the compression and vibration of the casting, the weight of people, reinforcements and equipment guaranteeing conditions of safety, and lack of deformations. Furthermore, the safety of the lateral spacer guarantees its perfect positioning and respect of the geometry of the beams under the pressure of the concrete.

    Daliform Group is extremely precise with regard to respecting health and the environment having been the first to obtain Environmental Compatibility Certification (CCA) for its products.

  • Fire Resistance Certificate REI 180 for U-Boot Beton® issued by the CSI institute in Bollate (MI).
  • Certification of a Load Test on a sample with U-Boot Beton® issued by the University of Darmstadt.
  • Acoustic test according to the standard UNI EN ISO 140-6 - Measurement of acoustic insulation in buildings and building elements; Laboratory measurements of the insulation footstep noise issued by the Istituto Giordano di Gatteo (FC).
  • Acoustic test according to the standard UNI EN ISO 140-3 - Measurement of acoustic insulation in buildings; Laboratory measurements of the insulation of air-borne noise from building elements issued by the Istituto Giordano di Gatteo (FC).
  • Loading and breaking test certified by the University of Padua.
  • Environmental Compatibility Certification (CCA).
  • Member of the Green Building Council Italia.
  • System certification pursuant to ISO 9001- ISO 14001 - SA Standard 8000.

  • (Source:


    1. The entire surface of the slab to be cast on site is shuttered with wood deckings (or similar systems), then the lower reinforcement bars are positioned in two mutually perpendicular directions according to the design and the lattice for the upper reinforcement is arranged.
    2. The U-Boot Beton® formworks are positioned using the lateral spacers' joints to place them at the desired center distance that will determine the beam width. Thanks to the conic elevator foot, the U-Boot Beton® formworks will be lifted from the surface, making it possible for the lower slab to be formed. If double or triple elements are used, these elements must first be assembled, which will be supplied on distinct pallets in the yard.
    3. The positioning of the reinforcement is completed by placing above the U-Boot Beton® formwork the upper bars in the two directions as well as the reinforcement for shear and punching where necessary, according to the design.
    4. The positioning of the reinforcement is completed by placing above the U-Boot Beton® formwork the upper bars in the two directions as well as the reinforcement for shear and punching where necessary, according to the design.
    5. Once suitably set, the casting can be restarted from the starting point, completely burying the U-Boot Beton®. The casting is then levelled and smoothed in a traditional manner.
    6. Once the structure has hardened, the formwork can be removed. The surface is smooth in correspondence of the soffit.