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Voided biaxial slab

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Voided biaxial slab

Voided biaxial slabs are reinforced concrete slabs in which voids reduce the amount of concrete.

While concrete has been used for thousands of years, the use of reinforced concrete is usually attributed to Joseph-Louis Lambot in 1848. Joseph Monier, a French gardener, patented a design for reinforced garden tubs in 1868, and later patented reinforced concrete beams and posts for railway and road guardrails.

The main obstacle with concrete constructions, in case of horizontal slabs, is the high weight, which limits the span. For this reason major developments of reinforced concrete have focused on enhancing the span, either by reducing the weight or overcoming concrete's natural weakness in tension.

An early example is the Pantheon in Rome, build 125 AD. Although not reinforced, coffers were used to reduce the weight.

Prestressed concrete

Prestressed concrete, invented by Freyssinet in 1928, is a method for overcoming concrete's natural weakness in tension, thereby enabling longer span.

Hollow-core slabs

In the 1950s, hollow-core slabs were invented. These are prefabricated, one-way spanning, concrete elements with hollow cylinders. Due to the prefabrication, these are inexpensive, and reduce building time, but can be used only in one-way spanning constructions, and must be supported by beams and/or fixed walls.

Biaxial slabs

Due to the limitations in hollow-core slabs, primarily lack of structural integrity, inflexibility and reduced architectural possibilities, focus has been on biaxial slabs and ways to reduce the weight. Several methods have been introduced during the last decades, but with very limited success, due to major problems with shear capacity and fire resistance as well as impractical execution.

For decades, several attempts have been made to create biaxial slabs with hollow cavities in order to reduce the weight. Most attempts have consisted of laying blocks of a less heavy material like expanded polystyrene between the bottom and top reinforcement, while other types included waffle slabs and grid slabs.

Of these types, only waffle slabs can be regarded to have a certain use in the market. But the use will always be very limited due to reduced resistances towards shear, local punching and fire. The idea of placing large blocks of light material in the slab suffers from the same flaws, which is why the use of these systems has never gained acceptance and they are only used in a limited number of projects in Spanish-speaking countries.

Below are types of voided slab systems existing around the world (in alphabetical order):


The Airdeck concept was patented in 2003 and comprises an inverted plastic injection moulded element which is vibrated into the lower slab during the production process by a robotic arm. The advantage of this system is that no retaining mesh is required to hold down the voiding elements during on site pouring of the second layer. As the boxes can be nested there are transport advantages versus other voiding systems. The static calculations are according to standard Eurocode 2 norms.]


In the 1990s, a new system was invented, eliminating the above problems. The so-called BubbleDeck technology (Dutch: Bollenplaatvloer, German: Zweiachsigen Hohlkörperdecke, Icelandic: Kuluplotur, Danish: Bobledæk) invented by Jørgen Breuning, locks ellipsoids between the top and bottom reinforcement meshes, thereby creating a natural cell structure, acting like a solid slab. A voided biaxial slab is created with the same capabilities as a solid slab, but with considerably less weight due to the elimination of superfluous concrete.


The Cobiax system makes use of the same voided slab principles of creating voids within the concrete slabs to lighten the building structures. Elliptical and torus shaped hollow plastic members, termed as void formers, are held in place by a light metal mesh for easy installation between the top and bottom reinforcement layers of a concrete slab

U-boot Beton®

In 2001 an Italian engineer, Roberto Il Grande, developed and patented a new system of void formers, in order to decrease the transportation costs (and CO2 production). The product is U-Boot Beton®, and its biggest advantage is that it is stackable. A truck of U-boot means approximately 5000 m2 of slab, once void formers are laid down at building site. The second innovation is the shape: U-Boot Beton® creates a grid of orthogonal "I" beams, so the calculation of the reinforcement can be effected by any static engineer according to Eurocode, British Standards or any local standard.

U-Boot Beton® is a recycled polypropylene formwork that was designed to create two-way voided slabs and rafts. The use of U-Boot Beton® formwork makes it possible to create mushroom pillars, with the possibility to have the mushroom in the thickness of the slab. Thanks to the conic elevator foot, immerging the U-Boot Beton® formworks in the concrete casting will create a gridwork of mutually perpendicular beams closed from the bottom and the top by a flat plate that is created with a single casting; this results in considerable reduction in the use of concrete and steel.

U-Boot Beton® is used to create slabs with large span or that are able to support large loads without beams. Light and quick and easy to position, thanks to their modularity the designer can vary the geometric parameters as needed to adapt to all situations with great architectural freedom.

U-boot earliest projects were executed in 2002 and since that time it has been used all over the world[1]

U-boot catalogue [2] U-boot references [3]

U-boot system can be combined with other technologies like pre-fabricated slabs and post tensioned steel. The technology of voided slabs with post tensioned steel reduces the weight of slab and its thickness.

Polystyrene voiding blocks

A classic methodology for reducing weight of structural floors is the use of polystyrene blocks to reduce the amount of on-site concrete poured.


The geometry of the BubbleDeck slab is identified by ellipsoids of a certain size, placed in a precise modular grid. All geometrical parameters of the slab can be described by a single parameter, the modulus named “a”. Modulus and corresponding deck heights are manufactured in steps (modulus in steps of 25 mm, and effective heights in steps of 50 mm)[4]

In principle, fixing of the ellipsoids can be made in numerous ways, but using only the reinforcement meshes reduces superfluous material consumption and allows for an optimal geometrical proportion between concrete, reinforcement and voids.

The voids are positioned in the middle of the cross section, where concrete has limited effect, while maintaining solid sections in top and bottom where high stresses can exist. Hence, the slab is fully functional with regards to both positive and negative bending.


In principle, BubbleDeck and U-Boot Beton® slabs acts like solid slabs. Designing is consequently like for solid slabs, but with less load corresponding to the reduced amount of concrete. Investigations according to Eurocodes made at universities in Germany, Netherlands and Denmark, conclude that a BubbleDeck slab acts like as a solid slab.[5][6][7][8][9][10][11][12][13]

While a true biaxial slab as the BubbleDeck system must be calculated as a solid slab, ribbed slab systems, like the U-boot system, consisting of a grid of orthogonal "I" beams, must be calculated as beams.

The BubbleDeck technology is directly incorporated in national standards, such as the CUR in the Netherlands.[14]


The main difference between a solid slab and a voided biaxial slab refers to shear resistance. Due to the reduced concrete volume, the shear resistance will also be reduced. For a BubbleDeck slab the shear resistance is proportional to the amount of concrete, as the special geometry shaped by the ellipsoidal voids acts like the famous Roman arch, enabling all concrete to be effective. This is only valid when considering the BubbleDeck technology. Other types of voided biaxial slabs have reduced resistances towards shear, local punching and fire.

In practise, the reduced shear resistance will not lead to problems, as balls are simply left out where the shear is high, at columns and walls.[15][16][17][18][19][20]


As U-Boot Beton® is made of polypropylene, it is not toxic even if burnt. Moreover,the slab will not explode due to the escaping of over pressurised gas from the feet (4 feet for each formwork) that act as safety valves. Tests run at the CSI laboratory have demonstrated that with a cement cover of 3 cm the structure created with U-Boot Beton® is class REI 180.

As a BubbleDeck slab acts like a solid slab, the fire resistance is just a matter of the amount of concrete layer. The fire resistance is dependent on the temperature in the rebars and hence the transport of heat. As the top and bottom of the BubbleDeck slab is solid, and the rebars are placed in the solid part, the fire resistance can be designed according to demands.[21][22][23]


Tests have been carried out in Germany,[24] UK[25] and the Netherlands[26] according to ISO 140-4:1998, ISO 140-7:1998, ISO 717-1:1997 and ISO 717-2:1997 measuring impact and airborne sound. These tests show that 230 mm and thicker BubbleDeck® slabs can meet the national rules.


  • Low weight/stiffness ratio – influence of impact is proportional to weight.
  • Simplicity and symmetry and uniform extent – Lessen the impact effect. Uniform and continuous distribution/flow of forces,
  • Monolithic, continuous and ductile structure.

The BubbleDeck system fulfil these principles:

  • Saves 35% weight compared to a corresponding solid slab – equal stiffness.
  • Simple, monolithic behaviour, uniform and continuous distribution of forces.
  • Max ductile structure - increased ductility due to increased strength/weight ratio.


  • Dutch Standards: From November 2001, The BubbleDeck system is incorporated in the Dutch Standards (by CUR – Civieltechnisch Centrum Uitvoering Research en Regelgeving).
  • UK Standards: The BubbleDeck system can be treated as a normal flat slab supported on columns (BS 8110) according to CRIC (Concrete Research & Innovation Centre under the Imperial College of Science, Technology & Medicine), 1997.
  • Danish Standards: The BubbleDeck system can be calculated from recognized principles and within existing standards - Directorate of Building and Housing, Municipality of Copenhagen, 1996.
  • German Standards: The BubbleDeck system can be used according to existing technical standards according to Deutsches Institut für Bautechnik, 1994.



A two way spanning voided biaxial slab construction compared to a traditional two way spanning non voided biaxial slab construction:

  • The reduced weight of the slab will typical result in a change in design to longer spans and/or reduced deck thickness. The overall concrete consumption can be reduced with up to 50% depending on design, as a consequence of reduced mass in slabs, vertical structure and foundation.

A two way spanning biaxial slab construction compared to a one way spanning deck (traditionally a hollow core):

  • One way spanning decks are supported by a combination of walls and beams. This leads to rigid and inflexible structures. This type of structure should be used with care in seismic regions due to the risk of progressive collapse.[27][28]

As this floor type is made of complete prefab elements with no structural coherence, support moments are absent, resulting in increased material consumption.

A two way spanning voided biaxial slab construction according to the BubbleDeck system and U-Boot Beton® system, compared to older voided slab constructions:

  • Acts like a solid slab. Does not have the earlier problems with reduced resistances towards shear, local punching and fire.

In general

Benefits include:

  • Design freedom – flexible layout easily adapts to irregular & curved plan layouts.
  • Reduced dead weight -35% removed allowing smaller foundation sizes.
  • Longer spans between columns – up to 50% further than traditional structures.
  • Downstand beams eliminated – quicker and cheaper erection of walls and services.
  • Load bearing walls eliminated – facilitating MMC with lightweight building envelopes.
  • Reduced concrete usage – 1 kg recycled plastic replaces 100 kg of concrete.
  • Environmentally green and sustainable – reduced energy & carbon emissions.

8% of global CO2 emissions are due to cement production. 1 tonne of cement:[29]

  • Releases 1 tonne of CO2
  • Consumes 5 million BTU of energy
  • Uses 2 tonnes of raw materials

Due to the BubbleDeck technology's green credentials, the use of the BubbleDeck system qualifies for LEED points in North America.[30][31]

Uboot Beton® real advantages[32]

  • 1. INCREASED NUMBER OF FLOORS - Possibility to gain floors at the same building height (towers) and building volume.
  • 3. REDUCED SLAB THICKNESS - Thinner slabs but with equal loads and clearances, or bigger clearances with an equal thickness.
  • 4. REDUCTION IN THE NUMBER OF PILLARS - Facilitated use reallocation.
  • 5. REDUCTION IN THE NUMBER OF PILLARS - Facilitated use reallocation.
  • 7. REDUCED FOUNDATIONS - Less excavation.
  • 8. LESS DEEP FOUNDATION EXCAVATION - Lower costs for foundation excavations.
  • 9. IMPROVED ACOUSTIC BEHAVIOUR - Less acoustic transmittance.

We are incorrectly led to estimate the advantage of a slab lightened with 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 iron in the slabs, pillars 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 antiseismic advantages connected to reduced building weight; slimmer pillars and foundations, lower costs related to excavation for foundations; the arrangement, also irregularly if needed, of the pillars to reflect the architectural freedom of the structure. Reduction of work and overhead transfer of the formworks; advantages in on-site logistics.

LIGHT - THIN - BIDIRECTIONAL 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.

ECONOMIC 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. Also indicated for the top-down technique. 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 purposes. If a false ceiling, is required it can be created faster.

FLEXIBLE Span up to 20 m. No beams between pillars. Reduction in the number of pillars. Can be used together with prefabs. Does not require handling and/or hoisting equipment. Possibility of single direction structures thanks to the bridge accessory.

EARTHQUAKE PROOF Lower seismic mass. Fewer dimensional limitations for the elements. Double slab, upper and lower.

OPEN SPACES Larger spaces. Greater architectural freedom. Simplified changes to the purpose of use.

FIRE RESISTANT Considerable fire resistance certified REI 180 with a concrete cover of only 3 cm.

IMPROVED ACOUSTIC BEHAVIOUR Thanks to the increased stiffness of the lower and upper slabs, acoustic transmittancy is decreased.


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.

U-Boot Beton® is 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 manoeuvrability, can be used to make horizontal structures without the help of handling and hoisting equipment. With U-Boot Beton® also foundation rafters can be created with a larger thickness with a reduced amount of concrete.

Formworks for two-way voided slabs

The Biaxial BubbleDeck system can be implemented in three versions according to degree of prefabrication:

  • “Reinforcement modules”: Comprising prefabricated “bubble-lattice” sandwich elements to be placed on traditional formwork. Building time is reduced compared to conventional on site construction. Suitable for the majority of new-build projects, also suspended ground floor slabs and alteration/refurbishing projects.
  • “Filigree elements”: Where the bottom side of the 'bubble-lattice' unit is furnished with a pre-cast concrete layer which replaces the horizontal part of the formwork on the building site, optimizing both building time and quality by prefabrication.

Acts directly like a seamless ceiling. Suitable for the majority of new-build projects.

  • “Finished elements”: Finished panels, complete precast slab elements. These can be used for limited areas such as balconies or staircases.

The BubbleDeck technology can benefit most buildings. However, as it is a biaxial deck technology, the use will focus on biaxial slab designs.

Functional applicability: Residential living, offices, utility and industrial buildings. Used in offices, apartments, villas, hotels, schools, parking, hospitals, laboratories and factories.

As a consequence of the reduced load, it is possible to achieve larger spans than a solid slab. Depending of the design, spans of 20 to 40 times the deck height are possible. Cantilevers can be made 10 times the deck height. By incorporating PT cables, these spans can be further enhanced.

The effect of PT cables in a BubbleDeck slab is enhanced, because of the relative high deck height compared to the moment strength. This combination could seem like the perfect match for several applications.



The overall floor area can be divided down into a series of planned individual elements, up to 3 m wide dependent upon site access, which are manufactured off-site using MMC techniques. These elements comprise the top and bottom reinforcement mesh, sized to suit the specific project, joined together with vertical lattice girders with the void formers trapped between the top and bottom mesh reinforcement to fix their optimum position. This is termed a ‘bubble-reinforcement’ sandwich, which is then cast into bottom layer of 60 mm pre-cast concrete, encasing the bottom mesh reinforcement, to provide permanent formwork within part of the overall finished slab depth.

On site the individual elements are then ‘stitched’ together with loose reinforcement simply laid centrally across the joints between elements. The splice bars are inserted loose above the pre-cast concrete layer between the bubbles, and purpose made mesh sheets tied across the top reinforcement mesh to join the elements together. After the site finishing, concrete is poured and cured. This technique provides structural continuity across the entire floor slab – the joints between elements are then redundant without any structural effect – to create a seamless biaxial floor slab.


Installation of U-Boot Beton®
Two-way voided slabs in reinforced concrete with U-Boot Beton®

Installation of U-Boot Beton®[33]

  1. The entire surface of the slab to be cast on site is shuttered with wood deckings (or similar systems), then the lower reinforconcrete bars are positioned in two mutually perpendicular directions according to the design and the lattice for the upper reinforconcrete is arranged.
  2. The U-Boot Beton® formworks are positioned using the lateral spacers joints to place them at the desired centre distance that will determine the beam width. Thanks to the conic elevator foot, theU-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 reinforconcretes 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 concrete casting must be performed in two phases to prevent the floatation of the formworks: an initial layer will be cast to fill a thickness equal to the height of the elevator foot. Casting will continue for this first portion of the slab until the concrete starts to set and become semi fluid.
  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.

The BubbleDeck concept simplifies the placement of installations like ducts and heating/cooling systems directly in the slab. This enhances the nature of the slim flat slab structure. The tubes can either be placed in the bubble-lattice as prefab, or onsite before concreting.

Thermal heating/cooling in slabs can substantial reduce the energy consumption.[34][35][36][37][38][39]


The possibilities of the concept are shown in the following examples of constructions made by the BubbleDeck technology:

University, Utrecht in the Netherlands':

Vogaskoli, School in Reykjavik, Iceland:

Sogn Arena, Oslo in Norway:

City Hall and Offices, Glostrup in Denmark:

Between 2002 and 2008 full building regulation approval was issued to 12 UK and Channel Islands projects that have been completed, including Salisbury Law Courts and 96 apartments in Le Coie Social rented flats together containing over 10,000 sq ft (930 m2) of BubbleDeck floors. In 2007 one floor of two UK projects were partially completed due to reticence of one building control body following which another building control firm was prepared to approve. Irrespective of which the design & build contractor decided to switch to a conventional solid concrete slab structure. The British Board of Agrément undertook a full technical assessment of the BubbleDeck system which they have confirmed is acceptable, pending further production and site installation assessment. Since 2008 the BubbleDeck system continued to be marketed in UK.

Since 2001, millions of U-Boot Beton® have been deployed in the implementation of works in various Countries throughout the world. Works of various dimensions, types and complexity, often born of the pencil-stroke and genius of famous designers, like Jean Nouvel, Richard Meier, Daniel Libeskind, Zaha Hadid,Renzo Piano, Mario Botta, ...

Some examples:

City Life Milano Italy

Architectural planner: Arata Isozaki & Associates, Zaha Hadid Architects, Studio Daniel Libeskind

ITC Lab (Leed Platinum) Italy

Architectural planner: Richard Meier & Partners Architects Master plan: Jean Nouvel Ateliers

Vulcano Buono Italy

Architectural planner: Renzo Piano Building Workshop

Beirut Terraces Lebanon

Architectural planner: Herzog de Meuron

Prizes and awards

  • The BubbleDeck technology have received several prizes and recognitions:
  • The Dutch Building Prize, the Netherlands 1999
  • The Industrial Environmental Prize, the Netherlands 1999
  • The Stubeco Building Prize for Execution, the Netherlands 2000
  • Innovation Award, the Netherlands 2000
  • RIO Award, Germany 2003
  • “Building of the Year” for Office buildings, Denmark 2004
  • Jersey Construction Awards: “Best Use of Innovation”, Jersey 2005

BubbleDeck technology was nominated for the ”European Environmental Prize for Sustainable Development”

The U-Boot Beton® technology received prizes and recognitions:

  • "Innovation in Construction" 2012 - St. Petersburg
  • "Città Impresa – 1000 fabbricatori di idee" 2012 - Italy

Product certifications and tests

The U-Boot Beton® technology have numerous product certifications and tests:

  • 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.


See also


  1. ^ [1]
  2. ^ [2]
  3. ^ [3]
  4. ^
  5. ^ Martina Schnellenbach-Held, StefanEhmann, Karsten Pfeffer: “BubbleDeck - New Ways in Concrete Building”. Technische Universität Darmstadt, DACON Volume 13, 1998
  6. ^ Martina Schnellenbach-Held, Karsten Pfeffer: “BubbleDeck Design of Biaxial Hollow Slabs”. Technische Universität Darmstadt, DACON Volume 14, 1999
  7. ^ BubbleDeck Report from A+U Research Institute /Professor Kleinmann - the Eindhoven University of Technology / the Netherlands, 1999
  8. ^ BubbleDeck Test Report by Koning & Bienfait b.v. / The Netherlands, 1998
  9. ^ Report of BubbleDeck from Technische Universitaet in Cottbus
  10. ^ Report from the Eindhoven University of Technology / the Netherlands: ” Broad comparison of concrete floor systems”. December 1997
  11. ^ BubbleDeck Report from Technical University of Denmark, 2003
  12. ^ Report from Adviesbureau Peutz & Associes b.v.: ”Comparison of BubbleDeck vs. Hollow core”. Netherlands, 1997
  13. ^ "Optimising of Concrete Constructions"; - The Engineering School in Horsens / Denmark, 2000
  14. ^ : CUR-aanbeveling 86-01
  15. ^ Martina Schnellenbach-Held, Heiko Denk: “BubbleDeck Time-Dependent Behaviour, Local Punching Additional Experimental Tests”. Technische Universität Darmstadt, DACON Volume 14, 1999
  16. ^ Schnellenbach-Held, M., Pfeffer, K.: “Tragverhalten zweiachsiger Hohlkörperdecken, Beton- und Stahlbetonbau” 96 [9], 573-578 (2001)
  17. ^ Pfeffer, K.: “Untersuchung zum Biege- und Durchstanztragverhalten von zweiachsigen Hohlkörperdecken”. Fortschritt-Berichte VDI, VDI-Verlag, Düsseldorf 2002
  18. ^ "Punching Shear Strength of BubbleDeck" - The Technical University of Denmark, 2002
  19. ^ BubbleDeck Test report from University of Darmstadt by Markus Aldejohann, Martina Schnellenbach-Held, 2003
  20. ^ BubbleDeck Report from AEC Consulting Engineers Ltd. / Professor M.P. Nielsen - The Technical University of Denmark, 1993
  21. ^ BubbleDeck Test report from University of Darmstadt by Markus Aldejohann and Martina Schnellenbach-Held, 2002
  22. ^ TNO-Report on BubbleDeck for the Weena Tower / Rotterdam / the Netherlands, 1997
  23. ^ TNO-Report for 230 mm BubbleDeck: ”Fire-safe in 120 minutes” the Netherlands, 1999
  24. ^ German Test Certificate Number P-SAC 02/IV-065 according to DIN 4102-2 concerning BubbleDeck® slabs, 2001
  25. ^ BubbleDeck Test Report from Ian Sharland Ltd Airborne and Impact Sound Insulation”.November 2005
  26. ^ BubbleDeck Test Report from Adviesbureau Peutz & Associes b.v.: ”Sound Resistance”.March 2004
  27. ^ Report on building systems in relation to seismic behaviour
  28. ^ "Investigation of seismic behaviour of hollow-core slabs by various methods" by Dr. M.R. Adlparvar et al., Azad University Tehran South Unit
  29. ^ Report from American Society of Civil Engineers: "Structural engineers, sustainability and LEED", p. 33, by Diana Klein
  30. ^ Read, Jones and Christoffersen: BubbleDeck LEED points in North America
  31. ^ Report from American Society of Civil Engineers: "Structural engineers, sustainability and LEED", p. 39 by Diana Klein
  32. ^
  33. ^
  34. ^ Reports from European Concrete Platform: "Concrete for energy-efficient buildings - The benefits of thermal mass"
  35. ^ "Cooling and heating of buildings by activating their thermal mass with embedded hydronic pipe systems" by Bjarne W. Olesen, Ph.D. and D. F. Liedelt, Technical University of Denmark
  36. ^ Article from Concretethinkerz: "Radiant Floors"
  37. ^ "Radiant heating and cooling by embedded water-based systems" by Bjarne W. Olesen, PH.D., Technical University of Denmark
  38. ^ "Thermal advantages of concret - a European study" by Jesper Sand Damtoft, Report from Teknologisk Institut
  39. ^ "Heating and cooling with thermoactive hydronic elements" Report from COWI, 2006

External links

  • Arabian Business
  • WNIB online
  • Bouwweb
  • BD online
  • Ny Teknik
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