Voided Slab

September 15, 2017 | Author: Suresh Chandra Mangena | Category: Bending, Concrete, Manmade Materials, Building, Mechanical Engineering
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A concrete block is one of several precast concrete products used in construction. The term precast refers to the fact that the blocks are formed and hardened before they are brought to the job site.

In the 1950s, hollow-core slab were invented. The voided or hollow core system was created to reduce the weight of the concrete from the system. this concept removes and replaces concrete from center of the slab, where it is less useful with lighter material in order to decreases the dead wt of concrete floor.however,these hollow cavities significantly decrease the slab resistance to shear and fire, thus reduce its structural integrity.

The first hollow concrete block was designed in 1890 by Harmon S. Palmer in the United States. After 10 years of experimenting, Palmer patented the design in 1900. Palmer's blocks were 8 in (20.3 cm) by 10 in (25.4 cm) by 30 in (76.2 cm), and they were so heavy they had to be lifted into place with a small crane. By 1905, an estimated 1,500 companies were manufacturing concrete blocks in the United States.

These early blocks were usually cast by hand, and the average output was about 10 blocks per person per hour. Today, concrete block manufacturing is a highly automated process that can produce up to 2,000 blocks per hour


 Bubble

deck slab is the slab in which some amount of the concrete is replaced by the plastic bubbles or ellipsoid which are made by the waste plastic material, which reduces the self weight of the structure.

 Design

of this type of the slab is based on the euro and the British codes.

In the 1990ies, a new system was invented, eliminating the some of the problems. It is used in Dutch:German invented by JORGEN BREUNING. He locks ellipsoids between the top and bottom reinforcement meshes, thereby creating a natural cell structure, acting like a solid slab.  The slab is created with the same capabilities as a solid slab, but with considerably less weight due to the elimination of excessive concrete. 

Denmark North America



Brazil Australia New Zealand

 Saves 30 to 50 % weight compared to a corresponding solid slab – equal stiffness.  20% concrete reduction in other components.  The reduced weight of the slab will typical result in a change in design to longer spans and/or reduced deck thickness.  It is also seismic friendly as it lowers the total weight of the building.  Reduced concrete usage – 1 kg recycled plastic replaces 100 kg of concrete.  The company estimates that building costs are reduced by 8 to 10 %.

SITE INSTALLATION ( Type A- Filigree Elements) •

Temporary Support – Propping on parallel beams

Placing Elements – Semi pre-cast elements mechanically lifted into position •

Joint Reinforcement – Insert loose bottom splice bars and tie top mesh across joints between elements •

Perimeter shuttering – Fix shuttering to bottom pre-cast concrete layer & tie to top mesh reinforcement •

Soffit shuttering – Prop plywood across joints between element bays and between elements & columns •

Preparation – Seal joints between elements, clean and moisten bottom pre-cast concrete layer •

Concreting – Pour, vibrate and aggregate in-situ concrete

Temporary works – Remove, typically after 3 – 5 days, according to specific site advice •

Finishing – no further work required.

Typical arrangement of props and propping beams Loaded trailers arriving on site

Lifting element into position

Aligning bubbles between elements

Pouring, Vibrating & Floating Site Concrete

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.

Most attempts have consisted of laying blocks of a less heavy material like expanded polystyrene between the bottom and top reinforcement.

But the use will always be very limited due to reduced resistances towards shear, local punching and fire.

which is why the use of these systems has never gained acceptance and they are only used in a limited number of projects

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, Bubble Deck slabs acts like solid slabs. Designing is consequently like for solid slabs, just with less load corresponding to the reduced amount of concrete. Thorough investigations according to Euro codes are made at universities in Germany, Netherlands and Denmark, concluding that a Bubble Deck slab acts like as a solid slab.

 Only

top compressive portion and bottom reinforcing steel of a solid concrete slab contribute to flexure stiffness in bending.  Bubble deck removes concrete from the center of the flexural slab and replaces with hollow HDPE spheres. It is having equal bending stiffness as solid slab.  But technical university of Denmark also carried out test on stiffness of bubble deck slab. they verified the result and they found out, for same strength, bubble deck has 87% of bending stiffness of similar solid slab but only 66% concrete volume due to HDPE spheres.

 As

a result, deflection was higher in bubble deck.

 However,

significant lower dead weight compensated for the slightly reduced stiffness and therefore bubble deck gave higher carrying capacity.

 As,

reduced permanent load positively affects long term response in the serviceability limit state design, which governs crack propagation.

 It

has been concluded that adding a minimum amount of extra reinforcing steel would satisfy the criteria.

 The

main difference between a solid slab and a voided, voided 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 ,hence enabling all concrete to be effective.  The reduced shear resistance will not lead to problems, as balls are simply left out where the shear is high, at columns and walls

 In

calculations, a reduction factor of 0.6 is used on the shear capacity for all bubble deck slab.

This guarantees a large safety margin. Areas with high shear loads need therefore a special attention, e.g. around columns. That is solved by omitting a few balls in the critical area around the columns, therefore giving full shear capacity.

 The

simple Bubble Deck is cast over the pre-fabricated “bubble lattice” on traditional formwork.(cast in situ)  In

the filigree-element Bubble Deck the bottom side of the „bubble-lattice‟ unit is furnished with a pre-cast concrete layer which on the building site replaces the horizontal part of the formwork.(semi pre cast)

 The

simple Bubble Deck may also be delivered to the building site as pre-cast factory-made slabs.(pre cast)


-Grade of steel: Generally Fe

500,550. -Rebar size depends on the thickness of the slab and span.

-spacing: Max 1 m. or maximum 3 balls between two girder. Two types: (a). Self supporting (b). Trussed type.



Main bar 10mm minimum – for 200 to 300 mm slab thickness. 12mm- for size ≥300 mm

 Plastic

balls or ellipsoids are made up of the plastic

waste.  Diameter:  Material

always 0.9 of the slab size.

of balls: 1.polyethin. 2.pvp- poly vinyl propylene. 3.pvc- poly vinyl chloride.

Concrete Type: self compacting concrete Grade: Any grade of concrete can be used, generally M 20, 30 grade is use.

 The

largest Bubble Deck structure so far erected in Great Britain. The structure comprises 7,800 m2 of Bubble Deck floor slabs between 3 and 6 stories high supported on in-situ reinforced concrete columns. Over £400,000 of savings were realized as a direct result of incorporating Bubble Deck into this project, amounting to a 3% saving off the total project cost.


Sogn Arena, Oslo in Norway

City Hall and Offices, in Denmark

Bubble deck-advanced structure engineering by Paul harding,managing director bubble deck C.I.ltd. Bubble deck structure solution (UNITED KINGDOM) Structural Behavior of bubble deck slab by Massachusetts institute of Technology

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