A SEMINAR ON

VOIDED SLAB(BUBBLE DECK TECHNOLOGY)

PREPARED BY: KETAN DHAMELIYAEn No:- 120070720010

Department of Structural EngineeringBVM Engineering College, Vidyanagar.

EARLY DISCUSSION HISTORY OF HOLLOW CORE SLAB BUBBLE DECK TECHNOLOGY COMPONENTS BENEFITS

PHASE-2FLOW OF PRESENTATION.. How to Install ?? Composition Bending stiffness & Deflection Shear

SITE INSTALLATION

• Temporary Support – Propping on parallel beams • Placing Elements – Semi pre-cast elements mechanicallylifted into position• Joint Reinforcement – Insert loose bottom splice barsand tie top mesh across joints between elements• Perimeter shuttering – Fix shuttering to bottom pre-castconcrete layer & tie to top mesh reinforcement• Soffit shuttering – Prop plywood across jointsbetween element bays and between elements & columns

• Concreting – Pour, vibrate and aggregate in-situ concrete• Temporary works – Remove, typically after 3 – 5 days,according to specific site advice• Finishing

Typical arrangement ofprops and propping beams Loaded

trailersarriving on site

Liftingelementintoposition

Aligning bubbles between elements

Pouring, Vibrating& Floating SiteConcrete

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

COMPOSITION

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.

THEORY 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(EC2) are made at universities in Germany, Netherlands and Denmark, concluding that a Bubble Deck slab acts like as a solid slab.

BENDING STIFFNESS AND DEFLECTION 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.

The Eindhoven University of Technology and the Technical University of Delft in the Netherlands have performed experiments on the bending stiffness of Voided Slabs.

They focused on the smallest and largest depths of slabs,230mm and 455mm.

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.

SHEAR

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.

The reduced shear resistance will not lead to problems, as plastic bubbles, the shear resistance of a BubbleDeck slab is greatly redused compared to a solid slab.

From theoretical models, the shear strength of the voided slab was determined to be 60-80% of a solid slab with the same depth.

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.

Professor Kleinmann at the Eindhoven University of Technology in the Netherlands, performed physical shear tests to compare a solid slab with BubbleDeck slab.