1. “AdvanceConstructionTechnologyin Mega
Project”
( Bubble Deck Slab System)
Submitted By
Shah Tejas
Chauhan Abhijitsinh
Guided By
Prof. Jaynilya Vagasiya
A Project Report Submitted to
Gujarat Technological University
in Partial Fulfillment of the Requirements for
the Degree of Bachelor of Engineering in
CIVIL ENGINEERING
GROW MORE FACULTY OF ENGINEERING,
HIMMATNAGAR
2. - 2 -
DECLARATION
I hereby certify that I am the sole author of this report and that neither any part of this
work nor the whole of the work has been submitted for a degree to any other University
or Institution. I certify that, to the best of my knowledge, my work does not infringe upon
anyone’s copyright nor violate any proprietary rights and that any ideas, techniques,
quotations, or any other material from the work of other people included in my report,
published or otherwise, are fully acknowledged in accordance with the standard
referencing practices. Furthermore, to the extent that I have included copyrighted material
that surpasses the bounds of fair dealing within the meaning of the Indian Copyright Act,
I certify that I have obtained a written permission from the copyright owner(s) to include
such material(s) in my work and have included copies of such copyright clearances to my
appendix. I declare that this is a true copy of my report, including any final revisions, as
approved by my supervisor.
Date:
Place:
3. CERTIFICATE
This is to certify that project work embodied in this report entitled “Advance
Construction Technology In Mega Project” Sub Topic is “Bubble Deck Slab System”
was carried out by Mr.Tejas Vijaykumar Shah at Growmore faculty of Engineering
for partial fulfillment of B.E. degree to be awarded by Gujarat Technological University.
This project work has been carried out under my supervision and is to the satisfaction of
department. The students work has been published/accepted for publication.
Date:
Place:
Internal Guide Head of Deptartment
Prof .Jaynilya Vagasiya Prof. Mayank
Patel
Principal. Dr. Samir Patel
4. - 4 -
CERTIFICATE
This is to certify that project work embodied in this report entitled “Advance
Construction Technology In Mega Project ” Sub Topic is “Bubble Deck Slab
System” was carried out by Mr.Chauhan Abhijitshin at Growmore faculty of
Engineering for partial fulfillment of B.E. degree to be awarded by Gujarat
Technological University. This project work has been carried out under my supervision
and is to the satisfaction of department. The students work has been published/accepted
for publication.
Date:
Place:
Internal Guide Head of Deptartment
Prof .Jaynilya Vagasiya Prof. Mayank Patel
Principal. Dr. Samir Patel
5. Abstract
Nowadays world is facing problem of global warming, which is mainly responsible
for the carbon emission. There is a great energy consumption and carbon emission
in manufacturing of the concrete. In Voided-slab system, concrete is replaced by the
ellipsoid made up by the plastic wastes, which replace the 30 % to 50 % concrete
compare to the normal slab. So this system is environmentally green and sustainable
- reduces energy and carbon emission. Concrete building can be considered as large
energy consuming items in the Indian construction industry. So in manufacturing of
different materials or building component great energy is consumed and which
results in CO2 emission. Concrete is the major energy consuming material, and it can
be replaced by the plastic spheres, which reduce the carbon emission and utilize the
plastic waste.
The present study is an attempt to understand the exact behavior of the Bi-axial
voided slab. There are chances of reduction of the strength and different failure
pattern than the normal concrete slab. Main objective of the study is to compare the
parameters like deflection, strain and failure pattern. For this purpose eight slab
panel were cast with different thickness, different sphere size. Load-deflection, load-
strain parameters are compared for better understanding of the behavior of the bi-
axial voided slab. Comparison is also done according to economical point of view.
6. - 6 -
Acknowledgements
I would first of all like to thanks Ass. Prof. Jaynilya vgasiya , guide whose keen
interest and excellent knowledge base helped me to carry out the dissertation work.
His constant support and interest in the subject equipped me with a great
understanding of different aspects of the required architecture for the project work.
He has shown keen interest in this dissertation work right from beginning and has
been a great motivating factor in outlining the flow of my work.
I would like to thank the Almighty, my family and all my friends, for supporting and
encouraging me in all possible ways throughout the dissertation work.
-
9. 3.10 Localfailure Mechanism[8] . . . . . . . . . . . . . . . . . . . . . . . .
3.11 V-notch failure mechanism[8] . . . . . . . . . . . . . . . . . . . . . .
3.12 Splitting failure mechanisms[8] . . . . . . . . . . . . . . . . . . . . . .
3.13 Cover bending failure mechanisms[8] . . . . . . . . . . . . . . . . . .
4.1 Sandwiched layer of the Bi-axial voided slab . . . . . . . . . . . . . .
4.2 Cortical section near the column in the flat slab system[11] . . . . . .
5.1 Differentplastic sphere used during the experimental work. . . . . .
5.2 Fixture for punching the holes in plastic sphere . . . . . . . . . . . .
5.3 Binding wire passed through the plastic sphere . . . . . . . . . . . . .
5.5 hooks to hold the plastic sphere against the verticalupward movement
5.6 Mesh of the plastic spheres . . . . . . . . . . . . . . . . . . . . .
5.8 Formwork for the slab . . . . . . . . . . . . . . . . . . . . . . . . . .
5.9 Concreting of the slab . . . . . . . . . . . . . . . . . . . . . . . . . .
5.10 Cube test for the Bi-axial voided slab . . . . . . . . . . . . . . . . . .
5.11 3D view of the setup . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.12 Model of the experimental setup . . . . . . . . . . . . . . . . . . . .
5.13 P3 Strain indicator . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.1 Plan view of the cubes with and without the plastic sphere. . . . . .
6.2 Comparison of the average cubic compressive strength . . . . . . . . .
6.3 Comparison of the average cubic compressive strength . . . . . . . . .
6.4 Comparison of the failure loads in Punching shear test . . . . . . . .
6.5 Comparison of the failure loads in Flexure test . . . . . . . . . . . . .
6.6 Comparison of the failure loads in Flexure test . . . . . . . . . . . . .
6.7 Comparison of the failure loads in Flexure test . . . . . . . . . . . .
6.16 Failure pattern of the cube . . . . . . . . . . . . . . . . . . . . . . . .
6.17 Failure pattern of the cubes having plastic spheres . . . . . . . . . . .
6.18 Failure pattern of the slab VS1 in Punching shear . . . . . . . . . . .
6.19 Failure pattern of the slab VS2 in Punching shear . . . . . . . . . . .
10.
11. Chapter 1 Introduction
1.1 General
On a planet with finite natural resources and an ever-growing built environment,
engineers of the future must consider the environmental, economic, and social
sustainability of structural design. Design and construction practice should be such
that it must significantly reduce, or eliminate the negative impact of buildings on the
environment and its occupants. In order to mitigate the negative impact of buildings
along their life cycle, sustainable structural engineering has emerged as a new
building design philosophy, encouraging the use of more environmentally friendly
materials, the implementation of techniques to save resources and reduce waste
consumption. Voided slab can be considered as the one component of sustainable
structural engineering which minimize the concrete usage and also utilizes the
plastic waste. The major advantage of this system is that, it reduce the concrete
quantity considerably, hence large amount of the CO2 emission can be reduced
associated with concrete manufacturing. In case of manufacturing of the R.C.C most
of the energy is consumed in manufacturing of the steel reinforcement and the
cement. So if there is reduction in concrete there will be reduced energy
consumptions and reduced CO2 emission. So construction practice is made more
environment friendly compare to normal structural system.
The Voided slab is a biaxial concrete floor system developed in Europe. High-density
polyethylene hollow spheres replace the ineffective concrete in the center of the
slab, thus decreasing the dead weight and increasing the efficiency of the floor.
These biaxial slabs have many advantages over a conventional solid concrete slab:
lower total cost, reduced material use, enhanced structural efficiency, decreased
construction time, and is a green technology.
12. CHAPTER 1. INTRODUCTION 2
Through tests, models and analysis from a variety of institutions, Bi-axial voided slab
was proven to be superior to the traditional solid concrete slab. The reduced dead
load makes the long-term response more economical for the building while
offsetting the slightly increased deflection of the slab. However, the shear and
punching shear resistance of the is significantly less than a solid deck since
resistance is directly related to the depth of concrete. Design reduction factors have
been suggested to compensate for these differences in strength. This system is
certified in the Netherland, the United Kingdom, Denmark and Germany and known
as the Bubble Deck
slab system.
1.2 Need of Bi-axil Voided slab
Sustainable engineering is nothing but a design and construction practices that
significantly reduce, or eliminate the negative impact of buildings on the
environment and its occupants. India is developing country and hence selection of
materials and technologies for the building construction should satisfy the felt needs
of the user as well as the development needs of the society, without causing any
adverse impact on environment with economy. Indian construction industry is one
of the largest in terms of employing manpower and volume of materials produced
(cement, brick, steel and other materials).India is responsible for input of energy
resulting in the largest share of CO2 emissions (22%) into the atmosphere. Demand
and supply gap for residential
building-
20 million units in 1985 to 45 million units in 2010.
Cement (75 million tonnes per annum)
Steel (10 million tonnes per annum)
Bricks (70 billion per annum)
13. CHAPTER 1. INTRODUCTION 3
These are the largest and bulk consuming items in the Indian construction
industry. So in manufacturing of different materials great energy is consumed, which
results in CO2 emission. Today the biggest problem is green house effect and carbon
emission is responsible for the green house effect. So this type of the system is better
option compare to the other systems because of reduced concrete usage by utilizing
the plastic waste.
1.3 Concrete floor system
Some of the commonly used floor systems are Flat plate, Flat slab, One-way concrete
ribbed slab, waffle slab, Band beam slab, Hollow-Core slab. These concrete floor
systems are in use today, and are shown in Figure 1.1 and Figure 1.2.
Flat plate system : This type of system is without any column drop panels, beam
or cross girders. Used where spans are not large and loads are not heavy. Can be
used with irregular spaced column layout. Economical up to 4.5 to 7.6m.
Flat slab system: A beamless system with thickened slab at the region of
columns and walls. Thickened portion called drop panels, reduces shear and
negative stresses around the column. Criteria for thickness is check in punching
shear around the columns and long term deflection of slab. In high rise building slab
thickness vary from 127 to 254mm for spans of 4.6 to 7.6 m.
One-way concrete ribbed slabs: Most popular system in North America.
Eliminate concrete in solid slab below neutral axis, by forming voids. Distribution
ribs are placed approximately 3m centers for span greater than 6m. Economical up
to 9m to 10.6 m span.
Waffle slab system: It is also called as two-way joist system. To reduce the dead
load of a solid slab by construction domes in a rectilinear manner. Domes are
omitted near column. Thickness is governed by deflection, punching shear around
14. CHAPTER 1. INTRODUCTION 4
column and shear in ribs. More efficient for span range 9m to 12m and economical
between 9 to 15 m.
Figure 1.1: Flat plate system, Flat slab system, One-way concrete ribbed slabs, Waffle
slab system,
Band beam system: System uses wide shallow beams. Consists of a uniform slab
with thickened portions below the slab along the column lines parallel to the longer
spans. The thickened portions of the slab, commonly referred to as bandbeams, are
post-tension. One of the main advantages of this system is that long, unobstructed
spans can be achieved with a minimum structural floor depth. Significant cost
savings.
15. CHAPTER 1. INTRODUCTION 5
Hollow-Core slab: This slabs are used for the one-way slab spanning. The precast
concrete slab has tubular voids extending the full length of the slab, typically with a
diameter equal to the 2/3 to 3/4 of the slab. This makes the slab much lighter than a
massive floor slabs of equal thickness or strength. Reduced weight is important
because of less transportation cost and less cost of material (concrete). The slabs are
typically 120 cm wide with standard thicknesses between 15 cm and 50 cm. The
precast concrete I-beams between the holes contain the steel wire rope that provide
bending resistance to bending momentum from loads.
Figure 1.2: Band beam system, Hollow-Core slab
1.4 Applicability of Bi-axial voided slab system
Bi-axial voided slab minimize the concrete usage by replacing the concrete with
plastic balls made up from the plastic waste. 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. 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.
16. CHAPTER 1. INTRODUCTION 6
This system is best suitable for the large span structures were column free area is
require. This system is economical for the large span structures like, office building,
shopping malls, parking structures,etc.
This system is not advisable for small scale and small span structure because it will
not prove economical.
Figure 1.3: Cross section of Bi-axial voided slab system [3]
1.5 Comparisonwith normal slab
Two-way voided deck slab provides the potential for savings on materials, floor
depth, slab weight, foundation and build-time if incorporated at the design stage.
It allows for a considerable reduction in volume and weight of the slab without
compromising the strength. It provide a very cost-effective alternative to achieve the
required deflection criteria in long span application. More number of the floors can
be constructed within the same height. Consider the benefits according to a typical
4,500 m2 office building with 7.5m × 7.5m meter multiple spans between in-situ or
precast concrete columns.
Table 1.1: Comparison with the normal slab on the basis of sustainability [4]
Slab Site conc. Site conc. Total slab Embodied Carbon
Depth Volume Quantity Dead load Energy Emissions
(mm) m3/m2 m3 (Tonnes) (Giga j.) (Tonnes)
Solid slab 310 0.31 1,395 3,376 3,278 522
17. CHAPTER 1. INTRODUCTION 7
Voided slab 230 0.11 495 1,758 1,707 272
It saves 80 0.20 900 1,618 1,571 250
Assumptions:
(1) Typical office live load 2.5kN/m2+1.5kN/m2 for lightweight partitions,
computer floor, finishes & services.
(2) Energy from materials transport cement 50 miles, aggregate 10 miles (to
ready mix plant) and concrete 5 miles (to site).
1.6 Advantages of Bi-axial voided slab system
Advantages of Bi-axial voided slab system are as follows[3]:
• Approximately 41% embodied carbon reduction.( In slab only).
• Saves 35% weight compared to a corresponding solid slab having equal
stiffness.
• Wide open spaces, column free area.
• Construction time reduces with the precast slab system.
• 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.
• It is also seismic friendly as it lowers the total weight of the building.
• Reduced concrete usage 1 kg recycled plastic can replaces 100 kg of concrete.
• Lighter weight slabs means reduced costs for foundations.
• Ideal for poor ground conditions.
• It is having lower heating/cooling costs.
• Low weight/stiffness ratio.
• Building costs are reduced by 8 to 10 %.
• More number of the floors can be accommodating within the same height.
18. CHAPTER 1. INTRODUCTION 8
1.7 Objective of study
Aim of the project is to understand the behavior of the slab after installation of the
plastic spheres by experimental work. Design of the slab will be carried out
considering the normal slab condition. By the experimental work the performance of
the voided slab will be observed and compared with the normal slab and reduction
factor will be established.
1.8 Scope of the work
• Introduction to the Bi-axial voided slab system.
• Design of the tow-way slab.
• Developing the testing setup for the slab testing.
• Procuring the plastic balls.
• Casting of slab panels.
• Observation of behavior of the slab under bending and shear failure.
• Observation of the deflection, strain, failure load.
• Comparison of the test observation with the design.
• Comparison of Bi-axial voided slab system with the normal slab system,
according to the comparison multiplication factor will be given.
1.9 Organization of the work
Following line of action was decided.
The Major Project is divided into seven chapters. They are as described below:
Chapter 1 introduces the topic and gives a general information about the Bi-axial
voided slab system, applicability of the systems, advantages of system, objective of
work, and scope of the work.
19. CHAPTER 1. INTRODUCTION 9
Chapter 2 is about the literature review. This chapter will give idea about the
papers referred. This chapter will give brief about the papers which are important
for major project work.
Chapter 3 is for understanding the system and the specification of different
component, design aspect, design of the bi-axial voided slab.
Chapter 4 is about the design of the slab.
Chapter 5 will provide information about the experimental work, that is size of the
slab, size of the plastic sphere, spacing of the spheres in slab, casting procedure,
detailing of the reinforcement, dimension of cover, testing setup, equipment and
tools to be used for the testing, parameters to be observed while testing loading
pattern.
Chapter 6 will have Results and Discussion. This chapter will be comparison based.
Chapter 7 will include Summery, Concluding remark, Future scope of work.
20. Chapter 2
Literature Survey
2.1 General
For the objective of major project an extensive literature review relevant to Bi-axial
voided slab is carried out. This chapter explores various details of papers on the bi-
axial voided slab system, from structural engineering point of view.
2.2 Literature Review
Various literature related to effective vertical load resisting system(Bi-axial voided
slab) are studied and brief review is presented below.
Embodied energy of common and alternative building materials and
technologies -By B.V. Venkatarama Rcddy: K.S. Jagadish. This paper includes the
information about the alternative roofing systems like- SMB filler slab roof, RC
ribbed slab roof, Reinforced brick panel roof. Unreinforced masonry vault roof.
Energy of different alternative roofing systems has been discussed and compared
with the energy of conventional reinforced concrete (RC) slab roof. Total embodied
energy of a multi-storied building, a load bearing brickwork building and a soil-
cement block building using alternative building materials has been compared.
10
Method for Bubble Deck Concrete slab with gasps -By Sergiu Calin and
Ciprian Asavoaie. It gives short Description of the Bubble Deck slab. The Bubble
Deck Method for the two directions reinforced composite concrete slab with gaps
was invented in Denmark. By this system we can achieve saving of concrete and
energy in buildings construction. By introducing the gaps leads to a 30 to 50%
21. CHAPTER 2. LITERATURE SURVEY 11
lighter slab. Due to this there will be reduction of the loads on the columns, walls
and finally on the entire building. Bubble Deck slab elements are plates with ribs on
two directions made of reinforced concrete or precast concrete with spherical
shaped bubbles. These slab elements have a bottom and an upper concrete part
connected with vertical ribs that go around the gaps. Cross section is shown in
Figure. 2.1. The bubbles are made by embodying high density polypropylene (HDPE)
in the concrete, arranged according to the project and placed between the
reinforcement meshes. The material is such that, it does not react chemically with
the concrete or the reinforcement, it has no porosity and has enough rigidity and
strength to take the weight of the concrete during the casting of the slab.
The nominal diameter of the gaps may be of: 180, 225, 270, 315, or 360 mm. The
Figure 2.1: Arrangement of sphere and Rebars
minimum distance between gaps is 1/9 of the gaps diameter. The total height may
be: 230, 280, 340, 390 or 450 mm. The weight of Bubble Deck slabs is function of its
dimensions and its a fact that regardless of the diameter of the bubble used,
respectively the thickness of the slab, the own weight stays practically constant. In
order to increase the shear strength capacity and bending moment in the ares with
stress concentration it is possible that in these areas gaps are not provided Figure
22. CHAPTER 2. LITERATURE SURVEY 12
Figure 2.2: Arrangement of Balls near the shear zone and transverse reinforcement
Bubble Deck institute -product introduction. This paper includes the
introduction to the system. It includes the brief about the composition of the
slab,Theory, Shear, Fire, seismic, Advantage. This paper gives comparison with the
normal slab system. This paper also gives idea about the installation process of the
system. It is also having the information of the project were this system is used.
Omnia and Cobixial flooring system -Hanson Heidelberg Cement Group. This
paper includes the information about the similar kind of slab system with some
alteration. The name of the system is Omnia and Cobiaxial. This paper includes
information about the installation process and accessories. It gives the idea about,
how the formwork is provided, distance of the propped, shuttering type. It also
23. CHAPTER 2. LITERATURE SURVEY 13
includes the Cobiaxial benefits. This paper gives information about the supporting
system, bearing on steel work, bearing on in-situ concrete, bearing on masonry.
CRU Recommendation 86. CRU- Center for civil engineering Research and codes, is
the guide line to be followed for the design of the bi-axial voided slab. It includes
Subjects and scope of application, Terms and definitions, Material properties,
Theories, Dimensioning and assessment, Design values of the shear resistance, Shear
stress to be resisted by the reinforcement, punching shear verification criterion,
Flexural stiffness, cracking, Detailing of the slab. It gives idea about how the required
reinforcement is determine, Reinforcement detail at the joints.
Bubble deck UK- Site Erction & installation Manual. This manual includes the
Bubble Decks construction package. It gives the construction stages of the system,
ie., Bubble Deck design, Drawing production, Construction planning, Product advice
and supports, Manufacturing product, Loose reinforcement and material, Site
Delivery, Site support, Site Inspection. This manual gives idea about the Pre-
Construction planning and its stages, Planning pre-cast elements. It also gives
information about the Erection of the temporary propping, Delivery, Lifting and
Placing of element, Aligning the bubbles between the elements, cut-outs, service
holes, Preparation of concrete, Removing temporary propping.
Bubble deck Flat slab solutions. This paper includes the information about the
design aspects. It gives detail about the Shear, Deflection, Contact between the
sphere & reinforcements, Effect of Voids upon Stiffness, Flexural Strength, Shear
strength, Durability, Results from tests, studies and reports, How the shear
accounted near the columns. For design of the slab which theories should be used
and which international standards should be followed is given. It gives criteria
related to the punching shear. According the manual EC2 is to be followed for the
shear criterion.
24. CHAPTER 2. LITERATURE SURVEY 14
For the deflection this paper suggest to follow the FEM analysis process and
combined with that EC0 should be followed. For design process Plastic design is
followed with ductility class B steel given in EC2.
Technical paper of Bubble Deck span guide. This paper is about the relation ship
between the span and depth. It gives the values of span to depth ratio for the simply
supported floors, continuously supported floors, cantilever slab. This paper is
having the table which relates the various thickness of the slab with the maximum
span. It also gives the values of the total concrete cover (c’) and effective depth for
the different size of the slab with different values of the fire resistance. sample
calculation is given in which Bubble Deck slab is found out for the given spans. FE
calculation results are also given for the single row with continuous bays, single bay
both direction and for cantilevers.
Moment capacity in a Bubble Deck joint - Tim Gudmand Hoyer. This
paper includes Backgroud theory, Failure Mechanisms in a joint, a case study of an
actual load carrying capacity, a case study for a design situation. The theory used in
this note is the theory of plasticity with some modifications. Moment capacity
equation in the case of bending failure is given in this paper. It also gives the
equation for the shear capacity of a rough joint. It gives the idea about the various
possible failure mechanisms. Total 6 type of failure mechanisms is given in paper. In
case study, calculation of the actual load carrying capacity is done, slab considered is
consisting of a precast bottom slab and a part cast in-situ.
Punching behavior of biaxial hollow slabs - By Martina SchnellenbachHeld,
Karsten Pfeffer. This paper gives the test specification and results of the test
carried on two different thickness of the slab. Because of its main field of application
as a flat slab, the punching shear capacity is one of the most interesting properties of
this slab. To investigate the influence of the cavities on the punching behavior. tests
were carried out at the institute for Concrete Structures in Darmstadt. In addition to
these tests nonlinear computations using the Finite Element Method were
25. CHAPTER 2. LITERATURE SURVEY 15
performed. The computations allowed parametric studies to get a better
understanding of the structural behavior without doing further expensive tests.
Finally, necessary modifications of existing design recommendations according to
the German design code DIN 1045 [1] were developed.
To investigate the punching shear capacity of the bi-axial hollow slabs, three
specimens with a thickness of 240 mm and three specimens with thickness of 450
mm were produced and tested. By choosing these two of thickness, which represent
practicable values, the influence of a possible size effect could be studied. The slabs
were cast with M25 concrete and M30 concrete. Each specimen included the slab
and a short column to simulate a realistic punching situation. The dimension of the
tested slabs are shown in Figure 2.3. During the test specimen was fixed in eight
points arranged in a circle with a radius of 1125 mm. The load was applied by the
hydraulic Jack at the center.
Figure 2.3: Slab panel details
26. CHAPTER 2. LITERATURE SURVEY 16
Issue for achieving an experimental model concerning bubble deck
concrete slab with spherical gaps. By- sergiu calin, ciprian asavoaie and N.
Florea. The paper is consisting of the experimental program which refer to the
concrete slab with the spherical gaps, existing in similar execution and loading
conditions as those from real construction. The monolithic slab at 1:1 scale is
constructed and subjected to gravitational static loads in order to determine the
deformation, cracking, and failure characteristics. The surface area of the slab is
42.51 m2. center to center distance between the column is 5 meter. The detail of the
slab spacemen is given in the Figure 2.4. Unit is in cm.
Figure 2.4: Slab panel details
Figure 2.5. shows the loading arrangement of the slab.
According to their observation, it will have a positive impact under technical, eco-
27. CHAPTER 2. LITERATURE SURVEY 17
nomic and social point of view materialized in- ensure certain rigidity in horizontal
plan of the reinforced concrete slab with spherical gaps based on which slab is
capable to transmit efficiently the horizontal loads specially the seismic loads.
The structural behavior of precast concrete sandwich panels (PCSP) under flexure is
studied both experimentally and theoretically. The details and results of the test
program are described, and the observed behavior patterns are discussed. The
theoretical investigation consists of finite element modeling of the test specimens.
The finite element results were compared with the experimental data.This paper
will be helpful for developing the testing setup for the two way slab system for
finding the flexural strength of the slab. This paper gives information about the
setup for the testing of the two way slab panel.
28. Chapter 3
Bi-axial voided slab component and
Design
3.1 Background
There are several components of the green building, Bi-axial voided slab can be
considered as the integral part of the green building system. The concept of reducing
the concrete by the plastic sphere is widely used in the other countries like
Denmark, Russia, North America, U.K., Australia, etc., There are mainly two kind of
the slab system is popular: (1) Bubble Deck slab system (2) Omnia and Co-biaxial
Flooring system. Both type of the system have the same concept but having some
slight differences in the components and some specification. In India Filler slab roofs
are popular. Filler slab roof is having the same concept but the basic difference from
the other system is, instead of the plastic spheres the replacing materials are
Stabilized mud blocks, or Burnt clay brick or Hollow concrete blocks.
Here we will discuss and give the overview of the Bubble Deck slab, because it is
widely used in the other countries. Different components of the system is shown in
the Figure 3.1. The main components of the system are, top and bottom
reinforcement meshes, plastic balls, lattice girder, concrete. Top reinforcement is
placed in such a way that, it locks the balls in the position. Lattice girder acts as
shear connectors and join the top and bottom reinforcement mesh and also
contributes in flexural strength.
29. CHAPTER 3. BI-AXIAL VOIDED SLAB COMPONENT AND DESIGN 19
Figure 3.1: component of the Bubble deck slab[3]
3.2 Component of the system
3.2.1 Plastic Sphere
Plastic spheres are made up of the plastic waste. Spheres are placed in between the
top and bottom rebar as shown in Figure 3.2. The sphere diameter is always 0.9 of
the slab size[2]. The cover to the sphere should be at least 1/9th of the sphere
diameter[2]. The cover to the sphere and to the reinforcement may vary. The
spheres are made of material that doesn’t react chemically with the concrete and/or
the reinforcement steel. It is made up from the material HDPE- High Density
polypropylene[2]. The sphere are non-porous and possess enough strength and
stiffness to carry applied loads safely. Sphere size generally provided is
180,225,270,315,360 mm[2].
30. CHAPTER 3. BI-AXIAL VOIDED SLAB COMPONENT AND DESIGN 20
Figure 3.2: Location of the plastic sphere
3.2.2 Lattice girder
Lattice girder is made of the steel rebar generally of Fe 415 and Fe 500. Rebar size
depends on the span, thickness of slab. It contributes in resisting flexural. Lattice
girder is spaced 1 to 1.5 m spacing or 3 sphere maximum[2]. Lattice girder is pre
fabricated. There are mainly two type (a) self supporting lattice girder and (b)
trussed type lattice girder. Girders are supplied in height increments of 10mm but
some suppliers may supply any size. The diagonals are at 65o[3] approximately in
case of the self supporting type while in case of the trussed type lattice girder
diagonals are at 45o[4] and must be welded securely to the longitudinal bars. The
standard girder spacing, as outlined in CUR 86 is two sphere maximum[7]. Greater
spacing is possible but the unit may become too flexible and crack more easily
during transit or handling. The longitudinal girder bar should be 10mm minimum
for the 200 and 250 modules and at least 12mm for 300 modules and above. The
girder web bar may usually be 7mm or 8mm and 8mm is preferred except in light
applications.
Following Figure 3.3 shows both type of the lattice girder.
31. CHAPTER 3. BI-AXIAL VOIDED SLAB COMPONENT AND DESIGN 21
Figure 3.3: Types of Lattice girder[4]
Positioning of the lattice girder: Figure 3.4 shows the location of the lattice girder.
Generally spacing of the girder is 3 sphere maximum between two girder. Lattice
girder are placed in position at the time of the casting of the bottom precast of the
slab. It is attached to the bottom reinforcement mesh. After placing the sphere it is
also connected to the top reinforcement mesh.
Figure 3.4: Position of the lattice girder[4]
32. CHAPTER 3. BI-AXIAL VOIDED SLAB COMPONENT AND DESIGN 22
3.2.3 Concrete
Self compacting concrete is used with smaller size of the aggregates. Generally M25
and M30 grade concrete is use in normal bi-axial voided slab. In case of the post
tension slab system minimum grade of the concrete is M40. According to the
requirement any grade of concrete can be used.
3.2.4 Top and bottom reinforcement
This system is provided with the top and bottom reinforcement both. The spacing
and size of the bars depends on the span and loading of the slab. Some time machine
made meshes are also provided which have one or more of the following
restrictions: -Maximum bar size 16 mm[6].
-Longitudinal bar spacing increments of 50 mm c/c (eq. 50mm/ 100mm/ 150mm/
200mm)[6].
-Cross wire spacing sometime sometimes in 25 mm increments but my be 25mm
increments but may be unrestricted according to machine type.
- Minimum distance from last bar to end is 25 mm[6].
Figure 3.5 shows the location of the top and bottom reinforcement mesh. Two
reinforcement meshes are connected by the lattice girder. The grade of the steel
rebars will depend on the design.
33. CHAPTER 3. BI-AXIAL VOIDED SLAB COMPONENT AND DESIGN 23
Figure 3.5: Position of top and bottom reinforcement mesh
3.2.5 Deck types of the Bi-axial voided slab
There are mainly three types of the deck (a) cast in situ (b) semi- precast (c) precast
deck.[3] Figure 3.6 shows the deck types.
Figure 3.6: Deck types of the bubble deck system[3]
In case of the cast in situ deck, whole work; placing of the rebar, placing of the
sphere, placing of the lattice girder is done at the site.
In case of the Semi-precast deck first bottom part of the slab is cast in the casting
yard and then they are placed in position. After placing the deck in position, spheres
34. CHAPTER 3. BI-AXIAL VOIDED SLAB COMPONENT AND DESIGN 24
and the top reinforcement mesh is placed and casting is carried out. Bottom deck
acts as the shuttering.
In case of the fully precast slab the whole slab is cast in the casting yard and then
it is lifted and placed in position. Precast slab is connected to the beams by the shear
connectors and u-pins at the edges.
3.3 Supportingsystem of the slab
While placing the precast slab mainly three conditions can be arrived:
(1)Bearing on the steel frame. (2)Bearing on in-situ concrete. (3)Bearing on ma-
sonry.[4]
(1) Bearing on the steel frame Figure 3.7.(a) shows the condition when the
deck is horizontal, deck is rested over the flange of the beam. Figure 3.7(a) shows
when all the peripheral beams are at same level. Minimum supporting length
required is 10 cm. Figure 3.7(b) shows the condition when the deck slab is inclined.
Due to the inclination there is a chance of the point contact between the slab corner
and the supporting beam. In this case the shape of the corner should be such that
there is a uniform support to the deck. Some time wedges are placed to have proper
supporting length. Figure3.7(c) shows the condition when the depth of the
supporting beam required is high. So to reduce the total height of the floor the
precast slab is rested on the web of the beam, for that a angle section is welded to
the supporting beam.
(2) Bearing on in-situ concrete Figure 3.8(a) shows the condition when
Support panels are on the formwork and beam is cast in-situ. Figure 3.8(b) shows
when supported on half-cast beams, links must be provided for the connection.
Figure 3.8(c) shows Where less than 55mm bearing is available, a suitable
35. CHAPTER 3. BI-AXIAL VOIDED SLAB COMPONENT AND DESIGN 25
temporary prop must be in place before placing the panel and left in place until the
in-situ portion has reached working strength.
(3)Bearing on masonry As shown in figure 3.9(a), panels are usually detailed to
take the full bearing of the internal skin of masonry. In Figure 3.9(b) shown that two
slab panels can be supported on 140mm wide load bearing block work with a 20mm
gap between. Figure 3.9(c) shows where less than 55mm bearing is available ie., on
100mm walls, temporary props should be in place prior to placing the panels.
3.4 Design of the Bi-axial voided slab
3.4.1 Design aspect
Shear: The shear resistance of Voided slab is a slightly conservative value, taken
from tests, which we use in design: 0.6 times the shear resistance of a solid slab of
the same thickness[10]. If this is exceeded by the applied shear, at a column, we
leave out the balls and use the full solid shear values. Test conducted in Germany,
Denmark and Holland have shown the resistance to vary from about 65% to
90%[10] of a solid
slab. Using our IS:456 one may calculate the critical shear at d distance from the 2
column face, where d is the effective depth of the slab. This would then be compared
to the calculated resistance.
-If the applied shear is less than the un-reinforced hollow slab resistance, no further
check is required.
-If the applied shear is greater than the hollow slab resistance we omit sphere and
make it solid then check the solid part.
-If the resistance is still greater than the solid slab resistance and less than the
maximum allowed, we provide shear reinforcements.
36. CHAPTER 3. BI-AXIAL VOIDED SLAB COMPONENT AND DESIGN 26
Flexure: A standard method may be used provided that the depth of concrete in
compression does not overlap the sphere zone by more than 20%[10]. This is almost
always the case in all but extremely heavily stressed slabs. The maximum moments
are usually over the columns or supports. A rectangular stress distribution or other
appropriate distribution may be used in the concrete. EC2 contains a useful and
simple method but other plastic methods may be used. Steel should be ductility class
B, especially if plastic design is used, unless special calculations prove class A to be
satisfactory[10].
Deflection: Span depth ratio calculations for deflections are very approximate and
are not appropriate in flat slabs of irregular layout except for the most simple or
unimportant cases. FE modeling, including non-linear cracked section analysis is
used to calculate the deflection using normal structural concrete with a Young’s
Modulus (secant) Ecm, multiplied by 0.9 and a tensile strength, fck multiplied by 0.8
(to reduce the crack moment). FE analysis is recommended for all slabs as there is
no practical manual method that can be used with confidence. Even unidirectional
spans can be very tedious in the computation of deflections.
Stiffness: Unlike hollow core units, Bi-axial voids are discrete sphere and not
prismoidal voids running the length of the span. This makes a huge difference to the
performance compared to hollow core sections. Test carried out in Denmark,
Germany and Holland show that the flexural stiffness is approximately 87% to
93%[10] of the same thickness of solid slab. In design average of 90%[10] and, in
addition, factor is applied to the cracking moment 80%[10] as recommended in
Dutch research. Seismic design: The concerns in Seismic design are largely similar
to any flat slab structure. Punching shear under seismic conditions is the most
critical issue and damage at the slab-column junction during sway reversals should
be properly considered as well as amplification of the punching shear due to the
vertical component of ground acceleration. In computing the building’s response,
the seismic designer should be closely engaged with determination of the mass and
37. CHAPTER 3. BI-AXIAL VOIDED SLAB COMPONENT AND DESIGN 27
the effect of this on modal spectrum. Using sphere a significant reduction of mass in
the floor plate may be realized together with an increase in modal frequency and
reduction in the sway forces due to lateral acceleration.
Span to depth ratio:
L/d is 30[9] for simply supported floors L/d
is 41[9] for continuously supported floors
L/d is 13.0[9] for cantilevers.
This basic principle has been verified for up to 4.5 kPa live + 1.5 kPa dead uniformly
distributed loadings following full calculation and proven by full finite element
analysis modeling to provide a generally reliable indication.
Approximate span for given Bubble Deck slab depth: To determine an in-
Table 3.1: Effective depth of the Bi-axial Voided slab[9]
Thickness(mm) Slab thickness 1 Hour Fr 1.5 Hour Fr 2 Hour Fr
mm mm mm mm
230 230 196 191 186
280 280 246 241 236
340 340 304 299 294
390 390 304 299 294
450 450 346 341 366
510 510 401 396 391
600 600 461 456 451
dicative possible maximum span for a given slab depth, multiply the relevant
Effective Depth (d) by the (span/effective depth ratio=(R) )for the appropriate slab
configuration given above. As an example for 280 thick slab, with 1.5 hour fire
resistance, (d) is 241 mm so 4l × d indicates a maximum 9.88 meter continuously
supported (multiple bay) span; 30 × d indicates a maximum 7.23 meter simply
38. CHAPTER 3. BI-AXIAL VOIDED SLAB COMPONENT AND DESIGN 28
supported (single bay) span, and 12.5 × d indicates a maximum 3.01 meter
cantilever is potentially feasible.
3.4.2 Failure Mechanism of the slab
The theory used is the theory of plasticity with some modifications. For slabs
consisting of two parts some special failure mechanisms may occur. The standard
failure mechanisms are shown in Figure 3.10, Figure 3.11, Figure 3.12.
There are mainly three types of Failure Mechanism[8]:
(a) Local failure Mechanism.
(b) V-notch failure mechanism.
(c) Splitting failure mechanism.
(d) Cover bending failure mechanisms.
For a failure involving a reinforcement bar subjected to a force P in the direction
of the bar.
The external work becomes:
We = P cos(α)
The dissipation is calculated as a contribution from a local failure mechanism L. a
failure in the surrounding concrete S and a contribution from the reinforcement B.
The work equation becomes:
nP cos(α) = nL + S + B (3.1)
The bond strength contribution from the local failure of one bar may be calculated
as:
(3.2)
The bond strength contribution from the failure in the surrounding concrete is:
39. CHAPTER 3. BI-AXIAL VOIDED SLAB COMPONENT AND DESIGN 29
(3.3)
The bond strength contribution from the reinforcement is:
(3.4)
Figure 3.10: Local failure Mechanism[8]
Figure 3.11: V-notch failure mechanism[8]
Figure 3.12: Splitting failure mechanisms[8]
In the case of the bending failure, the moment capacity may be calculated as:[8]
40. CHAPTER 3. BI-AXIAL VOIDED SLAB COMPONENT AND DESIGN 30
(3.5)
(3.6)
Where:
Figure 3.13: Cover bending failure mechanisms[8]
(3.7)
(3.8)
The shear capacity of a rough joint may in general be calculated as:[8]
0
τ = c + 0.75(rfyd + σ) (3.9)
When the external force gives rise to tensile stresses in the joint the shear capacity
should be calculated as[8]:
τ = 0.75rfyd (3.10)
41. Chapter 4
Design of the slab Specimens
4.1 Introduction
Experimental study is conducted on the 135 and 140 mm thick slab. From the 8 slab
panels 2 are plain slab and 6 are Voided slabs. From the 6 slab panels 2 slabs are
having the 135 mm size plastic spheres at 150 mm c/c, 2 slabs are having 135 mm
size plastic spheres at 125 mm c/c spacing and 2 slabs are having 110 mm size
plastic spheres at 150 mm c/c. Design of the slab is done according to the IS 456
:2000provision. After designing the slab as the normal slab plastic sphere were
installed in the slab at the spacing as mentioned earlier. For the analysis and design
of the Voided slab, element can be constructed in SAP 2000. Finite element model
can be prepared. Voided slab can be designated as a layered shell. For simplicity in
the Voided slab model, a rectangular layer of HDPE- High density polyethylene is
sandwiched in between two thin layers of the standard concrete on top and bottom
only. Standard material property is given to both the type of the material. It is shown
in Figure 4.1.
Here, we done the design of the slab as a simple concrete slab. Plastic spheres were
installed in the slab. We test the both the type of the slab and compare the results of
the experimental work, and reduction factor is established.
42. CHAPTER 4. DESIGN OF THE SLAB SPECIMENS 32
Figure 4.1: Sandwiched layer of the Bi-axial voided slab
4.2 Backgroundofthe theory
Generally Bi-axial voided slab system is used as the flat slab. But it can be used same
as the beam-slab system. The similar kind of the alternative system used in India is
Filler slab roofs. Filler slab roofs are basically solid reinforced concrete slabs with
partial replacement of the concrete in the tension zone by a filler material. It is a
Beam-slab system. A number of the filler materials can be thought of: (a) Brick (b)
Mangalore tiles, (c) Stabilized mud block, (d) Hollow concrete Blocks, (e) Hollow
clay tie blocks. Size and shape of the filler material are governed by the factors like
slab thickness, code guidelines on spacing of reinforcement bars, desired ceiling
finish, etc., and has to be carefully selected. Quantity of concrete in the tension zone
of slab that can be replace by the filler material depends upon the shape of the filler
material available and the thickness of the solid slab.
In experimental work we used the hollow plastic sphere instead of the various filler
material because of the certain advantages like, more lighter construction, benefit of
the arch action at the top, utilization of the plastic waste, finished surface is similar
to the normal slab.
When this system is used as the flat slab, shear on the periphery of the column is
critical. So critical shear near the column area is found out and the plastic sphere are
omitted at the critical zone near the column area.
43. CHAPTER 4. DESIGN OF THE SLAB SPECIMENS 33
Shear in Flat slab: According the clause 31.6. IS 456 : 2000 the critical section for
shear shall be at a distance d/2 from the periphery of the column/capital/drop
panel, perpendicular to the plane of the slab where d is the effective depth of the
section. The critical section is shown in Figure 4.2. for rectangular and circular
column. The normal shear stress in flat slabs shall be taken as V/b0d where V is the
shear force due to design load, b0 is the periphery of the critical section and d is the
effective depth.
Figure 4.2: Cortical section near the column in the flat slab system[11]
4.3 Design of the slab specimen
Two slab thickness were used for the experimental work with different percentage
reinforcement. There are mainly three type of the slab. The design of the slab is
given below.
44. CHAPTER 4. DESIGN OF THE SLAB SPECIMENS 34
(1) Design of the slab specimen
Assumed parameter for the slab specimen 1:
Assumed total load = 67 Kn/m2.
cover to the slab = 20 mm. Grade
of concrete M 25
Grade of steel Fe 415
End condition : Four side discontinous
Effective size of the slab panel: 1.5m × 1.5m
Thickness of the slab = 135 mm.
From IS 456 :2000 Table 26 αx = αy = 0.056.[11] Where αx and αy are the mo-
ment coefficient in x and y direction respectively.
Mu = 1.5 αxw l2
= 1.50×.056× 65× 1.52 =
12.66 Kn m.
Percentage steel =
where,
d= 111 mm
fck= 25 mpa fy
= 415 mpa b
=1000 mm
Pt = 0.2997 %
45. CHAPTER 4. DESIGN OF THE SLAB SPECIMENS 35
Area of steel = Ast
= 0.290×10 ×111
= 332.67 mm2
Spacing = ( 50.26×1000)/322
= 151.07 mm c/c
Providing 8 mm dia. bars at 150 mm c/c.
Actual Pt= 0.3
Shear check:
Shear at the end Vu= Wu × (lx/2)
=67× (1.5/2) =50.25
Kn
τv= Vu/(bd)
= 48.75×1000/(1000×111)
= 0.452 N/mm2
Actual Pt= 0.300 τc=
0.386 N/mm2
K= 1.3[11]
K τc = 0.5018 N/mm2 >τv (ok)
46. CHAPTER 5. EXPERIMENTAL WORK DETAILS 36
Chapter 5
Experimental work details
5.1 General
Aim of the project is to compare the shear and flexural capacity of the Normal
slab and the Bi-axial voided slab experimentally. For fulfilling the aim casting
of the 8 slab panels were carried out. For the testing of the slab setup for the
testing is fabricated and slab is tested under controlled condition.
Hollow Plastic spheres are the main component of the slab. Plastic spheres
were procured from the plastic industry. The material of the Plastic sphere is
HDPEHigh Density Polypropylene. Two sizes were used: (1) 95 mm size
sphere (2) 110 mm size sphere. The experimental setup is such that,
maximum size of the slab can be tested is 1.6m × 1.6m. This setup is able to
test both, two-way and one-way slab. The slabs are tested for the flexure and
punching shear test. The loading to the slab is applied by the hydraulic Jack,
supported loading frame. For flexure and punching shear test there are
different loading arrangement.
5.2 Detail of the slab specimens
For the experimental work, 8 specimens were cast and tested. The details of
the slab specimens are given in Table 5.1.
43
Table 5.1: Notation and detail of the slab specimens.
Sr. Slab Notation Thickness Diameter Diameter Spacing Testing
No. Type of slab of of bars of bars type
(mm) sphere (mm) (c/c)
1 Plain PS 135 - 8 150
2 Voided PS1 135 95 8 150 Punching
47. CHAPTER 5. EXPERIMENTAL WORK DETAILS 37
3 Voided PS2 135 95 8 150 Shear
4 Voided PS3 140 110 8 125
5 Plain PF 135 - 8 150
6 Voided VF1 135 95 8 150 Flexure
7 Voided VF2 135 95 8 150 Test
8 Voided VF3 140 110 8 125
Detail of the plastic sphere: During the Experimental
work Cue test was performed on the four type of the plastic
sphere. Figure 5.1 shows the four types of the plastic sphere.
Plastic sphere used in the slabs are 95 mm size type 2 and 110
mm, it is shown in Figure 5.1(b) and 5.2(d) respectively.
Figure 5.1: Different plastic sphere used during the
experimental work
Arrangement of the plastic sphere and reinforcement
details:
Normally for arrangement or fixing the plastic spheres top reinforcement is
use. But due to the top reinforcement there will be increase in the percentage
steel in the slab. So to keep the reenforcement as equal to the plain slab,
binding wire is used to hold the sphere in position. For this purpose there is
need to pass the binding wire from the plastic sphere. For passing the
binding wire 4 holes were made in the sphere exactly perpendicular to each
other. For making the holes at exact location, fixture is prepared with two
different sizes. Figure 5.2. shows the Fixture for 110 mm and 95 mm size
sphere. Height width and the depth of the box is kept equal to the diameter of
the Plastic sphere. Sphere is put inside the box and than through the holes of
the fixture hole is punched. After the hole is made, binding wire is passed
through the holes as shown in Figure 5.3.
48. CHAPTER 5. EXPERIMENTAL WORK DETAILS 38
Figure 5.2: Fixture for punching the holes in plastic sphere
Figure 5.3: Binding wire passed through the plastic sphere
For Better results Plastic sphere should be placed at the center of the squares
made by the rebars. For This purpose hooks are made at the 450 angle.
Binding wire of the sphere mesh is tide tightly to the inclined hooks as shown
in Figure 5.4. Plastic spheres are the hollow so it will act as air bubble, so
when we apply the needle vibrator sphere will try to come vertically upward.
Now binding wire is flexible, so at the time of the compaction plastic sphere
will come on the surface. So to overcome this difficulty U shaped hooks are
prepared to hold the plastic sphere in position. Two hooks were installed on
each side of the plastic sphere as shown in Figure 5.5.
49. CHAPTER 5. EXPERIMENTAL WORK DETAILS 39
Figure 5.5: hooks to hold the plastic sphere against the
vertical upward movement
Figure 5.6: Mesh of the plastic spheres
For quick installation, mesh of plastic spheres were prepared
as shown in the figure 5.6. This mesh can directly put on the
reinforcement and binding wire is tied to the hooks.
50. CHAPTER 5. EXPERIMENTAL WORK DETAILS 40
5.4 Volume of the slab
Table 5.2 shows the Final volume of the slab spacemen. In the calculation the
number of sphere is found out and total volume of sphere is calculated. Total volume
of sphere is deducted from the plain slab volume. Percentage reduction compare to
the normal plain slab is also shown in Table 5.2.
Table 5.2: Final volume of the slab specimen.
Slab Nos. Volume of Total volume Volume of reduction
Specimen of Sphere Sphere of Sphere Slab compare to
specimen solid slab
(m3) (m3) (m3) (%)
PS,PF - - - 0.304 -
VS1,VF1 64 0.000449 0.02874 0.275 9.4604
VS2,VF2 100 0.000449 0.04490 0.259 14.7819
VS3,VF3 64 0.00069 0.04416 0.271 10.8346
5.5 Casting of the slab
Casting of the slab is done one the leveled surface as shown in the figure 5.22.
Concrete Beams are used as the formwork.
The reinforcement mesh is not having any tie-up with the bottom part or to the side
forms, so at the time of casting when needle vibrator is applied, there are chances of
lifting of hole the reinforcement mesh. To overcome this difficulty, concreting is
done near the side forms and needle vibrator is applied. Due to the weight of the
concrete at each side, reinforcement will become stable. After completing the
concreting near the side formwork, concreting is done at the central areas . It is
shown in the Figure 5.23.
51. CHAPTER 5. EXPERIMENTAL WORK DETAILS 41
Figure 5.22: Formwork for the slab
Figure 5.23: Concreting of the slab
Cube test for the Bi-axial voided slab:
For testing the cubic compressive strength, plastic spheres were installed in the
cubes. Plastic spheres are air bubbles so at the time of the compaction it may get
displaced or come on the surface. To keep the plastic sphere at the center of
concrete cube, special mould is prepared as shown in Figure 5.24. Cube dimensions
are same as the standard cube, but the difference is, cube mould is having holes at
the center on each four side. Binding wire is passed through the hole and fixed to the
side of the cube.
It is shown in the Figure 5.24.
52. CHAPTER 5. EXPERIMENTAL WORK DETAILS 42
Figure 5.24: Cube test for the Bi-axial voided slab
Cube test was performed on four different sizes of the sphere: (1) 65 mm. (2) 95 mm
type1 (3) 95 mm type 2 (4) 110 mm spheres. For the experimental work it was
decided to use the 95 mm type 2 and 110 mm spheres. The size of sphere is readily
available in market. Weight of the plastic sphere was 15 gram and thickness of the
sphere wall was less then 1/2 mm. Trial was made, but at the time of the concreting
sphere were not able to maintain their shape, sphere were deformed due to the
concrete weight. To overcome these difficulty weight of the sphere was increased
50%. Final weight of the 95 mm size type 2 sphere is 22 grams and for 110 mm size
sphere weight is 35
grams.
5.6 Experimental setup details
Experimental work consisting of the Flexural test and Punching shear test. Setup is
made in such a way that flexural and Punching shear test both can be done in same
setup. Normally slab may be one way or two-way, this setup is able to test the slab in
both the condition one-way and two-way. Moreover any size of the slab can be
tested up to the maximum size of the 1.6 meter. Slab may be square or rectangular.
As shown in Figure 5.25., it is having the four supporting column and 4 peripheral
beams. Peripheral beams are clamped to the four supporting columns.
53. CHAPTER 5. EXPERIMENTAL WORK DETAILS 43
Figure 5.25: 3D view of the setup
Arrangement of the Strain gauges:
Arrangement of the strain gauges., four electrical strain gauges were installed. Strain
gauges position
Figure 5.33: Model of the experimental setup
54. CHAPTER 5. EXPERIMENTAL WORK DETAILS 44
5.7 Test observation to be taken
During the testing of the slab mainly 4 things is observed. (1) Strain (2) Deflection of
the slab (3) failure pattern (4) failure load. Strain is measured at the four location in
both the type of load condition as shown in Figure 5.32. Deflection of the slab is
measured at the center of the slab. Strain and the Deflection is observed at the
interval of the 10 KN. Figure 5.34 shows the P3 strain indicator.
Figure 5.34: P3 Strain indicator
5.8 Summary
The Details of the arrangement of the plastic sphere, detailing of the slab specimen,
casting of the slab, cube test for the Bi-axial voided slab, experimental setup details,
arrangement of the strain gauges, test observation to be taken, are covered in detail.
After conducting tests, the results for different slab specimens are obtained and
presented in chapter 6.
55. CHAPTER 6. EXPERIMENTAL RESULTS AND DISCUSSION 45
Chapter 6
Experimental Results and
Discussion
6.1 General
This chapter contains test results which include various parameters like Cubic
compressive strength of the normal cube and cube with the plastic sphere, Flexural
and Shear strength of the slab specimens, failure load, deflection of the slab
specimens, strain results. This all parameters are essential to understand the
behavior of the Bi-axial Voided slab. Results are also presented graphically.
As discussed in Chapter 5, four types of the plastic sphere were used to have some
idea about the cubic compressive strength of the Voided slab. Figure 6.1. shows the
plan view of the cube with and without the plastic sphere.
The formula for finding the cubic compressive strength is given below.
Cubic compressive strength =
Where, P = Failure load in Kn. A = Cross section area of the cube in mm2
For the cubes having the plastic sphere the cross section area will become plan area
of cube minus the area of the sphere. Figure 6.1 will give the better understanding.
65
56. CHAPTER 6. EXPERIMENTAL RESULTS AND DISCUSSION 46
Figure 6.1: Plan view of the cubes with and without the plastic sphere.
Plain cube cross section area A= 150× 150 = 22500 mm2.
For the cube having the plastic sphere of 65 mm size, A=
(150× 150) - 3318.30 = 19181.7 mm2.
For the cube having the plastic sphere of 95 mm size, A=
(150× 150) - 7088.21 = 15411.78 mm2.
For the cube having the plastic sphere of 110 mm size, A=
(150× 150) - 9503.31 = 12996.68 mm2.
Above areas are considered for finding the cubic compressive strength of the
concrete cube having the plastic sphere.
6.2 Results
6.2.1 Cube test
Cube test results for the 110 mm size sphere.
(a) 7 days Cubic compressive strength.
Table 6.6: 7 days Cubic compressive strength- 110 mm size balls type 2.
Description sample weight of Compressive Average
the specimen strength value
(kg) (Mpa) (Mpa)
1 8.550 24.44
plain cube 2 8.65 20.89 21.926
3 8.70 20.44
Cube with 1 6.78 21.54
plastic sphere 2 6.75 23.08 22.826
3 6.65 23.85
57. CHAPTER 6. EXPERIMENTAL RESULTS AND DISCUSSION 47
(b) 28 days Cubic compressive strength.
Table 6.7: 28 days Cubic compressive strength- 110 mm size sphere type 2.
Description sample weight of Compressive Average
the specimen strength value
(kg) (Mpa) (Mpa)
1 8.730 25.78
plain cube 2 8.80 29.56 27.778
3 8.56 28.00
Cube with 1 6.90 26.55
plastic sphere 2 6.70 26.93 26.545
3 6.86 26.16
6.2.2 Failure load of the slab specimens
Experimental failure load is given in Table 6.8.:
Table 6.8: Failure loads of the slab specimens
Sr. slab Failure load
No. type (KN)
1 PS 250
2 VS1 220
3 VS2 240
4 VS3 230
5 PF 330
6 VF1 310
7 VF2 320
8 VF3 325
6.2.5 Shear stress
Critical section is at a distance of the d/2 from the face of the column. At this section
shear stress is found out. Permissible shear stress for the plain slab specimen is 1.25
N/mm2. Table 6.9. shows the shear stress comparison. In Table 6.19. design stress
are given considering the slab section as the solid section.
Table 6.19: comparison of the shear stress
58. CHAPTER 6. EXPERIMENTAL RESULTS AND DISCUSSION 48
Sr. slab Failure load Design stress Shear stress
No. type (KN) N/mm2 N/mm2
1 PS 250 1.146 1.369
2 VS1 220 1.146 1.20
3 VS2 240 1.368 1.31
4 VS3 230 1.146 1.26
6.2.6 Bending strength
Actual Bending moment taken by the slab is shown in the table 6.20. Failure load is
taken in consideration and divided by the total area of the slab panel. This will give
the load in Kn/m2. It is considered for finding the actual bending moment induced.
Table 6.20: Bending strength of the slab
Nos. slab type Failure load Flexural
(KN) strength
Kn-m
1 PF 330 18.48
2 VF1 310 17.35
3 VF2 320 17.91
4 VF3 325 18.82
6.3 Discussion
Experimental work is mainly consisting of the observation of the failure load for
slabs, deflection of the slab with each load increment, stresses induced with the load
increase.
6.3.1 Comparison of the Cube test results
Figure 6.2. and Figure 6.3. shows the comparison of the cube test results during the
experimental work. As discussed in Chapter 5, mainly four type of the plastic
spheres are used for the cube test. Figure 6.2.(a) shows the 7 days average cube
strength of the sample having 65 mm size sphere, it is 18.513 Mpa while for the
59. CHAPTER 6. EXPERIMENTAL RESULTS AND DISCUSSION 49
concrete from the same batch, the average cube strength is 15.287 mpa. Reduction
in the average strength is 17.42 %. Figure 6.2.(b) shows the 28 days cube strength of
the sample having 65 mm size sphere. Reduction in the average strength is 23.18 %.
Figure 6.3. (a) shows the 28 days cube strength of the sample having 95 mm size
sphere- type 2. Increase in the strength is 3.38 %. Similarly for the cubes having the
110 mm size sphere, increase in the 7 days average cube strength is 3.9 %. and
decrease in the 28 days average strength is 4.45%.
Figure 6.3: Comparison of the average cubic compressive strength
6.3.2 Comparison of the failure loads
Figure 6.4. shows the failure load of the slabs tested under the central point load that
is under punching shear condition. Failure load of the slab PS, which is a plain slab is
250 KN. Slab VS1 is failed at the load of 220 KN which shows the decrease of 12
%. Slab VS2 is failed at the load of 240 KN which shows the decrease of 4 %. Slab VS3
is failed at the load of 230 KN. Volume of the slab VS3 is equal to the slab VS1 but,
60. CHAPTER 6. EXPERIMENTAL RESULTS AND DISCUSSION 50
VS1 is having the slab thickness 135 mm while slab VS3 is having the thickness 140
mm. Compare to the slab VS1 there is increase in the failure load by 4.54%.
Compare to the normal slab, there is a reduction in failure load by 8%.
Figure 6.4: Comparison of the failure loads in Punching shear test
Figure 6.5. shows the failure load of the slabs under flexural test. Failure load of the
slab PF, which is a plain slab is 330 KN. Slab VF1 is failed at the load of 310 KN which
shows the decrease of 6.06 %. Slab VF2 is failed at the load of 320 KN which shows
the decrease of 3.03 %. Slab VF3 is failed at the load of 325 KN. Volume of the slab
VF3 is equal to the slab VF1 but, VF1 is having the slab thickness 135 mm, while Slab
VF3 is having the thickness 140 mm. Compare to the slab VF1 there is increase in the
failure load by 4.83%. Compare to the normal slab, there is a reduction in failure
load by 1.5%.
61. CHAPTER 6. EXPERIMENTAL RESULTS AND DISCUSSION 51
Figure 6.5: Comparison of the failure loads in Flexure test
6.3.3 Comparison of the central deflection of the slabs
As shown in Figure 6.6. there is decrease in the displacements in case of the
punching shear test condition. Displacement of the plain slab at the failure load is
3.25 cm. while for VS1, VS2, VS3 displacement at the failure load is 2.763 cm, 3.235
cm, and 2.00 cm respectively. So in case of the VS1 there is 14.98 % decrease in
deflection.
For VS2 deflection is almost same compare to the normal slab while in case of slab
VS3 there is 38 % decrease in the deflection compare to the normal slab.
Figure 6.7 shows the graph of load vs deflection for the flexural test. Deflection
pattern is almost same for all the slab tested in flexure. Deflection of the slab PF,
VF1, VF2, VF3 at the failure load is 3.22 cm, 2.88 cm, 3.76 cm, 3.087 cm. There is
decrease of deflection 10.5 % in case of the slab VF1 compare to the normal slab,
while in case of the slab VF2 there is increase of deflection by 14.3 %. For the slab
VF3, deflection of the slab decreased by 4.34 %.
62. CHAPTER 6. EXPERIMENTAL RESULTS AND DISCUSSION 52
Figure 6.6: Comparison of the failure loads in Flexure test
Figure 6.7: Comparison of the failure loads in Flexure test
63. CHAPTER 6. EXPERIMENTAL RESULTS AND DISCUSSION 53
6.3.6 Failure Mode and Crack pattern
For the cube test the failure pattern is compared in the Figure 6.17. Figure 6.18.(a)
shows the failure pattern of the controlled cube specimen, while Figure 6.18.(b)
shows the failure pattern of the cube having 65 mm size plastic sphere. It was
observed that at the failure load failure is cone type. There is slight deformation of
the plastic sphere also.
Figure 6.18: Failure pattern of the cube
Figure 6.19.(a) shows the failure pattern of the cubes having the sphere of size 95
mm - type 1. Failure pattern of the cube having the sphere size 95mm - type 2 and
sphere size 110 mm is shown in Figure 6.19.(b). Failure pattern is almost same in all
the type of cubes having plastic spheres. There is a slight deformation in the plastic
spheres. In some cases the sphere were intake and there is no deformation.
64. CHAPTER 6. EXPERIMENTAL RESULTS AND DISCUSSION 54
Figure 6.19: Failure pattern of the cubes having plastic spheres
the failure pattern of the slab VS1 in punching shear test. We can see from the figure
that due to the plastic sphere near the column face, crack is started at exactly at the
column face. During the test no crack observed on the top part of the slab except at
the face of the column. Failure zone passes through the first row of the plastic
spheres. The angle of crack is 63.44o approximately. Failure zone was approximately
square.
65. CHAPTER 6. EXPERIMENTAL RESULTS AND DISCUSSION 55
Figure 6.21: Failure pattern of the slab VS1 in Punching shear
Figure 6.22. shows the failure pattern of the slab VS2 in punching shear test. Here
also failure at the top occurs exactly at the column face. But the failure zone passes
through the second row of the plastic sphere. Failure angle is and it is 66.91
approximately. Failure zone was approximately square.
66. CHAPTER 6. EXPERIMENTAL RESULTS AND DISCUSSION 56
Figure 6.22: Failure pattern of the slab VS2 in Punching shear
6.4 Summary
This chapter is more important from the experimental point of view. The results
observed during the experimental work were presented in this chapter. Results like
failure load, deflection of the slab, strain, shear stresses induced, flexural strength of
the slabs were compared, the results were also shown graphically. Failure pattern of
cube and the different slabs were also discussed.
67. Chapter 7
Summary, Conclusion and Future
Scope of work
7.1 Summary
Now a days sustainable developments are the most desirable for the better future of
upcoming generation. By the sustainable developments the negative impacts on the
environment can be reduced. Sustainable structural engineering is the most
important part of the sustainable developments. It is nothing but the environment
friendly and cost effective building technologies. There are several options available
to achieve the cost effectiveness and sustainable in the building.
In present study, from the various option available, concrete slab is selected to
achieve economy or sustainability. To achieve the economy plastic sphere were
installed to reduce the concrete in the slab. Concrete is the major energy consuming
material among other building material. Concrete is replaced by the plastic sphere at
the central part of the slab. Due to the reduction of the concrete there are chanced of
reduction of the shear strength and flexural strength of the slab.
Present study is consisting of the experimental work. 8 slab panel were cast for the
experimental work. The effective span or the size of the slab panel is 1.5m×1.5m.
From the 8 slab panel 2 panels were same as the plain slab and thickness of the plain
slab is 135 mm. From remaining 6 slab panels 2 slab panels are having the 64 sphere
in the slab panels and the thickness of the slab panel is 135 mm, size of the sphere is
95 mm. 2 slab panels are having 100 plastic sphere, distritbuted uniformly in the
slab panel and the thickness is 140 mm, size of the sphere is 110 mm.
68. CHAPTER 7. SUMMARY, CONCLUSION AND FUTURE SCOPE OF WORK 58
Here, there is mainly 4 category of the slab. One is plain, while other three are having
the plastic sphere. In three categories the percentage reduction of the concrete
comparers to the plain slab is 9.4604 %, 14.7819 %, 10.8346% respectively. On each
category Flexural and Punching shear test were performed.
As a part of experimental work, the setup for the testing of the slab panel is
developed. This setup is able to test the maximum panel size of 1.6 m× 1.6m. Both
the type, Two-way and One-way slab can be tested on the same setup. Flexure and
punching shear test can be performed on the same testing setup.
During the experimental work, failure load, shear stress developed, flexural
strength, deflection of the slab, strain induced in the slab is observed. Strain is
observed at 4 different location. For the Punching shear test strain is measured at
the distance from the face of the column, while in the case of the flexure test, strain
gauges were installed at the center of the two bearing plate in all four direction.
Results were compared graphically and reduction factor is given for the Bi-axial
voided slab.
7.2 Conclusion
Based on the study carried out in this project the following conclusions can be
drawn. Cube test:
From the cube test result we can say for the cubes having the plastic sphere of size
65 mm, 7 days and 28 days cube strength is 17.42 % and 23.18 % less then the
normal cube. While for the cubes having plastic sphere 95 mm size type, Cube
strength is almost same. There is increase of 1.81%. For the cubes having plastic
sphere 95 mm size type 2, there is increase of 3.10 % and 3.38 %, 7 days and 28
days cube strength respectively compare to the normal cube. For the cubes having
plastic sphere 110 mm size, there is increase of 3.9 % and 4.45 % 7 days and 28 days
cube strength respectively, compare to the normal cube.
69. CHAPTER 7. SUMMARY, CONCLUSION AND FUTURE SCOPE OF WORK 59
From the above observation we can say in most of the case the cube strength is
increasing except the cubes having the 65 mm size sphere. The reason for the
decrease in the cube strength is, there was not any arrangement to keep the sphere
exactly at the center of the cube mould. During the vibration it get displaced and
hance load distribution in the cross-section of the slab is uneven.
Slab test:
During the test deflection was observed. Deflection of the slabs in punching shear
test having plastic sphere is lesser then the normal slab. The deflection of the slab
VS1, VS3, is 14.98 % and 38 % lesser than the plain slab. In case of the slab VS2 the
deflection is almost same. For the flexure test deflection of slab VF1, VF3 is 10.5 %,
and 4.43 % lesser than the normal slab respectively. There is For the slab VF3,
deflection of the slab decreased by 4.43 % .
During the test, strain were observed at 4 location. Theoretically the strain value at
the four points should come same. But during the test the values are different.
Reason for this may be center of load application may not be exactly over the center
of the slab, there may be dislocation of the plastic spheres, improper compaction,
level difference in bottom surface,etc.,
During the observation failure pattern also observed. The failure pattern is almost
same for the flexure test condition. In case of Punching shear test condition, for the
plain slab the failure angle is 53.04o. For the slab PS1, PS2, PS3 angle of failure is
63.44o, 66.91o and 64.91o respectively. Ideally failure angle should be 45o. Failure
angle is more in case of the voided slab compare to the normal slab.
Shear stress is found out at the critical section for the all slab. Finally for the Voided
slab, to account the effect of the sphere on the shear stress, the multiplication factor
is given and factor is 1.15 . It should be multiplied to the shear force combining with
the partial safety factor.
70. CHAPTER 7. SUMMARY, CONCLUSION AND FUTURE SCOPE OF WORK 60
For the flexural strength, to account the effect of the sphere on the strength factor is
established. Factor is 1.1. At the time of the designing the voided slab for the flexural
strength, factor of 1.1 should be multiplied to the load combining with the partial
safety factor.
Here due to the limitation of the size of the test panel maximum reduction of the
concrete achieved is 14.78 %, compare to the normal slab volume. As the span
increase more concrete can be replaced by the plastic sphere. If the span is larger
more reduction in the self weight of the concrete can be achieved. So this system will
prove more cost effective and economical for the longer span of the slabs.
7.3 Futurescope of work
• Present study is conducted on the slab having end condition as the 4 side
discontinuous. so study can be extended by considering the different end
condition.
• Theoretical analysis can be perform. For the exect analysis FEM analysis can
be done.
• Percentage reduction of concrete in the slab can be changed and experimental
study can be done.
• Experimental study can be carried out on the cantilever slabs having the
plastic sphere.
71. References
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[5] Bubble Deck two-way hollow deck slab. By: Guomunur Bijornson.
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