Apply Structural Principles to Residential Low-Rise Constructions

This document discusses the application of structural principles to residential low-rise constructions. It covers topics such as reinforcement, concrete pouring, and precautions to be taken. The document provides a comprehensive understanding of the construction process.

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APPLY STRUCTURAL PRINCIPLES TO RESIDENTIAL LOW-RISE
CONSTRUCTIONS
By Name
Course
Instructor
Institution
Location
Date

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STIFFENED RAFT GROUND SLABS AND SUSPENDED SLABS
Task instructions:
 Use technical report template provided in with all technical data researched from AS2870 to be
referenced into completed Bibliography.
 Each step needs an individual image/s with appropriate heading and relevant text.
 You need to discuss things like the steel used as reinforcement (mesh, bars), the plastic products
required, the type of concrete used (strength grade, aggregate size, slump, curing process), formwork
etc…
 This assessment task covers 15% of your overall marks for this unit.
 No sharing of images or internet downloads accepted
 This Assessment Task is to be presented in a professional report format as set out in the report
template provided.

In a Word doc format (not in Pages Format) of the Assessment Task, dated with the unit code and title
and Assessment Task number.

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TABLE OF CONTENTS
Introduction................................................................................................................................4
Stiffened raft slab.......................................................................................................................5
Suspended floors........................................................................................................................6
Basic features of each concrete slab...........................................................................................6
The steel used as reinforcement (mesh, bars)............................................................................8
Laps in reinforcements...............................................................................................................8
Methods of concrete pouring...................................................................................................10
Precautions observed during concrete pouring.......................................................................10
CONCRETE USED.................................................................................................................11
Water-cement ratio...................................................................................................................12
EXCAVATION........................................................................................................................12
FORMWORK FOR GROUND AND SUSPENDED FLOORS.............................................14
Martials used in the construction of the formwork..................................................................15
CONCRETE CURING............................................................................................................17
Importance of concrete curing.................................................................................................17
CONCLUSION........................................................................................................................18
REFERENCES.........................................................................................................................20

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Introduction
The main function of the footing to distribute the vertical loads from the building to the
foundation and also to ensure that the building superstructure performs satisfactorily,
especially when it is on a foundation which is subjected to movement due to moisture
changes (National Research Council. Committee on Residential Slabs-on-Ground, 2017, p.
473).
The most common movement arises due to the changes in the reactive soils. The moment
soil becomes wet, it swells and increase in volume, and the same timey shrink as they dry out.
This is the reason why cracks appear in clay soil during the prolonged droughts. The
deeper or the more reactive the soil is affected the large the surface of movement will be.
The construction of a concrete slab on the ground during the construction process it is like
covering the ground with an impermeable membrane. The slab prevents any moisture rising
beneath the slab from evaporating soil below the slab will therefore remain damp and at the
same time the moisture content may even increase and this will result in a directs increase in
the rate of reaction hence making the soil beneath the slab to swell (Laws, 2011, p. 168).
Swelling soils are among the main geological hazards which causes a lot of damages to
buildings in different parts of the world. The main aim of this study is to investigate
broadly and in-depth the stiffened raft slab as one of the different foundations that are
available in the construction of a simple building on the Australian Expansive soils, and
at the same time to make better the utilization of its benefits ; economical to construct
and its ability to withstand rigidity against the anticipated large soils differential heave
as the floating foundation. In most cases concrete offers the flexibility of a structural
material which can be cast into almost any desired shape and size. The application of
concrete in the construction n can be able to respond to the many specific requirements and

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the different design consideration found in most modern residential buildings (Sipek, et al.,
2013, p. 552).
Stiffened raft slab
The stiffened raft slab is made up a concrete slab on the ground which is stiffened by the
integral edge beams and a grid of the internal beams, this type of a raft slab is also referred
to as a slab-on-ground footing. The floor slab in most cases is placed at the same time as the
internal and external beams which in most cases are reinforced. The internal beams are not
needed on sites which are considered to be stable while for the more-reactive sites the
beam quality and size of the reinforcement are increased in order to suit the site conditions.
The stiffened raft slabs in most cases require only concrete pour, which makes them to be
economical in labour and material use (Bolza, 2011, p. 296). On the uncontrolled fill sites
this can be adapted to be supported on the mass concrete piles/piles which are founded on
natural materials.

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Suspended floors
The three common suspended concrete floors which are suitable for the construction of
residential buildings are; composite steel/concrete, insitu concrete and precast concrete.
For many years the insitu concrete slabs have been used in the construction of the residential
buildings through the incorporation of fabricated systems is significantly helps in reducing
the cost of convectional framework, construction time and on-site activities. The savings
essentially result from the following;
 There is no convectional formwork which is required, with that there is minimal time
which is required for the placement and removal of any temporary propping.
 There is an intermediate, safe working area slab level which is provided. Beneath the
slab is a secure, waterproof area which is achieved, which is suitable for the possible
early fit-out and the storage (Commonwealth Scientific and Industrial Research
Organization (Australia). Division of Building Research, 2012, p. 327).
 All the floor elements are delivered to the site when they are required, hence
minimizing the site storage.
Basic features of each concrete slab
i) Insitu
This is the most flexible concrete slab in that the slab can be designed to carry the walls of
any type anywhere within their span, which is unrestricted by the position of the walls i.e.
the layout of the rooms below them. The insitu slabs are individually designed for specific
projects. In the insitu slabs support may take form of the beams or the walls, themselves
being supported by either the columns or the beams (Barnes, 2018, p. 784).

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ii) Composite steel/concrete
In this type of the concrete slab, proprietary steel decking acts as the non-recoverable
formwork and as the partial reinforcement for the floor slab. The decking spans in a single
way and generally will be continuous over several supports. The single spans are,
nevertheless common and acceptable. The support for this type of slabs is similar to the insitu
slabs.
iii) Precast concrete slab
This concrete slab makes application of precast planks or panels, which b spans in a single
direction. In most cases a concrete topping is needed, in some cases for structural purposes
and hence reinforced, sometimes only to offer a level surface for the application of the floor
finishes. Just as for the insitu floor slabs the support for the pranks can take many different
forms (Great Britain. Property Services Agency, Great Britain. Department of the
Environment, Great Britain. Ministry of Public Building and Works, 2014, p. 328).

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The steel used as reinforcement (mesh, bars)
The trench mesh was used for the reinforcement purposes and that was placed as in the
figure shown in the photo below. The top and the bottom of the raft footing was given enough
support during concreting and at the same time to provide the appropriate cover. Trench mesh
in the bottom of the beams which will required either proprietary trench mesh supports or the
ligatures and the bar chairs (United States. National Technical Information Service, 2014, p.
12). In scenario where the bars were used, they required ligatures and bar chairs or similar to
support them.
Fig: Trench mesh reinforcement
Laps in reinforcements
According to the AS 2870 Clause 5.3.2. the requirements for lapping of the reinforcement
were as follows.

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 The steel mesh was supposed to be lapped as shown in the figure below. I.e. the two
outers most cross-wire of the sheet was overlapped by the two outermost wires at each
other
Fig: lapping of the trech mesh reinforcement
 The trench mesh should be lapped 500mm
 At the ‘T’ junction all the reinforncement should lap the full the full width of the
intersection as shown in the figure below.

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Fig: lapping of the trench mesh at the ‘T’ junction
 All the bars at the ‘L’ junction were lapped in one of the ways which is shown in the
figure below.
Fig:laping of the bars at the intersections
Methods of concrete pouring
concrete pouring is a very important process which requires properly qualified persons and
considerable concentrations. The AS2870 has established a certain specification to ensure a
proper concrete pouring and prevent its segregation.
Precautions observed during concrete pouring
The AS2870 has offered a number of precautions which must be followed during the process
of concrete to ensure that concrete cures properly and effetely.
Some of the precautions that were observed during the pouring process include;
The time which was taken between adding water to dry mixture and the concrete pouring
process did not exceed 30minutes as stipulated in AS2870 since the temperature was normal.
Nevertheless, when the temperatures were above the normal temperature the time was
reduced to 20minutes, Admixtures were used to increase this time.

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Suitable techniques and equipment were considered to ensure that the concrete was able to
drop vertically to the specified locations without any restriction.
Free fall of concrete was continuous and possible separation was due to free falling of the
concrete over the reinforcement or the embedded objects was prevented.
The free distance of concrete was limited to 0.9 to 1.5m, and occasionally it was restricted to
0.6m.
It was required to be ensured that the b concrete was placed at or close to its final position to
be placed in order to prevent segregation.
CONCRETE USED
Concrete refers to the mixture of particles of sand and gravel, the aggregates are usually
bond together with cement. The fine aggregates which were used were natural sand, which
was washed and sieved to remove all the particles which were larger than 5mm, and the
coarse aggregates was gravel which was crushed, washed and sieved so that the particles
were able to vary from 5mm up to 50mm in size. The fine and coarse aggregate were
delivered separately. Through the correct combination of this aggregate, a concrete withy
very minimal spaces or voids was activated concrete which was achieved was considered to
be very strong.
The cement which was used was the ordinally Portland cement. The cement was
manufactured through the heating of the mixture of finely powered clay and limestone with
water to very temperatures of approximately 1200OC, at which the clay and the limestone
were fused together to form, a clinker.

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Water-cement ratio
The materials which were used in making concrete were mixed with water for two main
reasons i.e. firstly, to facilitate the reaction between the cement and the water, which leads in
the cement acting as a binding agent and secondly to make the concrete plastic so that it can
be easily placed during the construction process. The ratio of cement to water which was used
has a great impact on the final strength of the concreate. In the scenario where too much
little water was used the concrete which was obtained was too stiff to an extent that it was not
possible to be compacted and in the scenarios where too much water was used the concrete
was not able to develop full strength. During the mixing of the concrete very little water
required to ensure that a full chemical reaction was to take place within the concrete mix.
Any excess water was not used since it was too leave very small voids the moment the excess
water was to evaporate.
EXCAVATION
Generally, excavation refers to the process of loosening and taking out materials leaving
space below or above the ground. In this project the ground was excavated to the required
levels. all the roots and grass were dug out until the firm soil was reached. The excavation
was carried out in way which was to ensure that the excavated whole was bigger than the
required size to ensure that tit catered for formwork. All the edges and shapes were kept in
square shape.
Since the residential building which was to be constructed can be classified as a small
project or a confined space, the process of excavation was carried out by the use of manual
means where simple tools were used during the excavation, some of the materials that were
used include; shovels, wheelbarrows and picks. But in the scenarios where the construction
projects required heavy plants were to be used in the excavation. Some o0f the materials that

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were to be used include; backactors and bulldozers. The image below shows the excavation
which was carried out. The image below topsoil excavation which carried out.
Fig: Excavation by use of simple tools
The most common method of classifying the method of excavation is through the
classification of the materials which are being excavated i.e.;
i) Topsoil excavation
The topsoil excavation involves the removal of the exposed layer of the earth ‘s surface
which in most cases include any vegetation or any other decaying matter which can make the
soil compressible and hence unsuitable for the bearing structural loads. The depth of topsoil
excavation in most cases vary from one site to another depending on the depth of the top soil.
ii) Earth excavation

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This type of excavations the removal of the soil which is directly below the topsoil. The
removal of this materials is usually stockpiled and then used for the construction of the
foundation and embarkments
iii) Rock excavation
The rock excavation is the removal of the materials which cannot be excavated without the
application of special excavation techniques such as drilling or blasting by use of application.
iv) Cut and fill excavation
This is the process of excavation whereby the materials which are stripped or cut. The
removed earth and topsoil can be used as a filling material for the embarkments and elevated
sections. Also, the stripped materials can be used to form a level surface on which the
structure was to be constructed, as the elevated sections of the site are ‘cut’ and then moved
to ‘fill’ the lower section of the site.
FORMWORK FOR GROUND AND SUSPENDED FLOORS
Formwork is an open box or mold, like a container into which fresh concrete is poured into
and compacted. Once the concrete was set the formwork was removed and the solid mass was
produced in the shape of the inner face of the formwork. Falsework were used to support the
formwork system which holds the formwork in the right position.
The formwork which was used for the construction of the raft slab had the following
qualities.
i) Had sufficient strength to resist the pressure or the weight of the fresh concrete
together with any constructional live loads.
ii) The formwork had sufficient rigidity to retain the shape without undue deformation.

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iii) The formwork was economical in terms of the total cost which was incurred during
their construction.
iv) Sufficiently watertight to minimize the level of leakages experienced at the joints.
Martials used in the construction of the formwork
There are different materials that were used in the construction of the formwork and they
include;
i) timber
ii) plastics
iii) metals
1. Timber
a) Lumber
This is one of the materials which was used in the construction of the formwork and it
displayed excellent weight, strength, cost factor among other characteristics. The photo
below shows the formwork which was used during construction.

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Fig: Type of formwork used.
b) Plywood
The utilization of plywood in the concrete construction is aimed at achieving high quality
finishing. The utilization of the large sheets of plywood have greatly reduced the cost of the
construction and at the same time have contributed to the achievement of final smooth
surfaces which in return will reduce the cost of finishing the concrete surfaces.
2. Plastic formworks
The plastic formwork had an impervious surface which generally created a very smooth
surface to the concrete.
The plastic form in some sections were reinforced while others were self-supporting

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CONCRETE CURING
Concrete curing is the process of maintaining the enough moisture content and the
appropriate temperature in concrete at the early stages after pouring so that it can be able
to develope4 properties which the mixture was designed for.; The process of curing in
concrete starts immediately after placement and finishing so that the concrete can be
able to develop the required strength and durability. Without enough supply of moisture,
the cementitious materials in concrete cannot be able to react n to form a quality product. The
drying of concrete may remove the water which is required for this chemical; reaction
referred to as hydration and the concrete will not be able to achieve its potential properties.
Temperature was very essential factor attaining proper curing, since the rate of hydration
and is faster and hence the development of strength, is higher at higher temperatures.
Importance of concrete curing
There are many benefits which are associated with the concrete curing and they include;
i) Durability enhancement;
concrete which is well cured has a better surface which is hardened and will be able to
withstand the surface wear and abrasion. Curing at the same time increases the strength of
concrete, which prevents the entry of water-borne chemicals from entering into concrete
hence improving the overall durability and service life of concrete.
ii) Improved appearance and serviceability
The concrete slab which is allowed to dry out too early will generally have a soft surface with
very low resistance to wear and abrasion. Once concrete is allowed to cure properly it reduces
the crazing, dusting and scaling. The image below shows concrete which sufficiently cured.

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Fig: Sufficiently cured concrete
CONCLUSION
In conclusion, the main purpose of constructing a slab on the ground during the construction
is to cover the ground so that the water vapor contained in the soil does not evaporate. Once
the water vapor in the soil have been contained the soil will remain most and hence swell
thus reducing the rate of movement.
The stiffened raft slab is made up a concrete slab on the ground which is stiffened by the
integral edge beams and a grid of the internal beams, this type of a raft slab is also referred
to as a slab-on-ground footing. The floor slab in most cases is placed at the same time as the
internal and external beams which in most cases are reinforced. The internal beams are not
needed on sites which are considered to be stable while for the more-reactive sites the
beam quality and size of the reinforcement are increased in order to suit the site conditions.

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The stiffened raft slabs in most cases require only concrete pour, which makes them to be
economical in labour and material use.
REFERENCES

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Barnes, G., 2018. Soil Mechanics: Principles and Practice. 2nd ed. Chicago: Macmillan
International Higher Education.
Bolza, E., 2011. Division of Building Research Technical Paper. 2nd ed. Chicago:
Commonwealth Scientific and Industrial Research Organization.
Commonwealth Scientific and Industrial Research Organization (Australia). Division of
Building Research, 2012. Technical Paper. 4th ed. Texas: the University of Michigan.
Great Britain. Property Services Agency, Great Britain. Department of the Environment,
Great Britain. Ministry of Public Building and Works, 2014. Current Information in the
Construction Industry,. 1st ed. London: Property Services Agency Library Service,
Department of the Environment.
Laws, A., 2011. Site Establishment, Formwork and Framing. illustrated ed. London: Cengage
AU.
National Research Council. Committee on Residential Slabs-on-Ground, 2017. he Design
and Construction of Residential Slabs-on-ground: State of the Art. 3rd ed. Sydney: National
Academies.
Sipek, L., Sipek, M. & Foote, H., 2013. The Owner Builder. 2nd ed. Sydnay: Csiro
Publishing.
United States. National Technical Information Service, 2014. Government Reports
Announcements, Volume 74, Issues 21-26. 5th ed. Texas: National Technical Information
Service.

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