INDIVIDUAL PROJECT.

-i-

BTEC HIGHER NATIONAL DIPLOMA

In

CIVIL ENGINEERING

Edexcel International - UK

International College of Business & Technology

31 & 33, Hotel Road,

Mount Lavinia, Sri Lanka.

INDIVIDUAL PROJECT

By

A.F.HAZEEF AHAMED

MT/HNDCIVIL/05/103

Edexcel International - UK

ICBT Campus

INDIVIDUAL PROJECT.

-ii-

ACKNOWLEDGEMENT.

First of all I would like to express my gratitude with all my heart to

Almighty god for giving me the courage and the strength to complete this assignment.

As far as I concern I think it is my fortune following the course Civil Engineering at

ICBT. I think ICBT Campus is one of the institute seeks to give the best and updated

knowledge in theory and project works. This is the place where all the students’ future

is lightened up.

This dissertation was written as part of the final semester of the education as

Higher National Diploma in Civil Engineering. Many people have contributed to this

work. First of all, I want to express my gratitude to my senior colleges, they really gives

me great help and conduct which makes my report orientation and study scope smoothly

going. And then, I would like to say thanks to my friends He also helps me a lot this

time. He lends to me some reference books which are very helpful to my report.

A.F.HAZEEF AHAMED

MT/HNDCIVIL/05/103

INDIVIDUAL PROJECT.

-iii-

TTAABBLLEE OOFF CCOONNTTEENNTTSS

FRONT PAGE ………………………………………………………………………………………….

ACKNOWLEDGEMENT …………………………………………………………………………….

TABLE OF CONTENTS ......................................................................................................................... I

ABSTRACT ............................................................................................................................................ V

1.0 INTRODUCTION ............................................................................................................................... 1

1.1. BACKGROUND ................................................................................................................................... 1 1.2. AIM AND OBJECTIVES ....................................................................................................................... 4 1.3. METHODOLOGY ................................................................................................................................ 5

1.3.1. Literature review ...................................................................................................................... 5 1.3.2. Informal interviews .................................................................................................................. 5 1.3.3. Questionnaire survey ................................................................................................................ 5 1.3.4. Field survey .............................................................................................................................. 5

1.4. SCOPE AND LIMITATION .................................................................................................................... 6 1.5. STRUCTURE OF DISSERTATION .......................................................................................................... 6

2.0 LITERATURE REVIEW ................................................................................................................... 7

2.1. INTRODUCTION ................................................................................................................................. 7 2.2. DEMAND FOR HOUSING IN SRI LANKA .............................................................................................. 7 2.3. BUILDING SYSTEM ............................................................................................................................ 9 2.4. PREFABRICATED SYSTEM ................................................................................................................ 12

2.4.1. Types ...................................................................................................................................... 13 2.4.2. Process .................................................................................................................................... 14 2.4.3. Material .................................................................................................................................. 15 2.4.4. Advantages and disadvantages ............................................................................................... 16 2.4.5. Prefabrication of precast concrete .......................................................................................... 20 2.4.6. Types of precast structures ..................................................................................................... 23 2.4.7. Types of precast concrete elements ........................................................................................ 25 2.4.8. Advantages of Pre-cast Concrete system in prefabrication .................................................... 27 2.4.9. Disadvantages of Precast Concrete system ............................................................................ 30

2.5. PREFABRICATION APPLICATION IN BUILDING ELEMENTS ................................................................. 32 2.5.1. Foundations ............................................................................................................................ 32 2.5.2. Walls ...................................................................................................................................... 32 2.5.3. Floor and roof ......................................................................................................................... 32

2.6. SLAB SYSTEM IN HOUSING CONSTRUCTION ..................................................................................... 33 2.6.1. Conventional slab system ....................................................................................................... 33 2.6.2. SBS slab system ..................................................................................................................... 35

2.7. KIT FORM HOUSE ............................................................................................................................ 36 2.7.1. Erection of a kit form house ................................................................................................... 37 2.7.2. Benefits of the kit houses ....................................................................................................... 37

2.8. SUMMARY ....................................................................................................................................... 38

INDIVIDUAL PROJECT.

-iv-

3.0 RESEARCH METHODOLOGY ..................................................................................................... 39

3.1. INTRODUCTION ............................................................................................................................... 39 3.2. LITERATURE REVIEW ...................................................................................................................... 39 3.3. INFORMAL INTERVIEWS .................................................................................................................. 39 3.4. QUESTIONNAIRE SURVEY ................................................................................................................ 39 3.5. FIELD SURVEY ................................................................................................................................. 40 3.6. QUESTIONNAIRE STRUCTURE .......................................................................................................... 40 3.7. LIMITATION OF THE STUDY ............................................................................................................. 42

INDIVIDUAL PROJECT.

-v-

AABBSSTTRRAACCTT

Prefabrication has been used extensively and widely for many years around the world. It

has been widely adapted in housing construction. The main reason in adopting this

system particularly for housing construction is to boost the development of low cost

housing project for the lower income group.

This project was conducted to study the basic concept of and application of

prefabricated system in building construction. The study further assessed the benefit of

the using prefabrication system in building construction. The methodology adopted for

the study includes literature review, informal interview, field survey and using

questionnaire survey. An informal interview was carried out to facilitate on designing

the questionnaires. These questionnaires were then distributed to the respondents which

represent the professional in construction industry that have experience and knowledge

on the precast concrete technology. The study concluded that the prefabrication system

is viable alternative construction method that can improve construction industry with

regard to the achieving better quality of works and increasing productivity. The study

has determined that the adoption of this technology can greatly benefit the building

industry in various aspects such as reducing the construction cost, better planning and

design coordination. Speed of construction. Speed of construction, minimising

manpower involved in the project.

Key words: prefabrication, precast concrete

-vi-

INDIVIDUAL PROJECT.

-1-

CCHHAAPPTTEERR 0011

11..00 IINNTTRROODDUUCCTTIIOONN

1.1. BACKGROUND

Buildings should be designed with the system in mind, to best utilize the advantages of

the particular system. Before going to accomplish the construction work, the builder has

to choose a suitable system according to the client requirement and with the available

resources. In addition, the chosen system needs to be well specified to prevent major

problems during construction. Moreover, a poorly specified system could result in

misalignment of components, or incompatibility of the components with other systems,

structure, or existing conditions (Obiso 1997). Prefabricated systems have been widely

adopted in housing construction for the purpose of modular coordination, efficient use

of time and assure the quality of a product. Unlike the conventional practices of

construction, prefabrication guarantees the production of high quality building

components and facilitates the fast track construction. Chan (1998) mentioned that, the

quality of the prefabricated items is usually higher than the in-situ components and

speed of the construction is comparatively high.

Prefabrication has been used extensively and widely for many years around world (Hao

et al 2002).The application of pre fabrication techniques has signified a turning point in

the construction industry. Over the years, prefabrication has evolved to be one of the

most remarkable construction techniques in the industry (Chan et al, 2002). Unlike the

traditional concreting methods, prefabrication guarantees the production of high quality

building components and facilitates the fast track construction by removing those

concreting works from critical path into non-critical and dirty in-situ works into clean

all-weather precast factory production, leaving the assembly work to be performed on

site (Wong and Yau 1999 ). The application of prefabrication techniques has brought a

profound change in the development of the construction industry worldwide. Several

advantages are accrued from its use including less time and reliance on site labour,

easier site inspection, as well as greatly improved design details and quality control. A

wide use of prefabrication products would help to overcome many of the hurdles

INDIVIDUAL PROJECT.

-2-

inherent in traditional in situ construction, and engender move technically feasible and

cost effective installation. (Chan et al, 2002).

With the labour shortages prevalent in the building industry, prefabrication together

with the greater use of standardization and modular flat designs are frequently

considered in the design and construction of domestic buildings (Chan 1998). It was

clarified by Elliott (2000) that, a particular combination of material could be needed to

meet architectural requirement or speed of construction, but it may or may not have to

act compositely to do so. As it is common to all prefabrication, most of the work carried

out in the factory, leaving little to be done on-site. This increase the likelihood of more

efficient, high quality and faster construction being achieved (Rosenfeld 1994).

In Sri Lanka, the usage of prefabricated concrete in housing construction has been in the

increase after the Tsunami. The annual new demand for houses in Sri Lanka is

estimated to be around 100,000. In addition, there is an estimated housing shortage of

350,000. Further, about 30 % (about 1.3 million) of the existing houses are semi-

permanent, improvised, or unclassified needing substantial improvements. In addition to

individual housing, government supported programmes and private sector investments

are expected to provide 645,000 housing units during the ten year period up to 2016

(Central Bank Report, 2006). The construction of houses damaged by the tsunami will

pose a gigantic challenge in 2005. About 65,000 houses are estimated to have been

completely destroyed and 44,000 houses partly damaged by the tsunami in December

2004 (Central Bank Report, 2004).

The people who lost their shelters needed to resettle in permanent homes that they could

call their own and it should be build within the very short period, if their lives are to

regain any sense of normalcy. But how does one go about re-building? In this situation

any one can realize that the speed and cost as the main parameters of reconstruction

task. What are the low cost housing options that are available in Sri Lanka now and

what are building methods available to build those houses very quickly? To increase the

speed of the construction the contractors tense to use pre-fabricated system. The

National Engineering Research and Development (NERD) Centre attached to the State

Engineering Corporation (SEC) under the Ministry of Science and Technology has

INDIVIDUAL PROJECT.

-3-

come forward with several short and long term solutions, using innovative and cost

effective construction technology. Columns, beams, door frames, window frames and

many other components are pre-made out of concrete (The Sunday Observer, 2005). But

there is a question arising that, while achieving the speed of the construction by using

precast concrete elements, can they achieve the required quality of the building? If they

used prefabricated system, what would be the effect for the environment? There is a

labour shortage in construction industry in Sri Lanka. Therefore to overcome this

problem the contractor has to select a building system which required minimum labour

involvement. By doing this research it is intended to identify the benefit of pre

fabricated concrete structures in terms of cost, time, quality, environment friendly and

labour saving against the conventional system in Sri Lankan housing construction.

In a concrete frame building, floor construction is the most time and cost element,

representing about 70% of the super structure cost (Domel & Ghosh 1990; Goodchild

1997; Idrus 2001; Passiki et al, 1995). In addition, Elliot (2000), said that pre-stress,

precast concrete units provide the economical flooring systems in worldwide.

Considering the above information if the contractors use pre-stress concrete floor

system to housing construction such as suspended beam slab (SBS) instead of in-situ

concrete slab, how it is effective in terms of cost time and quality?

INDIVIDUAL PROJECT.

-4-

1.2. AIM AND OBJECTIVES

The study is carried out to examine the usage of prefabricated system in the housing

construction. The objectives of this study are as follows:

To study the basic concept of prefabrication system in building construction

To evaluate the benefit of using prefabricated system in Sri Lankan housing

construction

To ascertain the cost effectiveness of the prefabricated floor system against

conventional slab system in housing construction

INDIVIDUAL PROJECT.

-5-

1.3. METHODOLOGY

1.3.1. LITERATURE REVIEW

The study was initiated through a comprehensive review and an empirical study. A

literature method was carried out as preliminary study in gaining information about the

research topic and recently prefabricated system applied in the construction industry. It

is done by referring to many sources such as published books, articles in journals and

papers, other published research works, academic and research magazines, newsletters,

brochures and information from the internet.

1.3.2. INFORMAL INTERVIEWS

The empirical study used informal interviews and questionnaire. The informal interview

with experience personal regarding the usage of this prefabricated system was

conducted to obtain ideas and data valuable for designing the questionnaire.

1.3.3. QUESTIONNAIRE SURVEY

Questionnaires were distributed to gauge respondent’s opinion regarding the beneficial

in using this prefabricated system in the construction. It was distributed to the

respondents involve in the construction industry in Colombo area through electronic

mail and by hand. After the data had been collected, detailed analyses were done using

frequency analysis and Relative Indices RI technique.

1.3.4. FIELD SURVEY

Simple field survey was conducted to ascertain the cost effectiveness of the

prefabricated floor system against conventional slab system in housing construction.

INDIVIDUAL PROJECT.

-6-

1.4. SCOPE AND LIMITATION

The scope and limitation of this study is confined to housing construction only. The

research was based on the experience of local developers, engineering and architectural

consultants, building contractor, manufactures, quantity surveyors and government

building authorities on the usage of prefabricated system. The study considered only on

the use precast concrete element in housing construction. The data collected are only

confined to the respondents within the Colombo area. The identification of the cost

saving of prefabricated system is done only to the slab in two story housing projects.

1.5. STRUCTURE OF DISSERTATION

The dissertation is consisting of five chapters. First chapter discussed on the background

of the research, objectives, scope and limitation of the research and the research

methodology adopted to achieve the objective of the research.

Chapter 2 discusses about the building system and the basic concept of the

prefabricated system in building industry. Also the advantages, disadvantages of the

prefabricated system are discussed in this chapter.

Chapter 3 discussed in details the research methodology adopted for the study.

Chapter 4 illustrates the detail analysis of collected data and discuss about the research

findings.

Chapter 5 conclude the study and makes recommendations to the usage of

prefabricated system in housing construction in terms of design and total building cost.

INDIVIDUAL PROJECT.

-7-

CCHHAAPPTTEERR 0022

22..00 LLIITTEERRAATTUURREE RREEVVIIEEWW

2.1. INTRODUCTION

This chapter looks into key definitions, concepts, practices and procedures relevant to

this study. The first part of this report 2.2, discuss about the demand for housing in Sri

Lanka. In section, 2.3 discussed about the building system and different types of

building system adapted in other countries. Prefabricated system, types of prefabricated

system and process of prefabrication and the advantages and disadvantages of

prefabrication are described briefly in section 2.4. The section 2.5 described about the

prefabrication building methodologies for housing. Section 2.6 discussed about the slab

system in housing construction. Section 2.7 is consisting of the details of kit house. The

summary of this chapter is described in section 2.8.

2.2. DEMAND FOR HOUSING IN SRI LANKA

In 1948, the United Nation Declaration of Human Rights formally recognised the right

to decent housing for all human beings (Harun 1996). In Sri Lanka the demand for

houses and urban infrastructure is expanding rapidly with the population growth and

urbanisation. The population is growing at 1.1 percent annually, where as the urban

population is growing at a higher rate of 3 percent (Central Bank Report, 2006). Many

of developing countries faces higher urban population growth due to the migration of

population from rural to urban areas took place due to economics reasons. Hence, this

high population growth in developing countries has given rise to housing problems

where proper and adequate accommodation is an important need for every human being

(Rahim 2004). The annual new demand for houses in Sri Lanka is estimated to be

around 100,000. In addition, there is an estimated housing shortage of 350,000. Further,

about 30 percent (about 1.3 million) of the existing houses are semi-permanent,

improvised, or unclassified needing substantial improvements. In addition to individual

housing, government supported programmes and private sector investments are

expected to provide 645,000 housing units during the ten year period up to 2016

(Central Bank Report, 2006).

INDIVIDUAL PROJECT.

-8-

On 26th December 2004, an earthquake off Sumatra triggered a massive Tsunami that

devastated around two thirds of the coast of Sri Lanka and entire fishing communities

disappeared from some areas. A large proportion of economic losses is concentrated in

housing, tourism, fisheries and transportation while total losses were estimated to equal

4.4 percent of the GDP (Prabodha 2005). The construction of houses damaged by the

tsunami will pose a gigantic challenge in 2005. About 65,000 houses are estimated to

have been completely destroyed and 44,000 houses partly damaged by the tsunami in

December 2004 (Central Bank Report, 2004). Construction of 61,000 houses has been

completed by end of 2006 and construction of balance houses was in progress (Central

Bank Report, 2006). The people who lost their shelters needed to resettle within the

very short period. Therefore, it was recognised that the Speed as the main parameter of

reconstruction task. Rahim (2004) concluded that, the usage of prefabricated system has

been implemented due to the needs to provide housing for the people in a short period

of time given.

The demand for housing in Sri Lanka is very high in future. Therefore, the system that

the contractor going to use to build the houses is take major part in terms of achieving

the best quality, reasonable time and cost. According to the Daily Mirror (2005), the

prefabricated housing systems could be the ideal fast track solution in the process of

building new houses to compensate the totally destroyed houses from the Tsunami

devastation.

INDIVIDUAL PROJECT.

-9-

2.3. BUILDING SYSTEM The building should be designed with the system in mind, to best utilize the advantages

of the particular system. In addition, the chosen system needs to be well specified to

prevent major problems during construction. Moreover, it said that a poorly specified

system could result in misalignment of components, or incompatibility of the

prefabricated components with other systems, structure, or existing conditions (Obiso

1997). A building system is a highly engineered method of producing buildings or

building components in an efficient and cost effective manner. The use of building

systems is common in many different types of residential and commercial construction

(Wikipedia, 2007a). As foster (1997,p.20) mention, the component parts of the building

fabric, whatever the form of construction, must be fabricated and then assembled or

erected on the site to produce the completed building. These processes must be

organised and the manner of organisation differs from country to country and from time

to time in any particular country.

Foster (1997, p.26) identified some type of building systems developed in Great Britain.

Those are as follows,

Post-traditional or conventional building

Rationalised building

System building

Component building

Pre-assembly, prefabrication, modularisation, system building and industrialised

buildings are the terms which have been frequently used to describe that the

manufacture of building components are constructed either on-site or off-site in a

factory covering manufactured, modular and pre-cut or pre-engineered systems.

Although the terms, are often interchangeably used, their precise definitions depend

heavily on the users’ experience and understanding, which vary from countries to

countries.

Off-site fabrication is a topic of international interest and provides an effective

construction technique in terms of quality, time, cost, function, productivity and safety.

It is adopted worldwide as the ideal means of producing an immense array of elements

INDIVIDUAL PROJECT.

-10-

from structural members, cladding units, and bathrooms to fully-finished modular

buildings. (Hao et al, 2002).As an organisational process industrialisation may be

applied to any method of building and whether applied to traditional methods or factory

methods will introduce these four characteristics, a mechanised and continuous

fabrication and assembly process to speed up production and reduce labour

requirements, a standardisation of components to reduce cost and facilitate continuous

production and a properly integrated system of design, fabrication and assembly to

speed up the whole building process, with feedback from the fabricating and assembling

process to the designer so that changes and developments may be made leading to

reduced cost and greater productivity (Foster 1997, p.24).

The meaning of industrialisations is to build on site with elements or components

produced by series in plants. In addition, industrialization of building means that these

components can be assembled together even though they are produced on different

plants (Rahim 2004). For the building industry industrialisation involves the

rationalisation of the whole process of buildings (which includes the process of design,

the forms of construction used and the method of building adapted), in order to achieve

an integration of design, supply of materials, fabrication and assembly so that building

work is carried out more quickly and with less labor on site and, if possible, at less cost

(Foster 1997, p.24).

Generally, there are four types of building system available in Malaysia, namely

conventional, cast in-situ, prefabricated and composite building system (Chew 1986).

As in addition, each building system is represented by its respective construction

method which is further characterized by its construction technology, functional and

geometrical configuration (Walled et al 2003, cited Rahim 2004). Over a five-year

period, hundred of proprietary system where brought into existence, but few had any

real chance of achieving the size or continuity of orders that were essential to make

them viable. The use of industrialized system was not confined to housing; a proportion

of offices, factories, hospitals, stores and schools were constructed by industrialized

methods (Seeley 1973, p.68). Rahim (2004) concluded in his research saying that the

concept of prefabrication system as one of the industrialised building system.

INDIVIDUAL PROJECT.

-11-

Prefabricated housing Systems have become the conventional way to build a one or

two-story commercial, community or industrial building world-wide. Technological

advances in products and materials, combined with new manufacturing techniques, have

led to the development of structural systems, which are compatible with ordinary

construction materials (Daily Mirror, 2005). Prefabricated housing has been used in the

UK during periods of high demand, such as after the World Wars and during the slum

clearances of the 1960s. In total about one million prefabricated homes were built

during the 20th century, many of which were designed to be temporary. However,

problems arose over the quality of building materials and poor workmanship, leading to

negative public attitudes towards prefabrication (Parliamentary office of science and

technology 2003, cited Suriyaarachchi 1998). There has been a great improvement in

prefabricated housing over the past decades and it is becoming a valid alternative to

traditional housing (Wikipedia, 2007a).

The details that given by the construction relative professionals, there are four types of

building systems are identified in Sri Lanka. Those are traditional, insitu, prefabricated

and composite system. According to the mentioned information of the prefabricated

system, it is clearly understood that the application of the prefabrication system in

construction gives several advantages such as reduce the construction time and cost,

while achieving the best quality. Because of the huge demand for the housing in Sri

Lanka, the application of prefabricated system will become effective in building those

houses. Out of the all types of building system in Sri Lanka, the prefabricated system is

to consider my research in a comprehensive way.

INDIVIDUAL PROJECT.

-12-

2.4. PREFABRICATED SYSTEM Prefabricated system of construction means breaking a whole housing unit into different

components such as the floors, the walls, column, beam, roofs, etc. and having these

components separately prefabricated or manufactured in modules or standard

dimensions in a factory. The components are then assembled and erected on the site and

properly joined to form the final units (Chew 1986). Prefabrication is the practice of

manufacturing the components of an assembly in one location and assembling them in

another. This practice was widely used in the construction of prefabricated housing

during the 20th and 21st centuries. In theory, using a product made in a factory would

save time on-site and improve quality. However, prefabricated housing and many other

items acquired a certain level of stigma because of flimsy designs and low cost. There

has been a great improvement in prefabricated housing over the past decades and it is

becoming a valid alternative to traditional housing (Wikipedia, 2007a).

By using a prefabricated building system, as much as 50% of the total construction time

can be cut out of the schedule (Mark 1993). A shorter production time not only cuts

down direct and overhead costs, but also allows the house to be occupied sooner, as

recognized significant in the case of the large-scale flat production programmed in

Hong Kong (Chan et al, 2000). In addition he said that, in most cases, the saving in

construction time due to the employment of prefabricated elements has also significant

economic value to both the client and the contractor. As many prefabrication

technologies deliver a better product because building is done in a quality controlled,

sheltered environment, the move to more prefabrication in construction industry is

inevitable. It is seen as one of the tenets of improving construction in the 21st century

(Egan 1998; Chan & Chan 2002). This is also echoed by Ranford (2000), ‘a much

greater emphasis on off-site assembly was one of the key ingredients to changing the

construction culture to retain and recruit talent and at the same time deliver

improvements in performance required by increasingly demanding clients.’

INDIVIDUAL PROJECT.

-13-

2.4.1. TYPES

Mainly there are two types of prefabricated systems in the market (Chew 1986):

a) Fully Prefabricated Systems

b) Partially Prefabricated Systems

2.4.1.1. FULLY PREFABRICATED SYSTEMS

Fully prefabricated system is referring to the components produced in the factory and

transported to the construction site for erection. Fully prefabricated system can be

grouped under 3 categories based on these methods:

2.4.1.1.1. BIG PANEL SYSTEM

This consists of pre-cast wall (load bearing type) and slab elements. A heavy capital

outlay is required for this system because the usage of heavy moulds and machinery in

concrete mixing, transporting, lifting, storing and assembling. A maximum turn over

per day is a must in the production line because of the heavy initial capital cost for each

of the metal mould. In the operation which consists of preparing the bed, casting and

curing the concrete and stripping the moulds can be done within the shorter time.

Concrete is subjected to heat curing for hardening process for the panel can be lifted in

about three hours instead of the normal curing time.

2.4.1.1.2. THE FRAMING SYSTEM

The structural members such as the columns and beams are cast together to form a

frame. However the floors are cast separately as panels. Then the members are

transported to the site for erection and fixing. As for the wall, it can be non-load

bearing light weight material, hollow blocks and conventional bricks. The example of

components in this system is prefabricated bathrooms, toilets, staircases, balconies,

parapets, facades etc. The components can be fixed onto the main units.

INDIVIDUAL PROJECT.

-14-

2.4.1.1.3. MODULE SYSTEM

This system involves the casting of a unit in the form of module or modules.

Several of openings for doors, windows can be pre-formed in the steel mould before

casting.

2.4.1.2. PARTIALLY PREFABRICATED SYSTEMS

Partially prefabricated system is a type of system in construction where certain

elements that can be standardised are prefabricated in the factory while other

components are cast-in situ. In this construction method, the assembly of pre-cast

elements involve are floor slabs, wall, bathroom, staircase for incorporation into the

main unit. The columns and beams usually cast-in situ because it is easier and less

time-consuming. According to Chew (1986), this system usually give a more rigid

construction and better water tightness characteristic which are not usually found in Big

Panel and Farming System. The advantage of this system is in its low initial investment

because it is not necessary to have full automation factory with its supporting heavy

machineries.

2.4.2. PROCESS

Prefabricated system of construction means that breaking a whole housing unit into

different components such as the floors. The walls, columns, beams roofs etc. and

having these components separately prefabricated or manufactured in modules or

standard dimensions in a factory. The components are then assembled and erected on

the site and properly joined to form the final units (Chew 1986). The Figure 2.1 shows

the process of prefabricated system from design to form a final unit

INDIVIDUAL PROJECT.

-15-

Figure 2-1: The basic concept of prefabricated system

(Source: Rahim 2004)

2.4.3. MATERIAL

In Sri Lanka Steel, timber and precast concrete are the material widely used in the

prefabricated construction. Steels are economical to use only in wide span and high load

bearing structure such as where houses, store room and car park etc. because of the

short span the timber and precast concrete are suitable and economical in the pre

fabrication of the housing construction. But due to the unavailability of the timber and

government rules for cutting the trees, now days the timber is not extensively used in

construction. Precast concrete unites are very commonly used in the prefabricated

housing construction in Sri Lanka due to the several reasons such as easy availability of

material, economical, quality, etc..

Hybrid Concrete Construction (HCC) is a method of construction which integrates

precast concrete and cast in-situ concrete to take best advantage of their different

inherent qualities. The term hybrid concrete construction (HCC) describes the

INDIVIDUAL PROJECT.

-16-

combination of concrete with other materials (Goodchild 1995).The accuracy, speed and

high-quality finish of precast components can be combined with the economy and

flexibility of cast in-situ concrete. Hybrid concrete technology embraces a number of

different forms of structural frame, but in all cases precast concrete and cast in-situ

concrete elements are used where they are most appropriate for the project. The results

are remarkable: faster construction and considerable cost savings – in some cases of up

to 30% compared with conventional structural frame systems.

Figure 2-2: Concept of Hybrid construction

(Source: Trent Concrete Photo courtesy)

2.4.4. ADVANTAGES AND DISADVANTAGES

There are some advantages and disadvantages in prefabricated system. Those are

describing in detail below.

2.4.4.1. ADVANTAGES OF PREFABRICATED SYSTEM

Adoption of prefabrication system has many merits in the context of availability of

materials, labour and technical skills. Advantages of prefabrication are identified by

Adlakha & Puri (2003) as follows.

(1) In prefabricated construction, as the components are readymade, self-supporting,

shuttering and scaffolding is eliminated with a saving in shuttering cost.

(2) In traditional construction, the repetitive use of shuttering is limited, as it gets

damaged due to frequent cutting, nailing etc. On the other hand, the mould for the

INDIVIDUAL PROJECT.

-17-

precast components can be used for large number of repetitions thereby reducing, the

cost of the mould per unit.

(3) In prefabricated housing system, there is saving of time as the elements can be

casted before hand during the course of foundations being laid and even after laying

slab, the finishes and services can be done below the slab immediately. While in the

conventional in-situ RCC slabs, due to props and shuttering, the work cannot be done,

till they are removed. Saving of time means saving of money.

(4) In prefabricated construction, there is better quality control, shape and size of

precast elements. Therefore, in structural design, full advantage of properties of cement

and steel can be exploited. There is disciplined use of scarce materials like cement, steel

and timber.

(5) In precast construction, similar type of components are produced repeatedly,

resulting in increased productivity and economy in cost too.

(6) In precast construction, the construction is not affected due to weather, rain, wind

etc.

(7) In prefabricated construction, the work at site is reduced to minimum and therefore,

work is qualitatively better, more reliable and clean.

(8) Because of faster completion and reduction in time period of construction the houses

can be occupied earlier, which means early return of the investment.

Chan et al, (2003) recommends that, prefabrication will contribute to improved build

ability and associated efficiency gains in terms of time, cost, quality, safety and

environmental targets. Some of the benefits of prefabrication techniques are listed

below:

(a) Higher productivity levels of construction trades;

(b) Cost savings at every level of the supply chain due to mass production, e.g. labour

and materials costs;

(c) Faster return on investment for the client;

(d) Reduced programme durations for fixing and erection operations;

(f) Savings in space allocated to materials storage;

INDIVIDUAL PROJECT.

-18-

(g) Better quality control leading to more accurate profiles and dimensions of

components;

(h) Less materials wastage because of fewer defective products;

(i) Safer working environment at prefabrication factories;

(j) Enhanced teamwork spirit and manufacturing ethos under a repetitive production

process;

(k) More efficient testing requirements of the products at the manufacturing facility than

at the construction site;

(l) Less influence of site tasks by inclement weather conditions;

(m) Re-engineered project delivery and supply chain system based on wide scope of

prefabrication and preassembly; and

(n) Application to public and private sector housing, commercial building and road

construction projects in collaboration with industry and government partners.

A number of significant benefits provided by prefabricated elements comparing with

on-site building erection process as shown in the below table.

INDIVIDUAL PROJECT.

-19-

Table 2-1: Comparing the benefit of prefabrication and on-site erection

(Source: Hao et al. 2002)

Factor Prefabrication On-site

Quality

In a climate-controlled environment

using efficient equipment operated by

well-trained people.

Uncertain weather can result in less-

than expected construction.

Speed Speedy process (up to 70% less)

Time consuming. The process can be

delayed by weather or scheduling

conflicts.

Cost

Greater control over manufacturing

results dramatically reduces the chance

of cost overruns.

Uncontrollable variables such as

weather and scheduling can increase

the construction cost

Versatility Less More

Site space Panels arrive on a flat-bed trailer and are

installed with sufficient listing plants.

Bigger space is needed. In addition

costly scaffolding is often necessary for

installation.

Site

refuse Less waste is generated at the site.

A significant amount of waste

produced and removed from the site,

which often adds to cost.

INDIVIDUAL PROJECT.

-20-

2.4.4.2. DISADVANTAGES OF PREFABRICATED SYSTEM

There are some disadvantages also in prefabrication. Following are some disadvantages

identified by Adlakha & Puri (2003)

(1) As the precast elements have to behave monolithic on erections, extra reinforcement

may be necessary in some cases.

(2) Extra reinforcement is required to take care of handling and erection stresses.

(3) Temporary props may be required in some cases, before the in-situ concrete joints

achieve strength.

(4) The cracks may develop at the joints between the precast and in-situ concrete due to

shrinkage and temperature stresses. To overcome them, extra steel is required across the

joint.

(5) As there are chances of leakage/seepage through the joints between the precast

components, extra care is required to make them leak proof.

2.4.5. PREFABRICATION OF PRECAST CONCRETE

Prefabrication of concrete structures is one of the most remarkable developments in the

construction process of concrete structure in the last two decades (Bruggeling &

Huyghe 1991). According to Shahrul et al, (2003), numerous construction projects in

Malaysia have utilized prefabrication of pre-cast concrete technology structure

especially when the project requirement is to build in shorter period of time within the

given budget and quality workmanship. The major reason for acceptance of such system

is basically supply and cost of labour, speed of construction, wastage control etc. But

the context of Sri Lanka precast concrete construction was introduced during the period

of 1969 in Colombo port commission. But it was slow improvement for the introduction

construction stage. In 1979s pre stress concrete roof beam which span 20 ft from the

basic components for the school type building frame which is marketed successfully by

the State Engineering Corporation (SEC). Its versatility has been proved by its

beneficial use in low cost housing projects (Sri Lankan Building research, 1979).

Much more use of precasting and of-site prefabrication should be encourage for

reducing construction duration and maintaining consistently high quality standard of

the product (Chan et al, 2003). Usage of precast concrete technology in building

INDIVIDUAL PROJECT.

-21-

construction has contributed various benefits in terms of cost, time, manpower,

environment and quality (Rahim, 2004). Prefabrication is closely related to the

development of the pre-casting industry, which in turn is one of the important steps

towards industrialisation of the building industry. The cost of manufacturing of the pre-

cast elements should be low as possible. This result in the necessity of repetition of the

same production cycle on every working day (Bruggeling & Huyghe, 1991). To date,

the extensive use of prefabrication includes the production of pre-cast façades, pre-cast

staircases, semi-pre-cast slab, pre-cast partition wall and fabric reinforcement (Wong &

Yau 1999).

As mention by Idrus & Newman (2002), designers have a wide choice of structural

system for concrete frame buildings. They can choose from three basic types available:

in situ, pre-cast or hybrid construction. Bruggeling & Huyghe (1991) discussed that, it

has to be realised that the preparatory period of a prefabricated concrete structure is

totally different from that of concrete structure cast in situ. This means that the different

discipline will have to be followed by the architect and the designer in case of pre-cast

concrete structure. Not only the construction time – on the site – will be considerably

reduced, but the preparatory period should already be over when manufacturing of the

element starts. If the concrete structure is cast in site the preparation process may

overlap the construction process. In the case of prefabrication this overlap is impossible.

All the decision that influence the dimension and the shape of the concrete structure

must be taken a long time before the construction starts with the activities on the site.

If the parties involved in this process are skilled, the erection of prefabricated concrete

structure will take place with fewer problems than in the case of in situ concreting. All

the aspect of the design is, as a rule, considered that a basic condition for successful

prefabrication is a well-organised team of architect, designer, contractor and

manufacturer. (Bruggeling & Huygh 1991). For high rise development it was found that

generally the precast concrete where erected more quickly and cheaply than in situ

concrete system. In contrast, in situ concrete system often provides the cheaper method

for low rise dwelling although not the quickest. This result mainly from reduction in

repetition and standardisation in low rise housing compared with high rise construction.

INDIVIDUAL PROJECT.

-22-

Furthermore, the high initial cost of precast concrete factory and its high overheads tend

to make precast concrete unit expansive. Timber and steel frames have both been used

extensively for low-rise housing and have the benefit of fast erection time. Both

materials are relatively expensive (Seeley 1973, p.69).

Most popular building construction technology among various practices is the use if

prefabricated building components such as columns, beams, slabs, and items required to

roof structure. Most commonly the buildings are consist of structural skeleton to carry

and transfer the load. The precast usage was mostly significant on the low rise buildings

and package type housing units which was repetitive type construction. Apart from that

one other popular concept was the use of “building frame” for the low rise buildings,

housing units, secondary buildings and ware houses. The most significant feature with

this method was cheap rather than the conventional method, while it provides a simple

yet steady permanent structure, which could be erect within a short period of time

(Ediriweera 1988, cited in Suriyaarachchi 1998).

There are only few companies are manufacturing precast unites for housing

construction. Namely State Engineering Cooperation (SEC) and International

Construction Consortium (ICC) are the major two companies manufacturing precast

units for building construction. ICC introduces an effective alternative to in-situ

concrete slab call Suspended Beam Slab (SBS) pre stressed concrete floor system. This

system also coming under the category of partially pre-fabricated system. In this

construction method, the columns and beams are usually cast insitu. Considering the

span and the load bearing capacity the number of pre stressed beam using this system is

varies. There are single beams, double beams and continuous beams are available for

this type of flooring system. But single beam system is enough in housing construction

up to 4 meters of maximum span. Due to the several advantages, the application of SBS

concrete floor system is rapidly growing in building construction in Sri Lanka.

National Engineering Research and Development (NERD) also producing the same

type of slab system like SBS slab system. This system is called as NERD Floor-slab

System.

INDIVIDUAL PROJECT.

-23-

2.4.6. TYPES OF PRECAST STRUCTURES

(Elliott 2000; Rahim 2004) stated that there are three basic types of precast structures:

1. wall frame

2. portal frame

3. skeletal frame

2.4.6.1. WALL FRAME

The precast structure consist of vertical wall and horizontal slab units only. It is used

extensively for housing, offices, hospitals, multi storey hotels, commercials, retail units,

shopping complexes etc.

2.4.6.2. PORTAL FRAME

The precast structure consists of columns and roof rafters only. It is mainly constructed

for single storey retail warehouse and industrial manufacturing facilities.

2.4.6.3. SKELETAL FRAME

It is consists of columns, beams and slabs particularly for low rise buildings and with

a small number of walls for high rise building. It is used in constructing schools,

commercial, offices and car parks. The Figure below shows an example of skeletal

structure.

INDIVIDUAL PROJECT.

-24-

Figure 2-3: Skeletal structure

(Source: Rahim 2004)

Legend:

i. Main suspended beam

ii. Hollow core unit

iii. Internal Rectangular beam

iv. Gable spandrel beam

v. Gable beam

vi. Main edge beam

vii. Landing support beam

viii. Staircase and landing

ix. Ground beam

x. Column

xi. Wall

xii. Double tee unit

xiii. Internal beam

xiv. Main edge spandrel beam

INDIVIDUAL PROJECT.

-25-

2.4.7. TYPES OF PRECAST CONCRETE ELEMENTS

Rahim (2004) identified that, various precast concrete components have been

introduced through technology transfer from developed countries and research by the

local manufacturer. There are varieties of precast concrete components for use in

building construction available in the market such as:

Hollow Core Slab

Precast Solid Plank

Precast Half Slab

Precast Parapet and Facade

Precast Beam

Precast Column

Precast Staircase

Precast Double Tee Slab

Precast Waffle Slab

Precast Load Bearing Wall

Hollow core slab Solid plank Beam Half slab

INDIVIDUAL PROJECT.

-26-

Half Slab Staircase Facade Wall Panel

Column Waffle Slab Double Tee Slab

Figure 2-4: Example of precast concrete components

(Source: Rahim, 2004)

INDIVIDUAL PROJECT.

-27-

2.4.8. ADVANTAGES OF PRE-CAST CONCRETE SYSTEM IN

PREFABRICATION

The following are the advantages of adopting precast concrete in the construction.

2.4.8.1. ENVIRONMENT FRIENDLY

The use of conventional timber formwork are reduced to minimum or even eliminated

and less usage of scaffolding through the use of prefabricated components or system

formwork for site casting. This contributed less demand of timber and therefore reduced

the cutting of trees activities in our forest. It also produces minimum wastage due to

factory controlled prefabrication environment. There are also show a cleaner site with

less dumping of unwanted materials and debris within the site compound. A well-

managed and neater working environment at site can be accomplished. Since the

components are made in factory, there will be minimal noise and air pollution causes by

machineries, vehicles and during erection of structural works. All wasted concrete and

rejected in production can be recycled in the factory again and it being re-used in

production. This may minimises the dumping activities to the land fill in our country.

2.4.8.2. SPEED AND TIME SAVING

The introduction of prefabrication technology which replaces in-situ construction, it

helps to reduce the duration of the project. As the prefabricated components are being

cast at factory or off site yard, the preparation work can proceed concurrently. Once the

precast components arrived at the work site, installation works begin from unloading the

material from the transporter to the required location. According to the statistic from a

manufacturer the average rates of 40 to 50 pieces of precast components within eight

hours of working days are sent to site for installation. This innovative technology can

also minimizes the unnecessary works that lead to delays that may caused by site

weather, erection of formwork and pouring of cast in situ concrete for the particular

structure frame. During the construction stage, once the prefabricated components are

installed at the required structure, it provides a sturdy and safe working platform for

carrying out other site works. The duration taken to complete the installation of precast

concrete superstructure per floor is much faster compared to the conventional method.

INDIVIDUAL PROJECT.

-28-

2.4.8.3. LABOUR SAVINGS:

Most of the precast products are manufactured by a highly technology machine for a

long production line with minimum usage of labour. The required man power on site

is less which few site workers are required during installation of prefabricated panels

and others building works. Hence, it creates safer and neater sites due to reduction of

site workers.

2.4.8.4. HIGH QUALITY PRODUCT:

Basically the ranges of precast concrete products are manufactured in a controlled

factory which used high technology that complies with international and local

standards. The technology is controlled by the professional and experienced team

(designers and manufacturers) in order to produce high quality finished products as well

as to fulfil clients’ satisfaction. Most of the local manufactures of prefabrication

products has good construction practice with a high commitment in producing best

quality products and services towards achieving MS ISO 9001:2000 Quality

Management System through quality assurance and quality control. Most of precast

members used as part of the building structure must conform to all applicable design

and detailing according to BS 8110 Part 1: Section Five. On the other hand, the precast

work on site must be constructed according to the method statement to achieve the

accuracy and the quality of work as well as to meet the design requirement. This shows

the quality control plan need to be adopted during precast work. In practice, few forms

are used to implement the quality control of precast work on site. An example of these

forms is as follows:

i) Request of inspection and testing

ii) Checklist for precasting work in factory

iii) Checklist for the installation of precast beam

iv) Checklist for the installation of the hollow core slab and plank

v) Checklist for the installation of the precast column

INDIVIDUAL PROJECT.

-29-

2.4.8.5. COST ECONOMICAL AND EFFECTIVE:

The productions of prefabricated products are minimizing total construction cost.

With mass production which lead to faster construction time as well as savings in

material and financing costs.

As the process of construction speed up the construction loan periods are shortened and

it lead to income generated for the clients as well as for the interim payment to the

contractors and manufacturers.

In fact the prefabricated components may contribute to low maintenance cost. The

costing for personnel or labour are reduced comparing to the conventional method

where the panels are installed with the use of cranes machine and 2 experiences workers

for installation work. With the reduced slab weight the structure frame can made lighter

and reduced combined weight of frame and flooring system leads to lighter foundation

without compromise to quality and safety aspect.

2.4.8.6. SPACE EFFECTIVENESS

Basically the precast components are transported from factory and installed to the

required location. The panels reached on site are stack neatly and put temporary at a

side adjacent to the working area. On- site storage is unnecessary. The precast concrete

are unload from the truck to the structures at the same time is much ideal for the

constraint project site which usually in urban area. In spite of the reduced weight of

precast slabs, the handling costs are minimized and lifting of these components is easy

especially in congested site area.

2.4.8.7. ENHANCE BUILDABILITY

Build ability as the ability to construct a building efficiently, economically and agreed

quality levels from its materials, components and subassemblies. Hence, the project

team must ensure the continuity of activities by managing manpower, materials,

components and sub-assemblies are delivered to site, stored and installed according to

the building works.

INDIVIDUAL PROJECT.

-30-

2.4.8.8. PROVIDE VOID FOR SERVICES

The services such as electrical wiring, mechanical work and internal/external plumbing

and sewerage can be easily installed neatly by using void at hollow core. Well prepared

planning and supervision, these services can be installed through voids without

providing conduits. Hence, it is considered cost savings.

2.4.8.9. SOUND INSULATION

The precast concrete is resistant to airborne noise and transmission of impact noise. It

provide sound insulation superior to solid concrete slabs of the same mass.

2.4.8.10. HEAT INSULATION

The existence voids provides good heat insulation compared to solid slabs. It is believe

that it has better thermal insulation properties in cold or heat which contribute to cost

savings for heating and air - conditioning.

2.4.8.11. FLEXIBILITY

As an example, the hollow core slabs are designed to carry brick wall. It means that

flexibility for any renovation can be done where it involves the use secondary beams.

2.4.9. DISADVANTAGES OF PRECAST CONCRETE SYSTEM

Even though there are many benefits in the precast concrete system as describe above,

there are some disadvantages also in system. They are as follows.

INDIVIDUAL PROJECT.

-31-

2.4.9.1. IMPOSSIBLE DESIGN CHANGES

Freedom of changing after the design stage is less possible in the precast concrete

prefabrication system. If any changes required by user, it is very difficult to adjust an

existing system design to suit with specific needs of particular user. The design and

planning has to be firm at an earlier date than is the case with an in-situ structure. Last

minute changes cannot be accommodated once the precast members are cast and such

items architecturally fixing and holes for services must be known in time to be

incorporated in the detail of the members.

2.4.9.2. OTHER DISADVANTAGES

A required for large capital investment that makes the contractor very

susceptible to fluctuation in demand for building

The joint between members generate the problem to the Engineer. Skill

knowledge shall be required for the jointing and fixing of units

If a large number of units are required or if they large in size problem can be

arise for storage, transportation and erection costs.

Pestering is not suitable for irregular shaped buildings

There is a restriction on the size and weight of precast concrete units. In other

words it is significant that more plants and machineries are required for the

handling of precast items

Consumption of space for precast components with comparing steel structures

are large. Due to the heavy weight of the components, the structure has to

support the self loads and a result the components will be bulk rather than the

steel items.

INDIVIDUAL PROJECT.

-32-

2.5. PREFABRICATION APPLICATION IN BUILDING

ELEMENTS

In a building the foundation, walls, doors and windows, floor and roof are the most

important components.

2.5.1. FOUNDATIONS

According to the Adlakha & Puri (2003), for foundation, conventional methods using

in-situ techniques are found to be economical and more practical for low cost housing.

In seismic regions, special attention is required to make the foundations continuous

using horizontal reinforcement. Prefabrication is not recommended for foundation in

normal situation.

2.5.2. WALLS

In the construction of walls, rammed earth, normal bricks, soil cement blocks, hollow

clay blocks, dense concrete blocks, small, medium and room size panels etc of different

sizes are used. However, bricks continue to be the backbone of the building industry. In

actual construction, the number of the bricks or blocks that are broken into different

sizes to fit into position at site is very large. As a result of this, there is wastage of

material and the quality of construction also suffers. Increasing the size of wall blocks

will prove economical due to greater speed and less mortar consumption, which can be

achieved by producing low density bigger size wall blocks and advantages of industrial

wastes like blast furnace slag and fly ash can be made.

2.5.3. FLOOR AND ROOF

Structural floors/roofs account for substantial cost of a building in normal situation.

Therefore, any savings achieved in floor/ roof considerably reduces the cost of

buildings. Traditional cast-in-situ concrete roof involve the use of temporary shuttering

which adds to the cost of construction and time. Use of standardised and optimised

roofing components where shuttering is avoided prove to be economical, fast and better

in quality (Adlakha & Puri, 2003).

INDIVIDUAL PROJECT.

-33-

In a concrete frame building, floor construction is the most time consuming and costly

element of the superstructure cost. Therefore the selection of the floor construction

method is very important when compare to the other element of the building. Compared

with steel or timber, concrete floor systems are the more appropriate and popular choice

for concrete frame buildings.

2.6. SLAB SYSTEM IN HOUSING CONSTRUCTION The slab system in building construction can be classified in to three categories namely

inset, prefabricated, Hybrid construction. In Sri Lanka the application of the

conventional in-situ concrete slab system in building construction is higher than the

prefabricated system. It is used as a conventional method of construction. There some

prefabricated slab systems are adapted in housing construction in Sri Lanka. The slab

system called SBS pre-stressed concrete floor system is becoming popular in housing

construction.

2.6.1. CONVENTIONAL SLAB SYSTEM

A In-situ Concrete slab is a common structural element in buildings. In Sri Lanka and

most of the countries it is used as a conventional slab system. Horizontal slabs of steel

reinforced concrete, typically between 100 and 500 millimeters thick, are most often

used to construct floors and ceilings, while thinner slabs are also used for exterior

paving. Normally in housing projects the In-situ slab thickness is 150 millimeters. In-

situ concrete slabs are built on the building site using formwork a type of boxing into

which the wet concrete is poured. If the slab is to be reinforced, the rebars are

positioned within the formwork before the concrete is poured in.

Formwork, reinforcement, and Concrete are the three primary expenses in cast-in-place

concrete slab construction to consider throughout the design process.

Formwork is the term given to either temporary or permanent molds into which

concrete or similar materials are poured. In the context of concrete construction, the

false work supports the shuttering moulds. Traditional timber formwork is built on site

out of timber and plywood or moisture resistant particleboard. It is easy to produce but

time consuming for larger structures and the plywood facing has a relatively short

INDIVIDUAL PROJECT.

-34-

lifespan. It is still used extensively where the labor costs are lower than the costs for

procuring re-usable formwork. It is also the most flexible type of formwork, so even

where other systems are in use, complicated sections may use it.

Reinforcement can be used to increase the strength of concrete and to help control

cracking. Reinforcing bars are needed to resist the bending tension in the bottom over

the central portion of the span. Fewer bars are necessary on the bottom near the ends of

the span where the bending moment is small. For this reason, some bars may be bent so

that the inclined portion can be used to resist diagonal tension. The reinforcement must

be covered by a set amount of concrete which protects the steel from rusting. This is

called cover. The amount of cover depends on whether it is inside or outside and is

measured to the top or bottom of the outer surface. It is around 20-30 mm for slab.

Concrete is made by mixing cement, water, coarse and fine aggregates and admixtures

(if required). Aggregates are of two basic types. Those are coarse (crushed rock, gravel

or screenings.) and fine sands. Admixtures are mixed into the concrete to change or alter

its properties, is the time concrete takes to set and harden, or its workability.

After Concrete mixing amount of concrete should be transporting, placing, compacting

and finishing. Compaction is done by shaking or vibrating, the concrete which liquefies

it, allowing the trapped air to rise out. The concrete settles, filling all the space in the

forms. Curing means to cover the concrete so it stays moist. By keeping concrete moist

the bond between the paste and the aggregates gets stronger. Concrete doesn’t harden

properly if it is left to dry out. Concrete will take 28 days to harden properly, until that

the props can not be removed from the site and can not continue the construction on the

slab.

Form work and positioning the reinforcement work take more time in this conventional

slab system. Also Labour and machinery involvement is high in this method compare to

the prefabricated method.

INDIVIDUAL PROJECT.

-35-

2.6.2. SBS SLAB SYSTEM

One of the precast manufacturing and C1 grade construction company in Sri Lanka

namely International Construction Consortium Ltd (ICC) has designed a novel concrete

system, which allows to reduce time of a construction by almost half. (Factory profile-

ICC publication, 2003).

The SBS pre-stressed concrete floor system also helps to save over 30 percent the

concrete slab installation charges. ‘The system is easy and does not require skilled

labourers for installation’. Senior Project Manager ICC, Palitha Ranasinghe said.

The industry faces a problem when building several storied buildings as the masons

cannot construct an upper floor until the concrete slab laid gets hardened. This takes

around 20 to 30 days and stilts too are needed which makes work on the lower floors

impossible.

To overcome this problem, ICC has designed the SBS system which is now very

popular. No frame work is necessary for the slab and the soffit blocks once in place

offers an immediate working platform for further construction. Rapid method of

construction due to the use of precast elements and the non-use of frame work is a great

advantage under this system.

The SBS pressurised slab system is made up of four components, consisting of

Pressurised beam- Grade 40/10 concrete.

Concrete masonry soffit block of grade 10/10 concrete

Distribution reinforcement GI weld mesh 3mm (dia) 50 X 50 (sqrs)

Structural concreting topping grade 20/10 concrete

The sequence of installation of SBS slab in a housing construction is explained with

photograph in Annex -4

INDIVIDUAL PROJECT.

-36-

2.7. KIT FORM HOUSE One of the famous precast manufacturing company called International Construction

Consortium (ICC) has introduced a special housing unit, (KIT), designed and precasted

by them and comes down in knock down form. This can be easily assembled by four

workers in four days.

The lay-out of this KIT house can be designed and constructed according to the needs of

the end user. The owners can decide the material for wall cladding and finishing and the

company A would also supply an instruction manual and a tool kit. Kit form houses are

widely constructed everywhere in Sri Lanka. It is quietly enough for a family for their

living purpose. If the numbers of members are high in a family, there is a possibility to

merge the kit unit with another.

One unit of kit form housing is for a house with a plinth area of 40.69 m2. The house

could be developing to consist of living and dining room, bed room, a kitchen, a

varandah and a toilet. The Figure 2.5 shows the plan of Kit form house.

Figure 2-5: Plan of Kit form house

INDIVIDUAL PROJECT.

-37-

A kit form housing units consists of Column pocket footing, Pad footings, Columns,

Plinth beams, Tie beams, Toilet pedestal, Roof beams, Purlins, and lintels. The table 2.2

shows the detail about the each elements in a kit form house.

Table 2-2: Elements in a typical kit house

Elements Material Numbers

Column

pocket footing Precast concrete

9

Pad footings Precast concrete 4

Columns Pre-stressed

concrete

9

Plinth beams Pre-stressed

concrete

12

Tie beams Pre-stressed

concrete

6

Toilet pedestal Precast 1

Roof beams Pre-stressed

concrete

6

Purlins Timber 16

Lintels Pre-stressed

concrete

9

2.7.1. ERECTION OF A KIT FORM HOUSE

Now days Kit form houses becoming very popular in Sri Lanka due to reduce the

construction duration and to reduce the cost of the building. A kit form house can be

easily assembled by four workers in four days. The method of the erection of a typical

kit form house is explained with photograph in Annex -5

2.7.2. BENEFITS OF THE KIT HOUSES

The elements for the Kit are manufactured under TQM condition in the precast

factory. So the quality of the Kit house is high

The components which come in knock down form could be easily assembled at

ground level and erected by four workers in 4-5 days. The time taken to build

the same area of house in conventional method is very high Compare with this

INDIVIDUAL PROJECT.

-38-

method. So that by reducing the total duration of the construction and reducing

the labour involvement there is the huge amount of cost saving in this type of

Kit houses.

An erection manual with tools and implements required for erection is provided

and included in the kit.

The internal layout of the houses could be designed and constructed according to

the needs of the end user

The material for wall cladding and the type of finishes could be decided by the

house owners themselves based on their requirements and their budgets.

2.8. SUMMARY

In Sri Lanka the demand for houses and urban infrastructure is expanding rapidly with

the population growth and urbanisation. In addition most of the people who lived in

costrel area lost their shelters. This also increased the demand for houses. So there was a

need to build those houses in very short period. To achieve this target, using

prefabricated technology is better alternative for the conventional method. Numerous

constructions in the world have utilized prefabrication of precast concrete system

especially when the project requirement is to build in shorter period of within the given

budget and quality workmanship

Prefabrication is the practice of manufacturing the components of an assembly in one

location and assembling them in another. By using a prefabricated building system, as

much as 50% of the total construction time can be cut out of the schedule (Mark 1993).

There are mainly two types of prefabricated system adopted in building construction

namely, fully prefabricated systems and partially prefabricated systems. In Sri Lanka

Steel, timber and precast concrete are the material widely used in the prefabricated

construction. Precast concretes unites are very commonly used in the prefabricated

housing construction in Sri Lank due to the several reasons such as easy availability of

material, economical, quality, etc..

INDIVIDUAL PROJECT.

-39-

CCHHAAPPTTEERR 0033

33..00 RREESSEEAARRCCHH MMEETTHHOODDOOLLOOGGYY

3.1. INTRODUCTION The research objectives of this project report uses two methods: literature method and

empirical study. Firstly, the preliminary study is done to gather information about

research topic and recently technology applied in our construction building industry.

Informal interviews with professionals and experienced personnel in the usage of the

precast concrete in prefabricated system were carried out in designing questionnaire

form. Questionnaire survey forms are distributed to gauge respondents’ opinion

regarding the benefits in using prefabrication in the housing construction. The findings

of the study were discussed and few suggestions are listed. Finally, the study research is

concluded.

3.2. LITERATURE REVIEW A literature review was carried out as preliminary study in gaining knowledge of the

research topic. Through the literature review, research mapping was established. The

literature review was drawn by referring to several sources such from published books,

articles in journals and papers, other published research works, academic and research

magazines and newsletter, brochures and information from the internet

3.3. INFORMAL INTERVIEWS An informal interview with experienced personnel from the construction industry with

regards to the usage of precast prefabricated system in housing construction were

carried out. These interviews were conducted to obtain ideas and data valuable for

structuring the questionnaire survey form.

3.4. QUESTIONNAIRE SURVEY A questionnaire survey forms were distributed to the developers, architects,

engineers, manufacturers, quantity surveyors, government agencies, contractors and

consulting firms in eastern province. Some sets of questionnaire survey forms

were distributed to get the necessary details.

INDIVIDUAL PROJECT.

-40-

3.5. FIELD SURVEY

Simple field survey was conducted to ascertain the cost effectiveness of the

prefabricated floor system against conventional slab system in housing construction.

The cost detail of five number of two story housing projects, which are constructed by

using conventional in-situ concrete slab system, were selected within the addalaichennai

housing plan. As well as the cost detail of another five number of two story housing

projects were selected, which are constructed by using SBS slab system, while other

parameters are constrain.

Average cost of both slab system per square meter were calculated by using simple

average equation. The cost saving of the SBS slab system was calculated by comparing

the average unit cost of both Insitu and SBS slab system. The calculation part is

attached in the Annex 3.

3.6. QUESTIONNAIRE STRUCTURE

The questionnaire was structured into three sections:

Section A: Obtain information about the respondent’s profession and role in the

construction building industry and the organization in which he or she served.

Section B: Obtain information about the respondent’s working experience or

knowledge on the application of prefabrication system in the

projects involved by his or hers organization business area.

Section C: Evaluate the benefits of using precast concrete technology in

construction industry. And comments regarding the application of this

system in improving our construction industry.

Questions in Section C are based on Likert scale of five ordinal measures of agreement

towards each statements (from 1 to 5) as shown in the below Figure 3.1

INDIVIDUAL PROJECT.

-41-

Figure 3-1: Five ordinal measure of agreement of Likert scale

The data collected from the questionnaire survey was analysed using frequency analysis

and “Relative Indices” (RI) technique. RI was calculated using the following formula:

RI = ∑ (1n1 + 2n2 + 3n3 + 4n4 + 5n5)

5 (n1 + n2 + n3 + n4 + n5)

Where: ni = the number of respondent agreeing with each choice

The computation of RI using this formulae yield the value of RI ranging from

0.2 to 1.0, where 0.2 represent minimum strength and 1.0 the maximum strength. The

table below shows the categories for RI ranges.

Table 3-1: Categories for RI ranges

RI Range Category

0.20 - 0.35 Very Low

0.36 - 0.51 Low

0.52 - 0.67 Average

0.68 - 0.83 High

0.84 - 1.00 Very High

(Source: Rahim 2004)

INDIVIDUAL PROJECT.

-42-

3.7. LIMITATION OF THE STUDY This study is limited to literature review and evaluation from personnel involved in the

construction industry. The study considered only on the use precast concrete element in

housing construction. The data collected are only confined to the respondents within the

eastern area. The identification of the cost saving of prefabricated system is done only

housing projects.

The research methodology flowchart was shown in below Figure 4.2 which indicates

the general procedures for this study

INDIVIDUAL PROJECT.

-43-

Literature Review

Establish framework of

the research

Data collection

Data Analysis

Discussion

Conclusion

INDIVIDUAL PROJECT.

-44-

CONCLUSION.

This Individual Project would have given me a good

knowledge about prefabricated building and these constructions. I got

much information from all the sources possible. This assignment would

have helped us to come to know the methods used in the industry and

construction site. In today many buildings were built in this format. Its

method very easy way to the building.

INDIVIDUAL PROJECT.

-45-

REFERENCES & BIBLIOGRAPHY

1. Adlakha, PK & Puri, HC 2003, ‘Prefabrication building methodologies for low

cost housing’, IE Journal, vol. 84, pp. 4-9.

2. Al-Rashid, K, Kartam, N, & Koushiki, PA 2005, ‘Delays and cost increases in the

construction of private residential project in Kuwait’, Construction management

and economics, vol. 23, pp. 285-294.

3. Brook, KM, & Murdock, LJ 1979, Concrete material and practice, Edward Arnold

(Publishers) Ltd, London.

4. Bruggeling, ASG & Huyghe, GF 1991, Prefabrication with concrete,

A.A.Balkema Rotterdam, Netherlands.

5. Central Bank of Sri Lanka 2005, Central Bank Report 2004, Colombo.

6. Central Bank of Sri Lanka 2007, Central Bank Report 2006, Colombo.

7. Chan, APC & Tam, CM 2000, ‘Factors affecting the quality of building projects

in Hong Kong’, International Journal of Quality & Reliability Management, vol.

17, no. 4/5, pp. 423-441.

8. Chan, APC, Chan, DWM & Yeung, NSY 2002, ‘Application of prefabrication in

construction - A new research agenda for reform by CII-HK’, Conference on

precast concrete building system, Hong Kong.

9. Chan, APC, Lam, PTI & Wong, FKW 2006, ‘Assessing quality relationships in

public housing: An empirical study’, International Journal of Quality & Reliability

Management, vol. 23, no. 8, pp. 909-927.

10. Chew, SP 1986, ‘The scenario of industrial building system in Malaysia’,

Proceeding of the 1986 UNESCO/FEISAP regional workshop on “Towards

INDIVIDUAL PROJECT.

-46-

Industrialization In the Building Industry, July 29-31, Malaysia: UPM, Serdang,

pp. 126-128.

11. Chudley, R 1989, Building superstructure, Longman Group UK Limited, London.

12. Chudley, R 1999, Construction Technology, 3rd edn, Addition Wesley logman

Limited, London.

13. Domel, AW & Ghosh, SK, 1990, Concrete Floor Systems:Guide To Estimating

and Economizing, Portland Cement Association, Tokyo.

14. Egan, J 1998, Re-thinking construction, DETR. London.

15. Elliott, KS 2000, ‘Research and development in precast concrete framed

structures’, Prog. Struct. Engng .Mater, vol. 2, pp. 405-428.

16. Foster, JS 1997, Structure and Fabric part 1, Willianm Colwes & Sons Ltd,

London.

17. Glass, J 1999, The future for pre cast concrete in low rise housing, British precast

concrete federation, London.

18. Glass, J 2005, ‘A best practices process model for hybrid concrete construction’,

Construction management and economics, vol. 23, pp. 169-184.

19. Goodchild, CH 1997, Economic Concrete Frame Elements, British Cement

Association, Crowthorne.