Proposing a visualization technique for Optimization

Proposing a visualization technique for Optimization of the tower crane and material supply locations in a high-rise building site

Authors: Mohammadhossein Kashefizadeh1, Hamed Rahnama2 1. Master Graduate of Civil Engineering- Construction Management; UTM University of Malaysia, Email: [email protected] 2. PhD of Construction and Technology Management, UTM University of Malaysia

Abstract Efficiency of tower cranes largely depends on its location, and the supply point position which has a significant contribution to crane

cycle

time.

The

current

trend

in

practice

for

crane

positioning is to rely on experience than a technique, and the existing methods in literature suffer from some shortcomings such as predetermined crane and supply locations and twodimensional (2D) representation of the results. Therefore, the main aim of the present study is to propose a model to find the optimum tower crane and supply point locations in the site and the associated minimum completion time. The proposed model includes radial velocity, tangent velocity, crane working radius (CWR), considers a three-dimensional (3D) movement of the materials by crane and generates a heatmap visualization of the whole site. For this purpose, a model is initially proposed for the analytical modeling of average transportation time (ATT), and afterward,

the

flowchart

of

the

optimization

procedure

is

presented. In the next step, the model is implemented into a case study for evaluation purpose. Results show that the proposed model has a good convergence rate to the existing models and is capable of generating accurate solutions.

Keywords: Optimization of tower crane location, Optimization of material supply locations, High-rise building construction site, Algorithms; Project planning

2

Nomenclature Symbol

Description

x

Position at x-axis

y

Position at y-axis

z

Position at z-axis

k

Potential material demand points;

K

Total number of demand points in the site

i

Horizontal coordination of crane on the grid

j

Vertical coordination of crane on the grid

I

Horizontal coordination of Supply point on the grid

J

Vertical coordination of Supply point on the grid

Cx,

Cy, Coordinate of a tower crane;

Cz Dkx,Dky,

Coordinate of a demand point at location k;

Dkz Sx,

Sy, Coordinate of supply point;

Sz Vh

Hoisting velocity of hook (m/min);

Vω

Slewing velocity of jib(r/min)

Vr

Radial velocity (m/min);

Tr(i, j)k

Time for trolley radial movement of a tower crane at location k from a supply point i to a demand point j;

Tω(i, j)k

Time for trolley tangent movement of tower crane at location k from a supply point i to a demand point j;

Tv(i, j)

Time for hook vertical movement from a supply point i to a demand point j;

Ti, j k

Hook total travel time of tower crane at location k between a supply point i

3

and a demand point j; α

Degree of coordination of hook movement in radial and tangential directions in horizontal plane ranging between 0.0 and 1.0 continuously (where 0 stands for full simultaneous movement and 1 for full consecutive movement);

β

Degree of coordination of hook movement in vertical and horizontal planes ranging between 0.0 and 1.0 continuously (where 0 stands for full simultaneous movement and 1 for full consecutive moment); Demand points Crane Point (Minimum time)

Crane Points (Pre-determined) Supply Points (Pre-determined) Crane Point (Selected) Supply Point (Selected)

4

Table of Contents

1. 1.1 1.2 1.3 1.4 1.5 1.6 1.7 2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.7.1 2.7.1.1 2.7.1.2 2.7.2 2.8 2.9 2.9.1 2.9.2 2.10 2.11 3 3.1 3.2 3.3 3.3.1 3.3.2 3.3.3 3.3.4

Description Chapter 1: Introduction Background of study Problem statement Aim of study Objectives of study Scope of study Significance of study Summary of chapter Chapter 2: Literature review Introduction Background of IBS in Malaysia Classification of IBS in Malaysia Benefits of IBS Constraints and Barriers to of Using IBS in Malaysia Sequence of Construction for IBS Method Crane Factors Hard factors Operating Conditions Crane Specifications Soft Factors Modeling Techniques Mathematical models Representation of The Models Types of mathematical Models Similar Studies Summary of chapter Chapter 3: Research methodology Introduction Data Collection Steps to Build a Mathematical Model Problem Definition Model Construction Model analysis Implementation and Follow Up 5

Page 9 9 12 16 16 16 18 19 21 21 22 26 30 35 39 41 42 43 43 44 50 50 51 52 52 56 58 58 59 60 61 62 62 63

3.4 4 4.1 4.2 4.3 4.4 4.5 4.6 4.6.1 4.6.2 4.7 4.8 5 5.1 5.2 5.2.1 5.2.2 5.3 5.4 5.4.1 5.4.2 5.4.3 5.4.4 5.5 6 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 6.10 7 7.1

Summary of chapter Chapter 4: Data collection & modelling Introduction Problem Definition of the Model Model Construction Optimization Procedure Feasible working area Model analysis Determine and Test a Solution Interpret and Analysis Implementation Summary of chapter Chapter 5: Model analysis and findings Introduction Good Operator skill Supply Point: Inside Building Supply Point: Outside Building Poor Operator Skill Findings Radial and Tangent Index Analyses Crane Working Radius (CWR) Analysis Operator Skill Analysis Fix Time analysis Summary of chapter Chapter 6: model verification Introduction Comparison of the proposed model to MILP and GA Case study of an IBS Building Crane Specifications of the Construction Assumptions for the Proposed Building Data Input Sensitivity Analyses “What if” Analysis Discussion of the Results Summary of chapter Chapter 7: Conclusion Objectives Review 6

64 65 65 66 69 72 76 79 79 81 82 84 85 85 86 86 89 95 97 98 100 103 106 106 108 108 108 114 117 118 118 121 123 130 131 132 133

7.1.1 7.1.2 7.1.3 7.2 7.3

First objective Second objective Third objective Overall conclusion of the Study Recommendations References

7

133 134 136 136 137 140

8

CHAPTER 1

INTRODUCTION

1.1.

Background of Study

Accommodation is undoubtedly the first and most concern of human-being

worldwide.

The

rapid

growth

of

Malaysian

population has persuaded the Government to strive more for providing shelter for citizens.

Nevertheless, unfortunately, the intensive use of unskilled workers

and

construction

low

technology

methods,

besides

equipment poor

and

planning

and

out-of-dated unpredicted

events such as weather changes and machinery breakdown have eventually caused low productivity and poor efficiency of work at construction site. As a result they have led to unproductive practices and initially contribute to the late delivery of projects (CIDB 2003) & (Tenth Malaysian Master Plan, 2010). The

introduction

of

the

Industrialised

Building

System

(IBS) with the promise of improving productivity rate, lowering construction costs and meeting the growing demand for housing is indeed welcoming news to the country’s construction industry. Employing IBS systems in Malaysian construction industry has 9

profoundly helped to accelerate the construction process as well as complying with the Malaysian plans’ targets (Kamarual Anuar et al 2010).

Nevertheless, statistics show that the development rate is still behind schedule and the targets are not met yet. This phenomenon reveals us that although IBS has yielded a plenty of advantages, this industry still suffers from unpredicted delays which may arise from lack of skilled labour, weather variation, machinery

breakdown,

safety

deficiencies,

storage

limitations

and unexpected events and so on. Therefore, the Malaysian construction industry nowadays has to put more emphasis on the aspects of time, cost, and quality (CIDB, 2003).

Therefore, tenth Malaysian plant (2010) is striving to eliminate the challenges of industry via:

1.

Matching of supply and demand for affordable housing.

2.

Increasing quality of affordable new and existing housing.

3.

Meeting the call for environmentally sustainable design.

10

Figure 1.1: Sustainability criteria for construction industry. However, it can be said that each construction process is related to the four aspects, time is a significant aspect in the construction in which every project should be completed on time or earlier in order to prevent the undesirable losses of money. Therefore, the control of time in each construction process is very important. Other controlled

within

than that, each the

estimated

project cost.

now ought

The

quality

to of

be the

construction product is also a common issue that be disputed. In construction industry, time and cost optimization only makes sense once quality is maintained in a high level. The construction industry also faces the challenge of safety as the fourth challenge. Preventing accidents and implementing safety regulations at site are those issues with high degree of concern

Nonetheless, the improvement of productivity and quality while reducing completion time and optimizing incurred costs in building construction can be attained only through intensive planning

and

appropriate

building

practice

process.

Reducing

completion time of the assembly process of an IBS project by 11

proposing a better resource allocation in IBS system requires accurate scrutiny over the major causes and drivers of the delays. After finding out the obscures and obstacles in which cause timeincrease, an accurate planning and scheduling method must be called for to employ and resolve the problem.

1.2. Problem Statement As it can be seen in Figure 1.2, in the 7th Malaysia Plan, Malaysia planned to construct about 800,000 units of houses for its population. Nevertheless, despite numerous incentives

and

promotions to encourage housing developers to invest in such housing category; the achievements are somewhat disappointing with only 20 percent completed houses. In the 8th Malaysia Plan, almost another 800,000 units of houses were planned to build but the results were still unsatisfactory. Apart from them, with the announcement of the 9th Malaysia Plan, the country continues to embark on the development of affordable and sustainable low and medium cost housing. However, the country is facing a difficult task to accomplish the target of 600,000 to 800,000 houses during this period because the current building system being practiced by the construction industry is unable to cope with the huge demand (CIDB 2003) & (CIDB 2008) & (Eighth Malaysian Plan 2000) & (Ninth Malaysian Plan, 2006) & (Tenth Malaysian Plan, 2010).

12

Target

Achieve

Deficit

d

Figure 1.2: Construction performance of Malaysia based on master plans.

Not only the conventional building systems currently being practiced by the construction industry is unable to cope with the huge demand but also the recent implemented

Industrialised

Building Systems (IBS) have been disable to entirely live up to the demands. Although IBS has immense inherent advantages in terms of productivity, indoor quality, durability and cost, (W.A. Thanoon et.al, 2003), projects still suffer from poor planning due to lack of appropriate predictions during planning stage. Hence they must be adapted to deal with the effective integration of various

planning

elements

and

the

optimization

of

project

parameters. Time, cost, and quality are the prime objectives of a project that need to be optimized to fulfil the project’s goal (Prasanta Kumar Dey and Mario.T. Tabucanon, 1996). Safety 13

issues,

on-time

delivery,

enough

and

appropriate

storage,

equipment and machineries, efficient.

Site layout, hiring of skilled labours as well as general workers,

having

enough

capital

to

run

the

operation

are

somewhat critical factors in success of a project in which a good planning on resources will help to meet the client’s expectations within time. Kadir et al (2002) conducted a research and throughout

interview

with

professionals,

indicated

that

IBS

projects are highly dependent on number of skilled labour, availability

if

skilled

labour,

equipment

availability

and

performance.

Among various equipment and machinery in construction sites, crane is of the most paramount and critical one in IBS projects. They are usually located at a convenient and safe place where most of these heavy and bulky materials can be handled. there are many factors to be considered while locating a crane to undertake transportation tasks efficiently. Having a good facility layout including the crane and material supply locations is one of the most important parts to increase such production efficiency in construction sites. To cope with this issue, practitioners in the industry tend to rely much on experiences and always there is lack of a well-defined approach to come up with an optimal site layout for IBS construction projects (C. Huang et al, 2010). Although, cranes have been longley employed in construction projects within Malaysia, the Malaysian IBS industry still suffers from those aforementioned problems due to its newness. Due to the fact that the travel time of the crane as an important factor in 14

the repetitive

assembly process

of

and

IBS

project,

hence,

optimizing crane location as well as supply point can lead to significant

reduction

construction Eshwar,

projects,

Vellanki

Abidin,2007).

in

S.

the in

S.

duration

particular

and

cost

IBS-based

Kumar,2004)

&

of

repetitive

projects.

(Ahmad

B

(K.

Zainal

Figure 1.3 shows the pyramid of the current

problem in IBS construction industry.

7th, 8th and 9th Malaysian plans fail to comply

Neither conventional, nor IBS systems.

Industry needs integration with optimization

Time, cost & quality

Several critical drivers

Labor, Machinery, storage

Crane

Figure 1.3: Pyramid of current problem in IBS construction industry.

15

1.3.

Aim of Study The aim of this study is to propose a graphical mathematical

model to find out the best crane location as well as supply point by considering different crane specifications. The proposed model will be utilized to find the optimum completion time.

1.4 Objectives of Study: 1.

To develop the graphical mathematical model of crane movement in IBS projects.

2.

To Analyse and interpret the behaviour of the model for different demand layouts.

3.

To verify the model using data of the proposed IBS

building.

1.5 Scope of Study This study strives to focus the scope of work mainly on modelling the repetitive activities work-flow of IBS assembly step; as determined in Figure 1.4.

16

Figure 1.4: Steps of IBS construction.

Therefore it focuses on assembly and installation of IBS components

including

lifting

and

hoisting,

carrying

and

unloading of components by crane, including footings, beams, slabs, columns, walls.

Among several items in assembly process, the study will only focus on the performance of the crane and the machineries are excluded.

As illustrated in Figure 1.5, the activities sequence is all finish-to-start activities; and other types of activities such as startto-start or start-to-finish activities are excluded.

Activity 1

Activity 2

Activity 3

Figure 1.5:. Representation of the Activities Sequence.

Also, some assumptions have been made in this study. although there is a wide range of factors contributing in project completion time (also including interruption and delays), this study embraces only three major factors, three crane criteria, such 17

as Radial and Tangent velocities and Crane working Radius besides two human factors of operator skill and fix time due to skill of labour.

Moreover, only deterministic characteristics of work are involved in the study; and stochastic characteristics and sudden phenomena such as crane breakdown, weather variation or supply process delay are neglected.

1.6 Significance of the Study The study attempts to propose a better site layout design for IBS housing construction projects. The result of optimization by modelling in this study can be applied in the site layout of other IBS projects in wider

ranges. The study proposes a method

to facilitate the site layout design and crane positioning in IBS projects in order to achieve the minimum completion time.

Apart from its major advantage, this mathematical model applied in this study will be used as a guideline model for the contractor of IBS projects in the future to construct houses using IBS

components

with

minute

detail

information

regarding

problems and delay factors.

The proposed model can be a very useful model for prediction purposes. In other words, the total completion time of assembly in any similar IBS projects can be predicted and

18

calculated in advance. This provides useful information for cashflow management and resource allocation.

However, it is expected that this study contributes to expand the knowledge in field of IBS and help IBS for further develops and promote IBS as an innovative construction method in Malaysia.

1.7 Summary of Chapter First chapter introduced and elaborated the background of this study for further understanding on the problems that has been solved.

Malaysian

development

speed

construction By

industry

considering

the

suffers demands

from of

slow

housing

development and the need for construction industry to make changes, the introduction of the Industrialised Building System (IBS) with the promise of improving productivity rate, lowering construction costs and meeting the growing demand for housing is definitely welcoming news to the industry. However, slow development rate emerges from different reasons in which poor site layout is one of those. Crane is known as critical machinery within construction of IBS projects where its performance can remarkably affect the progress of project. This study is prepared to provide some information of IBS technology that can be implemented by all parties in construction project. With the extensive knowledge on the (IBS) may further expand and promote IBS as an innovative construction method in Malaysia,

19

at the same time prevent all the barriers to the adoption of IBS technology in construction Industry.

20

CHAPTER 2

LITERATURE REVIEW

2.1 Introduction This

chapter

presents

the

literature

associated

with

Industrialized Building System (IBS), history of development of IBS

within

Malaysian

construction

industry

and

attributed

regulations came into effect towards implementation of IBS. Likewise, various definitions along with different types of IBS concept

are

reviewed

and

subsequently

different

available

classifications which are well-known in Malaysia are addressed. Afterward benefits of implementation of IBS are scrutinized. Similarly, constraints of a broad implementation of IBS within Malaysian industry are overviewed. In the next step of the literature review, the sequence of an IBS project is defined and concept

of

repetitive

work

is

introduced.

Subsequently,

In

addition, several factors affecting in performance of the cranes are also highlighted.

The

last

but

not

least,

the

concept

of

mathematical

modelling is vastly elaborated in order to illustrate the path for 21

modelling purpose in subsequent chapters. Eventually, at the final part of the literature review, previous research done thanks to integration of mathematical models in construction and crane machinery is overviewed.

2.2 Background of IBS in Malaysia IBS is not new in the Malaysian construction industry, particularly the usage of steel structures and precast concrete for the

construction

of

bridges,

drains

and

other

infrastructure

projects. IBS began in early 1960s when Ministry of Housing and Local

Government

of

Malaysia

visited

several

European

countries and evaluated their housing development program. in the year 1964, the Government had launched pilot project on IBS to speed up the delivery time and built affordable and quality houses. As a result pre-cast, steel frame and other IBS were used as hybrid construction methods to build national landmarks such as Bukit Jalil Sport Complex, LRT and Petronas Twin Tower. It was reported that at least 21 manufactures and suppliers of IBS are actively promoting their systems in Malaysia (Kamarul Anuar et al,2007) & (Mohd Sapuan Salit, 2003)

In

June

1999,

the

CIDB

had

established

a

technical

committee to look into developing good environmental practices in the construction industry. Through September

the

2004,

‘2005 the

Budget’

government 22

announcement had

pledged

to

back

in

construct

100,000 units of affordable houses using IBS. In addition, all new government building projects were required to have at least 50% IBS content which had been calculated through the IBS Score Manual developed by CIDB (CIMP, 2006).

In June 2006, the Construction Industry Master Plan 20062015 (CIMP) has been published to chart the way forward for Malaysian construction. The CIMP has identified that the demand on

environmental

sustainability

is

necessary

to

achieve

and

sustain economic growth and social development. The following milestones have been highlighted under the roadmap to be achieved in 2015 (CIMP, 2006).

1. Foster a quality and environment-friendly culture and to increase customer demand in the global environment in construction 2. Encourage external accreditation in quality and environmental management, i.e. ISO 14001 certifications 3. Promote environment-friendly practices 4.

Initiatives on green building materials to ensure impact activities can

provide in order to spur economy and

social benefits at large.

Beginning from 2007 onwards, new incentives for IBS adopter has been introduced. The exemption of the levy (CIDB levy - 0.125 % of total cost of the project according to Article 520) on contractors that used some kind of IBS in 50% of the building components has been commenced since 1st January 2007. 23

In early 2007, IBS Centre had been established in Cheras to promote IBS in Malaysia and also to play the role of consultant. The centre is equipped with IBS show house and Research

and

Development

(R&D)

capacity.

Construction

Research Institute of Malaysia (CREAM) was initiated to manage IBS research.

To create a spill-out effect from public sector projects to private sector project, government had enforced the use of 70% IBS component in all government’s new building construction since

2008.

From

2006

to

2010,

in

approximate

of

320

government’s projects worth RM 9.43 billion had been identified to be carried out using the IBS. It is a huge market sector for IBS in Malaysia (CIDB, 2008). The new circular of ‘Surat Pekeliling Perbendaharaan Bil, 2007 Tahun 2008’ dated on October 2008 had emphasized on the full utilization of IBS for government’s projects in Malaysia. Among the pressing matters raised in the circular were the use of IBS component in government projects must not be less than 70% and the inclusion of IBS component as part of contract documents for all building works.

The current IBS systems used in Malaysia housing projects are large panel systems, metal form systems and modular system. The IBS system is largely used in Shah Alam, Wangsa Maju and Pandan area (Kamar, K. A. M, et al, 2009).

24

Malaysia Green Building Index (GBI) has been developed and widely used since 2009. This private sector driven initiative aims to promote sustainability in the built environment and raise awareness among the industry players about environment issues. Building will be awarded GBI rating score based on six key criteria;

energy

efficiency,

indoor

environment

quality,

sustainable site planning, material and resources, water efficiency and innovation (GBI Malaysia, 2007).

In 2010, the Government of Malaysia, through its plans has given priority to environmental friendly products and services that

comply

with

green

construction.

In

budget

2010,

the

Government has allocated RM 20M for this purpose (Zuhairi Abd.Hamid, et.al, 2009).

For a start, the government is conducting a baseline study for green technology in Malaysia. The baseline study comprise the

following

sectors;

energy,

waste

water,

building,

transportation, manufacturing, IBS and ICT (Zuhairi Abd Hamid, 2009).

The Practices

Technical in

environmental bodies,

the

Committee Construction

experts

academia

9

from

and

on

Good

Industry

government

construction

(TC9)

agencies,

related

Environmental comprises professional

associations.

Six

working groups have been established. Under the TC9, CIDB had published Environmental

Strategic Practices

Recommendations in

Construction

for

Improving

Industry

which

highlighted recommendation to be the strategic way forward in 25

environment in Malaysian construction industry adopted by all players. The recommendations are summarised as strengthening the development approval process as well as Enhancing law and enforcement (CIDB, 2006).

The

success

of

precast,

steel

and

hybrid

construction

contributed to the rapid creation of numerous beautiful and quality structures. The survey done in Malaysia revealed that the most popular and widely used system by the contractor is a formwork system (31%). It is in the form of aluminium, metal and plastic formwork which are proved to be flexible and cost effective.

The

precast

and

steel

frame

system

also

gained

substantial popularity at 26 % and 23 % respectively while only 7% of the respondents had ever used timber frame systems (Kamarul Anuar Mohamad Kamar et.al, 2009).

The process of development of IBS in Malaysia has come out with several IBS buildings where some of most significant of them of the Bukit Jalil Sports Complex and Games Village, the Petronas

Twin

Towers

and

the

LRT

lines

and

tunnels.

Nevertheless, the usage of IBS in housing project is still very low if compared to the conventional method.

2.3

Classification of IBS in Malaysia According

to

CIDB

(2003),

from

the

structural

classification, there are five IBS main groups identified as being used in this country which are tabulated in Table 2.1. Also, 26

Kamarul Anuar Mohd Kamar et al (2011) compiled all existing IBS systems and classified them in Table 2.2.

Table 2.1: Different IBS systems available worldwide. System

Description The system includes precast concrete

Precast concrete framing,

columns, beams, slabs, walls, “3-D”

panel and box systems

components concrete, as well as permanent concrete formworks. The ystem includes tunnel forms, tilt-up

Steel formwork systems

systems, beams and columns moulding forms, and permanent steel formworks.

Steel framing system

The system covers steel trusses, columns beams and portal frame systems.

Prefabricated timber

The system prefabricated timber trusses

framing systems

beams and columns. The system includes interlocking concrete

Blockwork systems

masonry units (CMU) and lightweight concrete blocks.

27

Table 2.2: Classification of IBS definition (Kamarul Anuar Mohd Kamar et al, 2011) Classification

Sub-categories Panel system

Mazjub’s Building System

Box system

Classification

Frame system Conventional building system

Industrialized System

Cast in situ formwork system

Classification (Razai-Badir’s

Table or tunnel formwork

Classification)

Prefabricated system Composition system Timber

Warszawski’s Building System

Steel

Classification 1

Cast in situ concrete Precast concrete Linear Skeleton

Warszawski’s Building System

Planar

Classification 2

Planar systems Three dimensional box systems Pre-cast concrete-framed building Pre-cast concrete wall system Reinforced concrete building with

IBS Classification (UTM)

pre-cast concrete slab Steel formwork system Steel-framed building and roof trusses

Bruno-Richard’s IBS

Site intense kit part 28

Classification

Factory made module Hybrid Volumetric system Panellized system

Off-Site Manufacturing (OSM)

Hybrid system

Classification

Sub-assemblies and component system Modular system Component manufacture and sub-

Pre-assembly and pre-fabrication

assembly

Classification

Non-volumetric sub-assembly Volumetric pre-assembly Precast concrete training Panel and box system Steel formwork systems

IBS Classification (CIDB)

Steel framing systems Prefabricated timber framing system Block work system

Table 2.2: Classification of IBS definition (Kamarul Anuar Mohd Kamar et al, 2011) (Continue) Classification

Sub-categories Component manufacture and sub-

Pre-assembly and pre-fabrication

assembly

Classification

Non-volumetric sub-assembly Volumetric pre-assembly Precast concrete training

IBS Classification (CIDB)

Panel and box system 29

Steel formwork systems Steel framing systems Prefabricated timber framing system Block work system Volumetric Panellized Modern method of construction

Hybrid

(MMC classification)

Subassemblies and components Non off site Modern Methods of Construction Volumetric Panellized

Modern method of construction

Hybrid

(MMC classification)

Subassemblies and components Non off site Modern Methods of Construction

2.4 Benefits of IBS Various researches are conducted by various professionals and scientists of construction industry in favour of highlighting several benefits of IBS. A comprehensive overview on the work done by each research in favour of benefits of IBS, gives us a good perspective regarding this new concept. The research of Badir et al, (2002), W.A. Thanoon et al (2003), Roger-Bruno Richard (2005), Blismas, N., C. Pasquire and A. Gibb. (2006), Gorgolewski, M. T. (2005), Ali Mohammed Alshawal (2006), Foong Kok Li (2006), Ahamad Razin B Zainal Abidin (2007), 30

Jaillon, L., C. S. Poon and Y. H. Chiang. (2009) & Baldwin et.al (2009), Kamarul Anuar et.al (2010 A), Riduan Yunus, Jay Yang (2011). Table 2.3 presents the brief of the previous studies.

Table 2.3: Benefits of IBS systems Benefit factor

Description The repetitive use of system formwork made up steel,

Cost saving

aluminium, etc and scaffolding provides considerable cost savings. Faster completion due to the usage of standardised components and simplified construction process.

Reduces Build time

Build faster since on-site and manufacturing activities are usually undertaken in parallel. The number of labour required in IBS is far lower than those required in traditional method. Necessary to

Labour reduction

emphasises that the relatively far fewer workers still need to be imparted training and skill appropriate to IBS. IBS products are manufactured in a casting area where critical factors

Higher quality

including temperature, mix design and stripping time are closely

31

checked and controlled; ensuring that the quality of IBS products are better than cast-in-situ concrete. All construction elements are fabricated at factory. IBS eliminate Solving skill shortage

extensive use of carpentry work, bricklaying, bar bending and manual job at site. Up to 40-50 % of the input in conventional construction, especially in skilled trades such as

Saving in manual labour onsite

formwork, masonry, plastering, carpentry, tiling, and pipelaying (electrical and water supply). IBS construction site look much tidy and organised compared to the wet and dirty conventional method

Clean site condition

sites. Unlike conventional sites, Wastage of temporary works such as timber formworks is not there in an IBS site.

Table 2.3: Benefits of IBS systems (Continue) Benefit factor

Description Rate of housing scheme dramatically enhanced by

Increase construction build rate

increasing the number of house completion over the period of time. This will help developers to meet 32

the demand in housing. Wastage is reduced greatly due to prefabrication of most of the building components. Waste reduction

Prefabrication in factory enables waste reduction through process orientation that entails controlled production and standardise process. There is direct cost saving in material, labour, and construction over-head. Construction of

Potential cost and financial

prefabricated elements results in

advantage

reduction in the use of scaffolding, shuttering and other temporary support compare to onsite construction. Fewer tradesmen visiting construction site in IBS projects has reduced local disturbance. This

Less disturbance to community

benefit is critical for hospital, school and hotel refurbishment projects, particularly in the city centre area. Due to factory-controlled prefabrication environment, many

Aesthetical Value of Products

combinations of colours and textures can be applied easily to the architectural or structural pieces. A

33

range of sizes and shapes of components are produced, providing flexibility fresher look. Operation is not affected by adverse weather condition since

Less adverse weather interruption

component is prefabricated in a factory controlled environment. IBS allows flexibility in architectural design in order to

Higher flexibility in design

minimise the monotony of repetitive facades. Using prestressed precasts such as the Hollow Core slabs and Double-

Greater Unobstructed Span

T beams offer greater unobstructed span than the conventional reinforced concrete elements. Faster delivery with decrease costs of labour will give hand to faster

Faster capital turn-over.

turnover of working capital and also save in the life-cycle costs of the finished buildings. Since prefabricated components require less repair and preventive

Lower maintenance expenses

maintenance so it helps to reduce the maintenance expenses IBS also promotes economic and

Minimise the environmental

environment sustainability as

impact of construction

component moulds could be used

34

repeatedly for different projects, allowing economic of scale and reduction in amortisation cost. All of the above simplify the Lower Total Construction Costs of

construction processes and increase productivity, quality and safety. As

Ownership

a result, the total costs of construction are reduced Contributes in reducing Time and

Increasing sustainability feature

Cost

Table 2.3: Benefits of IBS systems (Continue) Benefit factor

Description Tidier site with less deal of waste contributes to mitigate the site

Reduce safety and health risk

hazards and risk, hence ameliorating the health of site. Tidier site with less deal of waste contributes to mitigate the site

Reduce safety and health risk

hazards and risk, hence ameliorating the health of site.

2.5

Constraints and Barriers to of Using IBS in

Malaysia There are many constraints to the widespread adoption of industrialized procedures for housing. These have strong effects 35

upon the choice of materials. Several of studies by Albert G. H. Dietz,(1971), Ali Mohammed Alshawal (2006), Ng Soon Ching (2006), Foong Kok Li (2006), Albert G. H. Dietz,(1971), Ali Mohammed Alshawal (2006), Ng Soon Ching (2006), Foong Kok Li (2006) are associated with barriers of IBS in global and Malaysian scopes are carried out, where Table 2.4 them.

Table 2.4: Barriers of Implementing IBS in Malaysia Barrier factor

Description

Building codes

Codes are inherently sensible and too conservative and differ from each other, leading impossibility to produce in large volume, the standardized components necessary to the success of industrialization. Issues regarding the legislative

Labour

matters plus problems associated with hiring related skilled labour, There is neither clear procedure for

Certifying renovation

the introduction of innovative ideas nor central accepted and recognized certification board to examine new ideas and issue certificates. The successful ones are the well-

Management organization

managed ones

36

Table 2.4: Barriers of Implementing IBS in Malaysia (continue) Barrier factor

Description

The excessive tendency toward

The excessive tendency toward

repetitiveness

repetitiveness and standardization in public projects, where industrialization was most widely applied, resulted in monotonous complexes that very often turned into dilapidated slums within several years. Industrialized systems were

Rigidity against change

considered very rigid with respect to changes, which might be required in the building over its economic life. The technology, organization, and

Lack of educational courses

design of prefabrication building systems never became an integral part of the professional knowledge of engineers and architect, obtained as other subjects through a regular academic education. Makes it difficult to justify large

Wide swings in houses demand

capital investment high interest rate and cheap

Contractors prefer to use labour

labour cost

intensive conventional building system because it is far easier to lay off workers during slack

37

period. IBS process requires high precision

High construction precision

and needs meticulous monitoring, which is difficult to achieve. Majority of labours are foreigners

lack of skilled workers

and may not possess the required skill and have to be retrained. Fragmented nature of the

Consensus is required in the use of

industry

IBS during planning stage. However, the owners, contractors and engineers still lack of scientific information about the economic benefits of IBS.

Lack of research and

The R&D activities is neglected

development

and is receiving less attention in the area of novel building system that uses local materials.

Poor documentation of economic

The economic benefits of IBS are

benefits of IBS

not well documented in Malaysia. Past experiences indicated IBS is more expensive due to fierce competition from conventional building system. Government has not provided

Lack of incentives

intensive programme to encourage the stakeholders. New industrialized dwelling may

Public acceptance

fail if does not match the public 38

approval even if it is being the best or the lowest cost Malaysian industry, within a short

Volatility of the building market

period of time experienced a general decline in demand for large public housing projects. The successful ones are the well-

Management organization

managed ones

2.6 Sequence of Construction for IBS Method IBS method emphasizes on prefabrication concept. Firstly, the design stage is carried out where the IBS components are designed according to specifications. Then, the components are prefabricated

at

factory,

where

manufactured

according

to

specifications.

Quality-controlled

components specified and

of

IBS

dimensions

highly

aesthetic

are and end

products through the processes of controlled pre-fabrication and simplified installations has maintained and ensured the quality of work in the construction industry.

The IBS components are then transported to the site from the factory for assembling process. At site, the IBS components are assembled accordingly with the assistance of a crane. The reduction

of

standardized

construction components

waste

and

less

with in-site

the

usage

works

of

provides

the a

cleaner site due to lesser construction waste. Finally, the final unit of the building is finally assembled and ready for occupation. 39

As it can be understood from Figure. 2.1, the fifth step is assembly step. Most of significant drivers of work delays take place in this step and completion time of a project substantially relies on the performance of this step. The performance of work in this step is highly dependent on several factors in which any single factor might be capable of causing profound impacts on the quality of project, i.e. the delivery time and cost of work. Figure 2.2 depicts the steps of assembly process. As it can be realized form the pictures, crane is an integral part and vital factor in assembly process in which the total completion time of the project is undoubtedly dependent on the capability and performance of the crane in this step. In other words, crane is the critical factor in this step.

Figure 2.1: Sequence of activities in IBS construction method.

40

Figure 2.2: Sequence of assembly process.

2.7 Crane Factors Crane

machinery

is

of

significant

factors

in

housing

construction. The engineers should know how many cranes must be utilized in order to obtain optimum resources. Crane is also important in IBS construction besides all the activities in IBS construction are using crane. Housing construction differs than tall building construction where it use tower crane to install the components. So it is economic in term of cost of crane. Therefore, there is a dire need to focus on analysis of crane factor in the study.

In general, cranes are categorized into two categories: mobile crane and fixed crane, where each category also includes several types. Cranes generally involve two classes of factors or 41

considerations which affect the selection and performance of them:

1.

Hard

factors:

comprises

tangible,

quantitative,

formal

considerations. Typical factors of this class include technical specifications of the equipment, physical dimensions of the site and constructed facility, and cost calculations. 2. Soft factors: mostly intangible, qualitative, and informal in nature

such

regarding

as

safety

considerations,

company

market

fluctuations,

purchase/rental,

policies and

environmental constraints (Aviad Shapira, et al, 2007)

Both soft and hard factors are capable of substantially affect

decisions

made

early

in

the

selection

process

and

performance of the crane. In construction industry, decisions are made taking into account of some considerations in terms of method/algorithms, modus operandi, and operation time.

2.7.1 Hard Factors These factors are vital and deterministic for the decision making in regard of crane performance or any other equipment. These factors are well defined, optimally reflect all constraints, and

cater

to

all

needs,

and

are kind

deterministic in nature.

42

of quantitative

and

2.7.1.1 Operating Conditions 

Location and dimensions of available space



temperatures ranging



The atmospheric conditions



Electrical classification



Electrical power characteristics: Power for operating the equipment will be Supplied



Site ground conditions



Interaction with other equipment.

2.7.1.2 Crane Specifications 

Hook Capacity: tones, total lift,



Operating speed including bridge, trolley and hoist speeds,



control type,



Type of service required from the crane,



Heights of the crane including Operating floor to hook in high position. Operating floor to underside of building structural steel, Operating floor to high point of crane. Load charts:



Load charts: which provide the authoritative load capacity for all crane configurations at all ranges



Boom length range: The longer the boom, the better operators work in distance, in other words, Length of the boom provides a vast domain of operation for tower cranes.

43



Boom extension: For pick and carry operation, boom must be centred over front of machine, mechanical swing lock engaged and load restrained from swinging.



Counter-weight: In order to obtain a balanced condition for the crane, the counter-weight should be designed in an adequate

quantity

so

that

the

crane

will

stay

in

a

equilibrium condition during operation. 

Radius: Governing factor on the operation of a crane among several barriers, for instance, a tower crane located and surrounded by a plenty of under-construction buildings. This restriction will decrease the radius of the swing, consequently, lessened radius decreases the output of crane.



Working Range: Working range diagram shows the crane’s reach and load capacity will be significantly reduced at long radii



Outrigger: The soil must be capable of bearing the crane pressure, otherwise the outrigger loads must be distributed over an area large enough to avoid overloading the soil.

2.7.2 Soft Factors Some soft factors have a bearing on cost estimates or may even

be

qualitative,

converted subjective,

into

monetary

contextual

terms.

factors,

Soft

factors

are

which

reflect

the

complexity and uncertainty prevalent in construction decision making.

44

The following factors are sought and extracted through literature review (Aviad Shapira, et al, 2007): 1. Company policy toward own versus rent: “Own” policy may result in purchasing equipment that, with a view to future projects, exceeds the requirements of a particular project, whereas “rent” policy is likely to produce a solution for current project.

2.

Company

project

forecast:

This

factor

influences

current

purchase/rent decisions, and thus may affect the equipment selected for a particular project under discussion.

3. Commercial considerations: The desire to start operating part of the constructed facility earlier than the rest of it may affect equipment

selection

e.g.

refraining

from locating

tower

crane in underground parking or tower of climbing placing boom inside elevator shaft.

4.

Procurement client/owner

method

and

dictates

subcontracting:

certain

Quite

requirements

often that

the

affect

equipment selection.

5. Company project specializations: A company may specialize in certain classes of construction, e.g., high-rise buildings; precast structures. It also influences the type, experience, and

size

of

the

company’s

equipment

department, which, in turn, affects cost estimates. 45

maintenance

6. Administration of day rentals: Extensive use of equipment e.g., concrete pumps, truck loaders rented for short durations, reflected in frequent ad-hoc coordination and rescheduling, impairs on-site managerial convenience and flexibility.

7. Dependence on outsourcing: Outsourcing increases dependence on factors outside the site management control, chances of mishaps, and uncertainty in general. Avoiding it may lead, for example, to favouring on-site plant for precast elements over ordering them externally.

8. Shifting responsibility to external party: Favouring ready-mixed concrete over on-site concrete production or favouring the ordering of precast elements over on-site fabrication has an advantage in terms of quality assurance of the product as well as contractual liability to this quality.

9. Night shifts Work: affecting site management and safety concerns.

10. Progress plan and timetable: The number and location of cranes and other equipment must take into account the project progress schedule. For example, a crane located inside the building, or adjacent to one of the facades from the outside, is bound to hold up nearby works.

46

11. Tradition, previous experience: either on the market level availability of technical support, company level culture, or site management level personal preference.

12. Pieces of equipment to manage: Essentially a trade-off between operation flexibility and backup for contingencies versus wider control span and complex coordination. 13.

Labour

availability:

Manpower

shortage

increases

the

attractiveness of automated systems.

14. Noise levels: Give preferences to electric over diesel powered equipment. 15. Site accessibility: Narrow roads may limit the size of precast concrete elements or steel trusses transported to the site, which in turn may affect equipment size requirements.

16. Heavy traffic: For projects located in urban areas near busy roads, heavy reliability on continuous external supply may be abandoned in favour of on-site production.

17. Owner/client satisfaction: The owner/client may have certain preferences not necessarily corresponding to preferences of the construction company that the company may wish to consider.

18. Poor visibility due to weather conditions: Projects located in certain geographic areas may be given to long periods of limited on-site visibility due to fog, haziness, etc., which may affect equipment selection. 47

19. Strong winds: In areas given to strong winds, tower cranes may be preferred over mobile cranes. Also, the use of forming systems that climb automatically without crane assistance may be considered so as to avoid craning of large forms.

20.

Equipment aside,

age

newer

and

reliability:

equipment

is

Technological likely

to

advantages

encounter

less

operational problems and downtime, and thus offers better service overall.

21. Obstruction of crane operator view: Even with signal persons, this could become a major safety hazard lower productivity is another result, and hence should be taken into account when

equipment

selection

and

location

alternatives

are

considered. Operator vision aids.

22. Available space: Can crane fit on jobsite or not. 23. Site congestion: Tight sites give preference to fixed over mobile equipment and to the location of equipment inside rather than outside the building.

24. Obstacles on site: Commonly power lines and adjacent structures affect productivity and safety.

25. Overlapping of crane work envelopes: Overlapping tower cranes often are unavoidable, whether because of reach limits

or

daily

schedule 48

demands.

Careful

work

and

designation of forbidden zones help coping with safety hazards, but work may be slowed down.

26. The ability of the boom configuration to reach all required positions.

27. Availability of the boom to move over existing obstacles while performing required movements.

28. Safety: Crane accidents due to overturning. It requires initial planning

and

problems

to

engineering be

to

encountered

overcome during

the

the

potentially

completion

of

project. It requires following the safety instructions.

28. Type of job: -

What kind of job do we expect from the crane?

-

Is it required to use the crane in a big construction project

or a small one? -

Is it required to hoist material or goods?

-

Is it required the crane to load heavy loads or only normal

goods and material? -

Is it required to use for elevated heights or to use for long horizontal distance?

-

Is the speed of operation important and governing or not?

-

Job requirements

-

What is the size and shape of the work area we are looking

to 49

2.8 Modeling Techniques A model is an abstraction of reality and is simplified and idealized representation of reality. An equation, a diagram and a map are each an example of a model. A good model captures very

important

innumerable

details

minor

of

details

the that

reality would

without obscure

including

rather

than

illuminate. A model is a selective abstraction because only those details that are considered to be important for the problem are included in the model. To illustrate, designing a car is a good example. In car design process, shape, size, weight, engine power, torque and such stuff are come to mind, but other factors such as colour, radio type, and interior design are not considered. So in modelling, it is important to consider which important factors to be considered. (Richard Tewksbury, 2009).

2.9

Mathematical Models Mathematical models lend themselves to the computational

power inherent in calculators and computers. They provide an idealized abstraction of situations, activities, processes, etc, for quantitative methods.

Mathematical

models

are

made

up

of

constants

and

variables. Constants are fixed or known quantities not subject to variation, where VARIABLEs can take on different values and can

be

generally

either

probabilistic

represented

by

or

numbers 50

deterministic. and

Constants

variables

by

are

letters.

(Richard Tewksbury, 2009) & ( William J.Stevenson & Ceyhun Ozgur, 2005).

The use of computers has extended modelling by allowing combinations of data, interaction, repetition, sound, graphics, and other displays as outputs for various types of mathematical modelling.

2.9.1 Representation of The Models Models which are representations of the real world objects can be represented in three common types:

1. Iconic models are scaled down versions of the real thing. 2. Analog models: use other media such as electric current to represent the modelled phenomena. 3. Symbolic: mathematical models which depend on notation.

Therefore, the representation of the mathematical models can be classified as: 1.

Analytical models - based on symbol manipulation, e.g.

algebra. The result is a mathematical function (formula). 2.

Numerical models - manipulate numerical quantities. The

results are numbers.

51

2.9.2 Types of mathematical Models A mathematical model can usually be any of these types: • Cross Section which is used to describe a phenomenon at a particular point in time. E.g. A balance Sheet describes the state of an enterprise at some date. • Time Series which describe one or more characteristics over a series of time intervals. Time series models are sometimes fitted to historic data and extrapolated to estimate future values. Such models attempt to predict the future from past trends. • Combined or comprehensive which are intended to describe a number of phenomena over several periods of time. They are a 'time series of cross sections'. The foster model is an example of a comprehensive type model that is used to predict the status over several periods of time.

2.10 Similar Studies Lim,

Chae-Yeon

et

al.

(2011),

propose

an

Automatic

Arrangement Algorithm for Tower Cranes Used in High-rise Apartment Buildings. Their model contributed in finding an optimum solution among several alternatives for installation areas of tower cranes, satisfying the conditions of lifting work finding the feasible area for crane location. The shortcoming of their model was the disability to involve intangible factors. Also their model cannot

deal with

different

locations for crane. 52

crane types

and

different

C. Huang et al. (2010) conducted a research regarding Optimization of tower crane and material supply locations in a high-rise building site by mixed-integer linear programming. In their research, they proposed a mathematical model for crane travel time, and they found out the optimum crane location and supply points, using linear programming model. In their model, they initially select 8 points for demand points as well as crane positions and crane locations. The shortcoming of their model is that the points are determined by the users and it is not comprehensive. So the final answer may not be the best solution. Likewise, their model cannot take into account of different crane types and different specifications.

Sawhney and Mund (2001 and 2002) proposed two models for crane type and crane model selection. Their method is to initially by defining

Eight crane types in first phase; and crane

models from updateable database in second phase. Selection of crane type is done by means of ANNs-based matching process and Selection of crane models by screening of crane database to meet limited number of physical criteria. The shortcomings of their models are that the tower crane selection is done without reference to crane location and merely few intangible factors considered. Moreover, “Binary” approach “yes/no” problematic is applied which the accuracy is very low. Their model cannot provide explanation as to how the solution was derived.

53

Tam et.al. (2001) proposed a model for Single tower crane and supply locations optimization based on Gas. In their model, Crane locations and supply positions, were determined by user by means of 3D coordination. Their method is to find out a Random generation of initial feasible locations of crane and supply locations and then repetitious improvement of solutions by means of GAs operators until no further improvement is achieved. This method was very difficult to use and no intangible factors were involved. Moreover, Restricted to location of crane and dealing with one crane type only as well as assuming that the shortest angular movement is performed are other shortcomings of their proposed model. Harris and McCaffer, (2001), based on Multi attribute-decision-making-based

models,

proposed

a

Systematic

plant selection which was capable of involving all User-generated alternatives of the entire plant types, models, locations. Their method of solution was to generate feasible alternatives by user, and identify the best location by a ranking system of 0–10. Computation of an overall rate for each alternative, used to compare them all. In their model, although many intangible factors were involved, ranking of disparate factors in a single context and by the same scale may yield non-optimal selection. Moreover,

Results

are

sensitive

to

formulation

of

selection

factors.

Zhang et al. (1999) proposed a model for determining the location optimization for a group of tower cranes. In their model, the crane locations were to be within permitted area determined by user by means of coordinate. In their research, their method was to generation of initial feasible location area, and then 54

reallocation of tasks to optimize workloads and finally, the Final optimization of location for each crane. The shortcoming of their model was that No intangible factors were considered. And also the location of the cranes were restricted. This model also was capable of dealing with one crane type only.

Choi and Harris (1991) proposed a model for single crane location optimization. In their model, the crane locations were determined by user by means of coordinates.

Their applied

method was computation of hook travel time for each location and selection of location with minimum hook travel time. The shortcoming of their system was that no intangible factors were considered in the modelling and also the modelling was restricted to only the location of crane and could only deal with only one crane type, therefore, the crane specifications could not be changed. In this model it was also assumed that the shortest angular

movement

would

be

performed.

Moreover,

in

their

model, the height dimension of the supply and demand points were ignored and only 2D modelling was done. Likewise, only it was assumed that radial, vertical and tangent movement used to take place simultaneously.

Also,

C.

Huang

et

al.

(2009)

conducted

a

research

regarding optimization of material hoisting operations and supply points

in

multi-storey

building

construction

by

mixed-integer

programming.in their research , they proposed a mathematical model in which as capable of predicting the travel time of a tower crane in high-rise buildings.

55

Shu-Shun

Liu

et

al.

(2012)

proposed

a

mathematical

modelling for optimization of crew in a linear schedule project. Their proposed model was useful to improve the efficiency of ork and reducing completion time.

Xianwen Wu et al. (2011) in their research, improved the hoisting mechanism of crane by optimizing the main technical parameters of crane were.

K. Eshwar et al. (2003) proposed a model for optimal deployment of construction equipment using linear programming with fuzzy coefficients. In their research, they proposed a method to identify the optimum number of pieces of equipment required to complete the project in the targeted period with fuzzy data.

2.11 Summary of Chapter Through literature review a lot of information is obtained for this study, especially on the IBS construction in recent construction industry. There are advantages and disadvantages, opportunities

and

barriers

in

implementing

Compare to the conventional,

IBS

technology.

IBS offer better construction

process especially on the productivity, time, cost, quality, and other

extra

benefit

constructability and so

on

the

safety,

simplicity,

clean

site,

on. Malaysian Government is currently

very active in promoting the usage of prefabricated materials, particularly

IBS

components.

The

advantage

of

employing

decision making approach for problem solving is studied and it is 56

concluded that this approach will help the industry to optimize its process via any attributed methods. Moreover, the significance of quantitative and deterministic methods is also addressed in this review. A critical review on the background of modelling in construction indicates that the literature profoundly suffers from a lack of study on performance of cranes, in particular in IBS projects. Optimization of crane location as well as critical factors in crane performance is of most important topics missing in literature. Critical factors attributed to travel time of crane are not illustrated and although much research is done regarding finding the optimum crane location, there is not any specific study to find out the best spectrum locations for crane.

57

CHAPTER 3

RESEARCH METHODOLOGY

3.1 Introduction The research methodology in this chapter serves as a tools to achieve the objectives and scopes of the study. This chapter includes procedures, data collection and alanysis methodology as shown in Figure 3.1.

58

Identification of topic and define current problem

developt the mathematical model, analyse and interprete the behaviour of the model.

Set the objectives, scope and structure of study

Conduct site survey to investigate the major criteria of crane, interrelate the factors, set the objective function

Secondary literature review to:

Preliminery Literature review on the current status of the topic

Identify factors affecting in performance of cranes in assembly of IBS projects

verify the model by a proposed IBS building and find the minimum time attributed to optimum crane and supply locations.

Conduct and interpret sensitivity analyses and "what if" questions. Critical discuss on the findings

Make conclusions and recommendations regarding the topic

Figure 3.1: Flowchart of study

3.2 Data Collection Stage three of methodology is data collection. The data collection initially puts emphasis on the assembly sequence of IBS components in the project by a crane; and subsequently the associated factors in performing the job by the crane, since crane is the most critical equipment in site with regard to assembly process. Then, data gathering concentrates to identify variables and constraints of the assembly process. Data collection involves the details of the process cycle of assembly at site; starting from lifting and hoisting of components by crane.

59

In order to collect necessary data for the study, some approaches are chosen to achieve a highly reliable data, such as: 1.

Conducting a comprehensive literature review in favour of

the topic. Literature review is a secondary data collection to describe, summarise,

evaluate,

clarify

information.

Reading

materials

or to

integrate

the

content

find

the

factors

out

of and

variables contributing in the assembly process of IBS project are published journal, articles, text book and other relevant reading material.

2.

Conducting site Survey and Site Studies.

A site study is an inspection on area where work is proposed, to gather necessary information for a particular purpose. In this study, similar projects which are in progress will be visited and observed to find out the necessary information for the study. In this stage, activities are concentrated and the required data of travel time is obtained by direct observation. This study afterward models travel time of crane in the assembly process of IBS building by employing the data collected in this step.

3.3 Steps to Build a Mathematical Model Figure

3.2

demonstrates

the

quantitative model.

60

sequence

of

creating

a

Figure 3.2: Steps of creating a quantitative model.

3.3.1 Problem Definition The first

step

in

problem solving

is

careful

problem

definition. It is important to resist the temptation to rush through this stage in order to begin working on the model and the solution.

Therefore,

the

first

step

comprehensive literature review lends

of

data

itself to

gathering

i.e.,

elaborate the

problem. This step was carried out in the first chapter of this study.

Good

problem

definition

may

also

involve

observing

current situation or process in order to better understand it. Most often, it is highly desirable to talk with the people who are closely involved (e.g., workers, supervisors, managers). Not only do such people usually possess considerable knowledge and insight that 61

enable them to suggest potential solutions, they are the ones who live with solutions. Therefore, during the site survey, some interviews are conducted with the operators of the cranes. Once the problem has been reasonably defined, it is time to construct a model.

3.3.2 Model Construction Modelling should be an accurate, yet relatively simple, representation of reality. Hence, the model should reflect the major aspects of the problem as simply as possible. In other words, the more complex the model, the more costly and timeconsuming it is to build and the more difficult to understand. Conversely, if a model is too simple, perhaps it cannot provide an adequate portrayal of reality, thereby decreasing the chances of finding a reasonable solution to the problem. Therefore, in this step, the model must cover the most important factors of crane performance in order to avoid any future complexity causing misunderstanding.

3.3.3 Model Analysis The nature of analysis depends on the type of the model that is used. In this study since it is aimed to portray the situation with a high degree of certainty, hence the algorithms can help to identify optimal solutions.

62

Since time is the measure of effectiveness in the model of this study, the solution chosen will be the one that is projected to yield the best completion time. This measure of effectiveness will come from the objective of the research.

An important part of model analysis is to determine how sensitive a particular solution is to the changes in one or more of the constants in the model. This is referred to as sensitivity analysis. Sensitivity analysis can be used to learn if changes in the values of certain constants used in the model will have any effect on the solution and if so, what that effect would be. The reason of using sensitivity analysis is to answer “what if…” type questions. For example, would it be still efficient if a change the supply point?

3.3.4 Implementation and Follow Up Once the appropriate solution has been identified, it must be implemented through a numerical example for verification purpose. Other purposes of this step are to evaluate the reliability as well as ensuring correctness of applying the proposed model. Once this step is conducted, the results will be critically analysed and discussed to address new findings.

The

mathematical

modelling

in

this

study

will

be

conducted by Excel software. The reason of using this software is

63

its

embedded

mathematical

object

facility

for

the

modeling

process.

3.4 Summary of Chapter The structure of the methodology is designed parallel to the main goal of this study. In general, the study was the pilot study on IBS approach in construction industry. Different aspects and features of IBS assembly process were elaborated. Literature review in this step assisted in forming the foundation of the study by seeking similar previous studies and models. After conducting site

survey,

the

critical

factors

in

assembly

process

are

highlighted and therefore the frame of modelling is narrowed. Using the gathered data, equations associated with the crane performance are formulated. Subsequently, the graphical scheme of the model is proposed as well and finally a model for the travel time of crane in assembly process of IBS house has been proposed.

64

CHAPTER 4

DATA COLLECTION & MODELLING

4.1 Introduction Data collection of this study involves a great deal of data gathered

from

comprehensive

literature

review

on

similar

previous research and site survey. Initially, the previous research in

this

field

is

reviewed

to

cater

appropriate

background

knowledge about the project and also as a basis for subsequent data gathering required.

All factors contributing in the performance of the crane was

determined

through

literature

review

in

advance.

Site

observation is carried out on an IBS project using precast components.

Throughout

the

site

survey,

the

major

criteria

associated with the crane performance are highlighted within the site survey and the relation between those criteria are determined 65

prepare

the

mathematical

mathematical analyses

model

and

is

model.

Afterward,

portrayed

interpretation

the

subsequently.

techniques

are

graphical Then,

identified

the

to

be

conducted in next chapter. By the time these steps are done, using the gathered data, we shall develop the mathematical graphical model of the assembly process.

4.2 Problem Definition of the Model Site survey and observation was carried out in an IBS project using precast components which is located in Johor state, Malaysia. This project is a 4-storey project whereby the first and second levels are parking levels and the third and fourth levels include the shopping lots and offices.

This

project

is

using

all

precast

components

in

the

construction process, including beams, columns, slabs and walls. Moreover, the installation process is being done using 4 mobile cranes simultaneously.

Hard

and

Soft

factors

associated

with

the

crane

performance were addressed through literature review. In this step of study, it was initially strived to find out the most important factors construction

site,

among all afterward

those aforementioned site

conducted.

66

survey

factors

observations

in

were

After observations, it was found that the travelling time of the components by the crane is substantially dependent on some major factors, Some of these factors characteristics

of

the

components

are attributed

and

some

to

other

the

factors

considerably are associated to the crane specifications as shown in Table 4.1. Afterward, the schematic movement of the crane hook in the process of hoisting the components is drawn in Figure 4.1. Likewise, vertical movement of crane is shown in Figure 4.2.

Table 4.1: Major criteria in crane performance for an IBS project Crane

Site

specifications Characteristics

Human factors Skill of the

Available

operator to

Crane working

positions for

simultaneous

Radius

crane & Supply

radial &

points

tangential movement

Ability of

Distance

crane to carry

between

material in

Demand point,

different radii

Supply point

(Load chart of

and Crane

crane),

location

Hook hoisting

Elevation of the

velocity,

Demand point,

67

Labour skill in handling components

Attach & Detach time of Components

Horizontal and Hook radial

vertical

Labour Skill in

velocity,

Coordination of

installation

hook movement Difficulty of hoisting due to inappropriate

Efficiency

controlling systems.

Crane

Shape Colour

Refered to Velocity Distance Demand Point Supply Point Hook Length Hook Extension Tangent Velocity Radial Velocity Hook coordination Velocity

Figure 4.1: Graphical Demonstration of Crane Movement.

68

Figure 4.2: Vertical Movement of the Crane's Hook.

4.3 Model Construction In this study, the impacts of the site characteristics are excluded from the modelling for sake of simplicity in the model. As an outcome of the observations, by linking the major criteria in Table 4.1, and the schematic movement of the crane, excluding the site characteristics, the mathematical model for cycle time of the crane is developed.

Travel distance between the supply and demand points could be calculated by the following equations: 𝛥 √(

= −

2

) +

−

2

4.1

69

𝛥( √(

𝛥( √(

)= 2

−

) +

2

−

4.2

)= 2

−

) +

−

2

4.3

Using equations, the radial and tangent movements are calculated as below:

Radial movement: 𝑇 =

− 𝛥(

|𝛥

Where,

)|

4.4

is radial velocity which is a specification of the

crane. Tangent movement time can be calculated from Eq. 4.5 which is available in literature (C. Huang et.al. 2010):

𝑇

=

𝐴 𝑐𝑐𝑜𝑠 𝑉𝑤

Arccos φ ≤ π

2

2

2

((𝛥 𝑆𝑗 𝐷𝑖 ) −(𝛥 𝐷𝑖 𝐶 𝑘 ) −(𝛥 𝑆𝑗 𝐶 𝑘 ) )

(

2.𝛥 𝐷𝑖 𝐶 𝑘 .𝛥 𝑆𝑗 𝐶 𝑘

)

0 ≤

4.5

Likewise, horizontal movement time is calculated by (C. Huang et al, 2010):

𝑇ℎ

= 𝑀𝑎𝑥(𝑇

𝛼. 𝑀𝑖𝑛(𝑇

𝑇

𝑇

)+ 4.6

)

70

Where,

𝛼 is skill of the operator to simultaneous radial & tangential

movement and it may vary in a range of 0 to 1, depending on the operator skill.

𝑇𝑣 =

|

−

|

4.7

𝑇ℎ

Where, 𝑇 location

is the total travel time of tower crane at

between supply point

and demand point

. It can

be calculated by specifying the continuous type parameter 𝛿 for the degree of coordination of hook movement in vertical and horizontal planes. 𝛿

could vary depending on different site

conditions and might be influenced by several factors such as the visibility level due to environmental and weathering effects, obstruction of the operator’s vision because of materials or other barriers.

Moreover, varying from any atmosphere and individual to another, the efficiency of work could differ, therefore, for the efficiency, 𝛾

is also

employed.

Employing all aforementioned coefficients, we will come up with the total travel time of crane as below:

𝑇

= {𝑀𝑎𝑥 (𝑇

𝑇

+ 𝛿. 𝑀𝑖𝑛(𝑇

) 𝑇

)}

71

4.8

𝐻𝑜𝑖𝑠𝑡𝑖𝑛𝑔 𝑡𝑖𝑚𝑒 𝑓 𝑜𝑚 = {∑ 𝑇

𝑓𝑜 𝑎𝑙𝑙 } + 𝑇𝑓

𝑇𝑜𝑡𝑎𝑙 𝑇 𝑎𝑣𝑒𝑙 𝑡𝑖𝑚𝑒 𝑓 𝑜𝑚 = 𝛾 [{∑ 𝑇

4.9

𝑓𝑜 𝑎𝑙𝑙 } + 𝑁𝑇𝑓 ]

4.10

ATT = ∑𝐾 1𝑇 (4.11)

4.4. Optimization Procedure The main contribution of the present study is the flowchart which is presented in this section. Figure 4.3 illustrates the flowchart of optimization process using the proposed model. As shown in Figure 4.3, application of the analytical model in the modeling procedure is divided into input of six steps. In the first step, the crane specifications such as hoisting velocity of hook, slewing velocity of jib, radial velocity, tangent velocity and CWR are defined in the model. In the gridding step, the site layout is divided into to m horizontal and n vertical grids. Third step is to locate demand points on the grids regarding to coordinates in site layout, and to set the initial location of crane and supply point in (0,0) coordination. A schematic representation of the second and third steps can be seen in Figure 4.4. The fifth step deals with the crane loop, the step to which finds out the minimum hook ATT by Equations (4.1) to (4.11). The assigned coordination of the supply and crane points start with the coordinate (0,0), and by examining crane location in all grid coordination of (i,j) and keeping fix supply point as initialized before in (I,J), ATT for crane in all (i,j) coordination can be calculated. Locating the supply and crane points continuously goes on in order to cover all the 72

possible coordinates. The sixth step is to calculate the minimum of all minimum ATTs that calculated in step 5 and constitute them in (I,J) coordination to identify the optimum position of supply point and crane location as well. In this step by examining storage area in all grid coordination of (I,J), the minimum ATT heatmap of site layout can be drawn as a schematic shown in Figure 4.5.

73

Step 1 Step 2 Step 3

Step 4

Step 5

Step 6

Figure 4.3. Optimization modeling flowchart

74

n

Demand point

. .

Supply point

. .

Crane Position

. . . . . 4 3 2 1 0 0

1

2

3

4

5

.

.

.

.

.

.

.

.

m

Figure 4.4. Demands point positioning and initial positioning of crane and supply point on grids

n

n

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

4

4

3

3

2

2

1

1

0

0 0

1

2

3

4

5

.

.

.

.

.

.

.

.

m

0

3

4

5

.

.

.

.

.

High

Medium

Minimum

2

Storage Area

Low

Demand point

1

Crane Position

Figure 4.5. A schematic Heatmap diagram of supply points (left) and crane location (right)

75

.

.

.

m

4.5. Feasible working area Prior to

optimization, it

is necessary to

fine feasible

working area. In order to find out the feasible working area for the crane as well as the feasible Supply point, the site survey was conducted with focusing on the way the technicians locate the crane and subsequently the Supply points.

During the site survey, it was observed that for erecting the components in a Precast project, they usually use Mobile Cranes rather

than

tower

cranes,

since

Mobile

cranes

have

more

flexibility than tower cranes and moreover, tower cranes are mostly used for high-rise buildings with one or only a few buildings to be covered. In contrast, Mobile cranes are used for those kinds of buildings that are usually one or multi-storey buildings

and

simultaneously

several

same

buildings

are

proposed to be built in a certain adjacent area.

Throughout the site visit, it was observed that, most often, the crane positioning is done based on the experience of the operators. In the site visit, it is found out that for these types of buildings; usually the operators tend to divide the building area into several workface so that they proceed each workforce block one by one. The division technique is mostly experimental and based on the expertise of the operators with taking into account of the most important factor: Crane Work Radius (CWR) and coverage range.

76

A

schematic

method

of

determining

the

feasible

is

proposed considering the CWR. In this model, the proposed building or site layout is divided into several blocks (workface) as it is depicted in Figure 4.6. This Figure shows the minimum working radius required in order to cover the Demand point. Using the minimum CWR required in Figure 4.6, the feasible supply area is found as shown in Figure 4.6 which is determined for taking into account of site space limits. As indicated in Figure 4.7, the area which are totally covered by all for Radii, are the feasible areas in order to locate the supply point to cover the Block.

After finding out the feasible supply points, the next step is to transfer objective function and data of the demand points to the software; (Eq. 4.1 to Eq. 4.11) in objective I. Figure 4.8 shows the appearance of the model after inputting the data to the software. The expected result is as shown in Figure 4.9.

Working Radius

1

2 3

L1 4 6 L2

5 7 8

L 9 11

10 12 13

L3 14

15

W

Figure 4.6: Minimum working radius required.

77

Feasible Supply Area

Figure 4.7: Feasible supply area for a block. Demand Points x y

1 6 1 -1

2 5 1 -1

3 4 1 -1

4 3 1 -1

5 2 1 -1

6 1 1 -1

7 6 -1 1

8 5 -1 1

9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 4 3 2 1 0 0 0 0 0 0 0 0 0 0 0 0 -1 -1 -1 -1 -6 -5 -4 -3 -2 -1 6 5 4 3 2 1 1 1 1 1 6 5 4 3 2 1 -6 -5 -4 -3 -2 -1

### ### ###

-4

Storage

Crane -20 -19 -18 -17 -16 -15 -14 -13 -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1

X

Y

-4

0 20

+ -

Demand Position Supply location crane location

16.0

20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 -11 -12 -13 -14 -15 -16 -17 -18 -19 -20

0

1

2

3

4

5

6

7

8

9 10 11 12 13 14 15 16 17 18 19 20

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201.25

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V

10

w

4

CWR

51

a

0.2

Fix

8

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1

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3

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4

### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ###

5

### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ###

6

### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ###

7

### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ###

8

### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ###

9

Good Bad

Figure 4.8: The Appearance of the developed model in Excel Software.

78

27 26 25 24 23

28 25 25 16 12 10 10 3 4

-3

-2

Schematic show of the building on the grid sheet

30 28 28 25 16 12 10 10 5 3 1 4 5

3 2 1 -1 0 -2 -3 -4

1

30 28 28 25 16 12 10 10 5 3 1 4 5 4 5

2

29 28 28 25 16 11 10 10 6 3 1 3 5 4 4 5 9

3

28 28 25 16 12 10 10 6 2 1 2 5 4 6 6 9 12 30

4

28 25 16 12 10 10 6 2 1 2 5 4 5 9 9 12 19 25

5

25 16 12 10 10 6 2 1 5 4 6 6 9 12 16 20 25

6

16 10 10 10 10 10 10 6 10 6 4 6 3 4 3 1 2 1 3 3 4 6 6 9 9 12 15 25 25

7

8

9

6 6 4 5 4

7 6 6 5

7 8 8

1 3 6 9 12 15 18 21 24 27 30

Most Desirable

Least Desirable

Supply point Demand Point Crane Location 10 11 12 13 14 15 16 17 18 19 20 21 22

Figure 4.9: Schematic Show of the Building on the Grid Sheet

4.6 Model analysis Model analysis involves three steps: 

Determine a solution



Test the solution, and



Interpret and analyse the results.

This analysis is conducted in Chapter 5 of the thesis.

4.6.1 Determine and Test a Solution In order to analyse the model, a plan is determined to be tested as shown in Figure 4.10. After importing of the model in the Excel Software, then we shall calculate the travel time for every

grid-point

(Orange

colour 79

in

Figure

4.10).

The

implemented image of the model data is as Figure 4.11. The criteria in which are the assumptions of the model are: Radial and Tangent Velocities, Crane Working Radius (CWR), Efficiency of Work, Operator Skill, Fix Time attributed to handling of material by labour. The outcome of this stage will be the graphical indication of the OCL’s coordinations subjected to different Supply point coordination.

27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 -3 -2 -1 0 1 -2 -3 -4

Schematic show of the building on the grid sheet

31 27 23 20 16 12 9 5

2

3

4

5

6

7

1 8 9

32 33 30 28 29 26 24 25 21 22 19 17 18 15 13 14 10 11 8 6 7 Supply point 4 Demand Point 2 3 Crane Location 10 11 12 13 14 15 16 17 18 19 20 21 22

Figure 4.10: Schematic plan proposed for testing purpose.

Coordination of the

Demand Point

Supply Point Coordinatio

Figure 4.11: Data input to the developed model in software. 80

4.6.2 Interpret and Analysis In this step, by changing the variables and constraints, effect of different alternatives within different variables and assumptions of the model

is analysed and interpreted. The

behaviour of the model is analysed in this step. In the model analysis, there are three important indices: 𝑅𝑎𝑑𝑖𝑎𝑙 𝐼𝑛𝑑𝑒𝑥 =

𝑅𝑎𝑑𝑖𝑎𝑙 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 𝑇𝑎𝑛𝑔𝑒𝑛𝑡 𝑒𝑙𝑜𝑐𝑖𝑡𝑦

4.12

𝑇𝑎𝑛𝑔𝑒𝑛𝑡 𝐼𝑛𝑑𝑒𝑥 =

𝑇𝑎𝑛𝑔𝑒𝑛𝑡 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 𝑅𝑎𝑑𝑖𝑎𝑙 𝑒𝑙𝑜𝑐𝑖𝑡𝑦 𝑎𝑛𝑒 𝑊𝑜 𝑘𝑖𝑛𝑔 𝑅𝑎𝑑𝑖𝑢𝑠 = {𝑀𝑎𝑥 𝛥(

4.13 𝑊𝑅 ) 𝐴𝑛𝑑 𝛥(

) }

4.14

The other important factors in this modelling are the operator skill and the Fix time which are totally related to the skill of the operator and the labours of the project.

This analysis interprets that what is the behaviour of the model if the project is using different specifications, i.e., what will be the new OCL and the minimum completion time. However, various interprets can be carried out from the graphs and the detail analyses of the model is conducted in Chapter 5.

81

4.7 Implementation Whenever numerical modelling is employed in connection with engineering decision-making, it is expected to prove the reliability. Nobody can base decisions on computed information without proving that information is reliable enough to support those decisions. Therefore, the implementation must be done by using real data of a similar building and modelling that building in this proposed model. This step will be conducted in Chapter 6 of this study.

Likewise, Sensitivity analyses are conducted in order to describe how much model output values are affected by changes in model input values. It is the investigation of the importance of imprecision or uncertainty in model inputs in a modeling process. The exact character of a sensitivity analysis depends upon the particular

context

and

the

questions

of

concern.

Sensitivity

studies can provide a general assessment of model precision when used to assess system performance for alternative scenarios, as

well

as

detailed

information

addressing

the

relative

significance of errors in various parameters. Thus, sensitivity analysis can address the change in ‘optimal’ system performance associated with changes in various parameter values, and also how ‘optimal’ decisions would change with changes in resource constraint levels or tar-get output requirements.

Sensitivity coefficient is the derivative of a model output variable with respect to an input variable or parameter. Implicit in 82

any

sensitivity

analysis

are

the

assumptions

that

statistical

distributions for the input values are correct and that the model is a sufficiently realistic description of the processes taking place in the system.

The

importance

of

the

assumption

that

the

statistical

distributions for the input values are correct is easy to check by using different distributions for the input parameters. If the outputs vary significantly, then the output is sensitive to the specification of the input distributions, and hence they should be defined with care.

A relatively simple sensitivity coefficient can be used to measure the magnitude of change in an output variable Q per unit change in the magnitude of an input parameter value P from its base value P0. Let SIPQ be the sensitivity index for an output variable Q with respect to a change ∆P in the value of the input variable P from its base value P0. Noting that the value of the output Q(P) is a function of P, the sensitivity index could be defined as: SIPQ = [Q(P0+∆P) – Q(P0 - ∆P)]/ 2∆P (4.15) A dimensionless expression of sensitivity is the elasticity index, EIPQ, which measures the relative change in output Q for a relative change in input P, and could be defined as: EIPQ = [P0 / Q(P0) ] SIPQ (4.16)

83

4.8 Summary of Chapter This chapter presents a complete data collection which is required

to

develop

the

model.

A

pilot

study

on

crane

performance factors is carried out. For modelling purpose, a big deal of necessary data is gathered through previous related research

and

preliminaries

data

regarding

factors

affecting

performance of the cranes in construction, then major crane factors in IBS projects have been determined through site survey. Site survey is conducted on an IBS project. Then, the major factors are interrelated and the mathematical model of the crane cycle

time

is

accomplished.

Then,

the

graphical

model

is

supplemented to the mathematical model and finally the model is developed

and

hence

the

first

objective

of

the

study

is

accomplished. After completion of the mathematical model, the analysis and interpretation techniques for the model behaviour are determined elaborately.

84

CHAPTER 5

MODEL ANALYSIS AND FINDINGS

5.1 Introduction In this chapter, it is strived to find out how the model works, its behaviour in various Demand layouts, and also to interpret the results of the model. Hence, various site layouts are taken into account for the purpose of finding the Optimum Crane Locations (OCL), and Optimum Supply Point (OSL) as well as the minimum completion time. Three different site layouts are rectangular, circular

and

cross

which are shown in Figure 5.1.

sectional

Demand

layouts,

in

In all following analyses, there

are 5 important criteria