1 -Thesis Final Sep4

A DISSERTATION

ON

SCHEDULING OF MULTI SPAN BRIDGES: AN APPLICATION OF REPETITIVE SCHEDULING

METHOD

Submitted to Rajiv Gandhi Prodhyogiki Vishwavidhyalaya, Bhopal (MP)

For Partial fulfilment of requirements of Master of Engineering (Civil)

with specialization in Construction Technology and Management

2009

Submitted byKAVI PRAKASH

Department of Civil Engineering MADHAV INSTITUTE OF TECHNOLOGY AND SCIENCE (An autonomous Institute under R.G.P.V., Bhopal)

Gwalior (MP)

MADHAV INSTITUTE OF TECHNOLOGY AND SCIENCE (An autonomous Institute under R.G.P.V., Bhopal)

Gwalior (MP)

2009

RecommendationThis dissertation work entitled “SCHEDULING OF

MULTISPAN BRIDGES: AN APPLICATION OF

REPETITIVE SCHEDULING METHOD” submitted by

KAVI PRAKASH for partial fulfilment of the requirement of

Master of Engineering Civil with Specialization in Construction

Technology and Management is satisfactory account of his

dissertation work and recommended for the award of degree

Dr. S.K. JainProfessor and Head Department of Civil EngineeringM.I.T.S., Gwalior-5

Dr. M.M. PandeProfessor Department of Civil Engineering and Dean (Academic)M.I.T.S., Gwalior-5

Prof. Y P SinghDirectorM.I.T.S., Gwalior-5

CANDIDATES DECLARATION

I hereby declare that the work, presented in the dissertation

entitled “ Scheduling of Multispan Bridges : An Application of

Repetitive Scheduling Method” in partial fulfilment of the requirement

Master of Engineering Civil with specialization in Construction

Technology and Mangment is an authentic record of my own work carried

out under the guidance of Dr. M. M. Pande , Professor of Civil

Engineering and Dr. S .K. Jain , Professor and Head , Department of Civil

Engineering, Madhav Institute of Technology and Science, Gwalior.

The matter embodied in this dissertation has not been submitted by me for

award of any other degree or diploma

KAVI PRAKASH

This is to certify that the above statement of the candidate is true to best

of our knowledge

Dr. S K JainProfessor and Head Department of Civil EngineeringM.I.T.S. Gwalior-5

Dr. M M PandeProfessor Department of Civil Engineering and Dean (Academic)M.I.T.S. Gwalior-5

ABSTRACT

The scheduling problem posed by multi span bridge has the characteristics of

problem posed by linear repetitive construction however the repetitive units in

this case of bridge may vary greatly in work from one unit to the other. The

network methods are not effective to address such problems. When two

activities are independent of each other, network techniques are incapable of

scheduling the activities logically. Additional artificial constraints are required

to schedule the activities which have constant production rate. These methods

are not efficient in addressing problems of continuous utilization of resources.

Line of Balance (LOB) is well suited for repetitive activities where different

crews performs the activities one after the other; however this is not effective

in scheduling multi span bridges where large numbers of activity are

dependent on each other. Further, LOB is primarily a technique with emphasis

on continuous utilization of resources and therefore is not ideally suited for

scheduling bridges where activities and quantum of work varies from one unit

to another.

Linear scheduling Method developed primarily for scheduling linear activities,

like pipelines, highways etc. This method uses different type of activities viz

bar, line and block activities which are scheduled using a graph with time and

distance as axes. An algorithm developed for linear scheduling method for

repetitive projects known as Repetitive Scheduling Method makes use of

precedence diagram for repetitive unit attempting to provide advantages of

both Line of Balance and CPM techniques. The method takes care of both

resource continuity constraint as well technical constraints. This study deals

with application of Repetitive Scheduling Method for scheduling of multispan

bridges. The effectiveness of this method for scheduling of multispan bridge is

analysed by comparing it with other scheduling method like precedence

diagramming and Line of Balance Technique. Results obtained from the

different methods show that use of repetitive scheduling method provides

more effective scheduling addressing both, continuous utilization of resources

and minimum schedule duration.

Acknowledgement

I feel great pleasure in expressing my heartfelt indebtedness and gratefulness to

Dr. M.M. Pande, Professor, Department of Civil Engineering and Dean (Academic),

MITS, Gwalior who has guided and encouraged me at all stages of this work. The

confidence which he instilled and precious advise he gave can not be acknowledged

through words. The efforts and cooperation provided by him and enriching

suggestions given are gratefully acknowledged.

I am very thankful and indebted to Dr. S.K. Jain, Professor and Head, Department of

Civil Engineering, MITS, Gwalior for all the careful efforts, kind cooperation and

benevolent behaviour. The confidence which he posed in me and highly valued

inputs which he provided has lead to current shape of this dissertation. It is a

pleasure acknowledging his invaluable help and support.

I sincerely thank all the faculty members of Department of Civil Engineering who

willingly provided assistance and learning when ever it was needed. I will ever to

indebted to them for all their advice. I also express thankfulness to all the staff

member of Department of Civil Engineering, MITS, Gwalior, for all their help.

Any work requires time. I thank my wife, Deepika and son, Kavvya for allowing use of

their share of time for this work. I also thank my parents, Dr. Manorama and Dr.

Prakash Chandra Mahajan for their spirited support. I express my gratefulness for my

family members and friends who have helped in completing this dissertation by the

way of encouragement and cooperation.

In the end I thank all those who have knowingly or unknowingly helped me with this

work.

Kavi Prakash

Contents

CERTIFICATE ...…..…..…………………………………………………………………………………………………i

CANDIDATES DECLARATION.......................................................................................... ii

ABSTRACT..................................................................................................................... iii

Acknowledgement.........................................................................................................v

Contents....................................................................................................................... vi

List of Figures..............................................................................................................viii

List of Tables................................................................................................................. ix

List of Abbreviations......................................................................................................x

Chapter 1 INTRODUCTION.......................................................................................1

1.1 General...........................................................................................................1

1.2 Process of Planning.........................................................................................3

1.2.1 Pre Tender Planning................................................................................4

1.2.2 Post Tender Planning...............................................................................5

1.2.3 Operational or Detailed Planning............................................................5

1.3 Project Management and Scheduling.............................................................6

1.4 Purposes of scheduling...................................................................................8

1.5 Element of Project Scheduling........................................................................9

1.6 Work Break down Structure.........................................................................10

1.7 Scheduling Requirements in a Bridge Project...............................................10

1.8 Objective and Scope of Study.......................................................................12

Chapter 2 SCHEDULING TECHNIQUES & THEIR FEATURES.....................................14

2.1 General.........................................................................................................14

2.2 Bar Charts and Milestone Charts..................................................................15

2.3 Network Analysis Techniques.......................................................................16

2.4 Line of Balance..............................................................................................18

2.5 Linear Scheduling Method............................................................................19

2.6 Other Scheduling Method.............................................................................23

2.6.1 Computer Based Modelling of Project Schedule...................................23

2.6.2 Critical Chain Project Management.......................................................24

2.6.3 4 D CAD..................................................................................................24

2.7 Concluding Remarks.....................................................................................25

Chapter 3 REPETITIVE SCHEDULING METHOD.......................................................26

3.1 Introduction..................................................................................................26

3.2 RSM ACTIVITY LOGIC.....................................................................................26

3.2.1 Activity Logic Constraints.......................................................................27

3.3 RESOURCE CONSIDERATIONS.......................................................................27

3.3.1 Production Rates...................................................................................28

3.4 Control Points and Activity Relationships.....................................................29

3.5 Procedure for creating RSM schedule...........................................................32

3.5.1 First Stage of RSM..................................................................................32

3.5.2 The second stage of RSM.......................................................................32

3.6 Concluding Remarks.....................................................................................33

Chapter 4 APPLICATION OF RSM TO A BRIDGE......................................................34

4.1 General.........................................................................................................34

4.2 Salient Features............................................................................................34

4.3 Work Breakdown Structure (WBS)................................................................35

4.4 Resource Constraint......................................................................................40

4.5 Scheduling Using Precedence Diagramming.................................................40

4.6 Scheduling using Line of Balance Technique.................................................42

4.6.1 LOB chart for sub structure...................................................................42

4.6.2 LOB diagram for Superstructure............................................................44

4.7 Scheduling Using Repetitive Scheduling Method..........................................46

4.7.1 RSM Diagram of Substructure...............................................................47

4.7.2 RSM DIAGRAM of Superstructure..........................................................48

4.8 Results and Discussion..................................................................................53

4.8.1 Duration.................................................................................................53

4.8.2 Additional information..........................................................................53

4.8.3 Critical Path...........................................................................................54

Chapter 5 Conclusion.............................................................................................55

Bibliography................................................................................................................ 57

Annexure I......……………………………………………………………………………………………………….…60

List of FiguresFigure1.1 Ability to influence Cost 2

Figure 1.2 Planning Process 4

Figure 1.3 Project Management Triangle 7

Figure 3.1 Delay in Activities due to resource considerations 30

Figure 3.2 RSM diagram for three Units 31

Figure 4.1 Schematic Diagram of Digaru Bridge Plate 1

Figure 4.2 Bar Chart of Substructure Unit Plate 2

Figure 4.3 LOB diagram of Substructure Plate 3

Figure 4.4 Bar Chart of Superstructure Unit Plate 4

Figure 4.5 LOB diagram of Superstructure Plate 5

Figure4.6 Network Diagram of Substructure Plate 6

Figure 4.7 RSM Graph of Substructure Plate 7

Figure 4.8 Activity Logic Diagram 49

Figure 4.9 Activities in Soffit 50

Figure 4.10 Activities in Web 51

Figure 4.11 Activities in Deck 52

Figure 4.12 RSM Graph of Superstructure Plate 8

List of Tables

Table 1.1: Phases in Construction of Bridge____________________________________________2Table 2.1 Different Methods and suitability for different projects __________________________22Table 3.1 Activity relationship and Control Points_______________________________________31Table 4.1 Salient Features of Bridge__________________________________________________35Table 4.2 Work Breakdown Structure of Bridge_________________________________________36Table 4.3 WBS of Abutment /Pier ____________________________________________________36Table 4.4 WBS of PSC Box Girder ___________________________________________________39Table 4.5 Availability of Resources___________________________________________________40Table 4.6 Available and Allocation of resources after levelling____________________________41Table 4.7 Activity Table Substructure_________________________________________________43Table 4.8 Activity table superstructure________________________________________________45Table 4.9 Activities and Associated Resources_________________________________________46Table 4.10 Activities in Substructure Unit______________________________________________47Table 4.11 Activities in Soffit_________________________________________________________50Table 4.12 Activities in Web_________________________________________________________51Table 4.13 Activities in Deck_________________________________________________________51Table 4.14: Project Duration from different techniques__________________________________53

List of AbbreviationsCPM Critical Path MethodFF Finish to FinishFS Finish to StartLob Line of BalanceLRP Linear repetitive ProjectLSM Linear Scheduling MethodLSMh Linear Scheduling ModelPM Precedence DiagrammingPSC Pre Stressed ConcreteRSM Repetitive Scheduling MethodSF Start to Finish SS Start to StartWBS Work Breakdown Structure

Chapter 1

INTRODUCTION

1.1 General

Bridges are structures that cross over a body of water, traffic, or other

obstruction, permitting the smooth and safe passage of vehicles. In highway

transportation systems, the term “bridge” is usually reserved for structures

over bodies of water. Other terms like flyovers, overbridge, underbridge are

used where the highway across another highways or railway. The construction

of bridge has strong positive impact on economical and social development of

the areas to be served. This along with reliability of connection is the major

factor affecting the decision to invest in bridges. Major bridges represent

significant investment and considerable social political involvement is required

for deciding on making a bridge (Ostenfeld, et al. 2000).

Typical process for construction of large civil engineering structures like

bridges is given in the Table 1.1.These phases are also referred to as project

life cycle (Burke 2001). Planning is done for different phases. Proper planning

affects the cost of the project. The Figure 1.1 shows the influence of planning

on cost. Impact of planning reduces as the project is being constructed. If

correct choices are not made at the concept stage the resultant of cost are

increased much more than at a later stage.

Bridge project like other infrastructure projects are characterized by long

duration, large budget, and complexity. Construction of bridge projects is a

complex process that inherits uncertainty since the construction is executed in

different job conditions. These conditions includes unusual or complex works,

equipments breakdown, unfavourable weather conditions, and unexpected site

conditions. (Mazrouk, Zein and AlSaid 2006).

1

Table 1.1: Phases in Construction of Bridge

Phase Conceptual Planning and Feasibility Study

Design and Engineering

Procurement and Construction

Detailed Design and Startup

Execution Commissioning and Operation

Purpose Find out Needs, demands etcSocial, Economic, Environment feasibility

Designing the layout

Estimating of scope of work

Obtaining provider, contractor

Design of Bridge

Preparation of Drawings

Actual Execution

Bridge in Use

Outcome To build or not to build

What to Build Who will build Working Drawings

Bridge Proper

Return on Investment

.

Until a bridge is commissioned there is no return on investment for the owner.

An incomplete bridge is as good as no bridge hence successful construction of

bridge is utmost important for owner. Due to is very nature bridge are subject

2

Figure 1.1 Ability to Influence cost (Hendrickson 1989)

to large number of contingencies which if foreseen can save a lot of money.

Thus planning for bridge is very important.

At the Concept and Feasibility stage, selection of different type of bridge is

dependent on various factors like availability of resources, cost, time, and

nature of crossing. Bridges are classified according to different criteria. Span

arrangement of bridge is typically used to identify the bridge even after its

completion. On the basis of span arrangement bridges can be single or multi

span. A multi span bridge consists of one or more of foundation piers or

columns in addition to abutments. Generally, the span lengths of different

spans of bridge are same.

Once the decision for construction of a bridge is taken the planning for

construction of bridge is taken up. Essential aspects of construction planning

include the generation of required activities, analysis of the implications of

these activities, and choice among the various alternative means of performing

activities. Construction planners choose the best among numerous alternative

plans. Without planning the course of action may become somewhat aimless

with a succession of random changes in direction (Hendrickson 1989). The

plan of construction is generally included as a contract condition and work is

rarely started without a construction plan approved. Payment for bridge

construction contract and progress of work is monitored using construction

plan submitted and approved.

1.2 Process of Planning

The planning process is explained inFigure 1.2. During the project life cycle

this process is repeated for different phase of project life cycle. Planning for a

construction project can be divided in three main stages in the overall planning

cycle of construction project; pre tender planning, post tender planning and

operational planning, each associated with different stages in lifecycle (Sahai

2002).

3

Analyse Method Draft Sequence

Reject Impractical method Evaluate remaining methods within the draft sequence

Select Final Method,modify, select final sequence on the basis of overall cost

Prepare plan for Communication

Objective To determine the most economical method, sequence of each operation

Figure 1.2 Planning Process (Sahai 2002)

1.2.1 Pre Tender Planning

It primarily enables the estimator to determine the costs involved. The required

information concerning methods, plants, materials etc. is required by the

estimator in a concise form (i.e. data sheets and tables) in order that a quick

4

assessment can be made for higher management to decide on further action.

A secondary purpose of the “tender plan” is to provide a basis for the

subsequent contract plan. The amount of detail entered into at this stage of

tender planning will thus include both the time available and the degree of

competitive pricing of the tender for obtaining the contract. Scheduling in the

Tender Plan is generally to establish milestones.

At the tender stage sponsoring agency informs the executives regarding the

main objectives that are the extent of construction and the required completion

date. These call for an early assessment on aspects like methods to be used;

preparation entailed; scheduling and phasing of operations; available

resources; purchasing and supplies; and schedule of payments. These will all

be interdependent to various extents; without such assessments; any estimate

becomes a matter of conjecture, site management becomes mainly labour

supervision, and financial matters become crucial.

1.2.2 Post Tender Planning

After the tender stage planning much of the information required for planning

and scheduling becomes available. Planning at this stage goes into the details

of flow of funds with the associated progress of work. A check is then made

to ensure that the final ‘contract plan’ is at least as economical as that

submitted at the tender stage : It should be such that all company data on both

detailed tasks and overall stages of operation are based on the some

information, preferably obtained from reliable sources. The contract plan is

provided to site executive based on which the operations are planned.

1.2.3 Operational or Detailed Planning

The objective of the operational or detailed planning is to ensure that the most

economical method and sequence is used for each operation in compliance

with data is used in planning and estimation for the overall program of work. It

5

also becomes necessary to determine the timing of plant used, labour

requirements and availability of materials. The information can be recorded

either by a stage period planning which covers stages of construction. The

later is program setting which entails the detail plan for a period of perhaps

four to six weeks. In this way a forward view of at least three to four weeks

work is always maintained.

Planning subsequent to detail planning is stage planning. Stage planning is

used whenever it considered necessary to enlarge a section of contract plan.

Except for the stage planning being for a small part the process for stage

planning is same as for detailed planning

1.3 Project Management and Scheduling

A project schedule is so important that it is a customer specified requirement.

A schedule is conversion of project action plan into a operating time table

(Meredith and Mantel Jr 2003). Planning and Scheduling are often used

synonymously in context of project. Scheduling is part of the project planning

process. Planning can be used in a wider context with different objectives like

financial planning.

Project planning is the heart of proper project management because it

provides the central communication for the work of all parties. A bridge project

is undertaken to satisfy the goal of establishing connectivity. Satisfying a

project goal requires three constraints. Traditionally, these constraints have

been listed as "scope," "time," and "cost". These are also referred to as the

"Project Management Triangle” as shown in Figure 1.3 where each side

represents a constraint. One side of the triangle cannot be changed without

affecting the others (Lester 2003) & (Leach 2000).

Resources and Quality shown in the centre affects all the three constraint. The

schedule constraint refers to the amount of time available to complete a

6

RESOURCESQUALITY

COST

SCOPE SCHEDULE

project. The cost constraint refers to the budgeted amount available for the

project. The scope constraint refers to what must be done to produce the

project's end result. These three constraints are competing constraints. The

effect of changing three constraints is summarized as follows (Lester 2003):

(i) Increase in scope leads to increase in both cost and time;

(ii) Tight time schedule results in reduced scope with increased

cost;

(iii) Tight budget causes reduced scope with more time.

Figure 1.3: Project Management Triangle (Leach 2000) &

(Lester 2003)

It is the role of project planning team to prepare methods and layout statement

and work schedule to comply with these managerial requirements.

The final expression of planning is the documentation referred to as the ‘the

plan’ which consists of charts and schedules showing the various programs

required and is accompanied by a method ‘statement’ for the project.

Submission of Work plan and its approval is generally a contract condition.

This is also termed as master schedule.

7

1.4 Purposes of scheduling

Schedules cannot be 1:1 scale models of the construction process. The

schedule provides following information regarding the project:

i. Minimum stipulated requirements of project

The most common reason for the use of schedules today is to meet the

owner’s requirements to provide a monthly schedule update. In this

case, schedules are typically created by off-site scheduling consultants

who never discuss the project with the contractor or subcontractors.

After the submission of the initial schedule, it is updated monthly to

identify activities’ percentage complete.

ii. Checking the progress of the project by earned value analysis

Earned Value analysis requires that the schedule track both the time

and cost completion of each activity. First this means that the activities

in the schedule updates must reflect those tasks that are actually taking

place on the job site. Second, it means that each activity is required to

report two values: Percent Cost Completion, and Remaining Duration.

Separating cost from time allows activities that have large up-front costs

for equipment to correctly accrue costs. Another way that earned value

analysis can help the team understand what is a happening on the

project is to identify when work is falling behind schedule.

iii. Activities in progress

On complex projects, one of the most difficult coordination efforts is to

ensure that subcontracting crews arrive at the job site to complete their

work in an efficient sequence with other workers. One contractor out of

step results in rework. The coordination required is not a technology

problem it is a communication problem. The communication can,

however, be made more clear through the use of schedules. If

schedules specifically identify subcontractor activities, then the timing

for the arrival, scope of work, and departure of subcontractor crews can

be clearly described to the whole team. Using the schedule as a

8

communication vehicle may help decrease miscommunications. If there

are delays or scheduling conflicts, then the impacts of these delays on

following contractor and/or subcontractor activities may be clearly

identified.

iv. Effect of changes in schedule

If the baseline schedule accurately reflects the way that the prime and

subcontractors plan to do the work, and that the schedule is updated as

the project goes along, then the schedule can be used to evaluate what

would happen if changes are introduced to the plan. Schedule changes

will directly add or remove specific activities and may also impact other

activities or the overall completion of the schedule. A schedule that

accurately reflects the changes during the project will allow the entire

team to quickly understand the context in which a problem occurred

and the impact of that problem on other activities and the project

completion. Having an up-to-date schedule when a problem occurs will

assist the project team to resolve the issue and impacts rapidly and

then get on with the work. Usefulness of construction schedule helps to

predict progress of the projects, its completion time, task time, the

conflicts in work to sequence, and lastly to satisfy contractual

requirements.

1.5 Element of Project Scheduling

Basic elements of project scheduling are (Adeli and Karim 2001):

1. Creating the work breakdown structure where the total work needed for the

project is divided into recognizable and logical chunks of work called tasks.

2. Assigning resources to the tasks and estimating their durations.

3. Specifying scheduling constraints, which can be resource constraints or

logic constraints between the tasks.

4. Generating the optimal schedule by using an algorithm to appropriately

sequence and time each task in the project.

9

1.6 Work Break down Structure

The fundamental technique used for planning and managing a project is to

break down the scope of work into manageable tasks. This breaking of larger

tasks into smaller ones begins early in the project. This breaking develops

from the initial scope statement in a top down fashion, much like beginning at

the top of a pyramid and expanding downward (Ahuja 1984). The purpose of

the work breakdown structure (WBS) is to sub-divide the scope of work into

manageable work packages which can be estimated, planned and assigned to

responsible person or department for completion. The work breakdown

structure provides a structured breakdown of the scope of work into

manageable work packages which can be further developed into a list of

activities (Burke 2001) (Kimmons 1990). In case of a multi span bridge

construction project many activities are required to be repeated for

construction like shuttering and concreting. Thus a multi span bridge

comprises of partly repetitive activities for certain part while for other parts it

may not be repetitive.

1.7 Scheduling Requirements in a Bridge Project

Linear repetitive projects (LRP) (Ipsilandis 2006) are projects which involve

repetitive units of construction elements. Examples of linear repetitive projects

include high rise buildings, tunnels, highways, and pipelines. The repetitive

construction of these can monitored and planned in terms of number of floors,

tunnel rings, road sections, and joints of pipe, respectively. (Lutz and Hijazi

1993) Repetitive units can be further broken down into a sequence of

processes which are repeated for each unit of the project. For example, the

sequence of processes for a bridge having multiple spans include form

erection, steel placing, concrete placement, stressing, wearing coat,

expansion joints.

10

Here linear refers to construction projects the activities of which are repeated

continuously like highways, bridges, tunnels, railways, pipelines, sewers, and

follow one after the other. Repetitive is used for works like high-rise buildings,

mass housing. The repetitive nature of linear repetitive projects along with the

construction industry’s emphasis on standardization and modularization has

led to development of various planning techniques dealing with LRP.

Repetitive projects such as multi-span bridges require a different approach to

planning. In order to allow the optimum use of resources, crews and

equipment are required to yield the same production rate, in terms of

construction units. If activities are planned to be built in this way, all activities

could become critical since delay in one shall affect all subsequent activities.

When planning is based in construction units (floors, apartments, meters etc.)

and production rates, repetitive construction subdivisions can be considered.

The schedule can then be developed to generate the same work rate for all

crews. The number of crews is to be selected so that all crews will perform the

same amount of construction units in the same period of time. Various authors

have listed concerns in scheduling of repetitive projects (Arditi, Tokdemir and

Suh 2002) (Yang and Ioannou 2004).

Resources may have variable production rates and variable work

quantity at different work locations.

An activity may utilize multiple crews simultaneously. A crew may

perform multiple activities.

Activities may have multiple predecessors and successors. There may

be multiple relationships between each pair of predecessor and

successor.

The construction process, as defined by a set of activities and

relationships, need not be the same at every work location.

A full set of relationships (Finish-to-Start, Finish-to-Finish, Start-to-Start,

and Start-to-Finish) should be available.

11

Labour and equipment may change progress direction (east-to-west,

up-to-down, etc.) or have complex work sequences.

One activity may link to another activity at non-contiguous locations. For

example, a drywall activity on a specific floor should not start until the

completion of two higher floors of the preceding glazing activity to

ensure a weather-tight environment.

Activities may require space-buffer (lead-distance) in addition to time-

buffer (lead-time). The space-buffer may be non-integer, e.g., 1.5 km or

1/2 houses.

Activities may need resources that work back-and-forth in an area

within a certain period, such as excavation or traffic control. Other

resources may not work in this area at the same time.

Work interruption should be allowed.

The non-repetitive portion of project work should be incorporated into

the framework of repetitive scheduling.

Activity may have space-dependency like shuttering, placing steel and

concreting and time-dependency like stressing and concreting.

1.8 Objective and Scope of Study

The objectives of this study are outlined as follows:-

(i) To study different scheduling methods, which can be used to

schedule work execution of a multi span bridge,

(ii) To analyse the effectiveness of different methods of scheduling a

bridge consisting of repetitive activities,

(iii) To apply and examine Repetitive Scheduling Method which has

been proposed for repetitive works, and

(iv) Compare the result with the currently well known techniques of

Precedence Diagramming and Line of Balance technique.

12

The bridge was scheduled using precedence diagramming with the use of MS

Project 2002 while MS Excel spreadsheet software was used for Line of

Balance Technique and Repetitive Scheduling Model. The study concentrates

on scheduling of work on site without consideration towards procurement

action of materials resources like cement, steel etc. Study is limited in

application of scheduling methods to repetitive works activities required for

construction of foundation, substructure and superstructure. Scheduling was

not done for non repetitive activities where precedence requirement required

completion of work on approach road, guide bunds.

13

Chapter 2

SCHEDULING TECHNIQUES & THEIR

FEATURES

2.1 General

Attitudes toward the formal scheduling of projects are often extreme. Many

owners require detailed construction schedules to be submitted by contractors

as a means of monitoring the work progress. The actual work performed is

commonly compared to the schedule to determine if construction is

proceeding satisfactorily. Many field supervisors dislike formal scheduling

procedures and regard them irrelevant to actual operations and time

consuming distraction.

Use of formal scheduling procedures is advantageous whenever the

complexity of work tasks is high and the coordination of different workers is

required. After the completion of construction, similar comparisons between

the planned schedule and the actual accomplishments may be performed to

allocate the liability for project delays due to changes requested by the owner,

worker strikes or other unforeseen circumstances. Different bases exist for

preparation of schedules (Sahai 2002).

i. Arbitrary basis

In this basis the owner will best attain his or her objectives by telling the

contractors “what to do” and by restricting direction on “how to do it” the

matters of real significance. In this basis the owner will give the total

start and end time of major elements of the project.

ii. Intuitive Basis

14

In this basis of scheduling the contractor mostly uses his/her

experience and “gut feelings”. This basis is not useful when the project

is large because the complexity increases.

iii. Scientific Basis

Here the contractor breaks whole projects into some elements and

considers all factors such as man, machine, and material required,

critical time, start and finish time of all elements as well as his

experience.

Scheduling Approaches can be primarily classified as resource oriented and

time oriented scheduling techniques. For resource oriented scheduling, the

focus is on using and scheduling particular resources in an effective fashion.

For time oriented scheduling, the emphasis is on determining the completion

time of the project given the necessary precedence relationships among

activities. Hybrid techniques for resource levelling or resource constrained

scheduling in the presence of precedence relationships also exist.

2.2 Bar Charts and Milestone Charts

Bar charts were designed by Henry Gantt as a visual aid in planning and

controlling his ship building projects. In a bar chart the activities are first

plotted against the time axis. The scheduling of each activity is represented by

a horizontal line. The length of line is proportional to estimated duration of the

activity. For tracking the progress a second line is drawn beside the first line.

This second line was drawn as to indicate the actual status of work. The

relative position of these lines indicated the actual progress of the activity with

respect to planned progress (Burke 2001).

The purpose of a milestone schedule is to highlight the dates of significant

events. Milestones should be critical events which have serious schedule

15

implications (Ahuja 1984). Milestones are usually represented by single points

or diamonds. These represent dates when a particular event shall occur.

Bar charts have various disadvantages for scheduling complex projects. There

is no indication of interrelationships among activities. In developing a bar

chart, little analysis is done to find out how much time will be required. No

information about level of effort requirements is available. Despite these

shortcomings the Bar Chart continue to be used since Bar Charts are simple

to construct and easy to comprehend. Bar Chart can be summarized for any

desired level of WBS. With the advent of computer bar charts can be easily

updated (Bennet 2003).

2.3 Network Analysis Techniques

As a management tool, especially in project management of large capital

construction projects, network techniques are unsurpassed, if the activities

have been arranged in a logical, practical and easily identifiable manner by

experienced people (Lester 2003).

Basically the network is a flow diagram showing the sequence of operations of

a process. Each individual operation is known as an activity and each meeting

point or transfer stage between one activity and another is an event or node. If

the activities are represented by straight lines and the events by circles, it is

very simple to draw their relationships graphically, and the resulting diagram is

known as the network (Lester 2003).

Network analysis, as the name implies, consists of two basic operations:

1) Drawing the network and estimating the individual activity times

2) Analysing the activity times to find the critical activities and the float

in the non-critical ones. (Lester 2003)

16

The predominant technique used in building construction today is the Critical

Path Method (CPM). This technique has evolved over the past several

decades into highly sophisticated and computerized applications. This method

calculates the minimum completion time for a project along with the possible

start and finish times for the project activities.

The critical path itself represents the set or sequence of

predecessor/successor activities which will take the longest time to complete.

The duration of the critical path is the sum of the activities' durations along the

path. Thus, the critical path can be defined as the longest possible path

through the "network" of project activities, hance the name Network Analysis.

The duration of the critical path represents the minimum time required to

complete a project. Any delays along the critical path would imply that

additional time would be required to complete the project (Kerzner 2001).

Formally, critical path scheduling assumes that a project has been divided into

activities of fixed duration and well defined predecessor relationships. A

predecessor relationship implies that one activity must come before another in

the schedule. No resource constraints other than those implied by precedence

relationships are recognized in the simplest form of critical path scheduling.

When the activities in Critical Path Method are shown as node with arrows

connecting them the Network Diagram is known as Precedence Diagram.

Precedence diagram has advantage over CPM in the since four types of

activity relationship can be represented (i.e. Finish to Start, Start to Start,

Finish to Finish, Start to Finish ) . Another advantage is that there is no use of

dummy activities as in CPM (Gray and Larson 2001).

Programme Evaluation and Review Technique (PERT) differs from CPM in

having three time estimate instead of one activity duration. Thus PERT

incorporates uncertainty in activity durations in analysis (Mahdi 2003).

17

Graphical Evaluation and Review Technique (GERT) is another modification

which allows for loops in the network (Moder, Philips and Davis 1964).

Network analysis offers all the advantage of being able to analyse the planning

data by holding the data in computer files. The planning data in a network is

linked through the logic that defines the relationship between the activities.

Thus changes can be made in the data relating to individual activities, i.e. the

duration, the resources etc. or changes can be made in the logical relationship

between activities and the consequences recalculated and represented. In

addition the steps to produce and process a network plan are more clearly

defined, self contained and offer a more rigorous approach to planning

complex operations.

Despite their extensive use due to obvious advantages these methods have a

number of shortcomings. Primarily these are due to their inability to address

continuity of work which may result in crews being idle. Multiple-crew strategy

is difficult to implement in the network methods. The network diagram is not

suitable for monitoring the progress of a project. Network methods do not

provide an efficient structure for the representation of repetitive tasks. There is

no consideration of the location of work in the scheduling (Adeli and Karim

1996). For all practical purposes Precedence Diagramming has superceded

CPM for scheduling due to its extensive use in computer softwares.

2.4 Line of Balance

Line of Balance is primarily a production management method. Used primarily

for repetitive projects, a Line of Balance (LOB) chart does not show direct

relationships between individual activities. It shows an output relationship

between different operations in that one operation must be completed at a

particular rate for the subsequent relationship to proceed at the required rate.

Only the critical are important activities are included for the purpose of

scheduling through Line of Balance chart (Chitkara 1998).

18

This technique has been applied in construction work mainly in building of

houses and to a lesser extent for jetty work and in conjunction with networks of

roads. Line of Balance is a planning technique for repetitive work, and the

principles employed in it are taken from the planning and control of

manufacturing process. The basis of the technique is to find the required

resources for each stage of operation so that different stages are not

interfered with and the target output could be achieved. The completed

schedule is based on chosen resources; therefore the rate of construction

calculated takes account of these resources. This is difficult for the network

calculations, with separated logic and resource allocation.

The main concept of LOB is the work continuity of the labour teams over the

construction units. The purpose of this technique is to calculate the required

resources for each stage of production so that the following stages are not

delayed and target output is achieved (Harris and Ioannou 1998).

Updating a LOB schedule is difficult once the project has started, and if the

rates of the construction prove to be different from those of calculated values.

This difficulty arises from the fact that the resources, that is teams of men with

different skills, are already on site. Various challenges in adoption of Line of

Balance techniques in construction industry have presented (Arditi, Tokdemir

and Suh 2002). However the method has been adopted by some large

construction firms (Henrich and Koskela 2006).

2.5 Linear Scheduling Method

Alternate techniques to bar charts and networks that were developed in the

last 30 years are known under the generic term, ‘‘linear scheduling method.’’

The general consensus is that linear scheduling methods are well suited to

projects that are composed of activities of a repetitive nature. (Arditi, Tokdemir

and Suh 2002). Indian Roads Congress (IRC SP:14 1979) suggests for use of

19

CPM in case of highways by dividing each activity into small portion and

schedule as a separate activity. This gives a ladder like schedule.

Linear Schedule is a simple diagram to show location and time at which a

certain crew will be working on a given operation. Linear Scheduling Method

(LSM) is a graphical scheduling method focusing on continuous resource

utilization in repetitive activities. LSM is used mainly in construction industry to

schedule resources in repetitive activities commonly found in highway,

pipeline, and high-rise building projects. These projects are called repetitive

projects or linear projects. The main advantage of LSM over Critical Path

Method (CPM) is its underlying idea of keeping resource work continuously. In

other words, it schedules activities in such a way that:

i. Resource utilization is maximized.

ii. Interruption in on-going process is minimized, including hiring-and-

firing.

iii. Effect of learning curve phenomenon is minimized.

In LSM the activities are plotted on Graph where time is one axis and distance

is the other axis. The controlling path is obtained by linking the least distance

point between the activities. Linear construction consists of a group of

operations that involve repetitive ‘‘units’’ of construction elements. Highways,

high-rise buildings, tunnels, and pipelines are good examples that exhibit

repetitive characteristics where the same basic unit is repeated several times.

Multiple-dwelling, multiple-floor, or linearly progressive projects allow

construction to proceed in a repetitive fashion, allowing for cost and time

efficiencies. To achieve these possible efficiencies, it is necessary to balance

the crews. By such scheduling, a construction manager achieves continuity in

the placement of all repetitive elements, thus maximizing the productivity of

labour and equipment. In Linear Scheduling Method three types of activities

are recognized (Harmelink and Rowings 1998)

i. Linear Activity

20

Linear activities are activity which has a production rate. These

activities tend to progress continuously over length or units utilizing

same crew and resources.

ii. Bar Activity

Bar Activities are those which occupy small space and large time.

These activities do not allow any other activity to proceed for some

time.

iii. Block Activity

Block Activities are those which occupy both space and time. A block

activity generally means that the activity in progress is discrete and

cannot be assigned a production rate while it progress over some

distance or unit.

LSM diagram resembles the Objective Diagram of LOB technique. While

Objective Diagram is used to schedule or record the cumulative events of unit

completion LSM is used to plan or record progress on multiple activities that

are moving continuously in sequence along the length of a single project. This

method aims to provide a graphical view more efficiently representing linear

construction activities like highway and pipeline construction.

Linear activities have a production rate depending on resources required and

available. The activity is shown as line on the linear schedule graph with

production rate as slope of the line .The sequence of the activity to be included

in linear schedule is determined along with the time buffer and space buffer.

Time buffer is the time required between the start of succeeding activity and

end of proceeding activity. Space buffer is the distance required to allow two

activities to proceed without affecting is each other. The minimum time

constraint denotes the minimum time buffer between two activities—e.g., the

minimum time buffer between concreting and formwork removal allowing for

curing of concrete. The minimum distance/location constraint denotes the

21

minimum allowable distance between two activities to allow for the correct or

safe execution of work (Alexandros, John and Sergios 2007)

Linear Scheduling Method has been proposed by different names by different

authors. Different methods have been proposed for specific objectives by

different authors (Harris and Ioannou 1998)

Suitability of methods described in preceding sections for various purposes

has been studied (Harmelink and Yamin 2001). The Table 2.2 shows

suitability of the above described methods for different types of projects.

Table 2.2 Different Methods and suitability for different projects (Harmelink and Yamin 2001)

Type of project Scheduling method Main characteristic

Linear and continuous projects (pipelines, railroads, tunnels, highways)

Linear scheduling method

•Few activities all occurring at one place one after the other

Multiunit repetitive projects (housing complex, buildings) Line of Balance •Similar unitsHigh-rise buildings

Hard logic for some activities, soft for others,

Large amount of activities

Every floor considered a production unit LOB, VPM, PM • Repetitive activities

Refineries and other very complex projects

Complex design Activities discrete in

nature Crucial to keep project

in critical path PERT/CPM , PM

Complex Relationship Extremely large

number of activities

Simple projects (of any kind)Relatively few activities Bar/Gantt chart

• Indicates only time dimension (when to start and end activities)

22

Different models for identifying critical path or critical sequence for LSM have

been proposed by various authors namely the repetitive scheduling method

(RSM) by Harris and Ioannou, the linear scheduling model (LSMh) by

Harmelink and Rowings, the critical path linear scheduling method by Ammar

and Elbeltagi, and the repetitive project model by Kallantzis and Lambropoulos

(Alexandros, John and Sergios 2007). Repetitive Scheduling Model has been

described in detail in next chapter.

2.6 Other Scheduling Method

In addition to the methods described above, other scheduling methodologies

have been developed in recent years. Some of the methods are described in

subsequent paragraphs.

2.6.1 Computer Based Modelling of Project Schedule

With the availability of more powerful computers and software, the use of

advanced scheduling techniques is becoming easier and of greater relevance

to practice. (Hendrickson 1989) These techniques address some important

practical problems, such as:

scheduling in the face of uncertain estimates on activity durations,

integrated planning of scheduling and resource allocation,

Scheduling in unstructured or poorly formulated circumstances.

PERT and CPM can be modelled as linear programming problem with the

objective of minimizing project duration (Taha 2005). The growing availability

of computers allows computing power to solve larger mathematical models.

Computer models allow for both time and resource constraints while

modelling. Neural Network Technique has been developed for use in schedule

and cost optimization of projects (Adeli and Karim 1996). Multi objective

optimization has been suggested for scheduling linear repetitive projects

(Ipsilandis 2006). The success of computer based techniques is dependent on

23

proper modelling of the problem. Another advantage offered by use of

computers is in incorporating uncertainty in activity duration (Hendrickson

1989) by means of use of simulation.

2.6.2 Critical Chain Project Management

Critical Chain Project Management is based on the Theory of Constraint

developed by Eliyahu M Goldratt as applied to project management (Goldratt

1997). Theory of constraint says that there is generally one or two constraints

in a system. By concentrating on bottleneck the output can be maximised. This

is applied to project environment considering critical chain as bottleneck and

time available as inventory. Buffers are provided wherever required. The

critical chain can cater for both technical as well as resource constraints.

Critical Chain Project Management is a method of planning and managing

projects that puts more emphasis on the resources required to execute project

tasks. This is in contrast to the more traditional Critical Path and PERT

methods, which emphasize task order and rigid scheduling. A Critical Chain

project network will tend to keep the resources levelly loaded, but will require

them to be flexible in their start times and to quickly switch between tasks and

task chains to keep the whole project on schedule. CCPM is not a new

scheduling techniques instead adopts PERT/CPM. CCPM scheduling

provides for buffer before the critical path (bottleneck) but not anywhere else in

the network thus no float is given to any activity but rather float of all activity

are placed as a buffer before the critical path (Steyn 2002) (Leach 2000).

2.6.3 4 D CAD

This approach involves the combination of 3D design data with the added

dimension of time. Extending the traditional planning tools, visual 4D models

combine 3D CAD models with construction activities to display the progression

of construction over time. 4D CAD systems originated from the construction of

processing, power, and offshore plants where 3D modelling has long been

used for checking space conflicts of the complex piping systems.4 D CAD is

24

used for scheduling by including use of GIS in modelling construction. 3D

CAD is development of 3D Model on computer of a facility being designed.

The 4th dimension of time is applied so that this model shows the state of

works as the work progresses. In 4D CAD for planning of works it is attempted

to note location where a crew shall be working at a particular time by

modelling the construction sequence. The planning takes care that the crew

while working gets enough space for working and progress is not hindered by

other crews in vicinity. While great achievements have been made in applying

4D CAD to the construction of industrial facilities and commercial buildings

little has been done in road and bridge construction. This may be due to

limited computer support for construction planning of transportation

construction projects. Formally speaking 4D CAD is addition of time dimension

to standard 3 D models which are now commonly used in construction.

2.7 Concluding Remarks

Above methods are used in different types of construction works depending on

the availability of necessary information. The choice of scheduling method

depends on the requirements of the project. The use of computer based

modelling and simulation requires knowledge of modelling, the use of 4D CAD

requires availability of 3D CAD drawings, and the Critical Chain Project

Management requires details regarding details of buffers available for different

activity. These methods cannot be used since the necessary information was

not readily available. In comparison Repetitive Scheduling Method proposed

by Harris and Ioannou uses the data required for precedence diagramming

and can be utilized wherever precedence diagramming is used. Repetitive

Scheduling Method has been used in this study and same has been described

in details is the following chapter.

25

Chapter 3

REPETITIVE SCHEDULING METHOD

3.1 Introduction

Harris and Ioannou presented Repetitive Scheduling Model (RSM) as a

generalized approach to scheduling of linear and repetitive projects than Line

of Balance and Precedence Diagramming. It uses Precedence Diagramming

for planning of unit network. All the activity types (linear, bar, block) as used in

LSM are accepted in RSM. (Harris and Ioannou 1998).

An RSM schedule is shown as an X-Y graph where the axes represent units,

and time. In general for clearly delineating schedule information, in case of

construction of high-rise buildings, the units can be conveniently shown by

plotting on Y axis and time along X axis. The work progress of horizontal

construction projects e.g. highways, pipelines, canals, tunnels, bridges can be

plotted along X axis since unit represent length. A logical sequence is adopted

for representing the units of projects which are repetitive in nature.

3.2 RSM ACTIVITY LOGIC

The identification of the precedence constraints amongst the units is essential

in addition to establishing the pattern of repetitive units. A CPM precedence

network is drawn for each repetitive unit. A list of all the time consuming

activities is prepared for establish unit activity logic. A name and identification

symbol is assigned to each activity in the list for finding suitable relationship

with regards to related units, there by reducing redundancies. On examination,

the activity list will show a set of similar activities occurring repeatedly. A logic

diagram is prepared after all the activities of each repetitive unit are identified.

The precedence form is generally preferred but arrow network can also be

26

used. Each unit network should contain all technical logic relationships among

the activities. The main purpose of this diagram is to establish logical

relationships among the activities, resource considerations within this unit can

be temporarily ignored. Actual projects have complex relationships among

their activities which may be difficult to properly detail without a standard

procedure outlined above.

3.2.1 Activity Logic Constraints

The activities within a repetitive unit must be logically related as well as they

also must be logically related from unit to unit. The two types of constraints

that control unit-to-unit logic in RSM diagrams:

i) Technical Precedence Constraint

A particular work activity in the network of one unit must be

followed by a similar work activity in the network of a succeeding

unit to ensure that the flow of the technical work between the units is

maintained.

ii) Resource Availability Constraint

The resource assigned to an activity in one unit also must be

assigned to the similar activity in the succeeding unit to ensure that

the resource required in the first unit is available when needed by

the second unit.

The continuous resource utilization is neither ensured nor forced in the

schedule.

3.3 RESOURCE CONSIDERATIONS

Every activity requires the application of resources for its performance. Most

activities require that several resources like man, material, machine be

employed together. RSM assumes that only the most significant resource is

associated with an activity and all activities are defined using this assumption

(Harris and Ioannou 1998).

27

To cater for a second assumption that the same resource will be used for like

activities in successive repeating units, each activity’s resource must be

consistent from unit to unit. If an activity needs several significant resources

for its performance, different activities in parallel can be assigned for each

resource/crew. If several activities within a repetitive unit require the same

resource, the several activities are grouped into one common activity using

that resource to avoid the appearance of interruptions in resource usage

between units.

3.3.1 Production Rates

There are two important production rates associated with each activity, a

resource production rate and a unit production rate. (Harris and Ioannou 1998)

The resource production rate for an activity is defined as the amount of work

that can be done by the resource per unit of time. Resource production rate is

obtained from available databases. Resource production rate is an attribute of

the resource and thus remains constant in any unit involving the same activity.

The unit production rate is the number of repetitive units that can be

accomplished by a resource during a unit of time. The unit production rate is

the slope of a production line in an RSM diagram. The unit production rate is

directly proportional to the activity’s resource production rate and inversely

proportional to the quantity of work in the unit. In cases where activity duration

are known unit production rate is inverse of duration.

When the quantity of work in activities that repeat from unit to unit is not the

same in every unit, the unit production rates will vary depending upon the

amount of the work in each unit. Similarly, if the activity duration is not same in

different units, unit production rate changes.

28

3.4 Control Points and Activity Relationships

In an RSM graph activities are represented as continuos lines with interruption

indicating the interruption in utilization of the resource associated with that

activity. These lines are termed as production lines. The slope of this line is

proportional to unit production rate of the activity.

Production line of different activity can be parallel, diverging or converging.

Parallel production line indicates that both activities are progressing at the

same rate. Diverging production line indicate that rate of production of

successor is less than that of predecessor. Converging production lines mean

that rate of production of successor is greater than that of predecessor.

Resource is utilized continuously across different units with each resource

being associated with one activity. If an activity Y1 (where Y indicates activity

and 1 indicates unit) follows an activity X1 and has greater duration than its

predecessor, the resource associated with activity Y1 shall not be available for

the activity Y2 in subsequent unit till its utilization in first unit is not complete.

This will result in delay in start activity Y2 in second unit in spite of

predecessor activity X2 being complete in second unit. Similar for the activity

Y3 in third unit this delay is greater due to effect of delays in both unit 1 and

unit 2. The Figure 3.4 shows bar chart of how activities are delayed due to

resource continuity requirements in RSM.

In RSM graph the activity are represented as lines. The Figure 3.5(Harris and

Ioannou 1998)Figure 3.5 RSM diagram for three Units (Harris and Ioannou

1998)shows the activity shown in Figure 3.4 in RSM diagram. Due to non

availability of resource required for activity Y the project is duration is

increased. The location of activities Y1, Y2, Y3 is determined by the start of

activity Y3 and this point is the control point. In order to achieve continuos

resource utilization the activity Y1 and Y2 have to be delayed. The location of

Activity Y2 and Y1 is determined by the location of start of activity Y3. This

29

X1

X2

Y2

Y3

X3

Y1

Activity Y2 delayed due non availability of resources due to non-completion of Activity Y1

Delay in Activity Y3 greater than that of Activity Y2 due to addition of delays of previous units

Repetitive U

nits

point is defined as control point for activity X and Y since activities in other unit

are controlled by it. If production rate is of Activity X is increased the control

point will shift. With this the production line of activity Y will shift. If production

rate of activity X is changed the location of control point will not change

however the slope of production line will change. In this situation the

production line will rotate about the control point.

A control point in RSM can be defined as a point which can be used to

determine the location of all the activity of the same type in the project. These

point are required to be established to plan for increase and decrease in

production rates of the activities. Location of control point is determined by

production rates of activity and relationship between the activities. The Table

3.3 shows location of control point and activity relationship. The controlling

path or sequence is drawn by connecting the control points along the

production lines starting from the last activity

Figure 3.4 Delay in Activities (Harris and Ioannou 1998)

30

0 1 2 3 4 5 6 7 8 9 10 11

3

2

1

Repetitive Units X2

Y3X3

Y2

Y1X1

0 1 2 3 4 5 6 7 8 9 10 11

Figure 3.5 RSM diagram for three Units (Harris and Ioannou 1998)

Table 3.3 Activity relationship and Control Points

Activity Relationship

Slope of Production Line

Location of Control Point

Effect of change of Production rate of predecessor

Effect of change of production rate of successor

Finish to Start Convergence Start of successor in last unit

Shift in successor activity

Rotate about control point

Finish to Start Divergence End of successor in first unit

Shift of successor activity


Start to Start Convergence Start of successor in last unit



Start to Start Divergence End of successor in first unit



Finish to Finish Convergence Start of successor in last unit



Finish to Finish Divergence End of successor in first unit



31

Successor Activities delayed due to resource consideration

Control Point determines the start of Activity Y in all units

3.5 Procedure for creating RSM schedule

RSM schedule is created in two stages (Yang and Ioannou 2001)

3.5.1 First Stage of RSM

In the first stage, the forward pass computations of CPM are performed. The

first stage of RSM includes the following five steps:

(1) Establish the position and slope of production line of each activity by

assuming it starts at time zero..

(2) For each predecessor, determine the activity’s shifted position based

on each relationship (link) in every possible unit.

(3) Calculate the shift that is the difference between the shape starting at

time zero and the shifted position.

(4) Select the maximum shift over all units, all incoming relationships, and

all predecessors.

(5) Move the activity being scheduled to the position that results from the

maximum shift.

3.5.2 The second stage of RSM

The second stage is used to model the pulling effect of work continuity

automatically. It is built on an important assumption: each activity would have

no more than one ‘continuity predecessor’. This is one of the basic

assumptions of RSM. The activities linked by continuity relationships can form

a continuity activity chain. A continuity activity chain can be considered a

summary activity that utilizes the same crew. For each continuity activity chain,

upstream activities are pulled by the sum of lags within the chain to eliminate

gaps and ensure the continuous utilization of the resource from one activity to

the next. If gaps (work interruptions) are desired between activities, this stage

may be skipped. This stage consists of following steps:

32

(1) Locate continuity activity chains and sort them according to the

precedence order. This is similar to the topological sorting of

activities in the first stage.

(2) Increase the start time of the first activity in a continuity activity

chain by the sum of lags within the chain so that first activity is

continuous over all units and schedule other activities based on

the new start time of the first activity.

(3) First stage is required to be repeated for all activities other than

first activity.

(4) If the start time of the last activity in the continuity activity chain

increases, postponing the first activity in the chain would delay

the start time of the last activity and hence lead to a cycle.

Therefore in such a case this chain should be skipped and the

next chain taken up. If there is no effect on start time of last

activity in chain, change the start times of all activities in the

chain can be changed to the calculated ones and proceed to the

next chain.

3.6 Concluding Remarks

RSM considers resources continuity as well technical precedencies. In

projects availability of resources and their continuous utilization is very

important for project managers. A scheduling method which incorporates

continuous resource utilization can well and truly takes care of requirement of

project management especially for resource planning. RSM thus seems to be

a useful and efficient method which can be easily applied for scheduling of

bridges projects. Attempt is made to study the method for scheduling a

multispan bridge. The same bridge is also scheduled with other method to test

feasibility of the method for scheduling multispan bridge projects to compare

relative advantages and disadvantages of different methods

33

Chapter 4

APPLICATION OF RSM TO A BRIDGE

4.1 General

A 720 meter multispan bridge under construction, comprising of 16 spans, was

taken up for the purpose of study. The bridge is currently under construction

by defence in eastern sector. The total work involved in the bridge project

includes construction of a bridge over a meandering river along with its

approaches and guide bunds for river training.

All the superstructure spans and pier shaft and wells for abutments and piers

were alike with only minor difference. This meant that similar type of work was

to be repeated 16 times making this bridge a good case to apply scheduling

methods developed for repetitive works. Sixteen (16) Prestressed Concrete

Box Girders for superstructure and seventeen (17) solid piers over circular

wells as substructure are included as part of study. Other activities not being

repeated many times were not included in study due to time limitations.

Activity durations have been obtained from site executives and by experience.

These have been used from another nearby bridge under construction by the

same organisation and also from other bridge in the vicinity.

4.2 Salient Features

A bridge under construction over river Digaru in Arunachal Pradesh is used for

the purpose of study. The bridge is located on a meandering river with multiple

channel necessitating large length with multiple spans in a sparsely populated

forest area. Design details and construction methodology is elaborated in

Table 4.4. A schematic diagram of the bridge is attached as Figure 4.1.

34

Table 4.4 Salient Features of Bridge Feature Details

Length of Bridge 720 meters

Span Arrangement 16 span 45 meter each

Type of Superstructure Prestressed Concrete (PSC) Box Girder

Method of Prestressing Post Tensioning

Type of Substructure Solid Pier both for Abutments and Intermediate Piers

Type of Foundation Circular Well foundation for Piers and Abutments

Methodology of Construction Cast In situ

Proposed date of Completion 31 March 2010

Date of Start of Construction at site 26 Nov 2006

Working Period Throughout the Year

Founding RL of Wells 145.00 meter (from the temporary bench mark established

Top of Well 162.50 meters

RL of Soffit 167 meter

RL of Deck 170 meter

Width of Soffit 7.00 meter

Height of Web 2.75 meter

4.3 Work Breakdown Structure (WBS)

The work break down structure has been prepared, keeping in view the

reporting requirements. Each Abutment/Pier was divided in 10 main activities.

Some activities were further divided in sub activities. Each PSC Box girder

was divided into 7 main activities some of which were further divided into sub

activities. The division of activities into sub-activities was done in consultation

with site executives. The dependency relationship and duration were obtained

from other bridge being constructed in vicinity and from experience of bridge

site staff. The following tables (Table 4.5, Table 4.6,Table 4.7) give the details

of WBS of the bridge. Activities in WBS level 3, 4, 5 and 6 are shown in Table

4.6 for substructure and Table 4.7 for superstructure.

Table 4.5 Work Breakdown Structure of Bridge

35

BRIDGE (WBS level 0) Activities to be reported (WBS level 3)

SUB STRUCTURE (WBS level 1)

Abutment/Pier (WBS level 2) (repeated 17 times)

1 Making of island and placing of cutting edge

2 Casting of well kerb

3 Casting of well steining

4 Well sinking

5 Bottom plugging

6 Top plugging

7 Sand filling in well

8 Casting of well cap

9 Casting of abutment/pier

10

Casting of pier cap

SUPERSTRUCTURE (WBS level 1)

PSC Box Girder (WBS level 2) (repeated 16 times)

1 Fixing of bearing

2 Casting of PSC BOX Girder (including Erection of Shuttering and Concreting and stressing)

3 Casting of wearing coat

4 Casting kerb & handrail

5 Load Testing

6 Site Clearance

7 Fixing of expansion joints & drainage sprouts

Table 4.6 WBS of Abutment /Pier (highest level not included, shown for only one Abutment/Pier)

S No.

WBS Code

Activity Duration Precedence Relationship

1 1 Abutment/Pier 306.5 days2 1.1 Making of Island and Placing of

Cutting Edge 16 days3 1.1.1 Making of Island 1 day4 1.1.2 Placing and Fabrication of Well

Kerb 15 days3

5 1.2 Casting of well curb 21 days6 1.2.1 Erection of Shuttering 2 days 4

7 1.2.2 Cutting of Steel 0.5 days8 1.2.3 Placing of Steel 1 day 6,7

9 1.2.4 Pouring of Concrete 1 day 8

36

S No.

WBS Code


10 1.2.5 Removal of Shuttering 1 day 9

11 1.3 Casting of well steining 231 days12 1.3.1 Casting of 1st Lift 50.5 days13 1.3.1.1 Erection of Shuttering 2 days 57

14 1.3.1.2 Cutting of Steel 0.5 days 7

15 1.3.1.3 Placing of Steel 1 day 13,14

16 1.3.1.4 Pouring of Concrete 1 day 15

17 1.3.1.5 Removal of Shuttering 1 day 16

18 1.3.2 Casting of 2nd Lift 80 days19 1.3.2.1 Erection of Shuttering 2 days 58





24 1.3.3 Casting of 3rd Lift 109.5 days25 1.3.3.1 Erection of Shuttering 2 days 59





30 1.3.4 Casting of 4th Lift 61 days31 1.3.4.1 Erection of Shuttering 2 days 60





36 1.3.5 Casting of 5th Lift 90.5 days37 1.3.5.1 Erection of Shuttering 2 days 61





42 1.3.6 Casting of 6th Lift 120 days43 1.3.6.1 Erection of Shuttering 2 days 62





37

S No.

WBS Code


48 1.3.7 Concreting 7th lift 150 days49 1.3.7.1 Erection of Shuttering 2 days 63



52 1.3.7.4 Pouring of Concrete 0.5 days 51

53 1.3.7.5 Shuttering for False Steining 1 day

52

54 1.3.7.6 Pouring of Concrete 0.5 days 53

55 1.3.7.7 Removal of Shuttering 0.5 days 54

56 1.4 Well Sinking 235.5 days57 1.4.1 Well Sinking 0-2.1 25 days 10

58 1.4.2 Well Sinking 2.1 -4.2 25 days 17

59 1.4.3 Well Sinking 4.2-6.3 25 days 23

60 1.4.4 Well Sinking 6.3- 8.4 25 days 29

61 1.4.5 Well Sinking 8.4-10.5 25 days 35

62 1.4.6 Well Sinking 10.5 – 12.6 25 days 41

63 1.4.7 Well Sinking 12.6 – 14.7 25 days 47

64 1.4.8 Well Sinking 14.7- 15.5 25 days 55

65 1.5 Bottom Plugging 3 days 64

66 1.6 Sand Filling 3 days 65FS+21 days

67 1.7 Top Plugging 1 day 66

68 1.8 Well Cap 203.5 days69 1.8.1 Cutting of Steel Reinforcement

for well cap and pier 10 days50

70 1.8.2 Casting of Well Cap 1 day 69,67

71 1.9 Casting of Pier 6 days72 1.9.1 Shuttering 1st lift 1 day 70

73 1.9.2 Concreting 1st lift 1 day 72

74 1.9.3 Shuttering 2nd lift 1 day 73

75 1.9.4 Concreting 2nd lift 1 day 74

76 1.9.5 Shuttering 3rd lift 1 day 75

77 1.9.6 Concreting 3rd lift 1 day 76

78 1.10 Casting of Pier Cap 16 days79 1.10.1 Shuttering 7 days 76

80 1.10.2 Cutting of Steel 7 days 79

81 1.10.3 Concreting 2 days 80

38

Table 4.7 WBS of PSC Box Girder (highest level not included, shown for only one PSC box Girder)

S No.

WBS Code

Activity Duration Precedence Relationships

1 1 PSC BOX GIRDER 92 days2 1.1 Fixing Of Bearing 2 days3 1.1.1 Fixing of Bearing 1 day 9SS+3 days4 1.1.2 Casting of Pedestal 1 day 35 1.2 Casting of BOX GIRDER 85 days6 1.2.1 Erection of Staging and Shuttering 45 days7 1.2.1.1 Levelling of Ground 1 day8 1.2.1.2 Staging for Soffit 7 days 79 1.2.1.3 Shuttering for Soffit 10 days 810 1.2.1.4 Staging for Deck 7 days 711 1.2.1.5 Shuttering for Web 7 days 16,1012 1.2.1.6 Shuttering for Deck 7 days 1713 1.2.2 Casting of Superstructure 55 days14 1.2.2.1 Cutting of Steel for Soffit and Web 7 days15 1.2.2.2 Placing of Steel for Soffit 7 days 9,14,23FF+1 day16 1.2.2.3 Concreting of Soffit 3 days 15,23,2617 1.2.2.4 Concreting of Web 3 days 11,2718 1.2.2.5 Cutting of Steel for Deck 3 days 1419 1.2.2.6 Placing of Steel For Deck 7 days 18,1220 1.2.2.7 Concreting of Deck 3 days 19,2821 1.2.3 Cutting and Placing of Cables 16 days22 1.2.3.1 Cutting of Cables 8 days23 1.2.3.2 Placing of Cables 3 days 22,24,4,824 1.2.3.3 Making of End Block 12 days25 1.2.4 Crushing of Chips 20 days26 1.2.4.1 Crushing of Chips for Soffit 6 days27 1.2.4.2 Crushing of Chips for Web 6 days 2628 1.2.4.3 Crushing of Chips for Deck 8 days 2729 1.2.5 Stressing of Cables 9 days30 1.2.5.1 Stressing of Cable 1 day 20FS+21 days31 1.2.5.2 Grouting of Cables 1 day 30FS+7 days32 1.3 Casting of Wearing Coat and Crash Barrier 7 days33 1.3.1 Casting of Wearing Coat 5 days 3034 1.3.2 Casting of Crash Barrier 2 days 3335 1.4 Casting of Kerb and Hand Rail 2 days36 1.4.1 Casting of Kerb 1 day 2037 1.4.2 Casting of Handrail 1 day 3638 1.5 Load Testing 1 day 32

39

S No.

WBS Code

Activity Duration Precedence Relationships

39 1.6 Site Clearance 1 day 38,40

40 1.7Fixing of Expansion Joints and Drainage Sprouts 14 days

41 1.7.1 Fixing of Drainage Sprouts 6 days 3342 1.7.2 Fixing of Expansion Joints 14 days 30

4.4 Resource Constraint

Various resources are required for construction of bridge. Resources are not

available in infinite quantity. Availability of resources for the project is limited.

Major of resources required for the construction of bridge and maximum

quantity available is given in Table 4.8.

Table 4.8 Availability of ResourcesRESOURCE NAME MAXIMUM AVAILABILTY

Winch and Grab Bucket arrangement (used for sinking of well by grabbing in the well)

7 numbers

Crushing unit 1 no. 6-10 Tonnes Per Hour Capacity Volumetric Output 15 cu. m./day

Concreting Capacity 30-40 cu m per day using 5 batch mixers (each mixer capable of providing about 5-7 cu. m. of concrete per day/ depending on mix design

Circular Shuttering forms for well 2 sets

Welding set 1 No.

Skilled Manpower (1) Limited availability of Highly skilled, manpower due to which highly complex operations cannot be executed

(2) Semi skilled manpower available can be used as multi skilled personnel

Shuttering Forms for PSC box girders 4 sets

4.5 Scheduling Using Precedence Diagramming

The schedule contains nearly 2000 activities. Scheduling of the bridge is done

using precedence diagramming method with the help of MS Project 2002

software. Duration for one abutment/pier is 306.5 days as seen in Table 4.6

and duration for one box girder is 92.5 as seen from Table 4.7. Without using

resources levelling the project duration obtained is 399.5 days which is the

sum of duration of time required for completion of one abutment/pier and one

40

PSC box girder. Scheduling data obtained from MS Project software is

attached as annexure 1. The resource levelling tools available in the software

was then implemented. The duration of activities was kept fixed. The schedule

as obtained from the software after resource levelling is attached as

annexure 1. The software was not able limit allocation of resources up to the

maximum limit. The Table 4.9 shows the allocation and maximum quantity

available in percentage. There is an over allocation of resources which is

required to be resolved by delaying activity in the network.

Table 4.9 Available and Allocation of resources after levelling

Name of Resource Peak Requirements

Maximum Unit

Shuttering 800% 400%

Steel Cutting 600% 300%

Winch and Grab bucket arrangement 800% 700%

Concreting 1,300% 600%

Cutting Edge team 100% 100%

Welding Set 300% 100%

Jack 200% 100%

Grouting Pump 200% 100%

Cable Cutting 200% 100%

Stone Crusher 100% 100%

Steining form set 400% 200%

Girder Form set 600% 400%

Carpenter 100% 100%

Dozer 200% 100%

In precedence diagramming resource considerations are applied after network

has been prepared. Thus at the start of resource levelling procedure there is

an over allocation. After preparing the network the resources are levelled, by

delaying the activity within the slack/ float available. The rescheduling of

activities results in reduction in peak requirement of resources. Maximum

availability of resources cannot be enforced with the levelling procedure

resulting in over allocation. Since maximum resource constraint are fixed this

makes the schedule infeasible.

41

In case the resource constraints have to be fulfilled extensive reworking by

addition of artificial precedence relationships between different activities is

required. The additional dependencies between activities cater for continuous

utilization of resources from one activity to another in subsequent units are

needed to ensure and allow for resource continuity. This is not done in this

work due to limitations of time. The inability of network diagramming

techniques to handle resource utilization adequately is highlight in scheduling

repetitive projects.

4.6 Scheduling using Line of Balance Technique

The same Bridge was scheduled using Line of balance Technique. In the

bridge the substructure activities are repeated 17 times while superstructure

PSC box Girder is repeated 16 times. For applying Line of Balance technique

substructure and superstructure have to be dealt with separately to obtain

balance in the progress rate. This process of segmentation in superstructure

and substructure is required to avoid resources overlap and confusion in

decision making. Accordingly, two production diagrams and LOB chart have to

be prepared for substructure and superstructure.

4.6.1 LOB chart for sub structure

Activities in the superstructure have been revised from the precedence

diagram Table 4.6 of one unit due to some activities being necessarily

required to move at same pace. The revised activities are shown in Table

4.10. These activities have a time dependency due to the nature of work.

Activities like concreting and shuttering progress at rates equal to each other

since concreting can only be done when shuttering has been completed. As a

result, some of resources required these activities will have forced idle time,

especially concreting and reinforcement (placing of steel). Activities where

progress of one is dependent upon progress of another activity have been

42

replaced by one activity thereby reducing the number of activities.

Dependencies between the activities have been revised keeping in view of

reduction in number of activities. Activities have been grouped such that

duration of combined activity takes care of time required for all the activities

grouped together.

Table 4.10 Activity Table Substructure

S No

Activity Predecessor Duration

Crew

Start Day

End Day

Start Day

End Day

Start Day

End Day

First Seven Wells

Second Seven Wells

Last Three Wells

1 Making of Island and Placing Cutting Edge

15 1 0 105 254 359 541 586

2 Casting of well curb 1 5 1 66 111 329 364 576 591

3 Casting of 1st Lift 2FS+25 days 5 1 104 141 359 394 606 621

4 Casting of 2nd Lift 3FS+25 days 5 1 134 171 389 424 636 651

5 Casting of 3rd Lift 4FS+25 days 5 1 164 201 419 454 666 681

6 Casting of 4th Lift 5FS+25 days 5 1 194 231 449 484 696 711



9 Concreting 7th lift 8FS+25 days 5 1 286 321 539 574 786 801

10 Bottom Plugging 9FS+25 days 3 1 334 349 581 602 820 829

11 Sand Filling 10FS+21 days 3 1 358 373 605 626 844 853

12 Top Plugging 11, 1 1 373 380 620 627 851 854

13 Well Cap 10,12FF+3day 11 1 365 442 612 689 843 876

14 Casting of Pier 13 6 1 611 653 653 695 864 882

15 Casting of Pier Cap 14 9 1 620 693 693 756 870 897

Winch and Grab bucket arrangement is fixed for each well to be sunk, hence

well sinking is not considered as an activity, instead a finish to start

relationship between castings of lift with a buffer of 25 days has been used.

Due to limit on number of Winch and Grab bucket arrangement, seven wells

have been planned to be followed by seven wells and three wells. Table 4.10

gives the results of application of LOB technique. Cutting of steel is not

included as an activity since time required for the activity is very small and the

43

activity is not critical. The crew involved for cutting of steel will have a large

period of forced idleness. Production diagram of one unit is of substructure is

shown in Figure 4.2. Total duration of one well is 301 days. The details

obtained are used for Line of Balance calculations.

Objective Diagram for sub structure is shown in Figure 4.3. Total Duration for

Sub Structure Work is 897 days.

4.6.2 LOB diagram for Superstructure

As in substructure, in superstructure PSC box girder too revision is made to

activity details. Activity details in Table 4.11 have been revised from the

precedence Table 4.7 due to certain activity being necessarily required to

move at same pace. The nature of work of requires activity like concreting and

shuttering to progress at rates equal to each other as such these activity have

been replaced by one activity. These activities will have forced idle time for

crews since especially for concreting and reinforcement (placing of steel).

Dependencies of the activity have been revised keeping in view of reduction in

activity. Activities have been grouped such that duration of the activity taking

maximum time is treated as duration of the grouped activity. The nature of

work of requires activity like concreting and shuttering to progress at rates

equal to each other as such these activity have to be replaced by one activity.

These activities will have forced idle time for crews since especially for

concreting and reinforcement (placing of steel). Production diagram for one

unit of superstructure is shown in Figure 4.4. Total duration for one

superstructure span is 99 days. Four crews have been planned for casting of

box girders since four sets of shuttering forms are available.

Objective Diagram of the Superstructure (LOB chart) has been made such that

none of the activities cross each others path and have a balanced rate. Activity

44

Table 4.11 gives details of balance start and finish date for superstructure.

Objective diagram is shown in Figure 4.5.

Total Duration of Superstructure obtained is 478 day.

Table 4.11 Activity table superstructure

S No

Activity Duration Precedence Number Of Crews

Total Time Reqd.

Balance Start date

Balance Finish Date

1 Cutting of Steel 10 days 1 160 0 160

2 Casting of BOX GIRDER 55 days 3FF+4,1FF+10,4FF+38,5FF+38

4 220 36 324

3 Crushing of Chips 20 days 1 320 0 320

4 Cutting of Cables 8 days 1 128 0 128

5 Making of End Block 12 days 1 192 0 192

6 Forms in Place 78 days 2SS 4 312 36 348

7 Casting of Wearing Coat and Crash Barrier

10 days 6,10FF 1 160 188 358

8 Casting of Kerb and handrail

7 days 2 1 112 219 331

9 Site Clearance 1 day 10 1 16 462 478

10 Fixing of Expansion Joints and Drainage Sprouts

20 days 6 1 320 178 476

When the two LOB Diagrams are superimposed it can be seen that site is

required for superstructure on 36thth day from start of superstructure work

since shuttering activities start on 36th day (refer Table 4.11) while other

activities which can be executed else where can start by then. Work of last

three box girders is dependent on completion of last three wells. The

shuttering for last box girder shall finish by 348 days and hence will start on

270th day (refer Figure 4.4) after start of super structure work. To allow

uninterrupted progress of super structure work this can happen only after all

piers of substructure have been completed. This work is complete by 897 th day

(refer Figure 4.3). Superstructure Work can start 270 days before this on 627 th

day to allow for uninterrupted working in superstructure. In case the work is

started earlier there shall be a break in progress of superstructure work.

Total Project Duration is 627 + 476 = 1105 days

45

The duration is more than what obtained through precedence diagramming but

there is no over allocation of resources since production rate of resources is

balanced. Some operational problems are not ruled out since all activities

have not been included in unit plan. Activities having time or space

dependency will result in forced idleness for crew since such activities have

been included as a combined activity.

4.7 Scheduling Using Repetitive Scheduling Method

In RSM one resource is associated with one activity. Continuity in availability

of this resource in similar activity of subsequent unit is ensured. For purpose

implementing RSM a precedence diagram is first required. Each activity in this

precedence diagram is associated with one resource. Accordingly Activities

have been associated with resources. Same is shown in Table 4.12.

Table 4.12 Activities and Associated Resources

Activity Associated ResourceSinking of Well DD winch and Grab Bucket

arrangementConcreting of Lifts Shuttering crew and form work Shuttering of Wells Form work for WellConcreting Concreting EquipmentCrushing Crushing UnitSteel Cutting Steel CuttingPlacing of Steel(including fixing of Bearing and Placing of HT Strands)

Blacksmith and Welder

Shuttering of PSC Box girder Shuttering Crew and Formwork for Box Girder

Stressing JackGrouting Grouting PumpExpansion Joint and Drainage Sprouts Welding

4.7.1 RSM Diagram of Substructure

For drawing RSM diagram a single unit precedence diagram is required. This

diagram for typical substructure unit i.e. abutment/pier is same as that of

46

single unit precedence diagram for LOB. From Table 4.8 we know that seven

Winch and Grab bucket arrangement are available. In order to plan use of

seven available Winch and Grab bucket arrangements for 17 wells it is

obvious that Winch and Grab bucket arrangements have to be used twice or

thrice. Three Winch and Grab Bucket arrangements will be required to be

used thrice while remaining four will have to be used twice. In order to draw

RSM diagram first production lines for first unit are drawn. Production lines for

other units are similar. Activities in subsequent unit are pushed to new position

depending on the resource continuity by shifting the production lines on the

RSM graph.

Table 4.13 Activities in Substructure UnitS No. Activity Duration Predecessor

1 Making of Island Placing of Cutting Edge 16 days

2 Casting of well curb 5 days 1

3 Casting of 1st Lift 5 days 2FS+25 days

4 Casting of 2nd Lift 5 days 3FS+25 days

5 Casting of 3rd Lift 5 days 4FS+25 days

6 Casting of 4th Lift 5 days 5FS+25 days



9 Concreting 7th lift 5 days 8FS+25 days

10 Bottom Plugging 3 days 9FS+25 days

11 Sand Filling 3 days 10FS+21 days

12 Top Plugging 1 day 11

13 Well Cap 11 days 10,12FS+3 days

14 Casting of Pier 6 days 1315 Casting of Pier Cap 9 days 14

It is also known that two set of forms for well are available. Due to this it is

possible to divide the work in two parts. Accordingly for the purpose of drawing

RSM diagram the work is converted in to two parts: Three machines to be

used thrice for 9 wells and four machines to be used twice for 8 wells.

Continuos utilization of two shuttering crews is not enforced. Single Unit

Diagram for RSM has been drawn by precedence diagramming and is shown

47

as figure 4-6. RSM Diagram has been drawn accordingly and shown in Figure

4.7. 17th well and pier will be completed by 852nd days.

4.7.2 RSM DIAGRAM of Superstructure

Planning is done for four set of forms being used for four girders shuttering for

each girder is independent and hence not required to be considered for

resource continuity. Two construction joints are permissible after concreting of

soffit and web. Thus casting of soffit, web, and deck can be done in three

phases. For four span activities Concreting, Crushing and Shuttering each are

required for casting of soffit, web and deck. Steel Cutting and Placing is

required for deck and Soffit while auxiliary works are required only prior to

shuttering of deck. This allows for Soffit, Web and Deck to be taken as three

repetitive activities. The activity logic diagram is drawn as Figure 4.8 shows

that treating the three parts of deck separately as a typical repetitive unit is

possible.

4.7.2.1 Activities for Box Girder

Figure 4.8 shows that the casting of PSC box girder can be restructured in

three parts with similar activities and relationship namely Soffit, Web and

Deck. Each PSC box girder can be understood to consist of three similar

repetitive units, each typical unit comprising of shuttering, crushing of chips,

and concreting with other activities not repeating either in deck unit or soffit

units. This means that the superstructure work can be said to comprise of 48

units (each of the 16 box girders replaced by three units). Work for four spans

can be started simultaneously due to availability of four sets of forms (refer

Table 4.8). Scheduling for following four spans will be done when forms are

available for reuse after stressing is completed.

Shuttering activity is associated with two resources. To cater for underlying

assumption that one resource is required for each activity, activity of shuttering

has been replaced in two activities shuttering and formwork in place.

48

Auxiliary Works and Levelling

Shuttering

Placing of steel

Concreting

Crushing of Chips

Shuttering

Concreting

Crushing of Chips

Shuttering

Placing of steel

Concreting

Crushing of Chips

Finishing Activities

SOFFIT WEB DECK

Formwork in place will have a start to start relationship with shuttering and

finish to finish relationship with concreting since forms will be required till

concreting is complete. Shuttering activity for web requires 7 days after casting

of concrete for soffit. In RSM activities in subsequent unit are connected by

resources. In order to ensure shuttering is not commenced till concreting of

soffit is done the activity formwork in place, included with resource being

forms, has start to start relationship with shuttering which has shuttering crew

as its resource. Continuity of shuttering is not enforced. Similar situation occur

in shuttering of deck before concreting of web hence the activity formwork in

place has been introduced in deck also. Shuttering activity will for the duration

of concreting accordingly continuity of shuttering has not been enforced for

planning.

Figure 4.8 Activity Logic Diagram

4.7.2.2 Activities in Soffit

49

The Table 4.14 tabulates the activities for soffit and Figure 4.9 shows the

precedence diagram for them.

Table 4.14 Activities in Soffit

S. No Activity Duration Precedence

1 Levelling of Ground 1 day

2 Shuttering for Soffit 13 days 1

3 Formwork in place for soffit 23 days 2SS,8FF

4 fabrication of End block 12 days

5 Crushing of Chips 6 days

6 Cutting of Steel 7 days

7 Placing of Steel 7 days 6,2,4

8 Concreting of Soffit 3 days 7,5,2

Figure 4.9 Precedence diagram for Soffit

4.7.2.3 Activities in WebThe Table 4.15 tabulates the activities for web and Figure 4.10 shows the


50

Table 4.15 Activities in WebS. No Activity Duration Precedence1 Shuttering for Web 10 days

2 Formwork in place for Web 13 days 1SS,4FF

3 Crushing of Chips for web 6 days

4 Concreting of Web 3 days 1,3

Figure 4.10 Activities in Web

4.7.2.4 Activities in DeckThe Table 4.16 tabulates the activities for deck and Figure 4.11 shows the


Table 4.16 Activities in DeckS. No. Activity Duration Precedence

1 Cutting of Steel 3 days

2 Crushing of Chips 8 days

3 Placing of Steel 7 days 1

4 Formwork in place for Deck 17 days 5SS,6FF

5 Shuttering 7 days

6 Concreting 3 days 3,5

7 Kerb and hand rail 4 days 6

8 Stressing 3 days 6FS+21 days

9 Grouting 1 day 8FS+7 days

10 Wearing Coat and Crash Barrier 7 days 8

11 Expansion Joint and Drainage Sprout 20 days 10

51

Figure 4.11 Activities in Deck

RSM graph drawn for the superstructure is shown as Figure 4.12. From the

figure we can see that use of shuttering forms starts from 14 th day and

stressing for first span is complete by 115th day. After stressing is completed

shuttering can be reused, so one set forms can be reused after 102 days. Four

spans are complete in 187 days. For the super structure to complete total 494

days are required which is less than that obtained by LOB technique.

Start of superstructure work is dependent on completion of substructure work.

The substructure work will complete on 852nd day. Start of Shuttering for last of

the girders is planned from 337th day while for the first has been planned 14th

day from the start of shuttering work. From above it is clear that the

superstructure work should be so planned that shuttering of last girder may

start by 852nd day.

Thus total time required for bridge will be 852 – 337 + 494 = 1009 days.

While this duration is more than that of PM but there is no resource

constraint/conflict in the project unlike PM where resource utilization after

levelling is more than available resources.

52

4.8 Results and Discussion

4.8.1 Duration

Project duration obtained with the use of different methodologies is given in

the Table 4.17. It can be seen that duration obtained is least from precedence

diagramming. Time obtained with the use of RSM is greater than PM but less

than LOB.

Table 4.17: Project Duration from different techniquesMethod Total Time

ObtainedResource Constraint Remarks

PM 814.5 Over allocation not resolved

Additional time will be required to resolve over allocation

LOB 1105 No over allocation Maximum Time

RSM 1009 No over allocation All activities could not be considered

4.8.2 Information available

Soffit, Web, and Deck parts of superstructure are not same. Considering

similarity in activities (shuttering, formwork in place, concreting and crushing of

chips being part of each) these are used as repetitive units since in RSM there

is no requirement of all units to be same. Use of this repetitive pattern for

scheduling allows for continuity in use of different activities.

Graphical information is available in form of charts in LOB and RSM

techniques. From the graph the schedule start or finish date for an activity can

be read quickly. Precedence diagram could not be plotted in the same size of

paper to provide any worthwhile information.

On drawing RSM Graph as shown in Figure 4.12, it can be seen that two

shuttering crew can be used for shuttering of four spans using four sets of

forms. This information was not available from PM or LOB. Availability of

shuttering forms for reuse can also be seen from the graph.

53

Use of repetitive patterns as units allows planning for continuous use of

machines. This makes RSM more supportive to mechanization, since

advantages of mechanization can be achieved with continuous repeated

utilization of resource/ machine.

4.8.3 Critical Path

Critical Path is defined by the activities having no float. Complicated

dependencies in precedence diagram lead to large amount of float in various

activities, if all the activities are scheduled at early start. This means that a

large number of activities will be started but complete over a long time

resulting in confusion in monitoring progress. LOB technique does not show

any critical path. RSM has a concept of controlling sequence. The activities on

controlling path are to be monitored to avoid delay in the project. These

activities may or may not be critical as per precedence diagram. This indicates

which activities should be monitored to avoid delay on the project.

54

Chapter 5

Conclusion

The present investigations was undertaken to provide an elaborate study of

Repetitive Scheduling Method applied to a multispan bridge. This study also

entails a study of Precedence Diagramming and Line of Balance methods and

comparison of these methods with Repetitive Scheduling Method. The

following conclusions are drawn from the present study:-

1) Repetitive scheduling takes care of continuous utilization of resources

as compared to precedence diagramming. Repetitive Scheduling can

be implemented to take care of maximum resource availability. This is

not possible for both Line of Balance Technique and Precedence

Diagramming. The maximum availability of resources is often fixed for a

project. The advantage offered by repetitive scheduling method by

considering reuse of resources takes care of maximum availability

constraint in project scheduling makes it a candidate for use in case of

linear and repetitive projects where same resource has to be used

repetitively. The inability of Network techniques to address resource

constraints is especially obvious in repetitive projects. The reason for

this is that initial scheduling for all the activities have been made with

out resource consideration. Resource availability is considered to

readjust the activities.

2) RSM allows only one resource per activity. This is an impractical

assumption since in real life there will be more then one resource

associated with each activity. Precedence diagram of single unit drawn

for PM cannot be used for LOB and RSM. Reworking by taking care of

different constraints and reducing number of activities is required for

generating single unit precedence diagram bar chart. Lesser details are

included in Line of Balance technique. Precedence Diagramming allows

55

for maximum details to be incorporated. Details included in RSM are

less than PM but more than LOB.

3) Critical path allows managers information about where to concentrate.

Line of balance method does not have a critical path. This shortcoming

is adequately dealt by RSM. Controlling path of RSM can have activities

which not critical as per critical path network scheduling methods. This

is due to resource constraints.

4) More mechanization is possible if more work is done by repeated use of

similar unit i.e. repetitive work. Scheduling Technique which considers

necessity of continuous utilization of the resources is required in greater

number of projects as the complexity of project increases., in order to

achieve advantages of mechanisation. RSM has the potential to

address this problem which is not adequately done by network

diagramming.

5) RSM algorithm is complicated then both LOB and CPM however the

advantages in use of RSM make it a practical method which can be

utilized extensively. More information can be obtained from the RSM

graph, as compared to the network diagram or LOB chart.

56

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Documents

1 -Thesis Final Sep4