Construction Planning and scheduling Lecture notes

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LECTURE NOTES ON CONSTRUCTION PLANNING AND SCHEDULING Emad Elbeltagi, Ph.D., P.Eng., Professor of Construction Management Structural Engineering Department, Faculty of Engineering, Mansoura UniversityConstruction Project Management 2012 Copyright © 2012 by the author. All rights reserved. No part of this book may be reproduced or distributed in any form or by any means, or stored in a data base or retrieval system, without the prior written permissions of the author.PREFACE In the Name of ALLAH the Most Merciful, the Most Compassionate All praise is due to ALLAH and blessings and peace be upon His messenger and servant, Muhammad, and upon his family and companions and whoever follows his guidance until the Day of Resurrection. Construction project management is a relatively young field. However, its impact has been quite remarkable. It has become an important practice for improving the efficiency of construction operations around the world. This book deals with some topics and tools of the large field of project management. This book is dedicated mainly to undergraduate engineering students, especially Civil Engineering students where most of the applications are presented in the civil engineering field. It provides the reader with the main knowledge to manage a construction project from preliminary stages to handover. It includes seven chapters: Chapter 1 provides the planning stages of a construction project. Chapter 2 is dedicated for presenting different scheduling techniques along with the schedule representation. Chapter 3 is dedicated to discuss the scheduling methods on non-deterministic activity durations. Chapter 4 is dealing with both the resource scheduling and smoothing problems. The schedule compression is, also, presented in chapter 5. Chapter 6 is dedicated for the project finance and cash flow analysis. Finally, chapter 7 is dedicated for project control. Many solved examples have been added to enable the students to understand the material presented in this book. Also, each chapter is followed by exercises for training purposes. Finally, May ALLAH accepts this humble work and I hope it will be beneficial to its readers. iTABLE OF CONTENTS CHAPTER 1: PROJECT PLANNING 1.1 Introduction 1 1.2 Project Planning Steps 2 1.2.1 Work Breakdown Structure (W BS) 3 1.2.2 Project Activities 7 1.2.3 Activities Relationships 11 1.2.4 Drawing Project Network 17 1.3 Estimating Activity Duration and Direct Cost 24 1.4 Exercises 27 CHAPTER 2: PROJECT SCHEDULING 2.1 The Critical Path Method 34 2.2 Calculations for the Critical Path Method 35 2.2.1 Activity-On-Arrow Networks Calculations 35 2.2.2 Precedence Diagram Method (P DM) 42 2.3 Time-Scaled Diagrams 45 2.4 Schedule Presentation 47 2.5 Criticisms to Network Techniques 48 2.6 Solved Examples 49 2.6.1 Example 1 49 2.6.2 Example 2 50 2.6.3 Example 3 51 2.6.4 Example 4 52 2.7 Exercises 53 iiCHAPTER 3: STOCHASTIC SCHEDULING 3.1 Scheduling with Uncertain Durations 59 3.1.1 Program Evaluation and Review Technique 61 3.1.2 Criticism to Program Evaluation and Review Technique 68 3.3 Exercises 69 CHAPTER 4: RESOURCES MANAGEMENT 4.1 Resource Definition 72 4.2 Resource Management 73 4.3 Resource Allocation 75 4.4 Resource Aggregation (L oading) 75 4.5 Resource Leveling (S moothing) 77 4.5.1 Method of Moments for Resource Smoothing 78 4.5.2 Heuristic Procedure for Resource Smoothing 79 4.6 Scheduling with Limited Resource 88 4.7 Case Study 90 4.8 Exercises 97 CHAPTER 5: PROJECT TIME-COST TRADE-OFF 5.1 Time-Cost Trade-Off 100 5.2 Activity Time-Cost Relationship 101 5.3 Project Time-Cost Relationship 105 5.4 Shortening Project Duration 106 5.5 Exercises 116 iiiCHAPTER 6: PROJECT CASH FLOW 6.1 Contract Cash Flow 118 6.1.1 Construction Project Costs 119 6.1.2 The S-Curve 122 6.1.3 Project Income (C ash-in) 124 6.1.4 Calculating Contract Cash Flow 126 6.1.5 Minimizing Contractor Negative Cash Flow 131 6.1.6 Cost of Borrowing (R eturn on Investment) 133 6.2 Project Cash Flow 138 6.2.1 Project Profitability Indicators 139 6.3 Discounted Cash Flow 141 6.3.1 Present Value 141 6.3.2 Net Present Value (NPV) 142 6.3.3 Internal Rate of Return (IRR) 143 6.4 Exercises 144 CHAPTER 7: PROJECT CONTROL 7.1 Problems that may Arise During Construction 148 7.2 Schedule Updating 149 7.3 Earned Value Management 153 7.4 Exercises 157 REFERENCES 159 ivCHAPTER 1 PROJECT PLANNING This chapter deals with preparing projects plans in terms of defining: work breakdown structure, activities, logical relations, durations and activities direct cost. Terminology of project planning will be presented and discussed. Project network representation using different graphical methods including: activity on arrow and activity on node are presented. 1.1 Introduction Planning is a general term that sets a clear road map that should be followed to reach a destination. The term, therefore, has been used at different levels to mean different things. Planning involves the breakdown of the project into definable, measurable, and identifiable tasks/activities, and then establishes the logical interdependences among them. Generally, planning answers three main questions: What is to be done? How to do it? Who does it? In construction, for example, plans may exist at several levels: corporate strategic plans, pre-tender plans, pre-contract plans, short-term construction plans, and long-term construction plans. These plans are different from each other; however, all these plans involve four main steps: Planning & Scheduling 1 Dr. Emad Elbeltagi- Performing breakdown of work items involved in the project into activities. - Identifying the proper sequence by which the activities should be executed. - Activities representation. - Estimating the resources, time, and cost of individual activities. Detailed planning for tendering purposes and the preparation of construction needs to be conducted through brainstorming sessions among the planning team. The inputs and outputs of the planning process are shown in Figure 1.1. Contract information Activities Drawings Relationships among activities Specifications Method statement Available resources Responsibility PLANNING Bills of quantities Reporting levels Site reports Project network diagram Organizational data Activities duration Construction methods Activities cost Figure 1.1: Planning inputs and outputs Planning requires a rigorous effort by the planning team. A planner should know the different categories of work and be familiar with the terminology and knowledge used in general practice. Also, the planning tem should seek the opinion of experts including actual construction experience. This helps produce a realistic plan and avoids problems later on site. 1.2 Project Planning Steps The following steps may be used as a guideline, or checklist to develop a project plan: 1. Define the scope of work, method statement, and sequence of work. 2. Generate the work breakdown structure ( W BS) to produce a complete list of activities. 3. Develop the organization breakdown structure (O BS) and link it with work breakdown structure o identify responsibilities. Planning & Scheduling 2 Dr. Emad Elbeltagi INPUTS OUTPUTS4. Determine the relationship between activities. 5. Estimate activities time duration, cost expenditure, and resource requirement. 6. Develop the project network. 1.2.1 Work Breakdown Structure (WB S) The WBS is described as a hierarchical structure which is designed to logically sub- divide all the work-elements of the project into a graphical presentation. The full scope of work for the project is placed at the top of the diagram, and then sub-divided smaller elements of work at each lower level of the breakdown. At the lowest level of the WBS the elements of work is called a work package. A list of projects cativities is developed from the work packages. Effective use of the WBS will outline the scope of the project and the responsibility for each work package. There is not necessarily a right or wrong structure because what may be an excellent fit for one discipline may be an awkward burden for another. To visualize the WBS, consider Figure 1.2 which shows a house construction project. House Civil Plumping Electrical Foundations Walls/Roof Piping H/C Water Wiring Fittings Figure 1.2: WBS and their description As shown in Figure 1.2, level 1 represents the full scope of work for the house. In level 2, the project is sub-divided into its three main trades, and in level 3 each trade is sub- divided to specific work packages. Figure 1.3 shows another example for more detailed WBS, in which the project WBS is divided into five levels: Planning & Scheduling 3 Dr. Emad ElbeltagiLevel 1 Gas development project Level 2 Recovery unit 300 Process unit 400 Train 2 Train 1 Gas treating Separation and stabilization Level 3 Instrumentation Structural steel Civil Piping Level 4 Piping Level 5 fabrication Figure 1.3: Five levels WBS Level 1: The entire project. Level 2: Independent areas. Level 3: Physically identifiable sections fully contained in a level 2 area, reflect construction strategy. Level 4: Disciplines set up schedule. Level 5: Master schedule activities, quantity, duration. Example 1.1: The WBS for a warehouse is as follow: For more details, another two levels ( t hird and fourth levels) can be added as shown below: Planning & Scheduling 4 Dr. Emad ElbeltagiAccordingly, a complete WBS for the warehouse project can be shown as follow (F igure 1.4): Figure 1.4: Warehouse project WBS Planning & Scheduling 5 Dr. Emad ElbeltagiWBS and organizational breakdown structure (O BS) The WBS elements at various levels can be related to the contractors organizational breakdown structure ( O BS), which defines the different responsibility levels and their appropriate reporting needs as shown in Figure 1.5. The figure, also, shows that work packages are tied to the company unified code of accounts. The unified code of accounts allows cataloging, sorting, and summarizing of all information. As such, the activity of installing columns formwork of area 2, for example, which is the responsibility of the general contractors formwork foreman, has a unique code that represents all its data. WBS coding A project code system provides the framework for project planning and control in which each work package in a WBS is given a unique code that is used in project planning and control. The coding system provides a comprehensive checklist of all items of work that can be found in a specific type of construction. Also, it provides uniformity, transfer & comparison of information among projects. An example of this coding system is the MasterFormat ( F igure 1.6) which was developed through a joint effort of 8 industry & professional associations including: Construction Specifications Institute (C SI); and Construction Specifications Canada (C SC) . Figure 1.7 shows an example of the coding system using a standardize system as the MasterFormat. The Master format is divided into 16 divisions as follows: 1) General Requirements. 2) Site work. 3) Concrete. 4) Masonry. 5) Metals. 6) Woods & Plastics. 7) Thermal & Moisture Protection. 8) Doors & Windows. 9) Finishes. Planning & Scheduling 6 Dr. Emad Elbeltagi10) Specialties. 11) Equipment 12) Furnishings. 13) Special Construction. 14) Conveying Systems. 15) Mechanical. 16) Electrical. WBS ( Work elements) Project && Area 1 Area 2 Area 3 && Columns Slabs Beams Reinforcement Formwork Concreting && Control account Figure 1.5: WBS linked to the OBS 1.2.2 Project Activities The building block ( t he smallest unit) of a WBS is the activity, which is a unique unit of the project that has a specified duration. An activity is defined as any function or decision in the project that: consumes time, resources, and cost. Activities are classified to three types: Planning & Scheduling 7 Dr. Emad Elbeltagi OBS (Responsibility & reporting) Project manager Subcontractor General Subcontractor A contractor B Civil Electrical Mechanical superintendent superintendent superintendent Rebar Formwork Concrete foreman foreman foremanFigure 1.6: MasterFormat coding system Planning & Scheduling 8 Dr. Emad ElbeltagiProduction activities: activities that involve the use of resources such as labor, equipment, material, or subcontractor. This type of activities can be easily identified by reading the projects drawings and specifications. Examples are: excavation, formwork, reinforcement, concreting, etc. each production activity can have a certain quantity of work, resource needs, costs, and duration. Procurement activities: activities that specify the time for procuring materials or equipment that are needed for a production activity. Examples are: brick procurement, boiler manufacturing and delivery, etc. Management activities: activities that are related to management decisions such as approvals, vacations, etc. An activity can be as small as steel fixing offirst floor columns or as large as construct first floor columns. This level of details depends on the purpose of preparing the project plan. In the pre construction stages, less detailed activities can be utilized, however, in the construction stages, detailed activities are required. Accordingly, level of details depends on: planning stage, size of the project, complexity of the work, management expertise. Figure 1.7: An example of an activity coding system Planning & Scheduling 9 Dr. Emad ElbeltagiExample 1.2: Figure 1.8 shows a double-span bridge. Break the construction works of the bridge into activities. The plan will be used for bidding purposes. Hand rail Road base right Road base left Deck slab Precast beams Figure 1.8: Double span bridge A list of the double-span bridge activities is shown in Table 1.1 Table 1.1: Activities of the double-span bridge Activity Description 10 Set-up site 14 Procure reinforcement 16 Procure precast beams 20 Excavate left abutment 30 Excavate right abutment 40 Excavate central pier 50 Foundation left abutment 60 Foundation right abutment 70 Foundation central pier 80 Construct left abutment 90 Construct right abutment 100 Construct central pier 110 Erect left precast beams 120 Erect right precast beams 140 Fill left embankment 150 Fill right embankment 155 Construct deck slab 160 Left road base 170 Right road base 180 Road surface 190 Bridge railing 200 Clear site Planning & Scheduling 10 Dr. Emad Elbeltagi1.2.3 Activities Relationships In order to identify the relationships among activities, the planning team needs to answer the following questions for each activity in the project: - Which activities must be finished before the current one can start? - What activity( i es) m ay be constructed concurrently with the current one? - What activity( i es) m ust follow the current one? A circle of activity precedence will result in an impossible plan. For example, if activity A precedes activity B, activity B precedes activity C, and activity C precedes activity A, then the project can never be started or completed. Figure 1.9 illustrates the resulting activity network. Figure 1.9: Example of a circle of activity precedence Example 1.3: Suppose that a site preparation and concrete slab foundation construction project consists of nine different activities: A. Site clearing (of brush and minor debris), B. Removal of trees, C. General excavation, D. Grading general area, E. Excavation for utility trenches, F. Placing formwork and reinforcement for concrete, G. Installing sewer lines, H. Installing other utilities, I. Pouring concrete. Planning & Scheduling 11 Dr. Emad ElbeltagiActivities A ( si te clearing) and B ( t ree removal) do not have preceding activities since they depend on none of the other activities. We assume that activities C ( g eneral excavation) and D ( g eneral grading) are preceded by activity A (si te clearing). It might also be the case that the planner wished to delay any excavation until trees were removed, so that B (t ree removal) would be a precedent activity to C (g eneral excavation) and D ( ge neral grading). Activities E (t rench excavation) and F ( concrete preparation) cannot begin until the completion of general excavation and grading, since they involve subsequent excavation and trench preparation. Activities G (i nstall lines) and H (i nstall utilities) represent installation in the utility trenches and cannot be attempted until the trenches are prepared, so that activity E (t rench excavation) is a preceding activity. We also assume that the utilities should not be installed until grading is completed to avoid equipment conflicts, so activity D ( general grading) is also preceding activities G ( i nstall sewers) and H ( i nstall utilities). Finally, activity I (pour concrete) cannot begin until the sewer line is installed and formwork and reinforcement are ready, so activities F and G are preceding. Other utilities may be routed over the slab foundation, so activity H (i nstall utilities) is not necessarily a preceding activity for activity I (pour concrete). The result of our planning is the immediate precedence shown in Table 1.2. Table 1.2: Precedence relations for Example 1.3 Activity Description Predecessors A Site clearing - B Removal of trees - C General excavation A D Grading general area A E Excavation for utility trenches B,C F Placing formwork and reinforcement for concrete B,C G Installing sewer lines D,E H Installing other utilities D,E I Pouring concrete F,G Planning & Scheduling 12 Dr. Emad ElbeltagiExample 1.4: Determine the relationships between activities of the project studied in Example 1.2. Table 1.3: Solution of Example 1.4 Activity Description Predecessors 10 Set-up site - 14 Procure RFT - 16 Procure P.C. Beams - 20 Excavate left abutment 10 30 Excavate right abutment 10 40 Excavate central pier 10 50 Foundation left abutment 14, 20 60 Foundation right abutment 14, 30 70 Foundation central pier 14, 40 80 Construct left abutment 50 90 Construct right abutment 60 100 Construct central pier 70 110 Erect left P.C. Beams 16, 80, 100 120 Erect right P.C. Beams 16, 90, 100 140 Fill left embankment 80 150 Fill right embankment 90 155 Construct deck slab 110, 120 160 Left road base 140 170 Right road base 150 180 Road surface 155, 160, 170 190 Bridge railing 155 200 Clear site 180, 190 Logical relationship considering resource constraints For efficient use of resources or in case of constrained resources, it might be beneficial to consider the resources when determining the logical relationship among the activities that use the same resources. For example, consider the case of construction a simple project consists of three units and each unit has three sequential activities ( l ogical relationship). Planning & Scheduling 13 Dr. Emad ElbeltagiTable 1.4 shows the logical relationship among these activities assuming unconstrained ( r esources are available with any quantities) and constrained resources (o nly one resource unit is available from each resource type). Table 1.4: Logical relationships considering constrained and unconstrained resources Predecessors Predecessors Activity description (unc onstrained resources) (c onstrained resources) A1 Excavate unit 1 - - B1 Concreting unit 1 A1 A1 C1 Brickwork unit 1 B1 B1 A2 Excavate unit 2 - A1 B2 Concreting unit 2 A2 B1, A2 C2 Brickwork unit 2 B2 C1, B2 A3 Excavate unit 3 - A2 B3 Concreting unit 3 A3 B2, A3 C3 Brickwork unit 3 B3 C2, B3 Overlap or lag Overlap between activities (ne gative lag) is defined as how much a particular activity must be completed before a succeeding activity may start. The absence of overlap means that the first activity must finish before the second may start. A negative overlap ( l ag) means a delay is required between the two activities (Figure 1.10) -ve overlap (+ ve lag) +ve overlap (- ve lag) Figure 1.10: Overlap among activities Planning & Scheduling 14 Dr. Emad Elbeltagi

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