1 EASTERN MEDITERRANEAN UNIVERSITY FACULTY OF ENGINEERING DEPARTMENT OF CIVIL ENGINEERING CIVL 493 Construction Management Assoc. Prof. Dr. Ibrahim YITMEN Project Scheduling

2 Introduction to Scheduling Why We Need a Schedule: Why We Need a Schedule: Contractual obligation Contractual obligation To establish a sequence of work and timeframe for performance of construction activities To establish a sequence of work and timeframe for performance of construction activities To provide a communication tool between contractors, owner, A/E, subs, and suppliers To provide a communication tool between contractors, owner, A/E, subs, and suppliers To document modifications (“as-planned” versus “as-built”) To document modifications (“as-planned” versus “as-built”) To show the impact of productivity-related problems on project completion (weather, strikes, delays) To show the impact of productivity-related problems on project completion (weather, strikes, delays) Determine when to order and deliver materials and equipment Determine when to order and deliver materials and equipment

3 Types of Schedules Bar Chart Bar Chart Often called Gantt Chart Often called Gantt Chart Network Diagrams Network Diagrams Arrow Diagram Arrow Diagram Precedence Diagram Precedence Diagram Often called Critical Path Method (CPM) Often called Critical Path Method (CPM)

4 Formats of Schedules Summary schedule Summary schedule Shows major work elements, such as sitework, masonry, carpentry, electrical, plumbing, etc. Shows major work elements, such as sitework, masonry, carpentry, electrical, plumbing, etc. Detailed schedule Detailed schedule Work should be broken down into activities that comprise not more than 5% of total project Work should be broken down into activities that comprise not more than 5% of total project Short-interval schedule Short-interval schedule Identifies work for upcoming 2-3 weeks Identifies work for upcoming 2-3 weeks Usually prepared by superintendent Usually prepared by superintendent

5 Bar Chart Developed by Henry Gantt Developed by Henry Gantt Often called a Gantt Chart Often called a Gantt Chart Definition Definition A graphical description of a project consisting of well-defined collection of tasks A graphical description of a project consisting of well-defined collection of tasks

6 Activities are represented by bars in proportion to their duration Activities are represented by bars in proportion to their duration An activity is a task or closely related group of tasks whose performance contributes to the completion of the overall project An activity is a task or closely related group of tasks whose performance contributes to the completion of the overall project Example: Excavate foundation Example: Excavate foundation Activities are represented by bars in proportion to their duration Activities are represented by bars in proportion to their duration Bar chart is usually graphed on a calendar Bar chart is usually graphed on a calendar Can be as simple or detailed as necessary Can be as simple or detailed as necessary Bar Chart

7 Example Bar Chart JuneJulyAugustSeptemberOctober Excavation & Backfill Pilling Abutment No.1 Abutment No.2 Steel girders Concrete deck Finishing operations Time

8 Constructing a Bar Chart When constructing a bar chart, the following questions must be answered: When constructing a bar chart, the following questions must be answered: What time units should be used? (days, weeks, months) What time units should be used? (days, weeks, months) Should work days or calendar days be used? Should work days or calendar days be used? How do I schedule non-continuous work? How do I schedule non-continuous work? Additional information may be added to the basic bar chart Additional information may be added to the basic bar chart Cost of activity (“cost-loaded schedule”) Cost of activity (“cost-loaded schedule”) Labor required for each activity (“man-loaded”) Labor required for each activity (“man-loaded”) Materials required for each activity (“resource- loaded”) Materials required for each activity (“resource- loaded”)

9 Steps to Construct a Bar Chart Three basic steps to construct a bar chart: Three basic steps to construct a bar chart: 1. Break the job down into activities 2. Establish the sequence of work 3. Estimate activity duration

10 1. Break the Job Down Into Activities Use the Work Breakdown Structure (WBS) from the cost estimate Use the Work Breakdown Structure (WBS) from the cost estimate Add activities as necessary Add activities as necessary Rule of thumb: no activity should comprise more the 5% of the total scope of work Rule of thumb: no activity should comprise more the 5% of the total scope of work Rule of thumb: activity duration should range from 1 day to 15 days Rule of thumb: activity duration should range from 1 day to 15 days

11 Sequencing needs to take into account the relationships between activities Sequencing needs to take into account the relationships between activities There are four types of relationships that need to be taken into account. There are four types of relationships that need to be taken into account. 1. Physical: Exists between two or more activities when one cannot start until another is partially or totally complete (i.e., cannot pour footings until they have been formed) Exists between two or more activities when one cannot start until another is partially or totally complete (i.e., cannot pour footings until they have been formed) 2. Establish the Sequence Of Work

12 2. Safety: Exists when simultaneous performance of two activities can result in a safety hazard (i.e., in multi-story construction it is at times unsafe for crews to be working under one another) Exists when simultaneous performance of two activities can result in a safety hazard (i.e., in multi-story construction it is at times unsafe for crews to be working under one another) 3. Resource: Due to limited resource availability, two activities may not be able to use a resource at the same time (i.e., a crane cannot be used for both pouring walls and erecting steel) Due to limited resource availability, two activities may not be able to use a resource at the same time (i.e., a crane cannot be used for both pouring walls and erecting steel) 4. Preferential: How the contractor wishes certain activities to be sequenced How the contractor wishes certain activities to be sequenced 2. Establish the Sequence Of Work (continued)

13 3. Estimate Activity Duration How to estimate duration: How to estimate duration: From company’s historic records From company’s historic records From asking superintendent or foreman From asking superintendent or foreman From standard estimating guide From standard estimating guide From calculation using the Labor Hour Productivity equation From calculation using the Labor Hour Productivity equation

14 Labor-Hour Productivity Method Labor-Hour Productivity Method Total labor-hours required for an activity = Total labor-hours required for an activity = labor-hours /Unit x no. of units Total days = total labor hours labor-hours / day total labor hours crew size x hrs/day 3. Estimate Activity Duration (continued)

15 Using a Bar Chart for Planning and Progress Assume the progress of the activity as a direct linear function of the elapsed time Assume the progress of the activity as a direct linear function of the elapsed time Example: Example:

16 Bar Chart Progress Schedule Bar chart progress schedule should satisfy the following minimum requirements: Bar chart progress schedule should satisfy the following minimum requirements: Include activities that describe essential features of the work. Include activities that describe essential features of the work. Include start, duration, and completion date for each activity. Include start, duration, and completion date for each activity. Include quantity and the estimated daily production rate for controlling items of work. Include quantity and the estimated daily production rate for controlling items of work.

17 Definition Definition A network consists of two basic elements, nodes and links between these nodes A network consists of two basic elements, nodes and links between these nodes Activities on arrows (arrow diagram) Activities on arrows (arrow diagram) Activities are represented by two nodes and one link Activities are represented by two nodes and one link Activities on nodes (precedence diagram) Activities on nodes (precedence diagram) Activities represented by nodes and links represent the relationship Activities represented by nodes and links represent the relationship Network Diagrams

18 Clear and grub Cut and fill Arrow Diagram Excavate and form culvert Place base Construct culvert Pave Excavate and form culvert Pave Construct culvert Place base Cut and fill Clear & grub Precedence Diagram

19 Example: Retaining Wall Precedence Diagram Wall 1 Wall 2 Footing 1 Footing 2

20 Basic Rules of Network Logic (Precedence Diagram) Rule 1: Eliminate redundant linkages Rule 1: Eliminate redundant linkages

21 Rule 2: Close the network to give single beginning and ending nodes Rule 2: Close the network to give single beginning and ending nodes Networks may have only one initial event (with no predecessor) and only one terminal event (with no successor). Networks may have only one initial event (with no predecessor) and only one terminal event (with no successor). Basic Rules of Network Logic A B D C E Initial Event Correct Representation Terminal Event

22 Rule 3: Before an activity may begin, all activities preceding it must be completed (activities with no predecessors are self- actuating when the project begins). Rule 3: Before an activity may begin, all activities preceding it must be completed (activities with no predecessors are self- actuating when the project begins). Rule 4: All relationships are assumed to be finish to start. Rule 4: All relationships are assumed to be finish to start. Rule 5: Event numbers must not be duplicated in a network. Rule 5: Event numbers must not be duplicated in a network. Rule 6: No two events may be directly connected by more than one arrow. Rule 6: No two events may be directly connected by more than one arrow. Basic Rules of Network Logic

23 a) Finish-to-start relationship a) Finish-to-start relationship (Start of B must lag 5 days after the finish of A) b) Start-to-start relationship b) Start-to-start relationship (Start of B must lag 3 days after the start of A) Activities Relationships A B L = 5 or FS =5 A B L = 3 or SS =3

24 Activities Relationships c) Finish-to-finish relationship c) Finish-to-finish relationship (Finish of B must lag 3 days after the finish of A) d) Start-to-finish relationship d) Start-to-finish relationship (Finish of B must lag 45 days after start of A) A B L = 3 or FF =3 A B L = 45 or SF = 45

25 Sequencing and Numbering

26 Constructing a Precedence Diagram 1. Create activity list and eliminate redundancies 2. Construct precedence diagram 3. Arrange activities in a sequential order.

27 Time Values Associated With Each Activity 1. ESD  Early Start Date 2. EFD  Early Finish Date 3. LSD  Late Start Date 4. LFD  Late Finish Date

28 Scheduling Computations (Forward Pass Rules) Rule 1:The initial project event is assumed to occur at time zero. Rule 2:All activities are assumed to start as soon as possible, that is, as soon as all the predecessor activities are completed. Rule 3:The early finish time of an activity is merely the sum of its early start date and the estimated activity duration. EFD I = ESD I + T I Four rules of completing a Forward Pass: Four rules of completing a Forward Pass:

29 Scheduling Computations (Forward Pass Rules) – cont. Rule 4:At merge points, the early start is the largest value of the preceding early finish time. 2 EFD=6 4 EFD=9 6 Forward

30 Scheduling Computations (Backward Pass Rules) Rule 1:The late finish date of the last activity is equal to its early finish date. Rule 2:The late start date for any activity is found by subtracting the activity duration from its late finish date. LSD I = LFD I - T I Three rules of completing a Backward Pass: Three rules of completing a Backward Pass:

31 Scheduling Computations (Backward Pass Rules) – cont. Rule 3:In the backward pass, the late finish date of an activity is the smallest late start value of the following activities. 12 LSD=37 14 LSD=42 10 LFD=37 Backward

32 The Float Concept What is “float”? What is “float”? Float or slack is the amount of scheduling leeway that a network activity has Float or slack is the amount of scheduling leeway that a network activity has What is “total float”? What is “total float”? That time span in which the completion of an activity may occur and not delay the completion of the project That time span in which the completion of an activity may occur and not delay the completion of the project Equation for total float (TF): Equation for total float (TF): TF I = LFD I - EFD I = LSD I - ESD I = LSD I - ESD I

33 What is “free float”? What is “free float”? The time span in which the completion of an activity may occur and not delay the finish of the project or delay the start of any following activity The time span in which the completion of an activity may occur and not delay the finish of the project or delay the start of any following activity What is a link lag? What is a link lag? The difference between the early start date of an activity and the early finish date of the preceding activity The difference between the early start date of an activity and the early finish date of the preceding activity The Float Concept (cont.) Lag ij = ESD j - EFD i

34 How to determine free float: How to determine free float: Free float is the minimum value of the link lags of the link that follows an activity. Free float is the minimum value of the link lags of the link that follows an activity. FF 20 = Min = Min = Min = 1 = 1 Float Float { } {} The Float Concept (cont.)

35 Critical Path Example