CE 54100 Lecture _3 Construction Management - Planning & Scheduling_1

8/3/2019 CE 54100 Lecture _3 Construction Management - Planning & Scheduling_1

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THE CITY COLLEGE OF NEW YORK

CE 54100: HIGHWAY AND AIRPORT CONSTRUCTION

CLASS NOTES

FOR

LECTURES #3: CONSTRUCTION MANAGEMENT: PLANNING, DIRECTING ORGANIZING

AND CONTROLLING

(References: Construction Methods and Management by S. W. Nunnally, Chapter 16 pp 451-478)

CONSTRUCTION MANAGEMENT

Introduction

Modern complexities in construction projects have made it imperative that owners, planners and

contractors avail themselves of a system that allows for the efficient management of these projects. A

project is unique. Large projects sometimes have thousands of items that have to be executed and

managed in such a manner as to enable the synergistic completion of the project. To achieve the owner’sobjective in terms of project duration and budget the project must planned, scheduled, monitored and

controlled to ensure the timely, cost efficient and quality delivery of the project. Project activities

consume resources such as, time, money materials, equipment and people. If we were to allow the severalactivities to follow one after each other like ants on the march our projects would never come to an end.

Planning allows us to identify activities that could be conducted simultaneously and thereby reduce

project duration.

To begin the scheduling process, each activity of the logic diagram is then be time-loaded, the forward

pass done on the diagram to determine project duration and compliance with the objectives, and the backward pass done to determine the critical path and floats. From the scheduled logic diagram, the bar

chart schedule is then be plotted to indicate graphically, the start and end times (durations) of each

activity. Note that the bar chart (Gantt Chart), in isolation, is of no use and must be a product of a logic

analysis to enable the efficient management of the project.

PLANNING, DIRECTING, ORGANIZING AND CONTROLLING THE PROJECT

What is Project Management?

Project Management is defined as managing and directing time, material, equipment, human resources(personnel/labor) and costs to complete a project in an orderly, efficient and economical manner in order

to meet project objectives with respect to schedule and budget and deliver a quality product. Project

management is knowing where you are in a project and managing changes when problems arise to

achieve successful project goals. Project Management has 9 major categories, viz.:

1. Managing Project Scope (Includes aims, goals and objectives of the sponsor).

2. Managing Time (includes planning, scheduling and controlling the project to achieve time objectives).3. Managing Costs. (Financial control of the project. Includes accumulating, organizing and analyzing

data and reporting the cost information).

4. Managing Communication. (Keeps inflowing flowing among all members of the team).5. Managing Human Resources (includes directing and administering the people working on the project).

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6. Managing Quality Control (include ensuring the fulfillment of the quality established as a measure of

performance for thee project).7. Managing Contract/Procurement (includes selecting, negotiating and awarding orders and

administering procurement of materials, equipment and services).

8. Managing Risk (includes dealing with a level of uncertainty about the project based knowledge andexperience).

9. Managing Project Integration (includes project coordination among all project functionaries).

This list includes all of the encompassing elements of the body of Project Management. These elementsare addressed below with a brief description of the three important elements of a successful project:

Planning: What is to be accomplished? List of activities and required resources. Preparation of thelogical project-planning diagram.

Scheduling: When does a specific task have to start? What is its duration and end time?

Control: Tracking/monitoring time and cost. Analyze performance. Make the necessaryinterventions to preserve the integrity of the schedule and the budget.

Important to supporting the three elements are:

• Allocation of Labor/Personnel:

• Allocation of Capital Resources

• Use of Computer Applications to Aid Project Management:

The Five General Elements of Project Management

Per the Project Management Institute’s (PMI’s) Project Management Body of Knowledge, a project has 5

phases, which are compressed into the 3 elements discussed above. These 5 phases include:

1. Initiation

2. Planning3. Execution4. Monitoring and Control (Included in the rest)

5. Closeout

INTRODUCTION TO THE CRITICAL PATH METHOD (CPM)

The Critical Path Method (CPM) (essentially a construction tool) was developed between 1957 to 1958 byDuPont and Rand as a network planning method to improve planning and scheduling methods to reduce

project duration on plant overhaul, maintenance, and construction projects, using computers. The intent at

that time was to reduce project costs by finding the “optimum tradeoff of time (project duration) and total project cost. CPM was quickly recognized by professionals in government and industry and its use as a

cost saving tool commenced. Today, CPM is used widely for project scheduling to communicate project

details to the several layers of the organization.

The Critical Path Method applies the following network project modeling process or sequence of steps:

a. Define work tasks or activities b. Put activities in order of sequence

c. Diagram the activity sequence in network format

d. Determine activity durations

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e. Calculate the schedule and adjust to meet constraints

Here activities are defined, sequenced, diagrammed, activity durations assigned and the schedule iscalculated. The simple mathematical analysis in CPM is performed using the predecessor-successor

sequencing of activities and their durations. The mathematical algorithms used in the forward pass and

backward pass result in the minimum completion time for the project, as well as the start and finish timesof each activity. The Critical path on the network diagram is that path of activities that generates the

longest duration for the project within the network. All activities along this Critical path are called

Critical Activities. The sum of the activity durations along the critical Path indicates the minimum timewithin which the project could be completed. Any delay in a critical activity will increase the completiontime of the project by the value of that critical activity’s delay time. All activities that are not on the

critical path are called non-critical activities or float activities.

During the same time CPM was developed Booze, Hamilton and Allen developed the Program Evaluation

and Review Technique (PERT) for planning and controlling U.S. Polaris missile system development.

Both systems use the network diagram to show the relationships among the activities in a project. Thedifference between the systems is that CPM uses a fixed time estimates for activity duration, while the

PERT procedure assumes that time estimates for activity durations are independent random variables.

Therefore, PERT utilizes an average or mean time, and a variance (measure of dispersion or variation) for

each activity, calculated from a set of user provided values.

The advantage of the CPM is that it shows relationships between project activities, contrary to the bar

graph schedule. There is no way to determine from the bar graph whether the person preparing the graphwas aware of the relationships. Another failure of the bar graph is that it does not show those activities

which actually control project duration, better known as the critical activities, nor does it show the impact

of a delay or change of one activity on an entire project.The steps in bullets a through c above define the planning phase of the CPM process. We will discuss

this phase in some detail as it is important to developing a proper schedule for the project, which activities

are listed in bullets d and e of the five steps.

Why Do We Plan In Project Management/Construction Management?

We plan so that we can make logical decisions on a course(s) of action from a set of possible alternativecourses of action. Planning is considered to be the most important phase of the project. It is the first step

in the process, which sets the stage for either a successful project or a disaster.

The end product of the Planning Phase is the production of the Logic Diagram, which shows graphically,

all of the activities of the project laid out in a logical, sequential order. This plan is put together from a

harvesting of the thoughts and experiences of the staff and establishes a workable plan for the executionof the project. The student should note that the planning phase relies wholly on the human thought

process to develop the activity list and logic for the project. This is the most time consuming phase of the

project and the time spent in this effort is never wasted. The participants in the planning phase can almost

invariably be certain that they have a complete knowledge of what the project entails. No computer program can assist you in this effort. You must rely on the staff members who have the knowledge

derived from similar projects to prepare the Plan. The computer uses the Plan to prepare the Project

Schedule and assists in Project Control . The Logic Diagram, when completed, will provide a graphicaldefinition of the scope of the project.

The Planning Process has 5 stages, which the student must observe when developing the ProgrammingPlanning Diagram or Logic Diagram. They are:

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1. Establish the objectives.

2. Develop the Plan.3. Construct the Project Planning Diagram.

4. Establish the timing durations of the respective activities.

5. Identify costs and labor/personnel associated with each activity.

Let us now discuss these steps.

1. The Planning Process commences with the definition of the goals and objectives of the project.The goals and objectives would include:

a. Project start date

b. Project end date.c. Budget.

d. Expected results.

e. Milestone objectives for significant events within the project’s timeframe.f. Designated responsible personnel or departments for delivery of the objectives. These are

identified early in the project-planning phase and should be identified when setting the objectives.

2. Having established the objectives of the project the planning team then commences the

development of the Plan. Here defines the activities necessary to execute the project and establishesthe relationships between and among these activities. Communication is required among the team in

order to gather data from many persons and places. For example question like:

• When and from what source will the right crane be available?

• Are enough skilled masons available to complete e.g. the masonry work on time?

• Are enough skilled lathers available to complete the installation of the steel, reinforcementon time?

• What would be the impacts to the schedule of long lead items, such as elevators, escalators

etc that will require special fabrication at a manufacturing agency that has an existing backlog of

work?

• What are the activity relationships that can be determined from information from the

management team, accounting department, equipment department, plans and specs, a visit to thesite, the nature of the work, the owner, the banker, the sub-contractors, the government agenciesinvolved and their requirements and the suppliers.

The Project manager should note that good planning requires creativity and releasing oneself from

traditional company practices. Just because the company always did it this way, does not mean that itis the best way. By trying to break away from established “paradigms” or models or false constraints,

planners can incorporate new methods and approaches into the plan and schedule. One way in which

the Project manager could incorporate these new methods is by convening a “brainstorming” sessionwhere all members of the team are locked in a room to think out the solutions to problems. E.g. Say

the question is to find the best method of pouring concrete into elevated columns on a specific project,

the participants in a “brainstorming” session would each state the first method or solution that comes

to mind, no matter how way out the thought seems. When all thoughts are gathered they are discussed by the team and screened for the selection of the best alternative to be pursued.

In the development of the Plan:

• The list of activities necessary to be carried out to successfully complete the job must be

drawn up.

• The work breakdown structure (WBS), categorizing the activities under the respectivedisciplines/departments, is prepared. This is an excellent aid to organizing the work and its

activities. See examples of a Work Breakdown Structures below.

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• The job is delineated by determining the relationships between/among the activities.

Planning entails defining the activities necessary to construct the project and establishing therelationships between the activities.

• Determine which jobs must start before others (precedence chart) and those that follow

each other.

• Determine which activities could run concurrently. The Project Manager should note that

good planning requires flexibility. It is the natural tendency for first-time schedulers to build a

long chain of activities following one after the other, with no branches and with only one thinghappening at a time. The most efficient way to shorten a project’s duration is to have as many

activities as possible run concurrently, without hindering each other’s progress. Instead of having

single crews working consecutively on the project’s activities, there could be five or other number

of crews working concurrently on the site, though not interfering with each other’s progress.3. In the construction of the Project Planning Diagram, the sequence of the activities in the precedence

chart is shown graphically on the planning diagram. The entire project is first constructed in the

minds of the scheduling team, and then put on paper. The interrelationship between/among activities, building methods, problem solving and communications that define the plan, take place in this fertile

environment that defines the project in terms of the Plan and succeeding schedule. On reaching this

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point demonstrates that the planning phase has reached initial completion where a graphic display

could be shown of the project activities and their interrelationships. The figure below depicts a plot of a logic diagram and shows the rule for numbering the nodes. Note: The node numbers are not the

same activity numbers on the Precedence Chart, they must be allocated to the nodes as detailed

in the diagram below.

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4. In this step, the respective team members, based on their experiences on previous projects, determinethe duration of each activity.

5. This step identifies the activity cost and resources (labor/personnel, equipment) associated with each

activity on the diagram.

Scheduling

As we previously discussed, project planning addresses what work has to be done and project scheduling ,addresses when the work is to be done.

The complete schedule includes the following:

• Time schedule

• Resource schedule (Personnel/Labor)

• Cost schedule

However, we will deal with the timing schedule in this lecture

Manual Scheduling

It is essential that the student learn to schedule manually first, before using computer applications tocompute the schedule form the time-loaded logic diagram. Manual scheduling involves an initial analysis

of the project, prior to devoting time and effort to input the computer data. This allows for manual timing

adjustments before the time wasting efforts to effect these changes in the computer inputs.

Manual calculations include adding and subtraction functions with some level of accuracy. Initial

scheduling is done by placing the scheduled start and finish times of each activity, directly on the project-

planning diagram.

ELEMENTS OF THE INITIAL SCHEDULING EFFORT

The Earliest Start Time. This is the initial calculating element. This is the earliest possible time that an

activity can start according to relationships assigned. This allows early review of the project duration and

a check on whether the project objectives will be met. Here, any necessary changes in the time-loaded planning diagram could be made to meet these objectives.

The Critical Path. This consists of a continuous chain of critical activities from the start to the finish of

a project, each with zero float and which chain has the longest duration, and which in fact, determines the project duration.

Float. The amount of “slack time” or time difference between the calculated duration of the activitychain and the critical path is called the float. It permits an activity to start later than its early start and not

impact the project. Float can be classified either as total float or free float .

Total Float. This is the difference between how much time is available to perform an activity and how

much time is required. This is the measure of leeway in starting and completing an activity. It is a

measure of time units (hours, days, weeks, years) that an activity (or chain of activities) can be delayedwithout impacting the project end date.

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Free Float. Also referred to as an “activity float” because unlike total float, free float is the property of

an activity and not the network path that the activity is part of. Free float is the amount of time the start of an activity may be delayed without delaying the start of a successor activity.

Note again the following activity relationships:

Concurrent Activities are logically independent of one another and can be performed at the same time.

Predecessor Activity is one that must be completed before a new activity can commence.

Successor Activity is one that cannot start until a given preceding activity is completed.

THE SCHEDULING PROCEDURE

The prime concern in scheduling is timing - how much time each activity requires and when eachactivity will start and end. After the project-planning diagram (logic diagram) is completed the

scheduling process commences as follows:

1. Determine the required time (time estimate to complete each activity).2. Determine the available time to complete each project activity.

3. Compare the required time and the available time for each activity to determine the total float.

4. Determine the critical path activities (activities with zero float).5. Determine the float time of noncritical activities.

6. Compute the duration of the project via the critical path. If project objectives are exceeded adjust the

plan and the timing estimates.7. Obtain concurrence from all concerned and responsible parties for validation of the schedule.

8. Prepare a bar chart time schedule from the time-loaded plan.

TIMING ESTIMATES

Estimating the durations of activities in a project is not a one-time effort but the start of a dynamic

process, as changes need to be continually made throughout the duration of the project.

The three estimating phases of a project are:

1. When the project-planning diagram is essentially complete.

2. During the scheduling phase, when the initial estimates require revisions because they do not meet the

project objectives.3. Ongoing estimate changes of selected project activities during the conduct of the project to maintain

its planned schedule.

The initial estimate is based on how much time the activity requires. Staff that is familiar andexperienced with this type of activity makes this call. Staff desiring to be safe oftentimes overstates the

activity duration. When the project is totaled and if the initially estimated end date falls outside of the

project objective, every activity is then revisited and adjustments made to the individual activities to maketheir durations more realistic.

Periodic review of the project schedule will indicate project activities that are behind. This may requirerevisiting the project schedule to adjust the duration of critical activities. If the situation is serious,

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thereby impacting several of the critical activities, it may be necessary to revisit the plan and make the

adjustments there.

On the other hand if critical activities are completed ahead of schedule, future critical activities that may

have extended durations could be rescheduled to make good the extra time made available by the earlycompletions. Or, the Project Manager who is in control may attempt to look good and leave the schedule

as it is and forecast an early completion of the project.

MANUAL TIMING CALCULATIONS

Estimated time estimates, the basis for calculating the scheduled timing, need to be placed under eachactivity on the CPM project-planning diagram before beginning the schedule calculations. (Note that thisnumber is placed in the box node in the PDM method). The schedule for each project activity willinitially consist of its earliest start and latest finish times and total float value. Once the earliest startcomputations are complete, the project duration can be evaluated.

Calculating the Earliest Start Time

We discussed before, the earliest start time is the earliest possible time an activity can begin withoutinterfering with the completion of any of the preceding activities.

Use the following guides when calculating the earliest start times for the project activities:

Commence calculating earliest start times with the beginning node of the project-planning diagram(Figure 3. 1), below. The scheduled time of the beginning node is set at 0 weeks. (Since all of thescheduled times are in weeks, this unit of time will not be shown in our calculations but noted in thelegend of the diagram.)

• If only one arrow leads into a node, earliest start time for activities starting at that node is determined by adding the earliest start time of the preceding activity to the duration of the same preceding

activity. Procure interior items starts at Node 8, with earliest start time 8. It is the sum of the earliest

start time (6) (should be to left of node) for Design interior items that starts at node 4, plus its duration(2)

• If more than one arrow leads into a node, the earliest start time calculation will be dictated as shown inthe drawing below.

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• The largest sum total is the earliest start time for the node. In this example, the path through Install mechanical and electrical equipment, the larger of the two paths, totals 23 at Node 7, and becomes the

earliest start time of Construct phase II building.

Using this approach, all of the earliest start times for activities in the Christopher Design/Build Project are

calculated and added in Figure 3.1.

CALCULATING PROJECT DURATION

Review of the Figure 3.1 indicates that the sum of the activity durations along the critical path is 29 weeks

which is the earliest start of the node signifying the end of the project (11). This total duration on thetime-loaded logic diagram would indicate to the planner whether he met the time objective of the project.

This plan and schedule showed that a viable plan was prepared and that the 29 weeks duration desired by

the owner was met (10/2/95 to 4/23/1996).

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Calculating the latest Finish Time

The latest finish time is the latest time an activity can be completed without delaying the end of the project. The Project manager should note the following in determining the latest finish times for a

project:

• The project duration must first be established by calculating the early start times.

• The project duration is the latest finish time (as well as the earliest start time) of the end node of the

project.

• The calculation of the latest finish times involves working from the end node back through each node

to the first node in the project.

Let us look at Figure 3.1, with its project duration of 29 weeks. The activity 7,11 – (Construct Phase II

Building ) has a duration of 6 weeks. The latest finish time for activities coming into node 7 (3,7 and 6,7)

is 23 weeks. Note that if more than one arrow originates at a particular node the latest finish time iscalculated through each arrow and the smallest result recorded as the latest finish time. See the figure

below and Figure 3.2.

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The latest finish time for the activities that lead into node 4 is six weeks, the smaller of the two results.

Were the latest finish time for activities coming into node 4 set at eight weeks, there would not be enough

time remaining to complete activity 4, 5 by its required latest finish time of 10 weeks.

Figure 3.2 notes the latest finish times of the project activities. The plan and schedule thus far indicate thattiming objectives can be met, so we can continue without any changes or adjustments. If timing

objectives were not met, we would initially examine the critical items to determine if possible adjustmentswould resolve the timing problem. If the project duration is still in jeopardy, then timing adjustments may

have to extend to additional items in the project plan. This could require a review of the optional start and

finish times for all of the project items.

Float: - Optional Start and Finish Times

The float feature is one of the most important facets in project management. Its importance in project

scheduling is that it identifies the activities that have optional starting and finishing dates. These activities

have total float, which is the difference between the time available for performing a job and the timerequired to do it.

Available time = Latest time - Earliest time

Required time = Time estimate for completing the activity

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Figure 3.3 above shows another method for showing the total float. Time available for activity 4, 6

(Fabricate mechanical equipment) is the difference between the latest finis time and the earliest start time.

To determine the total float subtract the required time (time estimate) from the available time.

Total float is very important in the scheduling and controlling the project. Particular attention is paid to

activities with zero float (critical items) when there is a slippage in the schedule. These have no room for delays. Float activities, however do not have these restrictions and are not impacted by minor slippages in

the activities.

Note that the total float of an activity is the difference between its earliest start and the latest finish dates

and the duration. Float activities have optional start and finish dates. See 3.4 below.

PREPARING THE SCHEDULE CHART

In this the time loaded logic diagram the earliest start and latest finish are stated as well as the latest startand the earliest finish are listed to give the planner all of the available scheduling options. The following

formulas calculate the optional start and finish dates:

Latest start = earliest start + total float

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Earliest finish = latest finish - total float

Figure 3.5 (attached) shows the table of these total float calculations for the Christopher design/Build

Project.

SETTING UP THE CALENDAR SCHEDULE

The tabulated schedule in Figure 3.5 can be converted into a calendar schedule for better presentation andthe ability to better monitor the project. Tabulated schedule dates can be converted into calendar dates

using a calendar showing the months and years of the project. Start at zero weeks with the start date of

the project (in the case of the Christopher Project this is 10/2/95), which is also the start date of Design

structural steel (time: 2 weeks), for which activity the earliest finish date is 10/16/95, and so on for the

remainder of the activities. See Figure 3.6.

REVIEW OF THE PRACTICE PROBLEM IN CLASS.

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CE 54100 HOMEWORK #3 Saturday, September 17, 2011

AOA and AON LAB

You are the Facility Manager for an establishment and you propose to construct a shed, but resources arescarce and you want to optimize the use of your available resources (time, budget personnel material and

equipment) in this effort. You and your team have developed an activity list and you wish to produce a

time-loaded logic diagram using the CPM approach. Your specialist staff has made recommendations for your use in sequencing the project, and they are as follows:

• Clear Site follows Start and Remove Topsoil follows Clear Site

• Form Slab and Prefab Wood Walls can start after Remove Topsoil.

• Place Rebar/Embeds follows Form Slab and Pour Slab follows Place Rebar/Embeds.

• Erect Walls can follow Pour slab and Prefab Wood Walls.

• Place Trusses, Install Siding and Place Topsoil/Grade can follow Erect Walls.

• Place Roof Sheathing follows Place Trusses.

• Place Shingles follows Place Roof Sheathing

• Rough Electrical will precede Place Interior Paneling, which will in turn precede Install

Finish Carpentry and Finish Electrical.• Install Overhead Door and Rough Electrical can follow Install Siding.

• Exterior Trim Carpentry can follow Install Overhead Door

• Place Shingles, Install Finish Carpentry, Finish Electrical, Exterior Trim Carpentry

and Place Topsoil/Grade will precede Landscape. Note that Landscape is your last activity.

Complete the Precedence Chart and plot the CPM Logic Diagram (AOA approach) to show the respective

activities, and their durations.

Having plotted the time-loaded logic diagram for this project, determine the early starts for each activity,

via the forward pass and obtain the project duration from the early start data. You will then determine the

late starts for each activity, via the backward pass, having first established the project duration. You will

then prepare the Total Float Chart and finally using the data from the total float chart and the scheduled

logic diagram, plot the critical path, using double arrows along that path.

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BUILDING A SHED

Activity

No.

Activity Name Duration

(Days)

Precedes Follows Remarks

1 Clear Site 1

2 Remove Topsoil 1

3 Form Slab 24 Place Rebar/Embeds 1

5 Pour Slab 1

6 Prefab Wood Walls 2

7 Erect Wood Walls 1

8 Install Siding 2

9 Place Trusses 1

10 Place Roof Sheathing 2

11 Place Interior Paneling 1

12 Exterior Trim Carpentry 2

13 Install Overhead Door 1

14 Rough Electrical 1

15 Finish Electrical 1

16 Place Shingles 2

17 Install Finish Carpentry 1

18 Place Topsoil/Grade 1

19 Landscape 1

When you have completed the AOA plot, you now plot eh logic diagram again, this time using the AON

approach with square nodes.Having plotted the AON logic diagram, proceed to execute the forward pass, inserting the information

into the nodes as you proceed, and having determined the duration execute the backward pass, insertingthe information into the nodes as you proceed.You will then complete your scheduling activity by subtracting the EF from the LF to obtain the

respective Total Floats.

Compare the results with your AOA solution. Is there a difference?

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CE 54100 Lecture _3 Construction Management - Planning & Scheduling_1

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