CE 366
PROJECT MANAGEMENT AND
ECONOMICS
Robert G. Batson, Ph.D., P.E.
Professor of Construction
Engineering
The University of Alabama
Rbatson@eng.ua.edu
Chapter 4:
Project Planning
2
Critical Path Method (CPM)
• Based on a graphical model of project activities and
their time dependencies, which forms a “directed
network”
– More detailed than the Gantt Chart representation
– Enables utilization of a network algorithm to identify
“critical path” for project, and “slack” of all other activities
– Communicates complex job interdependencies to all
– Serves as a basis for fixing work schedules (calendar
dates)
– One mechanism for controlling project time, and replanning/rescheduling the remaining project activities as
necessary
• A computer-aided approach to the three-phase
procedure of project planning, scheduling, and time
monitoring/control
4.1
Construction Project Planning
• Draws focus to what must be done, how it will be
done, and in what sequential order
• Time-consuming and difficult, but extremely important
• CPM-based planning provides for logic and
thoroughness, at appropriate levels of detail for the
project
• Provides for learning by the project team, using
experience of team members and other in the firm
• Network development is iterative:
– Fill in details obtained from many sources
– Review, modify, improve in group meetings
– Solicit subcontractor and supplier participation in planning,
to identify potential problems and resolve them early
– Update network as project evolves (no plan is perfect)
4.2
Approaches to Project Planning
Five-step Approach
1. Determination of the general approach to the project
2. Breakdown of the project into activities
3. Ascertainment of the sequential relationship among
these activities
4. Graphic presentation in the form of a network
5. Endorsement by the project team
Two “planning methodologies”
• Beginning-to-end planning: presumes a level of
detail, or adds detail as planning proceeds
• Top-down planning (work breakdown structure):
Views project as a hierarchy of work, broken into
more detailed pieces at each “level” until sufficient
detail is obtained
4.3
Project (or Job) Activities
• A single work step that has a recognizable beginning
and end, and consumes time and resources
• Guidelines that may help identify/classify activities
1.
2.
3.
4.
5.
6.
7.
8.
•
By area of responsibility
By category of work (craft or crew requirements)
By category of work (using equipment requirements)
By category of work (using materials as guide)
By distinct structural elements
By location
With regard to owner’s work breakdown
With regard to contractor’s work breakdown
Level of detail that matches: owner and contractor
requirements, such as reporting to higher authority or
scheduling subcontractors; the project manager’s
“level of schedule control” planned
4.4
Job Logic
• The order, as determined by the planner, in which
activities are to be accomplished in the field
– Natural “precedence” relationships among two or more
– Independent activities that could proceed concurrently,
except for restraints
• Several approaches may be possible, and implications
must be determined in an engineering study
– Schedule implications revealed by CPM
– Cost implications revealed by cost estimating
• Identification and inclusion of restraints in scheduling
is a critical responsibility of the planner, working with
the project team
• Unexpected restraints are a major cause of cost
overruns and schedule slippage
4.5
Restraints
• Physical restraints
• Material restraints
– Design drawings and specifications
– Procurement steps
– Fabrication and delivery by selected vendors
• Equipments restraints
• Labor restraints
– Subcontractor crews
– Contractor personnel with special skills
• Owner-related restraints
– Delivery of owner-provided materials
– Turn-over of owner’s sites or facilities
• Safety restraints
4.6
Restraints in the CPM Network
• Some may be shown as time-consuming activities
• Restraints also may be shown as dependencies
between activities
• Restraints that involve competition for resources,
such as equipment or labor crews, may be
– “Hard-wired” with order of preference shown in
network.
– “Resource requirements with priority as a “side
constraint” that CPM refers to in the event of
competing needs
• Restraints may include milestone dates or date for
project completion; also dates by which a particular
activity cannot start before, or must end by
4.7
Top-Down Planning
• Preferred in the construction industry
• Break overall project into segments
• Each segment has a hierarchy of activity levels, referred to as
a Work Breakdown Structure (WBS) – a project outline
• Highway Bridge project has six major components (1-6) with
indentured levels and sublevels of activities, such as
4.0
Level 1
4.1
Level 2
4.1.1
Level 3
.
.
.
4.1.5
• See Appendix C
4.8
Work Breakdown Structure
• Other uses besides planning:
– Project progress reporting and summarization
– Cost reporting and summarization
– Starting point for work teams to plan their weekly work
• Developed by the project team from:
– WBS segments on completed projects
– Experience applied to the project documentation to date
– Brainstorming, if work segment is new to the group
• Once the WBS is completed to an acceptable level of
detail, creation of activity relationships representing
precedence and other restraints can begin
– Group or subgroup meeting; individual interviews
– Draw the linkage by hand, or in PM software (better)
– Review and revise as project network emerges
4.9
Network Symbolic Conventions
• Linkages are called “arrows” or “arcs”
• Activity-on-arrow (Appendix D)
– Arrows represent activities
– Dotted arrows represent logical connections
– Nodes (circles or boxes) represent logical
connections
• Activity-on-node (Precedence network)
–
–
–
–
Arrows represent dependencies among activities
Nodes (circles or boxes) represent activities
Most common in construction industry
Emphasized in Sears, Sears, and Clough
4.10
13
Precedence Diagram Development
• Correct diagramming is critical to project time management
–
–
–
–
Activities from WBS are placed in boxes
Activity dependencies and restraints are modeled as arrows
Resources are generally assumed available to cover demands
Time durations are ignored
• Each activity must be preceded by the project “start” activity or
by the completion of a previous activity
• Each activity must have at least one activity that follows, or the
activity “finish” of the project
• Milestones, such as “start” and “finish” nodes, have rounded
edges in text networks, and consume “zero time”
• Numbering conventions are required for computer-generated
networks; generally use increasing sequence of number from
start to finish
4.11
Highway Bridge Precedence Diagram
• Figure 4.2, General Job Plan
– Six major operations, in chronological order
– Could be derived from project Gantt Chart, as well
– For context, leading to managerial discussion and
agreement on general ground rules for project (p. 75)
• Figure 4.3, Precedence Diagram (planning version)
–
–
–
–
Built from WBS, Figure 4.2, and general ground rules;
Uses certain resource restraints,
Material restraints, and
Equipment restraints
4.13
16
Value of Precedence Network
• Project team has conceptualized entire project,
and is building commitment to the work and each
other
• Network is an expedient communication tool
– Between field and office (both contractor and owner)
– To orient new managers or the workforce
– Between prime contractor and subcontractor and
material suppliers
– Between contractor and engineer-architect
• Far superior to any form of bar chart or project
narrative
• Stage is set for sophisticated scheduling, and
project time control, once the project begins
4.14
Repetitive Operations
• Some projects naturally involve several parallel
strings of continuing operations, each in physical
proximity to others
• Figure 4.4, basic plan for pipeline relocation
• Figure 4.5, mile-by-mile plan with
– “Work categories” in left margin implying specialized
crews and their equipment move ahead, mile-by-mile
– Moving down the diagram are physical restraints or
precedence, with recognition that excavate and string
pipe can occur in parallel
• The dotted arrow exiting Activity 170 is the
“interface” between the precedence diagram for
Pipeline Relocation (Figure 4.5) and Pipeline
Crossing Structure (Figure 4.6)
4.15
19
20
21
Network Level of Detail
• Figure 2.1 gives overall flow among principle
operations of the entire project, which will be
constructed and managed separately
• Figures 4.3 and 4.5 are detailed precedence diagrams,
appropriate for field managers and workers
• Just like in Section 4.15, there will be important
interfaces between the networks for the major
subprojects
• A master network would likely consist of
– Precedence networks for each subproject at a high level
(e.g., Figure 4.2 and Figure 4.4)
– Important linkages between them
• Bottom line: Projects are communicated and managed
through a series of subnetworks, at appropriate level of
detail
4.16
Computer Applications in Planning
• Software such as MS Project, Primavera, Timberline
are used by construction firms, large and small, to:
–
–
–
–
Develop and document the network logic simultaneously
Easily review and revise the plan in group settings
Easily transmit plan to other
Readily apply scheduling algorithms as in Chapters 5,6,
and 7; resource and time management as in Chapters 8
and 9
• Enables
– Speedy project planning (an interesting career path, too)
– Combining subnetworks developed by different project
managers or subcontractors, to form a master network
– Team-building and commitment to project success
4.17
24