SCHEDULINGPERT NETWORKING AND LINEAR OPERATIONS

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SCHEDULING-PERT NETWORKING AND LINEAR OPERATIONS
CHAPTER - 8
VRML Model of NIST Research Facility Emission
Control System
VRML Excavator, Tower Crane and Dump Truck
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THE NEED

• Traditionally construction process information is
  communicated with paper documents and 2D CAD
  drawings
• Recently, the industry has embraced web-based
  technologies, but construction still uses
  document-based models.
• It is believed that transition model-based
  information can be done through web-based 3D
  models.
• Moreover, there is a need to easily model
  structures to be used in a web-based user
  interface.

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THE TECHNOLOGY

• The applicability of the VRML is being
  investigated for visualizing construction
  activities at a site and creating an advanced
  web-based 3D user to construction process
  information.
• The Computer-Integrated Construction Group at the
  NIST Gaithersburg, MD is developing this concept.
• These interfaces are based on web-based 3D
  visualizations of a model.

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INTRODUCTION

• Acquisition of Bar Charts and CPM
• PERT addresses variability of project duration
• Variability is defined in terms of three
  estimates
• Calculation of the expected duration time (te)
• Definition of normal distribution
• Standard deviation and variance
• Calculation of longest path and project duration
  using te
• Probability distribution longest path of te
  values as a mean of normal distribution

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Figure 8.1 Selected Areas under the Normal
Distributed Curve
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AN EXAMPLE OF PERT NETWORK

• Fig. 8.2 and table 8.1
• Calculation of expected duration, variance for
  each activity, the standard deviation
• What is the probability that the project can be
  completed in N days?
• What is the probability that the project can be
  completed in 19 days? (see fig. 8.3, and example

ta4tmtb
For instance for Activity 7
42813
45
7.5
te




6
6
6




2
9
2
(tb-ta)
(13-4)
a2




2.25
6
6
6
7
Table 8.1 Three Estimate Values and Calculated
Values for Each Activity
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Figure 8.2 Small PERT Network
Figure 8.3 Normal Distribution of Total Project
Durations for Small PERT Network
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PERT SHORTCOMINGS

• PERT results are too optimistic
• Assumption that duration is most probable value
  is not accurate
• PERT underestimates the duration, the cause is
  called Merge Event Bias
• One solution to the Difficulties is to use Monte
  Carlo Simulation

Figure 8.4 Merge Event Bias
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LINEAR CONSTRUCTION OPERATIONS

• Often construction sites have linear properties
  that influence the production sequence. (example
  road construction)
• The required sequentiality leads to the Train
  effect.
• That is, a section must be complete 5-in concrete
  before preceding to 9-in concrete. Therefore,
  the section can be thought of as a train or
  parade of work that must pass each station
  represented by the six construction process.
• Many types of project exhibit this kind of rigid
  work sequence.
• Examples
• A high-rise building, each floor to pass though a
  set of operations
• Tunnels are worked in sections
• Pipeline work

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Figure 8.5 Road Project Divided Into 14 Sections
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PRODUCTION CURVES

• Bar charts and network schedules provide only
  limited information when modeling linear
  operations and projects.
• They do not reflect production rate or speed with
  which section are processed.
• First unit delay occurs due to mobilization.
• Near completion, production rate declines due to
  demobilization.
• Max production is during mid periods of the
  process duration
• This leads to a production curve with the shape
  of a lazy S. (Fig. 8.6)
• The slope is flat at the beginning and the end,
  but steep in the middle.
• The slope of the curve is the production rate.
• These curves are called as time-distance,
  time-quality or velocity diagrams. (Fig. 8.7)
• The slope represents the number of unit produced
  over a given time increment.
• The slope of the curve, therefore represents the
  number of units produces over a given increment.
  This is the rate of production.
• Unbalanced production roles. (Fig. 8.9)
• Prevent work stoppage (Continuity of work)
• One way to avoid this is to control production in
  each process so that sloped of the curves are
  parallel.

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Figure 8.6 Production Curve
Figure 8.7 Velocity Diagrams for a Road
Construction Project
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Figure 8.8 Planned Status Construction at Week 12
Figure 8.9 Unbalanced Process Production Rated
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LINE-OF-BALANCED CONCEPTS

• LOB is a graphical method for production control
  integrating barcharting and production curve
  concepts
• LOC serves two fundamental purposes
• To control Production
• To act as a Project Management Aid
• Each objective is interrelated through 4 LOB
  elements
• The objective chart
• The program chart
• The progress chart
• The comparison

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Figure 8.10 Objective Chart
Figure 8.11 Program Chart with Lead Time in Work
Days
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Figure 8.12 Progress Chart
Figure 8.13 Progress Chart with Line of Balance
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Figure 8.15 Program Chart and Objective Chart
Figure 8.14 Schematic of Floor Cycle Work Tasks
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Figure 8.16 Enlarges Projection of Program Chart
onto Objective Chart
Figure 8.17 Line of Balance for Week 5
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8.7 LOB APPLIED TO CONSTRUCTION

• To illustrate the use of LOB in a construction
  context, consider a high-rise building in which
  repetitive activity sequences are a part of the
  floor-to-floor operation.
• Each floor consists of four sections (A, B, C,
  and D)
• Each floor section must be processes through the
  following work activities (1) erect forms, (2)
  Placing reinforcement, (3) Place concrete, (4)
  Dismantle forms, (5) Place curtain wall (exterior
  façade), (6) Place window.
• Figure 8-14 shows a schematic of the status of
  activities at a given point in time.
• The diagram in figure 8-15 shows the LOB
  objective chart for a 10-story building. The
  program chart for a typical section is shown
  above the objective chart.
• A diagram of Projection is shown in Figure 8.16
• The LOB values can be calculated by determining
  the slop relating horizontal distance (Lead time
  to vertical distance (required sections)).