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Construction planning scheduling
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Civil Engineering (CE)
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UNIT-
Construction Planning
1 Basic Concepts in the Development of Construction Plans
Construction planning is a fundamental and challenging activity in the management and
execution of construction projects. It involves the
Choice of technology
Definition of work tasks
The estimation of the required resources and durations for individual
tasks,
The identification of any interactions among the different work tasks.
A good construction plan is the basis for developing the budget and the schedule for work.
Developing the construction plan is a critical task in the management of construction, even if
the plan is not written or otherwise formally recorded. In addition to these technical aspects
of construction planning, it may also be necessary to make organizational decisions about the
relationships between project participants and even which organizations to include in a
project.
Sherlock Holmes noted that forming a construction plan is a highly challenging task.
Essential aspects of construction planning include the
Generation of required activities.
Analysis of the implications of these activities.
Choice among the various alternative means of performing activities.
In developing a construction plan, it is common to adopt a primary emphasis on either cost
control or on schedule control as illustrated in Fig. Some projects are primarily divided into
expense categories with associated costs. In these cases, construction planning is cost or
expense oriented.
Alternative Emphases in Construction Planning
DIRECT COST:
Amount spend for things which are directly involved in the project
Equipment.
Materials.
Labour cost etc.
INDIRECT COST:
Indirectly help to develop the project.
Borrowing expenses for project financing
Supervisor’s salary etc.
For some projects, scheduling of work activities over time is critical and is emphasized in the
planning process. In this case, the planner insures that the proper precedence among
activities is maintained and that efficient scheduling of the available resources prevails.
Traditional scheduling procedures emphasize the maintenance of task precedence (resulting
in critical path scheduling procedures) or efficient use of resources over time (resulting
in job shop scheduling procedures).
computer aided design (CAD) system may be helpful in simulating space requirements for
operations and for identifying any interference. Similarly, problems in resource availability
identified during the simulation of the construction process might be effectively forestalled
by providing additional resources as part of the construction plan.
Example: Roadway rehabilitation
An example from a roadway rehabilitation project in Pittsburgh, PA can serve to
illustrate the importance of good construction planning and the effect of technology choice.
In this project, the decks on overpass bridges as well as the pavement on the highway itself
were to be replaced. The initial construction plan was to work outward from each end of the
overpass bridges while the highway surface was replaced below the bridges. As a result,
access of equipment and concrete trucks to the overpass bridges was a considerable problem.
However, the highway work could be staged so that each Overpass Bridge was accessible
from below at prescribed times. By pumping concrete up to the overpass bridge deck from
the highway below, costs were reduced and the work was accomplished much more quickly.
1 Defining Work Tasks
The terms work "tasks" or "activities" are often used interchangeably in construction
plans to refer to specific, defined items of work. In job shop or manufacturing terminology, a
project would be called a "job" and an activity called an "operation", but the sense of the
terms is equivalent. The scheduling problem is to determine an appropriate set of activity
start time, resource allocations and completion times that will result in completion of the
project in a timely and efficient fashion. In this planning, defining work tasks, technology
and construction method is typically done either simultaneously or in a series of iterations.
The definition of appropriate work tasks can be a laborious and tedious process, yet it
represents the necessary information for application of formal scheduling procedures. Since
construction projects can involve thousands of individual work tasks, this definition phase
can also be expensive and time consuming. Fortunately, many tasks may be repeated in
Road below the
bridge
Surface replacement
work
Over passage bridge
different parts of the facility or past facility construction plans can be used as general models
for new projects. For example, the tasks involved in the construction of a building floor may
be repeated with only minor differences for each of the floors in the building. While
repetition of activities in different locations or reproduction of activities from past projects
reduces the work involved, there are very few computer aids for the process of defining
activities. More formally, an activity is any subdivision of project tasks. The set of activities
defined for a project should be comprehensive or completely exhaustive so that all necessary
work tasks are included in one or more activities.
The time required to perform an activity is called the duration of the activity. The
beginning and the end of activities are signposts or milestones, indicating the progress of the
project. Occasionally, it is useful to define activities which have no duration to mark
important events. For example, receipt of equipment on the construction site may be defined
as an activity since other activities would depend upon the equipment availability and the
project manager might appreciate formal notice of the arrival. Similarly, receipt of regulatory
approvals would also be specially marked in the project plan.
The extent of work involved in any one activity can vary tremendously in construction
project plans. A result of this process is a natural hierarchy of activities with large, abstract
functional activities repeatedly sub-divided into more and more specific sub-tasks. For
example, the problem of placing concrete on site would have sub-activities associated with
placing forms, installing reinforcing steel, pouring concrete, finishing the concrete, removing
forms and others. Even more specifically, sub-tasks such as removal and cleaning of forms
after concrete placement can be defined. Even further, the sub-task "clean concrete forms"
could be subdivided into the various operations:
Transport forms from on-site storage and unload onto the cleaning station.
Position forms on the cleaning station.
Wash forms with water.
Clean concrete debris from the form's surface.
Coat the form surface with an oil release agent for the next use.
Unload the form from the cleaning station and transport to the storage location.
This detailed task breakdown of the activity "clean concrete forms" would not generally
be done in standard construction planning, but it is essential in the process of programming
or designing a robot to undertake this activity since the various specific tasks must be well
defined for a robot implementation.
It is generally advantageous to introduce an explicit hierarchy of work activities for the
purpose of simplifying the presentation and development of a schedule. For example, the
initial plan might define a single activity associated with "site clearance."
Figure Illustrative Hierarchical Activity Divisions for a Roadway Project
1 Defining Precedence Relationships Among Activities
Once work activities have been defined, the relationships among the activities can be
specified. Precedence relations between activities signify that the activities must take place
in a particular sequence. Diagrammatically, precedence relationships can be illustrated by a
network or graph in which the activities are represented by arrows as in Figure.
Road Building Project with two culverts
Structures Roadway General
Culverts
Earthwork
Pavement
Excavation
Filling
Finishing
Watering Compaction Paving
Structural
excavation
Concreting Reinforcement
Excavation
Manual
Concrete
Batching
Concrete
Filling
The arrows in Figure are called branches or links in the activity network, while the circles
marking the beginning or end of each arrow are called nodes or events. In this figure, links
represent particular activities, while the nodes represent milestone events.
Figure Illustrative Set of Four Activities with Precedence
More complicated precedence relationships can also be specified. For example, one activity
might not be able to start for several days after the completion of another activity. As a
common example, concrete might have to cure (or set) for several days before formwork is
removed. This restriction on the removal of forms activity is called a lag between the
completion of one activity (i., pouring concrete in this case) and the start of another activity
(i., removing formwork in this case).
Three mistakes should be avoided in specifying predecessor relationships for construction
plans.
First, a circle of activity precedences 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 - Example of an Impossible Work Plan
Forgetting a necessary precedence relationship can be more insidious. For
example, suppose that installation of dry wall should be done prior to floor finishing.
Ignoring this precedence relationship may result in both activities being scheduled at
the same time. Corrections on the spot may result in increased costs or problems of
quality in the completed project.
Activities cannot be superseded.
prepared, so that activity E (trench 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 (install sewers) and H (install
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 (install utilities) is not necessarily
a preceding activity for activity I (pour concrete). The result of our planning is the immediate
precedence shown in Table.
TABLE Precedence Relations for a Nine-Activity Project Example
Activity Description Predecessors
A B C D E F G H I
Site clearing
Removal of trees
General excavation
Grading general area
Excavation for utility trenches
Placing formwork and reinforcement for concrete
Installing sewer lines
Installing other utilities
Pouring concrete
---
---
A
A
B,C
B,C
D,E
D,E
F,G
Figure Activity-on-Branch Representation of a Nine Activity Project
Alternatively, the nine activities could be represented by nodes and predecessor relationships
by branches or links, as in Figure. The result is an activity-on-node diagram. In Figure 9-6,
new activity nodes representing the beginning and the end of construction have been added
to mark these important milestones.
These network representations of activities can be very helpful in visualizing the various
activities and their relationships for a project. Whether activities are represented as branches
(as in Figure) or as nodes (as in Figure) is largely a matter of organizational or personal
choice. Some considerations in choosing one form or another are discussed in Chapter 10.
Figure Activity-on-Node Representation of a Nine Activity Project
It is also notable that Table lists only the immediate predecessor relationships. Clearly, there
are other precedence relationships which involve more than one activity. For example,
"installing sewer lines" (activity G) cannot be undertaken before "site clearing" (Activity A)
is complete since the activity "grading general area" (Activity D) must precede activity G
and must follow activity A. Table is an implicit precedence list since only immediate
predecessors are recorded. An explicit predecessor list would include all of the preceding
activities for activity G. Table 9-2 shows all such predecessor relationships implied by the
project plan. This table can be produced by tracing all paths through the network back from a
particular activity and can be performed algorithmically.
TABLE All Activity Precedence Relationships for a Nine-Activity Project
Predecessor Activity Direct Successor Activities All Successor Activities All Predecessor Activities
A B C D E F G H I
C,D
E,F
E,F
G,H
G,H
I
I
---
---
E,F,G,H,I
G,H,I
G,H,I
I
I
---
---
---
---
---
---
A
A
A,B,C
A,B,C
A,B,C,D,E
A,B,C,D,E
A,B,C,D,E,F,G
1 Estimating Activity Durations
In most scheduling procedures, each work activity has associated time duration. These
durations are used extensively in preparing a schedule. For example, suppose that the
durations shown in Table were estimated for the project diagrammed in Figure.
contractors and the owner. The number of crews working, Nij, is decided by the planner. In
many cases, the number or amount of resources applied to particular activities may be
modified in light of the resulting project plan and schedule. Finally, some estimate of the
expected work productivity, Pij must be provided to apply Equation (1). As with cost
factors, commercial services can provide average productivity figures for many standard
activities of this sort. Historical records in a firm can also provide data for estimation of
productivities.
The calculation of a duration as in Equation (1) is only an approximation to the actual
activity duration for a number of reasons. First, it is usually the case that peculiarities of the
project make the accomplishment of a particular activity more or less difficult. For example,
access to the forms in a particular location may be difficult; as a result, the productivity of
assembling forms may be lower than the average value for a particular project. Often,
adjustments based on engineering judgment are made to the calculated durations from
Equation (1) for this reason.
In addition, productivity rates may vary in both systematic and random fashions from the
average. An example of systematic variation is the effect of learning on productivity. As a
crew becomes familiar with an activity and the work habits of the crew, their productivity
will typically improve. Figure illustrates the type of productivity increase that might occur
with experience; this curve is called a learning curve. The result is that productivity Pij is a
function of the duration of an activity or project. A common construction example is that the
assembly of floors in a building might go faster at higher levels due to improved productivity
even though the transportation time up to the active construction area is longer. Again,
historical records or subjective adjustments might be made to represent learning curve
variations in average productivity.
Figure Illustration of Productivity Changes Due to Learning
Random factors will also influence productivity rates and make estimation of activity
durations uncertain. For example, a scheduler will typically not know at the time of making
the initial schedule how skillful the crew and manager will be that are assigned to a
particular project. The productivity of a skilled designer may be many times that of an
unskilled engineer. In the absence of specific knowledge, the estimator can only use average
values of productivity.
Weather effects are often very important and thus deserve particular attention in estimating
durations. Weather has both systematic and random influences on activity durations.
Whether or not a rainstorm will come on a particular day is certainly a random effect that
will influence the productivity of many activities. However, the likelihood of a rainstorm is
likely to vary systematically from one month or one site to the next. Adjustment factors for
inclement weather as well as meteorological records can be used to incorporate the effects of
weather on durations. As a simple example, an activity might require ten days in perfect
weather, but the activity could not proceed in the rain. Furthermore, suppose that rain is
expected ten percent of the days in a particular month. In this case, the expected activity
duration is eleven days including one expected rain day.
Finally, the use of average productivity factors themselves cause problems in the calculation
presented in Equation (1). The expected value of the multiplicative reciprocal of a variable
is not exactly equal to the reciprocal of the variable's expected value. For example, if
productivity on an activity is either six in good weather (ie., P=6) or two in bad weather (ie.,
P=2) and good or bad weather is equally likely, then the expected productivity is P = (6)(0)
+ (2)(0) = 4, and the reciprocal of expected productivity is 1/4. However, the expected
reciprocal of productivity is E[1/P] = (0)/6 + (0)/2 = 1/3. The reciprocal of expected
productivity is 25% less than the expected value of the reciprocal in this case! By
representing only two possible productivity values, this example represents an extreme case,
but it is always true that the use of average productivity factors in Equation (1) will result
in optimistic estimates of activity durations. The use of actual averages for the reciprocals of
productivity or small adjustment factors may be used to correct for this non-linearity
problem.
The simple duration calculation shown in Equation (1) also assumes an inverse linear
relationship between the number of crews assigned to an activity and the total duration of
work. While this is a reasonable assumption in situations for which crews can work
independently and require no special coordination, it need not always be true. For example,
design tasks may be divided among numerous architects and engineers, but delays to insure
proper coordination and communication increase as the number of workers increase. As
another example, insuring a smooth flow of material to all crews on a site may be
increasingly difficult as the number of crews increase. In these latter cases, the relationship
between activity duration and the number of crews is unlikely to be inversely proportional as
shown in Equation (1). As a result, adjustments to the estimated productivity from
Equation (1) must be made. Alternatively, more complicated functional relationships might
the variability of duration times; the variance is the value of the standard deviation
multiplied by itself. From historical data, these two parameters can be estimated as:
(1)
(1)
Where we assume that n different observations xk of the random variable x are available.
This estimation process might be applied to activity durations directly (so that xk would be a
record of an activity duration Dij on a past project) or to the estimation of the distribution of
productivities (so that xk would be a record of the productivity in an activity Pi) on a past
project) which, in turn, is used to estimate durations using Equation (1). If more accuracy
is desired, the estimation equations for mean and standard deviation, Equations (1) and
(1) would be used to estimate the mean and standard deviation of the reciprocal of
productivity to avoid non-linear effects. Using estimates of productivities, the standard
deviation of activity duration would be calculated as:
(1)
where is the estimated standard deviation of the reciprocal of productivity that is
calculated from Equation (1) by substituting 1/P for x.
1 Estimating Resource Requirements for Work Activities
In addition to precedence relationships and time durations, resource
requirements are usually estimated for each activity. Since the work activities defined for a
project are comprehensive, the total resources required for the project are the sum of the
resources required for the various activities. By making resource requirement estimates for
each activity, the requirements for particular resources during the course of the project can
be identified. Potential bottlenecks can thus be identified, and schedule, resource allocation
or technology changes made to avoid problems.
Many formal scheduling procedures can incorporate constraints imposed by the availability
of particular resources. For example, the unavailability of a specific piece of equipment or
crew may prohibit activities from being undertaken at a particular time. Another type of
resource is space. A planner typically will schedule only one activity in the same location at
the same time. While activities requiring the same space may have no necessary technical
precedence, simultaneous work might not be possible.
The initial problem in estimating resource requirements is to decide the extent and number of
resources that might be defined. At a very aggregate level, resources categories might be
limited to the amount of labor (measured in man-hours or in dollars), the amount of materials
required for an activity, and the total cost of the activity. At this aggregate level, the resource
estimates may be useful for purposes of project monitoring and cash flow planning. For
example, actual expenditures on an activity can be compared with the estimated required
resources to reveal any problems that are being encountered during the course of a project.
More detailed definitions of required resources would include the number and type of both
workers and equipment required by an activity as well as the amount and types of materials.
Standard resource requirements for particular activities can be recorded and adjusted for the
special conditions of particular projects. As a result, the resources types required for
particular activities may already be defined. Reliance on historical or standard activity
definitions of this type requires a standard coding system for activities.
In making adjustments for the resources required by a particular activity, most of the
problems encountered in forming duration estimations described in the previous section are
also present. In particular, resources such as labor requirements will vary in proportion to the
work productivity, Pij, used to estimate activity durations in Equation (1). Mathematically,
a typical estimating equation would be:
where Rkij are the resources of type k required by activity ij, Dij is the duration of activity ij,
Nij is the number of standard crews allocated to activity ij, and Ukij is the amount of resource
type k used per standard crew. For example, if an activity required eight hours with two
crews assigned and each crew required three workers, the effort would be R = 823 = 48
labor-hours.
From the planning perspective, the important decisions in estimating resource requirements
are to determine the type of technology and equipment to employ and the number of crews to
allocate to each task. Clearly, assigning additional crews might result in faster completion of
a particular activity. However, additional crews might result in congestion and coordination
problems, so that work productivity might decline.
Example: Pouring Concrete Slabs
For large concrete pours on horizontal slabs, it is important to plan the activity so that the
slab for a full block can be completed continuously in a single day. Resources required for
TABLE 1.7 Major Divisions in the Uniform Construction Index
0 Conditions of the contract
1 General requirements
2 Site work
3 Concrete
4 Masonry
5 Metals
6 Wood and plastics
7 Thermal and moisture prevention
8 Doors and windows
9 Finishes
10 Specialties
11 Equipment
12 Furnishings
13 Special construction
14 Conveying system
15 Mechanical
16 Electrical
While MASTERFORMAT provides a very useful means of organizing and communicating
information, it has some obvious limitations as a complete project coding system. First, more
specific information such as location of work or responsible organization might be required
for project cost control. Code extensions are then added in addition to the digits in the basic
MASTERFORMAT codes. For example, a typical extended code might have the following
elements:
0534.02220. A.00
The first four digits indicate the project for this activity; this code refers to an activity on
project number 0534. The next five digits refer to the MASTERFORMAT secondary
division; referring to Table 1.7, this activity would be 02220 "Excavating, Backfilling and
Compacting." The next two digits refer to specific activities defined within this
MASTERFORMAT code; the digits 21 in this example might refer to excavation of column
footings. The next character refers to the block or general area on the site that the activity
will take place; in this case, block A is indicated. The digits 00 could be replaced by a code
to indicate the responsible organization for the activity. Finally, the characters cf34 refer to
the particular design element number for which this excavation is intended; in this case,
column footing number 34 is intended. Thus, this activity is to perform the excavation for
column footing number 34 in block A on the site. Note that a number of additional activities
would be associated with column footing 34, including formwork and concreting. Additional
fields in the coding systems might also be added to indicate the responsible crew for this
activity or to identify the specific location of the activity on the site (defined, for example, as
x, y and z coordinates with respect to a base point).
As a second problem, the MASTERFORMAT system was originally designed for building
construction activities, so it is difficult to include various construction activities for other
types of facilities or activities associated with planning or design. Different coding systems
have been provided by other organizations in particular sub-fields such as power plants or
roadways. Nevertheless, MASTERFORMAT provides a useful starting point for organizing
information in different construction domains.
TABLE 1.7 Secondary Divisions in MASTERFORMAT for Site Work
02-
02-
02-
Subsurface investigation
Standard penetration tests
Seismic investigation
02-
02-
02-
02-
02-
Demolition
Building demolition
Selective demolition
Concrete removal
Asbestos removal
02-
02-
02-
02-
Site preparation
Site clearing
Selective clearing
Structure moving
02-140 Dewatering
02-150 Shoring and underpinning
02-160 Excavation supporting system
02-170 Cofferdams
02-
02-
02-
02-
02-
02-
02-
02-
02-
Earthwork
Grading
Excavating, backfilling and compaction
Base course
Soil stabilization
Vibro-floatation
Slope protection
Soil treatment
Earth dams
02-
02-
02-
02-
02-
02-
Tunneling
Tunnel ventilation
Tunnel excavating
Tunnel lining
Tunnel grouting
Tunnel support systems
02-
02-
02-
02-
02-
Piles and caissons
Pile driving
Driven piles
Bored/augered piles
Caissons
02-450 Railroad work
02-480 Marine work
02-
02-
02-
02-
02-
02-
02-
02-
02-
02-
02-
Paving and surfacing
Walk, road and parking paving
Unit pavers
Curbs
Athletic paving and surfacing
Synthetic surfacing
Surfacing
Highway paving
Airfield paving
Pavement repair
Pavement marking
02-600 Piped utility materials
02-660 Water distribution
02-680 Fuel distribution
02-700 Sewage and drainage
02-760 Restoration of underground pipelines
02-770 Ponds and reservoirs
02-800 Power and communications
02-880 Site improvements
02-900 Landscaping
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Construction planning scheduling
Course: Civil Engineering (CE)
999+ Documents
Students shared 1445 documents in this course
University: Anna University
Was this document helpful?
2
UNIT-1
Construction Planning
1.1 Basic Concepts in the Development of Construction Plans
Construction planning is a fundamental and challenging activity in the management and
execution of construction projects. It involves the
Choice of technology
Definition of work tasks
The estimation of the required resources and durations for individual
tasks,
The identification of any interactions among the different work tasks.
A good construction plan is the basis for developing the budget and the schedule for work.
Developing the construction plan is a critical task in the management of construction, even if
the plan is not written or otherwise formally recorded. In addition to these technical aspects
of construction planning, it may also be necessary to make organizational decisions about the
relationships between project participants and even which organizations to include in a
project.
Sherlock Holmes noted that forming a construction plan is a highly challenging task.
Essential aspects of construction planning include the
Generation of required activities.
Analysis of the implications of these activities.
Choice among the various alternative means of performing activities.
In developing a construction plan, it is common to adopt a primary emphasis on either cost
control or on schedule control as illustrated in Fig. Some projects are primarily divided into
expense categories with associated costs. In these cases, construction planning is cost or
expense oriented.
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