Transcript What Will You Learn

Estimating Activity Duration
• Time Interval
– Time Interval is selected according to the nature of
the activity (seconds - minutes …)
– It is common practice in construction industry to
use calendar day.
– Use one and only one time unit for any schedule
• Estimating Activity Duration
1.From Company’s Record
2.From Standard Estimating Guide
3.Interviewing Field Personnel
Weather and Contingency Allowance
• Two approaches for assignment of weather
allowance:
1.Add the Weather Allowance at the end of the project as a
separate activity
2.Add Weather Allowance to those affected by the weather.
– Can add weather allowance at the end of each construction
segment (site preparation, foundation …etc.
– Other contingency items
 Procurement Allowance
 Strikes
• Time Zone
– The close of the work period immediately preceding the start
of the project.
Precedence Diagram
• Advantages of Using Precedence
Diagram
1.No dummy activity are required.
2.A single number can be assigned to
identify each activity.
3.Analytical solution is simpler.
• Numbering System
Same concepts used in Arrow diagram
– Even or odd or in fives or tens
– Smaller numbers to the left
Redundant Linkages
20
A
30
B
40
C
(a) Incorrect Representation
20
A
30
B
40
C
(b) Correct Representation
Closing the network to give
single beginning and ending nodes
A
E
B
C
F
(a) Incorrect Representation
A
Start
Dummy
E
Finish
Dummy
B
C
F
(b) Correct Representation
Retaining Wall Precedence Diagram
Wall 2
Wall 1
Footing 2
Footing 1
20
Footing 2
40
Wall 2
10
Footing 1
30
Wall 1
Precedence Diagram Sequence Stepped and Numbered
10
A
5
Start
1
25
E
15
B
35
Finish
20
C
30
F
2
3
4
Advantage of Using
Precedence Diagram
1.No dummy activities are required.
2.A single number can be assigned for
identify each activity.
3.Analytical solution is simpler.
Constructing the Diagram
1.Constructing the Diagram
– Activities with no dependencies arranged
at the left
– Create a dummy start called “Contract
Award”
– Ball-of-string provides a mean to determine
sequence steps for each activity.
2.Arrange Activities in a Sequential Order
– Start by activity “Contract Award”
– Possible sequence step are these activities
located at the arrow head.
Create Activity List
• List all the possible activities beginning with
an active verb. (strip, repair...)
• Consider all procurement activities
– Obtain vinyl floor covering
– Obtain cabinet
– Painter availability. “Labor Procurement”
• Consider the relationship among the activities
• What does each activity depend upon?
• The planner must ask the field personnel how
they plan for the job, and why things should
be done the way proposed.
Constructing the Precedence Diagram
1.Create Activity list and eliminate
redundancies.
2.Construct Rough Diagram “Ball of string”
– Activities with no dependency arranged at the left
– Create dummy start if you have more than one
start “Contract Award”
– Ball-of-string provides a mean to determine
sequence steps for each activity.
3.Arrange Activities in a sequential order
– Start by first activity “Contract Award”
– Possible sequence steps are those activities
located at the arrowhead
Additional Rules/Practices
1.Event numbering is usually entered
after completing the diagram.
2.Common practice to assign i, j in such a
way that the number at the tail is small
than that at the head.
3.Choose some numbering pattern such
as
– Even number
– Odd number
Tabular Format (Precedence Diagram)
• Can be carried out on the tabular form
without preference to the diagram.
• Advantage: The time required to
construct the diagram is eliminated.
• Determination of early start and finish
date
• Start by time zero and add duration to
get EF for A, B, C, D
• For E choose the maximum EFD of 8 or
C
Determining Lag
LAG5-10
= ESD10 - EFD5 = 4 - 4
=0
LAG15-25 = ESD25 - EFD15 = 12 - 7 = 5
LAG20-25 = ESD25 - EFD20 = 12 - 6 = 6
Determining The Free-Float
• Free Float is the minimum of the lag of
the link that follow an activity.
• Look at the “Pre. Column” to find the
same number value of EF for terminal
activity “not following act.”
FF35 = LFD35 - EFD35 = 20 - 20 = 0
Determining the Total Float “Backward”
• Take TF of the terminal activity = 0
or FF35 = LFD35 - EFD35 = 20 - 20 = 0
TFI = Min (LAGIJ + TFJ)
TF30 = Min (LAG30-35 + TF35)
= Min (7 + 0) = 7
No other link
{
} { }
TF20 = Min LAG20-25 + TF25 = Min 6 + 0 = 6
LAG20-30 + TF30
1+7
INDF
• If the free float is zero - no INDF
INDFJ = FFJ - MaxI (TFI - LAGIJ)
INDF20 = FF20 - Max (TF5 - LAG5-20)
= 1 - (0 - 0) = 1
{
{ }
}
INDF30 = FF30 - Max TF15 - LAG15-30
TF20 - LAG20-30
=7 - 5 - 0 = 2
6-1