TH
HE basic network diagram is pre- pared on the assumption that resources are unlimited and available as required. As this will not be the situation in practice, it is necessary to smooth the possible fluctuating de- mand on the various types of re-
source.
Provided that the number of acti- vities is small and not too complicat- ed, manual methods of allocating resources can be used with reasonable results. One method of doing this is first to draw the arrow diagram to a time scale, as shown in Fig. 10, assuming that all activities start at their earliest times.
Vertical lines linking the activities preserve the sequence: dotted lines re-
floats. present dummies
and
As every activity is assumed to start at its earliest time, only free float is shown.
The time-scaled diagram shows clearly the number of jobs which are running parallel and, from this, the numbers of the resource under con- sideration can be plotted beneath the diagram in the form of a Histogram. This will show the fluctuation of de- mand on the resource. Fig. 10 shows
NETWORK ANALYSIS IN CONSTRUCTION
by P.A. Smith, AIOB
This is the last of the series of articles by Mr. P. A. Smith, who is a lecturer at Hong Kong Technical College. In it he des- cribes extensions of the basic technique of network analysis.
the fluctuation of demand on the re- source "Labourers”.
By moving activities within their float times, "peaks" in demand can be smoothed. Where an activity is on the critical path, any adjustment will extend the project time.
In the first instance, it is preferable to plot the Histogram for each re- source and attempt to do the "re- source levelling" without changing gang sizes or altering durations as these changes may create new critical paths.
An alternative method to Fig. 10 is shown in Fig. 11 this method is similar to that used in traditional bar charts. The total time available for carrying out the activity, i.e. the difference between Earliest start and Latest finish times are plotted as a continuous bar. The Earliest start plus the duration will give the Earliest Finish time and the portion remain- ing will be Total Float time.
Between
the Earliest start and
Latest finish times the actual sche- duled Start and Finish times as de- termined by resource requirements can be plotted.
If manual methods of resource levelling are carried out by an en- gineer with experience of bar-chart methods, this knowledge together with technical know-how can produce good results.
Although the method of levelling resources by making use of activity float times has been generally accept- ed, it has been shown by Kochanski3 that these methods can lead to un- economic solutions.
Use of Computers
A number of computer programmes are available for resource allocation. These programmes require that pri- ority rules specify the action to be taken when activities could be per- formed if the resources were avail- able.
Build Manholes
Float 4 Days
OR
2 8 2 L
Excavate for Drains
IL. MIC
Lay Drains
Float 2 Days
60
2 D. 2. L
I
70
Excavate to
Conc. Founds
6L
Start Bwk to D.P.C
90
(100)
4 B 2 L.
Set Out
Strip Site Red Levels
Start Exc. to Founds
Finish Exc. to Founds
to
20
30
40
50
1.L.
I.L. M/C I.L. M.C
I.L. M/C
I.L. M/C
Float 2 Days
LABOURERS
O-NWI
LABOURERS
CORN-O
All activities starting at their earliest limes
2
3
4
5 6
7
8
9
10
11
12 13
14
15
16
Resource levelled within float times
1
2
3
5
Fig. 10.
56
܂
17
་་
18
19 20 21
242
Start Conc to G F
Slab
40
[150]
6 L Conc to
Gr ¡Beam
Floats 1 Day
Finish Brickwork |lo_D.P.C.
8. 2. L. Reinft to
Form work to Ground Beam
Gr. Beam
120
4. C 2. L.
I
I Hardcore to G.F
4 L.
130 2.S.2.L. 6
Blinding to G.F
10
6 L.
23 24 25 26
27
28
29
30
31
32 33 34
10
11
12
13
14
15 16
17 18 19 20 21 22
23 24
25
26
27 28
29
30
31
12
33 34
days
Far East Architect & Builder August, 1967