AoA; AoN; Design and construction philosophy; EVA; Labour curve; Network programmes
The previous chapters described various methods and techniques developed to produce meaningful and practical network programmes. In this chapter, most of these techniques are combined in two fully worked examples. One is mainly of a civil engineering and building nature and the other is concerned with mechanical erection – both are practical and could be applied to real situations.
The first example covers the planning, man-hour control and cost control of a construction project of a bungalow. Before any planning work is started, it is advantageous to write down the salient parameters of the design and construction, or what is grandly called the ‘design and construction philosophy’. This ensures that everyone who participates in the project knows not only what has to be done, but why it is being done in a particular way. Indeed, if the design and construction philosophy is circulated before the programme, time- and cost-saving suggestions may well be volunteered by some recipients which, if acceptable, can be incorporated into the final plan.
Design and Construction Philosophy
1. The bungalow is constructed on strip footings.
2. External walls are in two skins of brick with a cavity. Internal partitions are in plasterboard on timber studding.
3. The floor is suspended on brick piers on an oversite concrete slab. Floorboards are T & G pine.
4. The roof is tiled on timber-trussed rafters with external gutters.
5. Internal finish is plaster on brick finished with emulsion paint.
6. Construction is by direct labour specially hired for the purpose. This includes specialist trades such as electrics and plumbing.
7. The work is financed by a bank loan, which is paid four-weekly on the basis of a regular site measure.
8. Labour is paid weekly. Suppliers and plant hires are paid 4weeks after delivery. Materials and plant must be ordered 2weeks before site requirement.
9. The average labour rate is £5 per hour or £250 per week for a 50-hour working week. This covers labourers and tradesmen.
10. The cross-section of the bungalow is shown in Fig. 47.1 and the sequence of activities is set out in Table 47.1, which shows the dependencies of each activity. All durations are in weeks. The network in Fig. 47.2 is in activity on arrow (AoA) format and the equivalent network in activity on node (AoN) format is shown in Fig. 47.3.
The activity letters refer to the activities shown on the cross-section diagram of Fig. 47.1, and on subsequent tables only these activity letters will be used. The total float column can, of course, only be completed when the network shown in Fig. 47.2 has been analysed (see Table 47.1).
Table 47.2 shows the complete analysis of the network including TLe (latest time end event), TEe (earliest time beginning event), total float and free float. It will be noted that none of the activities have free float. As mentioned in Chapter 21, free float is often confined to the dummy activities, which have been omitted from the table.
Table 47.1
Activity Letter
Activity–Description
Duration (Weeks)
Dependency
Total Float
A
Clear ground
2
Start
0
B
Lay foundations
3
A
0
C
Build dwarf walls
2
B
0
D
Oversite concrete
1
B
1
E
Floor joists
2
C and D
0
F
Main walls
5
E
0
G
Door and window frames
3
E
2
H
Ceiling joists
2
F and G
4
J
Roof timbers
6
F and G
0
K
Tiles
2
H and J
1
L
Floorboards
3
H and J
0
M
Ceiling boards
2
K and L
0
N
Skirtings
1
K and L
1
P
Glazing
2
M and N
0
Q
Plastering
2
P
2
R
Electrics
3
P
1
S
Plumbing and heating
4
P
0
T
Painting
3
Q, R and S
0
To enable the resource loading bar chart in Fig. 47.4 to be drawn, it helps to prepare a table of resources for each activity (Table 47.3). The resources are divided into two categories:
1. Labourers
2. Tradesmen
This is because tradesmen are more likely to be in short supply and could affect the programme.
The total labour histogram can now be drawn, together with the total labour curve (Fig. 47.5). It will be seen that the histogram has been hatched to differentiate between labourers and tradesmen, and shows that the maximum demand for tradesmen is eight men in weeks 27 and 28. Unfortunately, it is possible to employ only six tradesmen due to possible site congestion. What is to be done?
The advantage of network analysis with its float calculation is now apparent. Examination of the network shows that in weeks 27 and 28 the following operations (or activities) have to be carried out:
Activity Q
Plastering
3 men for 2weeks
Activity R
Electrics
2 men for 3weeks
Activity S
Plumbing and heating
3 men for 4weeks
The first step is to check which activities have floats. Consulting Table 47.2 reveals that Q (plastering) has 2weeks float and R (electrics) has 1week float. By delaying Q (plastering) by 2weeks and accelerating R (electrics) to be carried out in 2weeks by 3men per week, the maximum total in any week is reduced to 6. Alternatively, it may be possible to extend Q (plumbing) to 4weeks using 2men per week for the first 2weeks and 1man per week for the next 2weeks. At the same time, R (electrics) can be extended by 1week by employing 1man per week for the first 2weeks, and 2men per week for the next 2weeks. Again, the maximum total for weeks 27–31 is 6 tradesmen.
The new partial disposition of resources and revised histograms after the two alternative smoothing operations are shown in Figs 47.6 and 47.7. It will be noted that:
1. The overall programme duration has not been exceeded because the extra durations have been absorbed by the float.
2. The total number of man weeks of any trade has not changed, i.e., Q (plastering) still has 6man weeks and R (electrics) still has 6man weeks.
If it is not possible to obtain the necessary smoothing by utilizing and absorbing floats, the network logic may be amended, but this requires a careful reconsideration of the whole construction process.
The next operation is to use the EVA system to control the work on site. Multiplying for each activity, the number of weeks required to do the work by the number of men employed yields the number of man weeks. If this is multiplied by 50 (the average number of working hours in a week), the man-hours per activity can be obtained. A table can now be drawn up listing the activities, durations, number of men and budget hours (Table 47.4).
Table 47.2
a
b
c
d
e
F
g
h
Activity Letter
Node No.
Duration
TLe
TEe
TEb
d-f-c Total Float
e-f-c Free Float
A
1–2
2
2
2
0
0
0
B
2–3
3
5
5
2
0
0
C
3–5
2
7
7
5
0
0
D
4–6
1
7
6
5
1
0
E
5–7
2
9
9
7
0
0
F
7–9
5
14
14
9
0
0
G
8–10
3
14
12
9
2
0
H
11–12
2
20
16
14
4
0
J
13–14
6
20
20
14
0
0
K
14–15
2
23
22
20
1
0
L
14–16
3
23
23
20
0
0
M
16–17
2
25
25
23
0
0
N
16–18
1
25
24
23
1
0
P
19–20
2
27
27
25
0
0
Q
21–23
2
31
29
27
2
0
R
21–24
3
31
30
27
1
0
S
22–25
4
31
31
27
0
0
T
26–27
3
34
34
31
0
0
Table 47.3
Labour resources per week.
Activity Letter
Resource A Labourers
Resource B Tradesmen
Total
A
6
6
B
4
2
6
C
2
4
6
D
4
–
4
E
–
2
2
F
2
4
6
G
–
2
2
H
–
2
2
J
–
2
2
K
2
3
5
L
–
2
2
M
–
2
2
N
–
2
2
P
–
2
2
Q
1
3
4
R
–
2
2
S
1
3
4
T
–
4
4
As the bank will advance the money to pay for the construction in four-weekly tranches, the measurement and control system will have to be set up to monitor the work every 4weeks. The anticipated completion date is week 34, so that a measure in weeks 4, 8, 12, 16, 20, 24, 28, 32 and 36 will be required. By recording the actual hours worked each week and assessing the percentage complete for each activity each week the value hours for each activity can be quickly calculated. As described in Chapter 32, the overall percent complete, efficiency and predicted final hours can then be calculated. Table 47.5 shows a manual EVA analysis for four sample weeks (8, 16, 24 and 32).
In practice, this calculation will have to be carried out every week, either manually as shown or by computer using a simple spreadsheet. It must be remembered that only the activities actually worked on during the week in question have to be computed. The remaining activities are entered as shown in the previous week’s analysis.
Table 47.4
a
b
c
d
Activity Letter
Duration (Weeks)
No. of Men
b×c×50 Budget Hours
A
2
6
600
B
3
6
900
C
2
6
600
D
1
4
200
E
2
2
200
F
5
6
1500
G
3
2
300
H
2
2
200
J
6
2
600
K
2
5
500
L
3
2
300
M
2
2
200
N
1
2
100
P
2
2
200
Q
2
4
400
R
3
2
300
S
4
4
800
T
3
4
600
Total
8500
For purposes of progress payments, the value hours for every 4-week period must be multiplied by the average labour rate (£5per hour) and when added to the material and plant costs, the total value for payment purposes is obtained. This is shown later in this chapter.
At this stage it is more important to control the job, and for this to be done effectively, a set of curves must be drawn on a time base to enable the various parameters to be compared. The relationship between the actual hours and value hours gives a measure of the efficiency of the work, while that between the value hours and planned hours gives a measure of progress. The actual and value hours are plotted straight from the EVA analysis, but the planned hours must be obtained from the labour expenditure curve (Fig. 47.5) and multiplying the labour value (in men) by 50 (the number of working hours per week). For example, in week 16, the total labour used to date is 94 man weeks, giving 94×50=4700man-hours.
The complete set of curves (including the efficiency and percent complete curves) is shown in Fig. 47.8. In practice, it may be more convenient to draw the last two curves on a separate sheet, but provided the percentage scale is drawn on the opposite side to the man-hour scale; no confusion should arise. Again, a computer program can be written to plot these curves on a weekly basis as shown in Chapter 32.
Table 47.5
Period
Week 8
Week 16
Week 24
Week 32
Budget
Actual Cum.
%
V
Actual Cum.
%
V
Actual Cum.
%
V
Actual Cum.
%
V
A
600
600
100
600
600
100
600
600
100
600
600
100
600
B
900
800
100
900
800
100
900
800
100
900
800
100
900
C
600
550
100
600
550
100
600
550
100
600
550
100
600
D
200
220
90
180
240
100
200
240
100
200
240
100
200
E
200
110
40
80
180
100
200
180
100
200
180
100
200
F
1500
–
–
–
1200
80
1200
1550
100
1500
1550
100
1500
G
300
–
–
–
300
100
300
300
100
300
300
100
300
H
200
–
–
–
180
60
120
240
100
200
240
100
200
J
600
–
–
–
400
50
300
750
100
600
750
100
600
K
500
–
–
–
–
–
–
500
100
500
550
100
500
L
300
–
–
–
–
–
–
250
80
240
310
100
300
M
200
–
–
–
–
–
–
100
60
120
180
100
200
N
100
–
–
–
–
–
–
50
40
40
110
100
100
P
200
–
–
–
–
–
–
–
–
–
220
100
200
Q
400
–
–
–
–
–
–
–
–
–
480
100
400
R
300
–
–
–
–
–
–
–
–
–
160
60
180
S
800
–
–
–
–
–
–
–
–
–
600
80
640
T
600
–
–
–
–
–
–
–
–
–
100
10
60
Total
8500
2280
27.8
2360
4450
52
4420
6110
70.6
6000
7920
90.4
7680
Efficiency
103
99
98
96
Estimated final hours
8201
8557
8654
8761
Once the control system has been set up, it is essential to draw up the cash flow curve to ascertain what additional funding arrangements are required over the life of the project. In most cases where project financing is required, the cash flow curve will give an indication of how much will have to be obtained from the finance house or bank and when. In the case of this example, where the construction is financed by bank advances related to site progress, it is still necessary to check that the payments will, in fact, cover the outgoings. It can be seen from the curve in Fig. 47.10 that virtually permanent overdraft arrangements will have to be made to enable the men and suppliers to be paid regularly.
When considering cash flow, it is useful to produce a table showing the relationship between the usage of a resource, the payment date and the receipt of cash from the bank to pay for it – even retrospectively. It can be seen in Table 47.6 that
1. Materials have to be ordered 4weeks before use.
2. Materials have to be delivered 1week before use.
3. Materials are paid for 4weeks after delivery.
4. Labour is paid in the same week of use.
5. Measurements are made 3weeks after use.
6. Payment is made 1week after measurement.
Table 47.6
Week Intervals
1
2
3
4
5
6
7
8
Order date
Material delivery
Labour use
Material use
Labour payments
Pay suppliers
X
X
X
X
O
Measurement
M
Receipt from bank
Every 4 weeks
Starting week no. 5
R
First week no.
−3
−2
−1
1
2
3
4
5
Table 47.7
Activity
No. of Weeks
Labour Cost per Week
Material and Plant per Week
Material Cost and Plant
A
2
1500
100
200
B
3
1500
1200
3600
C
2
1500
700
1400
D
1
1000
800
800
E
2
500
500
1000
F
5
1500
1400
7000
G
3
500
600
1800
H
2
500
600
1200
J
6
500
600
3600
K
2
1300
1200
2400
L
3
500
700
2100
M
2
500
300
600
N
1
500
200
200
P
2
500
400
800
Q
2
1000
300
600
R
3
500
600
1800
S
4
1000
900
3600
T
3
1000
300
900
Material total
33,600
The next step is to tabulate the labour costs and material and plant costs on a weekly basis (Table 47.7). The last column in the table shows the total material and plant cost for every activity because all the materials and plant for an activity are being delivered 1 week before use and have to be paid for in one payment. For simplicity, no retentions are withheld (i.e., 100% payment is made to all suppliers when due).
A bar chart (Fig. 47.9) can now be produced, which is similar to that shown in Fig. 47.4. The main difference is that instead of drawing bars, the length of the activity is represented by the weekly resource. As there are two types of resources – men and materials and plant – each activity is represented by two lines. The top line represents the labour cost in £100units and the lower line the material and plant cost in £100units. When the chart is completed, the resources are added vertically for each week to give a weekly total of labour out (i.e., men being paid, line 1) and material and plant out (line 2). The total cash out and the cumulative outflow values can now be added in lines 3 and 4, respectively.
The chart also shows the measurements every 4weeks, starting in week 4 (line 5), and the payments 1 week later. The cumulative total cash is shown in line 6. To enable the outflow of materials and plant to be shown separately on the graph in Fig. 47.10, it was necessary to enter the cumulative outflow for material and plant in row 7. This figure shows the cash flow curves (i.e., cash in and cash out). The need for a more-or-less permanent overdraft of approximately £10,000 is apparent.