Construction Schedule

It is a schedule which represents the time table the various items of work. If the following data is collected, the construction schedule can be formulated.

·        Number of operations.

·        Output of labour and machinery.

·        Quantity of various items of work.

·        Number of field workers and other resources (machinery equipment etc.)

·        The order in which the work is to be taken in hand.

Example

A small scale construction organization has to carry out six activities as given below.

Activity	Duration in days
A	8 days
B	12 days
C	10 days
D	8 days
E	6 days
F	10 days

Prepare a network diagram and calculate Earliest Start Time (EST), Latest Start Time (LST) and Float. Mark out the critical path and find the total project duration.

Solution

·        The EST is calculated by starting from the event 1 i.e. Activity ‘A’ and giving it a time 0 (EST)

·        The EST of activity B = 0 + duration of activity ‘A’ = 0 + 8 = 8

·        The EST of activity C = EST of B + duration of activity ‘C’ = 8 + 12 = 20

·        The EST of activity F = EST of C + duration of activity ‘F’ = 20 + 10 = 30

(The path 1, 2, 3, 5 gives 30 days, whereas the path 1, 2, 3, 4 gives 22 days as EST of activity F)

Unless the bigger value (30) is taken and until the activity is completed, which requires (30) days to complete, the next activity ‘F’ cannot be started.

·        The EST of activity D = 0 + duration of activity ‘A’ = 0 + 8 = 8

·        The EST of activity E = EST of activity + duration of D = 8 + 8 = 16

·       The LFT is calculated in the same manner as EST by proceeding backward from the last event to the first one. LFT for activity F is ‘40’

·        LFT for activity C and E = 40 – duration of activity F = 40 – 10 = 10

·        LFT of activity D = LFT for activity E – duration of activity ‘E’ = 30 – 6 = 24

·        LFT for activity B = LFT for activity C – duration of activity ‘C’ = 30 – 10 = 20

·        LFT for activity A = LFT for activity B – duration of activity ‘B’ = 20 – 12 = 8

·   The LST for each activity is calculated from the relation, LST = LFT of an activity – duration of that activity

·    The EFT for each activity is calculated from the relation EFT = EST of an activity + duration of that activity. Total float = (LST – EST) OR (LFT – EFT)

Activity	Duration ‘D’	EST	LST (LFT – D)	EFT (EST + D)	LFT	Total Float	Remarks
A	8	0	0	8	8	0	Critical
B	12	8	8	20	20	0	Critical
C	10	20	20	30	30	0	Critical
D	8	8	16	16	24	8
E	6	16	24	22	30	8
F	10	30	30	40	40	0	Critical