D1: Cascade D1: Cascade (Gantt) Charts(Gantt) Charts

D1: Cascade (Gantt) Charts

A cascade (Gantt) chart is another way to represent the activities of an activity network.

(Gantt is the name of the man who invented the chart)

The Work Of Henry GanttThe cascade (Gantt) chart is used to highlight a few things, such as the critical path of the activity network and the float for any non-critical activity.

Imagine you have to draw a cascade (Gantt)chart for the activity network below.

D1: Cascade (Gantt) Charts

You must find the critical path and calculate thefloat for any non-critical activity in order to do this.

D1: Cascade (Gantt) Charts

You must find the critical path and calculate thefloat for any non-critical activity in order to do this.

D1: Cascade (Gantt) Charts

You need to calculate the floats of the activities.This identifies the critical path: activities with 0 float are on it.Remember that float is calculated using

F(i, j) = lF(i, j) = ljj – e – eii - a - aijij

In other words, start with the late event time at the head event of the activity you are considering. Subtract the early event time at the tail event and the duration of the activity itself.

D1: Cascade (Gantt) Charts

So… Activity Float

A 2

B 1

C 0

D 2

E 0

F 4

G 3

H 0

I 3

J 0

K 6

L 0

This means that the critical path must be

C, E, H, J, L

D1: Cascade (Gantt) Charts

The cascade (Gantt) chart is drawn on a gridthat has its x-axis at the top. The axis must go up to at least the minimum duration of the project.

Each activity is represented by a rectangle with its label in the middle.

The critical path runs just below the x-axis of the cascade (Gantt) chart. The rectangles that make it up touch each other and run from time 0 to the minimum duration of the project.

After that, each new activity is on its own row. It must start from its early event time. The activity’s float is added to the end of the rectangle and shaded in.

D1: Cascade (Gantt) Charts

The cascade (Gantt) chart for this question is:

C E H J LAB

DFG

IK

D1: Cascade (Gantt) Charts

Notes

•A cascade (Gantt) chart will be one of the last things you do for a critical path analysis question. For it to be right, you must have labelled the early and late event times on the network correctly – early mistakes mean lots of lost marks.

•Activities on some critical paths can overlap. If this is the case, adapt your cascade (Gantt) chart. Keep the critical activities together by stacking overlapping activities: C E H J L

K

D1: Cascade (Gantt) Charts