Figure 9-11. - Lead on start of a preceeding activity.
completed. This type of overlap is known as a lag. It is also a common occurrence that both the start and the finish of two activities maybe linked, but, in this case, they are accommodated by a combination of lead and lag.
As seen in figure 9-11, a lead (or partial start) is indicated by drawing the connector from the start of the preceding activity (1). In figure 9-12, a lag (or partial finish) is indicated by drawing the connector from the end of the following activity (3). The values may be given in the basic time units of the project, as with a delay, or as a percentage of overlap. In certain circumstances, they can be stated as quantities if the performance of the activity can be measured on a quantitative basis. The indication of the type and amount of delay, lead, or lag is generally referred to as a "lag factor."
In figure 9-11, Activity 3 may start when Activity 1 is 1-day completed, although Activity 2 must wait for the final completion of Activity 1. In figure 9-12, Activity 3 may start when Activity 2 is completed but will still have 1 day to go when Activity 1 is completed. The last phase of Activity 3 may not begin until Activity 1 has been completed. In figure 9-13, Activity 2 may start when Activity 1 is
Figure 9-12. - Lag on finish a of following activity.
Figure 9-13. - Start and finish lags on same activity.
advanced 3 days but will still have 4 days of work left when Activity 1 is completed.
SPLITTING CONNECTORS. - The number of sequencing connectors becomes large when a net work is of a great size. When two activities are remote from each other and have to be connected, the lines tend to become lost or difficult to follow. In such cases, it is not necessary to draw a continuous line between the two activities. Their relationship is shown by circles with the following-activity number in one and the preceding-activity number in the other. In figure 9-14, both Activities 2 and 6 are dependent upon Activity 1.
DIRECT LINKING USING AN EVENT. - When the number of common preceding and succeeding activities in a particular complex is large, as in figure 9-15, a dummy event or focal activity of zero duration may be introduced to simplify the network. The use of such a dummy event is shown in figure 9-16, which is a simplification of figure 9-15. Although the effect in terms of scheduling is the same, the introduction of the dummy improves the clarity of the diagram.
JOINING CONNECTORS. - In many in- stances, there are opportunities to join several
Figure 9-14. - Splitting connectors.Continue Reading