BET2413 Project Scheduling Lecture 6: Relationships in Project Network

Learning Outcomes LO1: Identify relationships in project network LO2: Differentiate different types of relationships in project network

Recap Leads and Lags are types of float In project management, there are four types of dependencies: –Finish to Start (FS) - Later task does not start until the previous task is finished –Finish to Finish (FF) - Later task does not finish until the previous task is finished –Start to Start (SS) - Later task does not start until the previous task starts –Start to Finish (SF) - Later task does not finish before previous task starts

Introduction The concept of Lead Time and Lag Time is very important in project scheduling network diagram. As a Project Manager, you must know about the Lead Time and Lag time in order to better understand your project plan and execute it accordingly.

Leads and Lags Usually, when the first activity finishes, a second activity starts. This type of activity sequence is called Finish to Start and it happens the majority of the time. However, there are many instances when other situations arise; e.g. a second activity starts while first activity is about to finish, or a second activity will start a few days after finishing the first activity. These two situations are termed as Lead and Lag.

Lead Time When the first activity is still running and second activity starts, this is called Lead, and the balance of time for the first activity is known as Lead Time. Lead Time is the overlap between the first and second activity.

Lead Time Example For example, let say that time duration for the first activity is 20 days, and for the second activity it is 15 days. As the first activity completes its first 15 days, you start working on the second activity. (Please note that the first activity still has 5 days to finish itself completely.)

Lead Time Example (Cont’d) In this case we’d say that Lead Time is 5 days, or Finish to Start activity has 5 days Lead Time

Lead Time – Real World Example You’re constructing a two-floor building, and now you have two activities in sequence; i.e. electrical work and painting. However, as you complete the electrical work of ground floor, you start painting it, and electrical work for first floor continues.

Lag Time When first activity completes, if there is then a delay or wait period before the second activity starts, this is called lag and the delay is known as the Lag Time Lag Time is the delay between the first and second activity.

Lag Time Example For example, the time duration for the first activity is 3 days, and for the second activity it is 2 days. After completing the first activity you wait for one day, and then you start second activity. (Please note that, here you start second activity after one day of completing the first activity.)

Lag Time Example (Cont’d) In this case we say that Lag Time is one day, or Finish to Start activity with one day delay or lag.

Lag Time – Real World Example Suppose you have to paint a newly constructed room. So the first activity would be applying the primer coating and then you will go for the final painting. However, after applying the primer coating, you must give it some time to dry properly. Once the primer coating dries, you can start final painting. The time given for coating to dry itself is called the lag time.

More Example Take the scenario of building two identical walls of the same house using the same material. Let's say, building the first wall is task A and building the second one is task B. The engineer wants to delay task B for two days. This is due to the fact that the material used for both A and B are a new type, so the engineer wants to learn from A and then apply if there is anything to B. Therefore, the two tasks A and B have a SS relationship.

Example (cont’d) The time between the start dates of the two tasks can be defined as a lag (2 days in this case).

Extended Network Techniques Lags –The minimum amount of time a dependent activity must be delayed to begin or end. Lengthy activities are broken down to reduce the delay in the start of successor activities. Lags can be used to constrain finish-to-start, start- to-start, finish-to-finish, start-to-finish, or combination relationships.

Finish-to-Start Relationship Start-to-Start Relationship Use of Lags

Use of Lags to Reduce Detail

Finish-to-Finish Relationship Start-to-Finish Relationship Combination Relationship

Extended Network Techniques Laddering –Activities are broken into segments so the following activity can begin sooner and not delay the work.

Example of Laddering Using Finish-to-Start Relationship