Tips on Linking Activities – Chapter 02

Continuing further on the topic with the summary of the previous article:

The links of ‘Start to Start’ or ‘Finish to Finish’ on their own are not sufficient for preparing the Schedule & Planners should not get carried away with the end dates alone, Planners must check each & every activity to ensure:

a)  The technical conditions are met with for both start and end dates for activities

b)  The idling or the over-allocation of resources.

Let’s check with some more limitations of these same links using the same example as given in Chapter 01. 

The Typical List of Activities were:

Block-work Masonry - Flat 101

Plastering – Flat 101

Painting – Flat 101

Block-work Masonry - Flat 102

Plastering – Flat 102,

Painting – Flat 102

Block-work Masonry - Flat 103

Plastering – Flat 103

Painting – Flat 103

Further for ease of understanding and meeting the technical conditions I am considering that for a flat the Block masonry takes 18 days & per wall 5 days are required. Similarly the Plastering takes 16 days total & per wall takes 3 days, further the Painting takes 18 days & per wall it takes 5 days. I have considered these durations so that the technical conditions are met which are:

1.  The Plastering can after 5+7 = 12 days after start of Block Masonry and can end only after 7+3 = 10 days after end of Block Masonry.

2.  The Painting can start after 3+7 = 10 days after start of plastering and can end only after 7+5 = 12 days after end of plastering.

3.  The Block Masonry of second flat can start after completion of block masonry of first flat and similarly for third flat it starts after completion of second flat. Thus the block masonry has link of ‘Finish to Start’

The Schedule with ‘Start to Start’ link will look like this:


Now consider the following various scenarios and their impact on the schedule and how ‘Start to Start’ link behaves:

1.    Start of Activity 01 – Block Masonry for Flat 101 is delayed by 3 days:


Updated Schedule shifts by 3 days and end date is revised by 3 days. Technical Conditions are meeting as in the original schedule.

2. Activity 01-Block Masonry Flat 101 is started on time but is delayed by 3 days in completion. 



Updated schedule will show overall delay by 3 days as the activities of Block Masonry are linked with ‘Finish to Start’ and for Flat 102 & 103 the Plastering and Painting activities will also shift by 3 days because of the ‘Start to Start’ link with Block Masonry. For Flat 101 the Plastering and Painting activities won’t show any delay as these were having ‘Start to Start’ link with Block Masonry of Flat 101, which started on the correct time & the delay was in completion only. Whereas the fact would be that both Plastering and Painting for Flat 101 will get delayed due to technical conditions and the updated schedule is not capturing it.

You can check with several such permutations and combinations:

Block Masonry starts late by 3 days but gets completed on original end date – Plastering & thus Painting will show a delayed start as well as delayed completion.

Block Masonry starts on original start date & completed earlier than original end date – Plastering & thus Painting will show the same start and end date as original schedule.

For these scenarios, although the updated schedule is giving incorrect picture, there is no flaw in meeting technical condition.

Now, let’s check how the schedule behaves for the same example with ‘Finish to Finish’ link:

The original schedule with ‘Finish to Finish’ links will look like this:



Can you notice that it is exactly same as the Schedule with ‘Start to Start’ link? Also all the technical conditions are met-with. 

Now consider the following various scenarios and their impact on the schedule and how ‘Finish to Finish’ link behaves:


1. Start of Activity 01 – Block Masonry for Flat 101 is delayed by 3 days:


Updated Schedule shifts by 3 days and end date is revised by 3 days. Technical Conditions are meeting as in the original schedule.


2. Activity 01-Block Masonry Flat 101 is started on time but is delayed by 3 days in completion.



Notice the overall end date, shifted by 3 days and also notice that all the activities also are shifted by 3 days, exactly same as in the first scenario. This thus ensures that the technical conditions are met with for the activities of Plastering & painting in Flat 101 as well where the block masonry was delayed by 3 days. Although the Plastering & thus Painting could have started earlier based on start date of the masonry, but the update is showing a delayed start, however is giving a correct end date to meet technical conditions.


3. Activity 01-Block Masonry Flat 101 is started late but completed on original end date


As you can notice in updated schedule the start & end date remain same for all other activities due to the no change in the end date for Block Masonry for flat 101. There is an issue that the Plastering and hence the Painting actually cannot start on the same date as in schedule as the technical conditions are not met-with. Although the end date as per updated schedule is not impacted, there would a 3 days delay for Flat 101 and Plastering and Painting for Flat 101 and 102 will have some overlap needing additional resources.   

Conclusion:

The real impact may not be seen as the technical conditions may not be met-with in the updated schedules in the following scenarios:

1.    Activities having ‘Start to Start’ link - If the predecessors of such activities though started on time are delayed in completion.

2.    Activities having ‘Finish to Finish’ link - If the predecessors of such activities though delayed in start, gets completed on time.

The planners have to keep an eye on predecessors of each activity that has either the ‘Start to Start’ or ‘Finish to Finish’ link and must cross verify after every update that all the technical conditions are meeting for either start or end date of activity.

Remember that the example is showing only three activities but practically there would be several activities which would have links with Plastering and Painting in Flat 101 and all of these will have some impact which will not be captured in the updated schedule and this would be a big flaw. Hence we need to go through all the Successors for activities having ‘Start to Start’ or ‘Finish to Finish’ links in detail to find out correct impact.

 

Happy Planning!

 

ADGP                         www.decodingcm.com                    https://decodingcm.blogspot.com







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