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Total Float

11 replies [Last post]
adab azeez
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In my project, There are three WBS. The first and third WBS are about project start and finish procedures. And the second WBS is about all project works of different desciplines. Is there any possible technique in P6 to identify the total float based on 2nd WBS start and end dates, not on the basis of entire project. Thanks in advance.

Replies

Anoon Iimos
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Simple answer is NONE. Your WBS1 drives WBS2, and WBS2 drives WBS3. That is how it is for sure. DO NOT PUT ANY CONSTRAINT! Simply disconnect WBS3 from WBS2, run your schedule and you will get your true float(s) for WBS 2. Up to you if you want to reconnect your WBS3 after.
Tom Boyle
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adab azeez,

As previously recommended by Zoltan and Santosh, the primary method to manipulate Total Float for a selected chain of activities is to modify the late dates using a (FOB) constraint.  You state that you have done this, but "...none of them is working."  Although you have not described why, I suspect that your interpretation of Total Float is complicated by the intersecting driving logic paths in WBS 2.  In P6 there are two obvious ways to differentiate those paths and gain clarity:

1. Set the date of the suggested FOB constraint on the WBS 2 completion milestone substantially (say ~100 days) before its Early date.  This will create negative float on the activities leading to the constrained milestone, while those (presumably WBS 3) activities that control the project's finish date will remain at TF~0.  The negative float is artificial.  While useful for identifying driving and near-driving paths to the constrained milestone, the values are essentially meaningless.  They should not be shared.

2. Remove the constraint, and replace it with a super-long dummy activity that is applied as a successor to the WBS 2 completion milestone.  Set the duration of this "super-long trailing dummy" long enough to substantially extend the finish date of the entire project.  (Also ensure that there are no other late or mandatory constraints and that the project has NO "Must Finish by" date assigned.)  As a result, the driving path to the WBS 2 completion milestone will have TF~0, and its near-driving paths will have small positive values.  Other activities (e.g. WBS 3) will gain substantial positive float.  In this case, the WBS 2 float values may be useful for internal reporting, but the corresponding float values for WBS 3 will be incorrect and should not be shared.

In general, your desire, "...I want the float based on WBS.2 finish date," is not universally compatible with accepted definition of Total Float.  In all cases, Total Float is the difference between an activity's Late date and the corresponding Early date, where these dates are derived from the most stringent restraints of the entire logic network.  If a given WBS.2 activity must be finished no later than a certain date to avoid delaying the project completion BUT a later finish could be allowed without violating the WBS.2 finish constraint, then the Late dates of the activity (and the corresponding Total Float) must reflect the most stringent successor condition - i.e. the project completion, NOT the WBS.2 finish.

Note: while these methods are useful for analysis of a well-constructed, logic-driven project schedule, their use must be TEMPORARY and for specific analyses only.  Any schedule modifications whose primary purpose is manipulation of Total Float should be reversed prior to any formal issue or distribution.  

While they are excellent analysis techniques, neither the MFP analysis suggested by Johannes nor the click-tracing method suggested (most recently) by Zoltan will affect the Total Float calculation.  Consequently, I don't think they address your explicit question. 


 

Zoltan Palffy
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add an activity code call it 2WBSCP for 2nd wbs critical path and give it a code value of 2CP

add the column 2WBSCP 

now filter for only the last activity of the 2nd WBS.

then go to the predecessor tab in the predecessot tab make sure that the total float, critical and driving are displayed in the predecesor window.

now high light the predecessor that has BOTH the driving and the critical boxes checked. If it is Both driving and critical boxes are not checked then click on the activity with the lowest total float value.

after the predecessor activit yis highlighted at the bottom  click on the GOTO button

keep doing this until you get back to the data date or the start of the project.

this will fill your screen with with all of the critical activities for the 2nd wbs

NOW in the 2WBSCP column assign the first activity the 2CP code or highlight all of the activities and right click and select assign and select 2WBSCP and choose 2cp as the code value

now you can add a filter 

where 2WBSCP equals 2cp

this will give you your critical path for th 2nd wbs

adab azeez
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Hi.. I have tried the multiple float path. But still it will calculate the float based on the finish date of entire project. I want floats based on the finish date of the second WBS. In my project there are three WBS : WBS.1. Operation shutdonw Activities WBS.2.Maintenance jobs WBS.3. Operation Start up Activities After wbs 1 is Compeleted, Wbs 2 will start.And after Entire WBS.2 is completed WBS.3 will start. There are multiple number of sub wbs in WBS.2. out of them we have an specific equipment ( wbs) which is our critical path based on longest path method. After this critical path activity is complete then only Wbs 3 ( operation start up activities) can be started. I have created a schedule and also assigned baseline. But the float calculated is based on the entire project finish date. Where as I want the float based on WBS.2 finish date.
Johannes Vandenberg
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Hi Adab

Can you not use "multiple floats paths" under the advanced tab of the scheduling options?

Have you maybe the "Must Finish date" box in the general tab project details filled with a date? 

Regards Johannes

adab azeez
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I tried both. But none of them is working.
Zoltan Palffy
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that is what I said 

Santosh Bhat
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Yes sorry it should've been a finish on or before constraint.
Zoltan Palffy
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ALWAYS use finish on or before if you use finish on it will not do what you want it WILL FNINSH on 

FINISH ON OR BEFORE Sets the late fnish date and is used during the backward pass of the schedule. It is a hard date that calculates the late dates starting at that date and goes backwards in time. 

adab azeez
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Thank you Santosh. I have done it. But unfortunately Could not see any result. The last activity of my second WBS is a Finish milestone. So I put constraint "Finish on" But no difference is observed yet. Is there any point I am missing? Please note that I have almost 25 sub WBS more under the second WBS.
Santosh Bhat
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Put a finish on constraint onto the last activity in the 2nd WBS.