It is hard to answer your question, because we don’t know the circumstances of the particular activities....

Alot of times a SS & FF can be used with the Pred activity including lags for both SS and FF, and usually you have to adjust the duration to make both of the Pred. Relationships as drivers...The asterict that will be on the pred. Box...

For example, if the pred is ISO issue and the current activity is spool fabrication...You could say SS lag 5 FF lag 60...The fabrication can’t start till 5 days after the first ISO is issued, but can’t finish until 60 days after the last ISO is issued...Then you would adjust the spool fabrication duration to make both of the pred relationships as drivers...

Hope this helped...

In addition, you have to consult your Construction Manager to reconcile the construction methodology and sequences of activities that he wants to implement during the construction. This will defined your logic and correct relationship of your activities. From there you can define which activities run on parallel (SS) and which activities need finish before other activities start (FS) and so on (SF, FF). Check your design, drawings and procurement items if constraining your activity. Check your deliverable dates and milestones that need to attain. After getting all information and derived to your schedule then review it again together with construction manager for any changes. I believed in this method will direct you on the correct path and produced a meaningful schedule that gives you a correct total float.

khawaja, I’m not quite sure I understand your question, but I’ll give it a shot...

1. In an FS relationship (unless there is negative lag!), the entire predecessor must be finished before the successor can start. If the link is instead SS (with or without an additional FF), then at least some of the successor can start before the predecessor is finished.

2. In general, FF+lag and FS+lag relationships are qualitatively different from SS+lag and SF+lag relationships.
a. In the two former cases, the time (and delay) is being added AFTER the completion of the predecessor. Therefore, for scheduling purposes, any lag where the relationship starts with F is like a separate activity, and can usually be modeled as such. If they are on the critical path, FF+lag and FS+lag can have their own separate DRAG and DRAG Cost.
b. In the two latter cases (SS+lag and SF+lag), the time (and delay) is because of WORK ALREADY MODELED in the predecessor activity! For example, if DIG TRENCH is an SS+5 predecessor of LAY PIPE, those 5 days are due to work scheduled for the first five days of DIG TRENCH. Therefore if that relationship (and lag) is on the CP, the DRAG and DRAG Cost belong to the predecessor (DIG TRENCH), and if we can get that first 200 metres of trench dug in three days, we will have reduced its DRAG (and the scheduled project duration) by two days.

3. I honestly have no idea what you mean by "a better way to attain a realistic TOTAL FLOAT" or why that goal is so important to you. DRAG, which might be important, is easier to compute with only FS relationships. But if you are going to limit yourself to FS relationships, you have to make sure that all activities are adequately decomposed ("DIG INIT. 100m. OF TRENCH" and "DIG REST OF TRENCH"), or you’ll end up with an unnecessarily elongated schedule.

In palindromic terms:

"No! I tag no legal SS lag ’elongation’."