Guild of Project Controls: Compendium | Roles | Assessment | Certifications | Membership

Tips on using this forum..

(1) Explain your problem, don't simply post "This isn't working". What were you doing when you faced the problem? What have you tried to resolve - did you look for a solution using "Search" ? Has it happened just once or several times?

(2) It's also good to get feedback when a solution is found, return to the original post to explain how it was resolved so that more people can also use the results.

SS+Lag plus FF+Lag

4 replies [Last post]
Sophia Gerami
User offline. Last seen 39 weeks 1 day ago. Offline
Joined: 4 Jul 2015
Posts: 2
Groups: None

I think we cannot have an activity with 2 relationships with the same successor activity(we need to decide the best logic) but my supervisor says we can have both SS+lag and FF+lag for one successor ! How can it be possible? it should be either SS+lag or FF+lag with the same successor. Do you agree or I'm wrong?


Zoltan Palffy
User offline. Last seen 9 hours 25 min ago. Offline
Joined: 13 Jul 2009
Posts: 2925
Groups: None

this is known as a compound relationship and is common.

if you only use a SS this could happen



Rafael Davila
User offline. Last seen 3 days 22 hours ago. Offline
Joined: 1 Mar 2004
Posts: 5018

Rafael Davila
User offline. Last seen 3 days 22 hours ago. Offline
Joined: 1 Mar 2004
Posts: 5018

The risks of splitting activities that shall be executed continuously can be far more dangerous than pretending concurrent logic does not exists. This is specially true if your model is to apply resource constraints, it might spread apart the segments of an activity that shall be continuous. In such case use of SS(+lag) in combination to FF(+lag) relationships will make a better model.

Best Regards, Rafael

Santosh Bhat
User offline. Last seen 22 hours 58 min ago. Offline
Joined: 15 Apr 2005
Posts: 330

Sophia, this is a common technique to schedule activities that might happen in parallel, but where the second activitiy is delayed. 

Think for example if yoare digging a long trench, do you wait for the entire trench to be finished, before you start laying pipe? or can you start laying a pipe say once the trench has moved along by a distance? and in the same way, you cannot finish laying the pipe until some time after the trenching is completed.  so a SS/FF link to the same successory reflects this.

It might not pass the DCMA checklist, but in my opinion, that should not be a factor in determing whats realistic.