Double relationship - Double trouble or playing football?

Hi Pio

It is not allowed - SS FF Links should never be used in a construction programme.

Best regards

Mike Testro

Hi Mike,

Thanks for the reply. Is there a reason why? what is the effect on the logic? AS I observe, the successor's FD will adjust automatically when the activity is delayed, even if the successor has already actually started. That means its realistic. Otherwise, if SS only was sued, the successor will not be affected if the activity will be delayed.

Pio

• From: http://www.mosaicprojects.com.au/PDF/Links_Lags_Ladders.pdf
• Managing the Overlap
  • However, if there is a need for Task A to continue to feed work to Task B our strong recommendation is to either: 
    • • Set the link type to ‘progressive feed’; a number of tools have this feature. Progressive feed only allows B to progress proportionally to A. 
    • • Use both a SS and a FF link to at least constrain the start and finish of B in relation to A. 

• If your current tool is incapable of either and you want to develop useful schedules that produce predictable results during the progress of the works either, stick exclusively to Finish-to-Start links, buy a software tool that works or add some additional logic to simulate the effect. 

• Do the right math and do not perform workarounds such as ss-ff or arbitrarily splitting into multiple activities to create only fs relationships that will fall short of modeling true continuous feed in addition to other undesired results.

• Get rid of incapable old fashioned software. Consider Spider Project that can perfectly model continuous feed using volume lag, software that only provide you with time lag is not good enough. 

• Rafael

This may apply to Column and Suspended Slab with Activities description as Columns & Suspended Slab.

Say Suspended Slab @ EL=+4.00 was casted yesterday, the columns @ EL=+4.00 and suspended slab @ EL=8.00 activities can now be started. The Activities for Forwmworks for Suspended Slab @ EL=8.00 may wait for some Columns to be started in order to commence but the Suspended Slab @ EL=8.00 can never be completed unless all Columns are completed.

Susp Slab SS+3d with columns

Slab FF+6d with columns

Although in some cases Suspended Slab may not need to wait for some columns to be started becasue Scaffoldings used for the safety purposes in casting of columns will be retained to be used for the slab formworks. Therefore Suspended Slab activities can start once predecessor slab already casted.

For Activites with a deeper details such as Formworks for Columns @ Grid 1 & 2, Grid A-M, Rebars for Columns @ Grid 1 & 2, Grid A-M, Laying of Scaffolding along Grid 1 & 2, Grid A-M, Casting of Concrete for Columns @ Grid 1 and so on.... the required Link is only FS.