Other Scheduling Methods - Construction Project Scheduling and Control - page 325

and a restraint from a point (event) within an activity representing some
portion completed to the start of another. The first is the traditional SS
restraint, but the latter is a new PS restraint. Similarly, RDM recognizes a
distinction between a restraint from the finish of one activity to the finish of
another, possibly with a specified period of delay, and a restraint from the
finish of one activity to permitting the continuation and completion of effort
on another. The first is the traditional FF, and the latter is the new FR, or
finish-to-remainder restraint.
4. Restraint reason/Why : RDM records (or, in some instances, calculates) the rea-
son why a restraint has been placed between two activities. The primary reasons
are either P (for physical) or R (for resource.) Since one of the attributes of a
good CPM is that each activity (other than the first and last) must have both a
physical predecessor to its start and a physical successor to its finish (to avoid
issues such as when a crew shows up to erect a roof and the walls have not
yet been erected), this information may be used to provide a better software
diagnostic to assure adherence to this rule. The “why” of the code is typically
“gravity” or “contract requirement” for physical restraints, and a listed resource
or activity code (such as subcontractor) for the resource restraints. The codes
may be augmented by a freeform description or title assigned to the restraint ,
similar to that provided to activities. A special form of the physical reason why
is coded as J (for just-in-time) and is used in calculation of a second backward
pass for determining the latest dates of predecessors to support the early start
of the immediate successor to the J restraint. Other special forms are used in
automated leveling routines and are beyond the scope of discussion of RDM
in this text.
5. Restraint relationship : RDM calculates and records the various relationships
between the two activities (or events) at the start and the finish of a restraint.
This calculation may be performed on all activity (or event) codes (including
resource codes) and registers when such a change. This, in turn, may be used
to create custom reports to highlight when there is a handoff between crafts or
subcontractors (calling for greater supervision by the project manager) or when
a crew moves from one location to another (calling for a manual or automated
check for a lag duration to account for moving of forms and equipment). Com-
parison of the two sets of activity codes may result in equal, not equal, greater
than, lesser than, one (or both) code fields blank, or other noted relationships.
(An increasing or decreasing crew size would be one example of differential
comparison.)
The implementation of RDM in commercial software is in its infancy.
Primavera Pertmaster 10 is currently the only product that implements this con-
cept. More information can be obtained at www.RDCPM.com.
10 Primavera Pertmaster has been renamed Oracle as Risk Analysis in the recent acquisition to Primavera by
Oracle.