Schedule Risk Analysis with Acumen: Varying Activity Constraint Type

Marty Fuentes
| December 15, 2020

This article provides an overview on how varying inputs and parameters affect the date outputs, in particular, the P0, P50, and P100 dates, in the Schedule Risk Analysis (SRA) with software Deltek Acumen Fuse. By understanding how Acumen behaves with respect to varying conditions, schedulers, risk managers, and key stakeholders alike will be guided on providing only realistic input values for the SRA.

In this analysis, the activity constraint type is varied while holding all other parameters constant. A simple schedule was developed using Primavera P6 for a straightforward understanding of the relationship between the inputs and the SRA results generated from Acumen.

The output shows that hard constraints should not be used in the Primavera P6 schedule when used for SRA. Soft constraints, on the other hand, have an impact on the deterministic dates and can be used in the schedule for SRA.

See also:

Building Information Modelling: The Future of Project Management

Schedule Risk Analysis With Acumen: Different Activity Types

Schedule Risk Analysis With Acumen: Effects of Floats And Lags on Results

Activity Constraint (Case 08).

Input

Risk assigned to a project with different types of activity constraint.
1 risk mapped to a single activity.
1,000 iterations set in Deltek Acumen Fuse.
All other parameters are set to be the same in each case/project shown in Figure 1 below.

Figure 1. Primavera Schedule with Different Activity Constraints.

Table 1. Risk Input for Different Activity Constraints.

Output

Figure 2. Risk Exposure Histogram Generated from Acumen (see tabulated values in Table 2).

Figure 3. Risk Drivers Generated from Acumen (see tabulated values in Table 2).

Analysis

Tabulation of the results of Figures 2 and 3 are shown in Table 2 along with calculations for analysis.

Table 2. Results and Calculations

Though C08B and C08C have deterministic dates (DT) differing from C08A driven by varying constraints on a start milestone activity, all returns the same P-dates as if ignoring the effect of the soft constraints assigned (start on or before, start on, and start on or after). The same can be said of cases C08D, C08E, and C08F with the assigned different kinds of finish milestone constraints (finish on or before, finish on, and finish on or after).

However, when a mandatory constraint is assigned, the schedule stopped from flowing resulting to P-dates the same with the DT.

In the last case, C08J, an As Late As Possible constraint is used. This constraint was just ignored by Acumen and the 50 working days (not visible in the schedule due to the effect of the constraint) total float when unconstrained buffered the deterministic date to shift by just 50 work days at P100.

Takeaways

Acumen analyzes the schedule as if there are no soft constraints assigned (start on, start on or before, start on or after, finish on, finish on or before, finish on or after, and as late as possible).
The resulting P-dates (P0, P50, P100) are residual to the max duration and the total float along the path being analysed in the schedule. The total float can be determined by removing the soft constraints. However, regardless of whether there are soft constraints assigned or not, the results will have the same P-dates.
Hard constraints (mandatory start and mandatory finish) “stop the flow” of the schedule and should not be used in Schedule Risk Analysis.