THE RESOURCE DRIVEN VS. THE LOGIC DRIVEN SCHEDULE

THE RESOURCE DRIVEN VS. THE LOGIC DRIVEN SCHEDULE

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For purpose of this presentation I am defining two resource leveling approaches.

I. Leveling the Resource Driven Schedule: does not depend on activity links to resource level the schedule. It is the resource leveling algorithm that works it out. All it requires is a mouse click to execute and get the resource leveled schedule. Updating is equally easy, activities are updated and at a single click of the mouse we get the resource leveled update schedule.

II. Leveling the Logic Driven Schedule leveling: requires a tedious process in order to level resources where the scheduler systematically delays some activities until all resource overloads are erased.

Schedulers must sequence activities that are using the same skilled resources by adding date constraints (which is discouraged) or sequencing the work activities by adding preferential ‘soft’ logic (which is better.) However, as the project progresses the original soft logic must be modified to reflect the ever-changing resource assignments. This process becomes a lot of work for the scheduler to perform and is error-prone, becomes even more difficult if project Owners are resistive to allowing logic changes in the schedule updates [1].

[1] Reviewing Resource Leveled Schedules Using P6™ by Ron Winter, PSP Fellow of AACE International

In order to create true Resource Driven models the planning tool shall be able to deal with the basic constraints and resource types such as:


Manpower is a common Renewable Resource Type
  • Date Constraints: Start No Earlier Than and Finish No Latter Than.
  • Renewable Resources: available on a period-by-period basis such as labor resources and equipment.
  • Consumable Resources: have a limited consumption availability such as materials, once depleted activity stops until replenished.
  • Spatial Resources: required by a group of activities, rather than a single activity as renewable resources. The spatial resource is occupied from the first moment an activity from the group starts until the finish of all activities from that group. Cannot be modeled as if traditional Renewable Resources.
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Materials such as bricks are a common Consumable Resource Type.

 

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Elevated slab forms that are to remain in the building until the concrete have enough strength are common Spatial Resource Type in construction schedules. They are moved to other slabs within the same building until the building is finished using the forms. Then they can be moved to another building.

The planning tool shall also be able to model common scenarios such as:

  • Variable Quantities and Workloads: It makes no sense to delay an activity just because out of 10 resources one is not available. Common practice is to start activity with some minimum number of resources at slower speed and increase speed as more resources become available.
  • Teams: if some member of the team is not available activity execution will be delayed until required members are available because they can work only as a team.
  • Independent Assignment: assigned resource may work on activity without interaction with others
  • Shift Assignment: multiple teams can be assigned to an activity independently of each other to work in different shifts.
  • Automatic Skills Assignment: Any resource might have different skills, might have different production rates for each skill and several resources might replace a single one to make up for lower production rates.

If you select a planning tool not capable of dealing with the listed resource types and resource scheduling scenarios you might end up with a schedule model that will not be a true Resource Driven Schedule.

For a detailed discussion on how to deal with such common resource types and scheduling scenarios please refer to Enhanced Resource Planning publication within the following link.

We must acknowledge the possibility of having equal duration alternate schedule sequences and Phantom Float or we might end up making our decisions using incorrect scheduling information.

Phantom Float can be defined as the difference between current schedule activity start and the earliest possible activity start among all possible equivalent schedules. Current scheduling software do not provide us with reliable Phantom Floats. Resource driven schedules are effective in neutralizing Phantom Float.

It is by modeling delays on a resource driven schedule that at a single click of the mouse we can figure out that delaying a critical activity on current alternative schedule does not necessarily delays the schedule, an equal duration alternative schedule surfaces showing true impact.

The Resource Driven Schedule shown in figure 1 illustrates how it is possible to have several feasible solutions that might be duration equivalent and how to deal with them.

The schedule logic is: no hard links among activities, 5 days duration for all activities, one Resource A and one Resource B are available, resource assignments as shown, using automatic resource leveling.

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Figure 2 represents another one among several duration equivalent schedules. Each possible duration equivalent schedule might show different order of activity execution, a different longest path sequence if considering soft links as well as different float values.

Our sample schedule can show how float behaves when we perform a delay analysis on a resource driven vs a logic driven schedule.

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Figure 3 represents the resource driven schedule after the delay event. The schedule is not delayed even when a critical activity was delayed.

The schedule was not delayed because an equal duration alternate schedule sequence takes its place.

Figure 4 represents the Logic Driven Schedule after the delay event.

The schedule is delayed.

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Leveling the updated Logic Driven Schedule without deleting old dependencies A→B→C and further delaying other activities yields a longer duration schedule.

Keeping old resource dependencies do not help in any case obstruct the view, it is better if all are deleted and then proceed with the leveling in a similar way the baseline schedule was leveled. No wonder automatic resource leveling starts by deleting all temporary resource dependencies.

Because leveling the Resource Driven Schedule is a much simpler method and the resource leveling computer algorithms will consistently yield shorter duration schedules than manual methods I see no reason to use manual methods.

As we can see Resource Driven Schedules are more flexible to handle unanticipated events as well as Phantom Floats.

Resource driven schedules are effective in neutralizing preferential logic and activity duration padding, the two principal culprits of float sequestration[2].

[2] How Firms Can Avoid the Construction Schedule Float Game, ENR article, July 26, 2017 by Allen Chilmeran.

Our Contracts and Specifications as well as Delay Practices should stop playing the float game and mandate the use of Resource Driven Schedules as well as the identification and justification of any preferential logic.

The specified Scheduling Tool shall be able to model all resource types and scheduling scenarios necessary to create a true Resource Driven Schedule.

Thank you Rafael Dávila

Comments

Phantom float in commercial

Phantom float in commercial scheduling software

Highlights

·  RCS neglects the resource relations that arise between activities when competing for the same but unavailable resources.

·  In schedules with phantom float, falsely labeled non-critical activities are likely resource critical.

·  Primavera P6 and MS Project v2016 still create phantom float in resource-constrained schedules.

·  P6 and MS Project calculate total float based on a “Time Context” (LFEF) ignoring the presence of resource constraints.

·  The total float reported by P6 and MS Project after RCS cannot be trusted or used to anticipate/mitigate delaying events.

This paper is totally

This paper is totally pointless Does none scrutinise these before wasting our time

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