King Fahad University of Petroleum and Minerals

Construction planning & scheduling CEM-510

PHANTOM FLOATBy k. kim & M. Jesus M. Garza, ASCE

Journal of Const. Eng. & Management

Presented

For : Dr . S. Al-Mohawis

By : Engr . Mostafa Darwish

Student # 220428

Nov. 1st, 03

OUTLINEOUTLINE

AbstractAbstract Introduction & Objective.Introduction & Objective. Problem Diagnosis.Problem Diagnosis. RCPM Algorithm.RCPM Algorithm. Application to Time Extension :Application to Time Extension :

- Initial completion time.- Initial completion time.

- Estimated completion time.- Estimated completion time.

- Rescheduled completion time.- Rescheduled completion time. Schedule stability.Schedule stability. Future studies.Future studies. Summary & Conclusion.Summary & Conclusion. Critique & Evaluation.Critique & Evaluation.

Abstract &IntroductionAbstract &IntroductionCompletion within time limit is essential for successful performance , Completion within time limit is essential for successful performance , regardless of the size .regardless of the size .

The basic assumption of the CPM, however, is that resources The basic assumption of the CPM, however, is that resources required by activities are unlimited , while some resources are highly required by activities are unlimited , while some resources are highly limited in practice. limited in practice.

Traditional (RCS) techniques can consider resource limitations, they Traditional (RCS) techniques can consider resource limitations, they do not provide the correct floats and critical path, as the CPM does .do not provide the correct floats and critical path, as the CPM does .

presents a resource-constrained critical path method presents a resource-constrained critical path method (RCPM)(RCPM) technique that capitalizes on and improves the existing technique that capitalizes on and improves the existing

critical path method ( CPM) and resource - constrained scheduling critical path method ( CPM) and resource - constrained scheduling (RCS) techniques.(RCS) techniques.

The difference between the "theoretical remaining " TF and the The difference between the "theoretical remaining " TF and the "actual remaining " TF referred to as "actual remaining " TF referred to as Phantom FloatPhantom Float in this study . in this study .

ObjectiveObjective

Develop a resource constrained CPM Develop a resource constrained CPM (RCPM)(RCPM) technique technique that takes advantages of both the CPM & the RCS that takes advantages of both the CPM & the RCS

techniques.techniques. : :

1- considers resource availability.1- considers resource availability.

2- correctly identifies floats & critical path.2- correctly identifies floats & critical path.

3- Provides a real stable schedule .3- Provides a real stable schedule .

Problem diagnosisProblem diagnosis

Activity sequence relies not only on technological Activity sequence relies not only on technological relationships but also on resource dependencies.relationships but also on resource dependencies.

there is a systematic way to identify the resource there is a systematic way to identify the resource dependency and to keep track of activity late finish time dependency and to keep track of activity late finish time considering both technological relationships & resource considering both technological relationships & resource

dependencies, then problem can be resolveddependencies, then problem can be resolved . .

RCPM AlgorithmRCPM Algorithm

RCPMRCPM algorithm is mainly composed of algorithm is mainly composed of fives stepsfives steps . an . an overview is shown in overview is shown in Table ITable I . . in order to make the problem simple, maximum available in order to make the problem simple, maximum available resource amount is assumed constant for whole project resource amount is assumed constant for whole project duration.duration.

RCPM AlgorithmRCPM Algorithm

STEP 1: CPMSTEP 1: CPM

similar to traditional RCS techniques similar to traditional RCS techniques the CPM is employed to find the early / the CPM is employed to find the early / late times and the TF of each activity , late times and the TF of each activity , applying forward and backward passes applying forward and backward passes assuming unlimited resources . A , B.assuming unlimited resources . A , B.

STEP 2 : Serial Method with creating STEP 2 : Serial Method with creating Resource Constrained Link .Resource Constrained Link .

serial RCS technique is to be applied , serial RCS technique is to be applied , all activities in the network are sorted all activities in the network are sorted by the LST ascending order and are by the LST ascending order and are checked for resource availability one at checked for resource availability one at

a time in the sorted ordera time in the sorted order . .

RCPM AlgorithmRCPM Algorithm

STEP 3 : Backward PassSTEP 3 : Backward PassA backward pass is required to find A backward pass is required to find LST considering both the resource LST considering both the resource links and the original technological links and the original technological relationship Fig 4relationship Fig 4

STEP 4: Finding more STEP 4: Finding more Resource LinksResource LinksTF of a critical activity is obvious in that TF of a critical activity is obvious in that any delay of it will extend the project any delay of it will extend the project completion time.completion time.

Activity for which TF is not zero may Activity for which TF is not zero may not have its full float if there is any not have its full float if there is any resource constraint in TF period.resource constraint in TF period.

RCPM AlgorithmRCPM Algorithm

STEP 5 : Finding Alternative Schedules STEP 5 : Finding Alternative Schedules every activity that has a successor by a resource link will be every activity that has a successor by a resource link will be checked for whether an alternative schedule is available.checked for whether an alternative schedule is available.

If there is no alternative schedule for activity, the original resource If there is no alternative schedule for activity, the original resource link will be restored.link will be restored.

Application to Time ExtensionApplication to Time ExtensionOriginal schedule Original schedule A warehouse project schedule from fondahl ( 1991) is used as time A warehouse project schedule from fondahl ( 1991) is used as time extension example, network shown in extension example, network shown in Fig10 Fig10

Application to Time Extension (cont.)Application to Time Extension (cont.)After resource constrained scheduling applied : There is no After resource constrained scheduling applied : There is no resource overrun, but the critical path is broken ( only the last two resource overrun, but the critical path is broken ( only the last two activities are critical ) and most TF values contain activities are critical ) and most TF values contain Phantom FloatsPhantom Floats. .

Shown inShown in Fig12 Fig12

Application to Time Extension (cont.)Application to Time Extension (cont.)

When The When The RCPMRCPM technique is also applied . the resource links are technique is also applied . the resource links are incorporated into the initial p3 schedule & the incorporated into the initial p3 schedule & the Phantom FloatPhantom Float is is removed and the critical path is continuous from the start through removed and the critical path is continuous from the start through the end project as shown the end project as shown Fig 14.Fig 14.

Change OrderChange Order

It is assumed that, the owner has informed the contractor that It is assumed that, the owner has informed the contractor that several components have been redesigned .with change order , the several components have been redesigned .with change order , the estimated durations of four affected activities have been increased estimated durations of four affected activities have been increased with the same daily resource requirement, as shown with the same daily resource requirement, as shown Table 4.Table 4.

Estimated Completion TimeEstimated Completion Timethere are three schedule type to Estimate the project completion there are three schedule type to Estimate the project completion time as a result of the change order : time as a result of the change order :

(1)(1) Resource limits are ignored Resource limits are ignored (CPM)(CPM) : : (2)(2) Resource limits are considered but the concept of Resource limits are considered but the concept of Phantom FloatPhantom Float

is Ignored is Ignored (RCS in p3 )(RCS in p3 )(3)(3) Both resource limits and Both resource limits and Phantom FloatPhantom Float are Considered are Considered (RCPM).(RCPM).

Table 5Table 5

Estimated Completion Time (cont.)Estimated Completion Time (cont.)A comparison of columns 7 and 2 in Table 5 revealsA comparison of columns 7 and 2 in Table 5 reveals

1-1- contractors who ignore resource limits altogether contractors who ignore resource limits altogether would a project completion time of would a project completion time of 27 days27 days before and before and after the change order . after the change order .

2-2- contractors who consider resource limits but ignore contractors who consider resource limits but ignore resource links , producing and disseminating schedules resource links , producing and disseminating schedules filled with filled with Phantom FloatPhantom Float, a completion time of , a completion time of 30 days30 days before change order before change order 37 days37 days after the change order. after the change order.

3-3- contractors who consider both resource limits and contractors who consider both resource limits and links would have a project completion time of links would have a project completion time of 30 days30 days before the change order and of before the change order and of 52 days52 days after the change after the change order.order.

Estimated Completion time (cont.)Estimated Completion time (cont.)

A comparison of columns 7 and 8 in Table 5 revealsA comparison of columns 7 and 8 in Table 5 reveals

1-1- contractors who ignore resource limits altogether would contractors who ignore resource limits altogether would still a project completion time of still a project completion time of 27 days27 days.. after the change after the change order . order .

2-2- contractors who consider resource limits but ignore contractors who consider resource limits but ignore resource links would a project completion time of resource links would a project completion time of 51 days51 days . .

3-3- contractors who consider both limits and links would contractors who consider both limits and links would project a completion time of project a completion time of 52 days52 days . .

There is no There is no Phantom FloatPhantom Float into schedules produced by into schedules produced by RCPM.RCPM.

Estimated Completion time (cont.)Estimated Completion time (cont.)

This Example ShowsThis Example Shows an unlimited resource CPM schedule is unrealistic condition and an unlimited resource CPM schedule is unrealistic condition and how how Phantom FloatPhantom Float could mislead project participants . could mislead project participants .

Scheduling with limited resources (Scheduling with limited resources ( RCS RCS and and RCPM RCPM ) after the ) after the change order has made the project duration nearly double as change order has made the project duration nearly double as compared to the CPM Schedule .compared to the CPM Schedule .in addition , there is a significant difference in completion times in addition , there is a significant difference in completion times between the estimated ( column 7 in Table 5 ) and the rescheduled between the estimated ( column 7 in Table 5 ) and the rescheduled (column 8 in Table 5 ) times for the RCS due to the presence of (column 8 in Table 5 ) times for the RCS due to the presence of Phantom FloatPhantom Float . .

Difference in RCS could cause disputes between the owner and the Difference in RCS could cause disputes between the owner and the contractor if they do not acknowledge the impact of contractor if they do not acknowledge the impact of Phantom Phantom FloatFloat . .

Summary & ConclusionSummary & Conclusion Proposed Proposed RCPM RCPM technique can identify real total float and correct technique can identify real total float and correct critical paths in a project schedule with limited resources.critical paths in a project schedule with limited resources.

Proposed Proposed RCPMRCPM technique takes advantages of both the CPM and technique takes advantages of both the CPM and the RCS techniques.the RCS techniques.

Gives correct time data that are prerequisite for successful project Gives correct time data that are prerequisite for successful project planning and control.planning and control.

Provides a certain level of stability that a traditional resource - Provides a certain level of stability that a traditional resource - constrained schedule rarely does .constrained schedule rarely does .

Many disputes among project participants are triggered by incorrect Many disputes among project participants are triggered by incorrect scheduling information.scheduling information.U.S. courts, in recent times , have realized that a CPM schedule U.S. courts, in recent times , have realized that a CPM schedule without resource constraints is not realistic . without resource constraints is not realistic .

Critique & EvaluationCritique & Evaluation

RCPMRCPM is more practical technique than is more practical technique than CPMCPM & & RCSRCS because : because :

takes resource constraint into consideration during takes resource constraint into consideration during planning & scheduling process .planning & scheduling process .

Gives more realistic Estimate of the project duration.Gives more realistic Estimate of the project duration.

Gives good chance to avoid disputes during construction Gives good chance to avoid disputes during construction phase.phase.

the the RCPM RCPM will become more valuable and their usage will become more valuable and their usage will be increased as their utilization is required by courts will be increased as their utilization is required by courts

of law.of law.