chapter 8: scheduling resources and...

Chapter 8: Scheduling Resources and Costs 4KF3

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Lecture Notes Scheduling Problems

There are two generic scheduling problems; 1. Time‐constrained project

2. Resource‐constrained project

Resource‐constrained Project

Prioritize and allocate resources to minimize delays and maximize resource utilization

Often achieved through levelling or smoothing

Time‐constrained Project

Expend resources to achieve schedule targets

Typically achieved through project crashing

Resource Leveling

Resource leveling aims to minimize the period‐by-period variations in resource loading

by shifting tasks within their slack allowances

The purpose is to create a smoother distribution of resource usage

Several advantages include: – Less hands‐on management is required

– May be able to use a “just‐in‐time” inventory policy


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Resource Levelling

When resources are leveled, the associated costs also tend to be leveled

The project manager must be aware of the cash flows associated with the project and of the

means of shifting them in ways that are useful to the parent firm

Resource leveling is a procedure that can be used for almost all projects, whether or not resources are constrained

Leveling Steps

Develop a network diagram – Determine the critical path – Find activity slack (or float)

Develop a resource loading table

Determine activity late finish dates

Identify resource over allocation

Level the resource‐loading table

Network Diagram

Your network will let you determine; o The critical path o Activity durations o Activity slack


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Determine Resource Hours

Note that the hours per day is less than eight – Resources are not always available full‐time

Step 1: Resource‐Loading Table

Step 2: Determine Late Finish Dates

This tells you which activities have slack and which activities are on the critical path

This in turn lets you identify your options


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Step 3: Identify Overallocations

Compare usage to a threshold value – January 12th uses 10 resources – too many

Step 4: Level

Level in order to resolve the overallocations

Leveling is an iterative (repeating) process

Resources loading is reconfigured to eliminate overallocations Step 4 – Phase 1

Identify candidates for reconfiguration – Look at the period of overallocation – Determine which activities utilize the resource(s) during that period Step 4 – Phase 1

Activities C, D, E contribute to the overallocation

Activity C is on the critical path

Activities D&E are candidates for reconfiguration

Step 4 – Phase 2

Select the activity to be reconfigured

Heuristic (rules of thumb) for prioritizing resource allocation; 1. Activities with the smallest amount of slack 2. Activities with the smallest duration 3. Activities with the lowest activity identification number


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4. Activities with the most successor tasks 5. Activities requiring the most resources

Step 4 – Phase 2

Activity E has the smallest amount of slack so Activity D should be changed

But that would mean splitting activity D

Step 4 – Phase 3

Make adjustments to the schedule

Here Activity E is delayed by 1 day

Repeat as Needed

January 12th no longer has an overallocation

Remember, that leveling is an iterative process

Each change has a ripple effect


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Step 3: Identify Overallocations

January 22 now has an overallocation

Step 4 – Phase 1

Identify candidates for reconfiguration – Activities E, F, I & J all utilize resources on the 22nd

Step 4 – Phase 2

Activities E & F have no slack time – they are on the critical path


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Step 4 – Phase 2

Activities I & J are candidates for reconfiguration

Activity I has the least slack so it gets the resources first, we will delay activity J

Step 4 – Phase 3

Make adjustments to the schedule

Here Activity J is delayed by 1 day

Resource‐Loading Charts

Steps; 1. Create the activity network diagram


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2. Create a table of listing activities, resource usage by activity, duration, early start, slack and late finish 3. List activities in order of increasing slack 4. Draw an initial resource‐loading chart

5. Rearrange activities within their slack 6. Rearrange activities with extra slack if necessary

Resource‐Loading Charts

Multi‐Project Environments

Key problems; – Inefficient use of resources – Resource bottlenecks – Ripple effects – Heightened pressure on personnel to multi‐task

The challenge is to balance the trade-offs between; – Schedule slippage

o Remember, late projects often incur penalties. – Resource utilization

o You want to smooth your utilization of resources across your portfolio of projects – In‐process Inventory

o In this case, in‐process inventory is project work delayed due to lack of resources

Resolving Resource Decisions – First in line

o Compare start dates – Greatest resource demand

o Allocate resources to projects with the greatest resource needs – Greatest resource utilization

o Minimize resource idle time – favour projects which use a variety of resources – Minimum late finish time

o Activities with the earliest late finish dates are assigned resources first.


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– Mathematical programming – Most possible jobs Time‐Phased Time Budget

Define work (what)

Identify time (how long)

Identify time‐phased budget (cost)

Identify resources (how much)

Identify responsible (who)

Identify monitoring points (how well) Critical Chain Path Management

Delays in many projects caused by: – Parkinson’s Law – Self‐protection

– Dropped baton – Excessive Multi‐tasking

– Resource Bottlenecks – Student syndrome

Critical Chain Project Management

Use true 50/50 estimates

Use buffers instead of slack: – Project buffer – Feeder buffer – Resource buffers

Buffers vs. Slack CPM – No Resources


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CPM – Resources Limited

CCPM

Using Buffers


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Reading Notes

Overview of the Resourcing Scheduling Problem

Will the assigned labour and/or equipment be adequate and available to deal with my

project? Will outside contractors have to be used? Do unforeseen resource

dependencies exist? Is there a new critical path? How much flexibility do we have in

using resources? Is the original deadline realistic?

Resource smoothing: if resources are adequate but the demand varies widely over the

life of the project, it may be desirable to even out resource demand by delaying

noncritical activities (using slack) to lower peak demand, and thus, increase resource

utilization

Resource-constrained scheduling: if resources are not adequate to meet peak

demands, the late start of some activities must be delayed, and the duration of the

project may be increased

Resource dependency takes priority for the technological dependency, but does not

violate the technological dependency

Types of Resource Constraints

1) People

2) Materials

3) Equipment

*Recognition of constraints before the project begins can avoid high crashing or delay costs

Classification of a Scheduling Problem

Time-Constrained Project: one that must be completed by an imposed date.

Resource usage should be no more than is necessary and sufficient

Resource-Constrained Project: one that assumes a level of resources available cannot be

exceeded.

Add as little time as possible

If the critical path is delayed, will resources be added to get back on schedule?

Yes: Time-Constrained Project No: Resource-Contrained Project


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Resource Allocation Methods

Assumptions:

o Splitting activities will not be allowed

o The level of resources allocated to an activity cannot be changed

Time-Constrained Projects: Smoothing Resource Demand

o Focuses on resource utilization

o Leveling: delay noncritical activities by using positive slack to reduce peak

demand and fill in valleys for the resources

o Three goals of soothing:

The peak of demand for the resource was reduced

Resources over the life of the project have been reduced

The fluctuations in resource demand were minimized

Resource-Constrained Projects:

o Heuristics: practical rule of thumb solutions

Do not always yield an optimal schedule, but they are very capable of

yielding a “good” schedule for very complex networks with many types of

resources

Allocate resources to activities to minimize project delay

The Parallel Method: minimizes project delay over a large variety of

projects.

An iterative process that starts from the beginning of project time

and, when resources needed exceed the resources available,

retains activities first by the priority rules:

o Minimum slack

o Smallest duration

o Lowest activity identification number

Computer Demonstration of Resource-Constrained Scheduling

Project management software is capable of assessing and resolving complicated

resource-constrained schedules using heuristics similar to what was described above

The Impacts of Resource-Constrained Scheduling

Limited resource schedule usually reduces slack, reduces flexibility by using slack to

ensure delay is minimized, and increased the number of critical and near-critical

activities

Parallel activities can become sequential

Activities with slack on a time-constrained network can change from critical to non-

critical

Splitting Activities

Splitting: a scheduling technique used to get a better project schedule and/or increase

resource utilization


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o A planner interrupts the work and sends the resource to another activity for a

period of time and then having the resource resume work on the original activity

o Can be a useful tool if the work involved does not include large start-up or

shutdown costs

Benefits of Scheduling Resources

Create schedule before to leave time for consideration of modifications to the plan

Resource schedules provide the information needed to prepare a quick means for

project manager to gauge the impact of unforeseen events such as turnover, equipment

breakdowns, or transfer for project personnel

Assigning Project Work

Project managers should match, as best they can, the demands and requirements of

specific work with the qualifications and experience of available participants

Pick people with compatible work habits to work together

Veterans should be teamed up with new hires

Future needs should be considered

Multiproject Resource Schedules

Three common problems encountered in managing multiproject resource schedules:

o Overall schedule slippage

o Inefficient resource utilization

o Resource bottlenecks

Companies using scheduling departments and outsourcing as a way to deal with these

issues

Using the Resource Schedule to Develop a Project Cost Baseline

Why a Time-Phased Budget Baseline is Needed

A time-phased baseline measures time differences between plan and actual

Without time-phasing cost to match your project schedule, it is impossible to have

reliable information for control purposes

Critical for creating the final step of creating your budget baseline

Planned value (PV): the outcome of these project allocations is the project cost

baseline which is used to determine cost and schedule variances as the project is

implemented

Earned value: project baselines will be used to compare planned schedule and costs

using an integrated system

APPENDIX 8.1: THE CRITICAL CHAIN APPROACH

“Critical Chain:” the project network may be constrained by both resource and technical

dependencies. Each type of constraint can create task dependencies, and in the case of

resource constraints, new task dependencies can be created;


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Time Estimates

Overestimating time constraints for safety (medium time is 30-40%)

Why, if there is a tendency to overestimate activity durations, and add safety to the end

of a project, do so many projects come in behind schedule?

o Parkinson’s Law

Work fills the time available

o Self-Protection

Peer pressure and fear of management

o Dropped baton

When one activity fails, it has a chain reaction

o Excessive multi-tasking

This adds time to each activity

o Resource bottlenecks

Tying up resources

o Student syndrome (procrastination)

Postponing the start of a task

Critical-Chain in Action

Use the 50/50 estimate approach to offset problems with time estimates

Three kinds of buffers in CCPM:

o Project Buffer

Added to the expected project duration

o Feeder Buffer

Added to the network where noncritical paths merge with the critical chain

o Resource Buffer

Come in at least two forms

Time buffer attached to a critical resource to ensure that the

resource is on call and available when needed

Buffer added to activities preceding the work of a scarce resource

Critical-Chain vs. Traditional Scheduling Approach

Parallel activities hold for resource conflicts

Buffers are dedicated time blocks

CCPM and Splitting Tasks

Three recommendations to reduce the impact of splitting activities

o Reduce the number of projects so people are not assigned to as many project

concurrently

o Control start dates of projects to accommodate resource shortages. Don’t start

projects until sufficient resources are available to work full time on the project

o Contract (lock in) for resources before the project begins


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Monitoring Project Performance

Buffer divided into three zones: OK, Watch and Plan, Act

The CCPM Today

CCPM does not address the biggest cause of project delays – ill-defined and unstable

project scope

Critics challenge assumptions about human behaviour

One of the keys to implementing CCPM is the culture of the organization

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