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CONCEPT Gantt Charts and Time- Scaled Networks

A picture is worth a thousand words. The network diagram is essential in calculating the schedule, but it can be terribly difficult to decipher on a large project. Thankfully, there are two very good alternatives, which display both the schedule information and the task

relationships. Gantt charts, named after Henry Gantt, who developed them in the early 1900s, have become the most common method for displaying a project schedule. Figure 10.9 is a Gantt chart for the home landscape project. It has the same schedule dates as the network in Figure 10.6. Notice that all the tasks are currently scheduled at their early start date-you can tell that because all noncritical tasks display float. The great advantage of the Gantt chart is its clarity: The horizontal axis shows the schedule and the vertical1 axis lists the work breakdown structure.

Another excellent graphic for displaying a schedule is the time.scaled

networkk (as shown in Figures 10.5 and 10.10). One advantage that this diagram has compared to the Gantt chart is the ability to condense the network onto less paper. On large projects, the Gantt charts can grow too large to print, whereas the time.scaled

network, because it combines many tasks on one line, can be made one.half

to one.tenth the height of the Gantt.

The initial schedule represents the combination of task sequence and task duration, but it's called an initial schedule because it hasn't taken into account people and equipment limitations. The next planning step uses the initial schedule as a starting point and balances it against the resources available to the project.

PLANNING STEP FIVE: ASSIGN AND LEVEL RESOURCES

The goal of resource leveling is to optimize the use of people and equipment assigned to the project. It begins with the assumption that, whenever possible, it is most productive to have consistent, continuous use of the fewest resources possible. In other words, it seeks to avoid repeatedly adding and removing resources time and again throughout the project. Resource leveling is the last step in creating a realistic schedule. It confronts the reality of limited people and equipment and adjusts the schedule to compensate.

Legend 1 Task 10 Duraton ES EF

LS|LFES Early start Milestone FL

Imposed mpletion

date is day 15. EF Early finish Start

LSLate start LF=Late finish FLHoat days

isn

Calculate late start dates backward fromm the deadline. 15

Task 1D Duration 12 days 2 4 days

3 4 days 1 day

12 days 6 5 days

FIGURE 10.8 Negative float. When imposed deadlines result in negative

FIGURE 10.8 Negative float. When imposed deadlines result in negative float, that is a warning the project is out of equilibrium. The cost, schedule, or scope objective must be revised

Wees ur 15

IDTask Name andscap ono and6capo B0 hrs.

3 Acquire lawn matona 64 hrs

4 Install sprinkler system 8hrs

5 donty apnnkior locations Dig trenches Tee

""Ppe and haroware

B Cover spnnkr y

lxed fee

angrass 368 nrs. 10 Rermove oeons 256 hrs Summay

6 hrs 11 epare so subordinate finish. Pant lawn s0ed 16 hrs. COr

ate finish 1 Plant shrubs 96 hrs Subordinate

start. y start

Neek of Ju ee of Ju 13 LaborHours S |WITE|S S|WIT|W|T|F|S| SMT|WIT|F|5 S|M T|WT |F| S S |MT

Weet of una

D ask Namee 14 Build fence **

T6 hrs. Cquire ence matenial 16 Install fence 328 nrs

17 32 hrs.

18 a poo BU nes

9 Instal tenCing and 9ales 144 nis

Paint/stain fence and gates 72 hrs.

Legend: Critical NoncriticalL loat t= Summary

The duration of a summary task is driven by its subordinate tasks.

The float tor a noncritical task begins at its early start and ends at its late finish.

This chart shows an early start schedule-all tasks are curently scheduled to begin on their earty start date.

FIGURE 10.9 Gantt chart for home

landscape project. Using the home landscape project as an example, we can see how resource leveling makes a project schedule more realistic. The network (Figure 10.6) shows, in terms of task scheduling, that it's possible to put in the lawm and build the fence at the same time. But when we consider that the family has only the three teenagers available to work on the project, that means they have just a total of 24 labor hours available each day (3 teens x8 hours per day). Trying to put in the lawn and build the fence concurrently is unrealistic because it would require each teen to work far more than eight hours a day for more than half the project. (The resource spreadsheet on the Gantt chart in Figure 10.11 indicates clearly how unrealistic the

the Gantt chart in Figure 10.11 indicates clearly how unrealistic the schedule is.) Resource leveling will adjust the schedule to keep the teens busy at a consistent, reasonable rate. Figure 10.12 shows the same project as Figure 10.11, but with the resources leveled.) Not only does resource leveling take unreasonable overtime out of their project, but it also keeps the teens employed for a longer time at a steady rate. That's usually an advantage for any project team.

Let's consider a few of the problems faced by project managers in this process of leveling resources.

Every project faces the reality of limited people and equipment. The

idea is to avoid both over. and under.

allocation. As the home landscape project demonstrates, too many concurrent taskS can call for more resources than are available. For example, as discussed, the initial schedule had the teens working on the fence and the lawn during the same period, and this resulted in the teens being over.allocated during the first

half of the project (they would have had to work more than eight hours a day to meet this schedule).

Project managers need to remember that whether it's teenagers planting the lawn, bulldozers, or programmers, there are rarely a bunch of spares sitting on the shelf. This over.

allocation problem can become especially acute if project managers i cino thot thOT nTTO 1owco nnlTT

.0JeCl ILldlldgtls Iletd tilltITLOtI

hat whether it's teenagers planting the awn, bulldozers, or programmers, here are rarely a bunch of spares itting on the shelf. This over.

allocation problenm can become specially acute if project managers magine that they have a large supply of a rare resource, such as the unlimited time of the only subject matter expert in the company. In this case, not only has the schedule become unrealistic, but the manager may have overloaded a key resource.

The other side of the problem is under.

allocation. If the project team isn't busy on your project, it will likely be reassigned to other projects and be unavailable when the next peak comes. In the worst case, during lulls in the project some of the unassigned people may get laid off, becoming permanently unavailable and taking valuable knowledge about your project with them.

weer of Jun 15 Week of Jun 22 Week of Jun 29 ek of Jul 6 Week of Jul 13

UESSMTWITLEISSMITIWLI|F Is|s |M|T|w|T|E s|sM| ACquire iawn materials

entih Design home landscap

ldentity sprinkder localions 6Dg trenches 8Cover sprnkder system

Remove debris Prepare S

12Plat lawn soed 1 Plant shrubs

Acqulte tence mate

Install pOsts nstsnnenO gates 17 TViark TencO Ino

Instal foncing and gatos

Legend: Critical Noncritical

FIGURE 10.10 Time.scaled network for home landscape project. This time.

scaled network has the same initial schedule information as Figure 10.9.

Wee Jun 15 Week f Ju 2 Week of Jun 29 Week of u Meek of ul 13 ID Task Labor Hours|8ITWFS8 WITw |ESIS IT|WTE|S|S|IT|WIT|F|S|SVIT

B0 nis Denign home lan ndbcape

Homeowner, teens 2 Put in lawn

536 hrs 3 Acquire lawn materials 64 hrs.

week of Jun 22 Week of Jun 29 Week o Jul 6 Week of Jul 13

SMT_WITIELSSMLTIWITLEIS|SMIT|WII|E Lss |M|T|w|T|E|ssM cure lawn materials

Design home landsCap

5euy sprinder locations Dig tronchos 8Cover sprinkler syslem

Hemove debris Pepdre 1 12 Plant lawn seed

Plant shrubs 13

ACOUire fence materia

Instal po Painvstain tenceland giates

Mark 1ence ane

Install foncing and gate

Legend: Critical Noncritical

FIGURE 10.10 Time.scaled network for

home landscape project. This time.

scaled network has the same initial schedule information as Figure 10.9.

Wee Jun 15 Weet d Jun 22 Week of Jun 29 Wes of u6 Wee of u 13

Labor HoursSUTW FSSWTWISSMT WTES 5VTWIT|F S|VIT|1D Task Niame eg nOmo andbcape

Homeowner, teens Put in lawn 536 hrs

ACquiro lnwn matoriaas 64 hrs eeer, Teens nstal sprKG 5y81em 8 hrs

5 dentty sprinkKICr locaOn 8 hrs Contractor, homeowner Dig trenches TOxea Tee

Contractor nstal pipe and hardware

Contraco Cover sprinkler system fixed fee JContractor

antgrass

Teens and youth group emove debris 11 Prepare SO 96 hrs. TetS,O 12 ant lawn seed o nis LTeens ant shrubs 6 hrs. Teens

Week d Jun Week of Ju Week of Ju 6 Week of Jul 13 T Tasi

14 A Labor HoursSITWTESSITWITIES|S|M|T|W|T|ELS|SNT |W|T|ES|5MT

15 ACquire tonce matena 16 hs |Homeowne

28 hrs

Mark fence lino 32 hs Homeowner. teans Install posts 80 hrs Teens nstal encing and gatos 144 nrs. Teens Paint/stan tence and gates 72 hrs

Woek of Jun 15 Wook of n 22 Wook of Jun 29

D Resource Name S VTWIESS V WHAS5MTW ESSMTWTESSD Legend d u6 Week of Jul 13

Crbcal FHomeownor 44 4 4 4 32 16 Teens 36 36 36 36 12

Contractor Youth group 40 40 40 40

Rototiller

Noncrtical L 64 40 56 56 56 56 16 24 24 24 24 24 40 24 24

Float 8 88

Summary

Hours per day

Ine resouroe Spreadsheel shOws the labor hours per day for each resource. Overallocaled resources are in italics. The tamily has three teenagers working on the project, for a total of 24 hours each day (3 teens @8 hours). There is only one homeowner, who is available for 8 hours a day Given this inial schedule, with all tasks beginning on their early start dates, both the homeowner and teens are overscheduled during much of the project

FIGURE 10.11 Gantt chart with resource spreadsheet for home landscape project.

A further problem arises if people working on this project are also

working on several others at the same time. If every project in the firm has wild swings in its resource requirements, it is almost impossible to move people smoothly between projects. Instead, people are yanked off one project to help another catch up, only to be thrown at yet another that is

FIGURE 10.11 Gantt chart with resource spreadsheet for home landscape project.

A further problem arises if people working on this project are also working on several others at the same time. If every project in the firm has wild swings in its resource requirements, it is almost impossible to move people smoothly between projects. Instead, people are yanked off one project to help another catch up, only to be thrown at yet another that is even further behind.

The Process of Resource Leveling

It is important to remember how we are defining the term resources. Resources are the people, equipment, and raw materials that go into the project. Resource leveling focuses only on the people and equipment; the materials needed for the project are dictated by the specifications.

Resource leveling begins with the initial schedule and work package resource requirements (see Table 10.1). The leveling follows a four.step

procesS:

1. Forecast the resource requirements throughout the project for the initial schedule. The best tool for this process is a resource

spreadsheet such as the one portrayed in Figure 10.11. This spreadsheet, correlated to the schedule, can forecast all thhe people and equipment needed on each day of the project. The initial schedule is sometimes called en.

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procesSS:

1. Forecast the resource requirements throughout the project for the initial schedule. The best tool for this process is a resource spreadsheet such as the one portrayed in Figure 10.11. This spreadsheet, correlated to the schedule, can forecast all the people and equipment needed on each day of the project. The initial schedule is sometimes called an early start schedule. At first, this might seem like good project management; that is, getting as early a start on everything as

possible. But an early start schedule usually has a lot of uneconomical resource peaks and valleys. For example, the over.

allocation of the teens during the first half of the home landscape project is the kind of misallocation common to early start schedules.

2. Identify the resource peaks. Use the resource spreadsheet (Figure 10.11) and the resources histogram (Figure 10.13) to find the periods in the project where there are unrealistic or uneconomical resource amounts.

3. At each peak, delay noncritical tasks within their float. Remember that float is schedule flexibility. Tasks with float can be delayed rithant ahaninr +ho nnoiart

HD. 94% 3. At each peak, delay noncritical

tasks within their float. Remember that float is schedule flexibility. Tasks with float can be delayed without changing the project deadline. By delaying these tasks, you'll also be filling in the valleys of the resource histogram; that is, moving tasks from periods of too much work to periods when there is too little work. This means that you will need fewer people and they will be more productive, but the deadline will stay the same. (A comparison of the initial schedule in Figure 10.11 with the leveled schedule in Figure 10.12 demonstrates how Task 5 was

delayed within its float, thus removinga resource peak for the homeowner on June 24.)

4. Eliminate the remaining peaks by reevaluating the work package estimates. Using the project float in

Step 3 may not be enough to eliminate all the peaks and valleys. For example, instead of having two or three people working together on a task, consider whether just one person could do the work over a longer period of time. (Task 12 in Figure 10.12 was changed from two teenagers for one day to one teen for three days.) Alternatively, available people might be added to a task to shorten its duration. W/hen merfnrmino thece chandec

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4. Enunue ne Tremannny peuksvby reevaluating the work package estimates. Using the project float in

teen for three days.) Alternatively, available people might be added to a task to shorten its duration. When performing these charnges, take note that each change to a work package estimate is going to change the amount of float, or time flexibility, for that task. In other words, after changinga work package estimate, you will need to return to step 4 and recalculate the initial schedule. Then you will also need to repeat the first three steps of resource

leveling. (This kind of recalculation is made much easier

by using project management software.)

CONCEPT What to Do If the Resource-Leveled Plan Is Still Unrealistic

Reestimating work packages and delaying tasks within their float can

OANGERD Computers Will Not Do

Everything Some of the tedious calculations

described here are easily performed by project management software, but don't be fooled. Computers really perform only two tasks: data storage and calculations. Even if you employya good software package, you will still have to understand each one of the steps in this chapter. (Appendix A summarizes the planning steps using the home landscape example.)

Wee of Jun 15 e d Jun 22 We of un 29 Wek of Jul6 Weebk of Jul 13 Week of u20 Week of u7

1DTaskName gn nome landscape

Labor Houre3NTWIOSBMIWEIFBSMTMIFSSMT|WTFSSMEINTESSMTWIEBBM1WIES 80 s Homeowner, toens

Putin lawnn 548 rs.

3 Acquire iawn materials 64 Homeowner, leens

Install sprinkler system B hws.

Oentty sprinkler locations 8 hrs. Contractór, homeowner Dig trenche

P anc naowaro

Contracior Cover spinkler system foe Contractor

380 s Plant ass

260 s eens and youth groupHemove debris PropareSO 96 Teens, rototiller

24 hs Toons Mant lawn sood ant snubs Teens

Task Name 14 Build fence

Wee dfun eek od in 7 Weck d un 29 Wee u 6 We d M13 Weex d Ju 20 Week of u 27 Labo tHours SIMTINIEISSTNT|ESSu TIWIT|EIS|S MITIWITEISISM T WNOSSMEWEFISSMTWEES

Acquire fence materia 16 s Homeowner Installtence 328 hvs

17 Mark lence line Homeowner, teens

80 hvs pos es

nstai lencng and gates 144 s Teens PinUothin ionco and gato5 72 hs Ieens

Legend Week un ekd an 2 Week o un 2 Week of u6 Woek of Jul 1 Wek d Ju 20 Resue NemeHTINEISSTINITESSMTMTESSMMEFSSMTMTFSSMTWTEISS WTNTES

v27

Critical omeowner 4444 8 a EBSMTWT|E IS

Teens ** 24 24 24 24 44 424 2a 18 16 24 4 2 224 a « «

3 Contractor 4 Youth group 443 404 40

5 Rolotll

Noncribcal L

SuTmimary

Hours per da

he leveled schedule has eliminated the task overlaps. which caused unrealistic work hours for the teens and homeowner.

3Skelayed 5 days to level homeowner whille keeping he sprinkler contractor on schedulk a5K T0eduCed leens to 4 hours per day feach) so they can participate in design home landscape at the same time (Design home lanv hours per day.) Added on addifional day for the youth group to wOrk on the task. This changed the task duration frorm 4 to 5 days and the total labor trom 256 hours to 260 hours. ask 12-Changed the lask from wo teens for one day (16 hours, labor) to one leen for 3 days (24 hours, labor) One teen working on the task alone won t be as efficient, but now

the other two teens can wOrk on Task 18 at he sarme time.

calls tor each teen to work 4

as 13. 5. and 17Delayed theseasks to level the project and their successor tasks were delayed as wel The new schedule is 10 OIKdays longer, but neither he teens nor the nomeawner are overallocaled on any day.

FIGURE 10.12 resource.leveled schedule for home

landscape project.

Gantt chart with