Tài liệu quản lý dự án - Project management chapter 10

Tài liệu quản lý dự án - Project management chapter 10

Project Scheduling Lagging, Crashing, and Activity Networks Chapter Outline PROJECT PROFILE A Crushing Issue: How to Destroy Brand-New Cars INTRODUCTION 10.1 LAGS IN PRECEDENCE RELATIONSHIPS Finish to Start Finish to Finish Start to Start Start to Finish 10.2 GANTT CHARTS Adding Resources to Gantt Charts Incorporating Lags in Gantt Charts PROJECT MANAGERS IN PRACTICE Major Julia Sweet, U.S Army 10.3 CRASHING PROJECTS Options for Accelerating Activities Crashing the Project: Budget Effects 10.4 ACTIVITY-ON-ARROW NETWORKS How Are They Different? Dummy Activities Forward and Backward Passes with AOA Networks AOA vs AON 10.5 CONTROVERSIES IN THE USE OF NETWORKS Conclusions Summary Key Terms Solved Problems Discussion Questions Problems Case Study 10.1 Project Scheduling at Blanque Cheque Construction (A) Case Study 10.2 Project Scheduling at Blanque Cheque Construction (B) 309 310 Chapter 10 • Project Scheduling MS Project Exercises PMP Certification Sample Questions Integrated Project—Developing the Project Schedule Notes Chapter Objectives After completing this chapter, you should be able to: Apply lag relationships to project activities Construct and comprehend Gantt charts Understand the trade-offs required in the decision to crash project activities Develop activity networks using Activity-on-Arrow techniques Understand the differences in AON and AOA and recognize the advantages and disadvantages of each technique PROJECT MANAGEMENT BODY OF KNOWLEDGE CORE CONCEPTS COVERED IN THIS CHAPTER Activity Definition (PMBoK sec 6.1) Activity Sequencing (PMBoK sec 6.2) Activity Resource Estimating (PMBoK sec 6.3) Activity Duration Estimating (PMBoK sec 6.4) Schedule Development (PMBoK sec 6.5) Schedule Control (PMBoK sec 6.6) PROJECT PROFILE A Crushing Issue: How to Destroy Brand-New Cars Mazda is facing a new challenge and has resorted to project management to find the best means to something unique for an automaker—destroy several thousand brand-new carp The story begins in 20'06, with the cargo ship Cougar Ace (see Figure 10.1), bound from Japan for Vancouver and, ultimately, the west coast of the United States with a load of new Mazda automobiles The 650-foot Pure Car Carrier (PCC) was improperly ballasted (weighted below water level) and carrying nearly 5,000 cars, stacked on 14 levels and tied down with nylon straps Somewhere in the middle of the Pacific, while the crew was pumping out and starting to replace the water used to ballast the ship, waves struck the Cougar Ace on the right side and because of poor stability, caused the ship to develop a 70-degree list Totally out of control, the ship drifted for over 300 miles over the next week When it was finally rigged with tow cables and brought safely to an Alaska port (a journey of another 450 miles), additional days were needed to finally control the severe list and right the ship, all the while maintaining its cargo of Mazda automobiles In the middle of August, nearly one month after the mishap, the Cougar Ace was brought back to nearly level, and initial inspection of the automobiles aboard seemed to suggest that they had sustained minimal damage from their weeks of hanging in their nylon slings Unfortunately for Mazda, this mishap came on the heels of Hurricane Katrina, when unscrupulous dealers and business people salvaged thousands of automobiles in the hurricane's aftermath and decided to pass them off as new cars, despite many of them having been submerged for several days Their electronic systems shot and with sand in the engine blocks, these cars were repainted and shipped south of the border to Latin American countries before the fraud was uncovered The result was a severe blow to the reputation of many of these automakers Mazda now faced a similar dilemma: what to with nearly 5,000 seemingly "new" cars that had been exposed to salt air and potentially damaging conditions for well over a month while at sea? Because of the after-effects of the "Katrina cars," Mazda opted to destroy the entire stock of cars (valued at nearly $100 million) salvaged from the Cougar Ace Its project, which took more than a year to devise, involved shipping the cars to Portland, Oregon, and creating a "disassembly line." Mazda had one guiding philosophy with the destruction: It had to be complete No air bags, steel alloy wheels, CD players, or tires were to be salvaged and sold on the aftermarket Mazda decided that the 10.1 Lags in Precedence Relationships FIGURE 10.1 311 Cargo Ship Cougar Ace with Its Load of New Cars risks were simply not worth its reputation to have these components offered for sale, particularly as Mazda could not guarantee that they would operate as intended The disassembly line is remarkably efficient: Cars are drained of all fluids, including oil, transmission and brakes fluids, and antifreeze, and are then sent to a demolition field, where their six airbags are simultaneously detonated Then the cars are sent to a car-crushing establishment, where it takes an additional 45 minutes to prepare each car for flattening Steel alloy wheels are sliced and tires are drilled through, while catalytic converters (containing platinum) are removed for retrieval of precious metals The cars are then flattened and taken to a salvage yard, where they are cut up into mountains of metal, with each piece no bigger than an ash tray The final step in the process is to ship the remnants to the docks and load them on ships bound for recycling plants in Asia Who knows; within months, they may be coming back as brand-new cars! INTRODUCTION The previous chapter introduced the challenge of project scheduling, its important terminology, network logic, activity duration estimation, and constructing the critical path In this chapter, we apply these concepts in order to explore other scheduling techniques, including the use of lag relationships among project activities, Gantt charts, crashing project activities, and comparing the use of Activity-on-Arrow (AOA) vs Activity-on-Node (AON) processes to construct networks In the last chapter, we used the analogy of the jigsaw puzzle, in which the act of constructing a schedule required a series of steps all building toward the conclusion With the basics covered, we are now ready to consider some of the additional important elements in project scheduling, all aimed at the construction of a meaningful project plan 10.1 LAGS IN PRECEDENCE RELATIONSHIPS The term lag refers to the logical relationship between the start and finish of one activity and the start and finish of another In practice, lags are sometimes incorporated into networks to allow for greater flexibility in network construction Suppose we wished to expedite a schedule and determined that it was not necessary for 312 Chapter 10 • Project Scheduling a preceding task to be completely finished before starting its successor We determine that once the first activity has been initiated, a two-day lag is all that is necessary before starting the next activity Lags demonstrate this relationship between the tasks in question They commonly occur under four logical relationships between tasks: Finish to Start Finish to Finish Start to Start Start to Finish Finish to Start The most common type of logical sequencing between tasks is referred to as the Finish to Start relationship Suppose three tasks are linked in a serial path, similar to Figure 10.2 Activity C cannot begin until the project receives a delivery from an external supplier that is scheduled to occur four days after the completion of activity B A Finish to Start lag of days between the completion of activity B and the start of activity C, shown in Figure 10.2, represents this case visually Note in Figure 10.2 that the early start (ES) date for activity C has now been delayed for the days of the lag A Finish to Start lag delay is usually shown on the line joining the nodes; it should be added in forward pass calculations and subtracted in backward pass calculations Finish to Start lags are not the same as additional activity slack and should not be handled in the same way Finish to Finish Finish to Finish relationships require that two linked activities share a similar completion point The link between activities R and T in Figure 10.3 shows this relationship Although activity R begins before activity T, they share the same completion date In some situations, it may be appropriate for two or more activities to conclude at the same time If, for example, a contractor building an office complex cannot begin interior wall construction until all wiring, plumbing, and heating, ventilation, and air conditioning (HVAC) have been installed, she may include a lag to ensure that the completion of the preceding activities all occur at the same time Figure 10.4 demonstrates an example of a Finish to Finish lag, in which the preceding activities R, S, and T are completed to enable activity U to commence immediately afterward The lag of days between activities S and T enables the tasks to complete at the same point 16 Fi 11 Design check Spec design t, C 15 l_ag 22 Bluepnilting FIGURE 10.2 Network Incorporating Finish to Start Lag of Days 30 R 36 \viring 31 33 ! ! , Plumbing S i 33 T 36 42 36 I IVAC Interior colltintlCn011 FIGURE 10.3 Finish to Finish Network Relationship 10.2 Gantt Charts 30 R 313 36 Lag Wiring 34 S 36 36 Plumbing T 39 iVAC 39 U 45 Interior construction FIGURE 10.4 Finish to Finish Relationship with Lag Incorporated Start to Start Often two or more activities can start simultaneously or a lag takes place between the start of one activity after an earlier activity has commenced A company may wish to begin materials procurement while drawings are still being finalized It has been argued that the Start to Start lag relationship is redundant to a normal activity network in which parallel or concurrent activities are specified as business as usual In Figure 9.20, we saw that Activity C is a burst point in a network and its successor activities (tasks D and G) are, in effect, operating with Start to Start logic The subtle difference between this example and a Start to Start specification is that in Figure 9.20 it is not necessary for both activities to begin simultaneously; in a Start to Start relationship the logic must be maintained by both the forward and backward pass through the network and can, therefore, alter the amount of float available to activity G Figure 10.5 demonstrates an example of a Start to Start network, in which the lag of days has been incorporated into the network logic for the relationship between activities R, S, and T Start to Finish Perhaps the least common type of lag relationship occurs when a successor's finish is dependent upon a predecessor's start (Start to Finish) Such a situation may be construction in an area with poor groundwater drainage The completion of the concrete pouring activity, Y, is dependent upon the start of site water drainage, W Figure 10.6 shows this relationship Although an uncommon occurrence, the Start to Finish option cannot be automatically rejected As with the other types of predecessor-successor relationships, we must examine our network logic to ascertain the most appropriate manner for linking networked activities with each other 10.2 GANTT CHARTS Developed by4-larvey Gailtt in 191 Gantt charts are another extremely useful tool for creating a project network Gantt charts estAliSE-a—tinie-Thflased network, which links project activities to a project schedule baseline They can also be used as a project tracking tool to assess the difference between planned and actual performance A 30 R 36 Wiring days 33 36 11VAC, 31 S 33 Plumbing FIGURE 10.5 Start to Start Network Relationship 36 U 42 4.- Interior construction 314 Chapter 10 • Project Scheduling 20 W 26 (i days 20 18 X FIGURE 10.6 Y 23 23 29 20 Start to Finish Network Relationship sample of a basic Gantt chart is shown in Figure 10.7 Activities are ordered from first to last along a column on the left side of the chart with their ES and EF durations drawn horizontally The ES and EF dates correspond to the baseline calendar drawn at the bottom of the figure Gantt charts represent one of the first attempts to develop a network diagram that specifically orders project activities by baseline calendar dates, allowing the project team to be able to focus on project status at any date during the project's development Some benefits of Gantt charts are: (1) they are very easy to read and comprehend, (2) they identify the project network coupled with its schedule baseline, (3) they allow for updating and project control, (4) they are useful for identifying resource needs and assigning resources to tasks, and (5) they are easy to create Comprehension—Gantt charts work as a precedence diagram for the overall project by linking together all activities The Gantt chart is laid out along a horizontal time line so that viewers can quickly identify the current date and see what activities should have been completed, which should be in progress, and which are scheduled for the future Further, because these activities are linking in the network, it is possible to identify predecessor and successor activities g 11 i 1 LLill_LIL 1111111 1111111 IlL_ii111,_ iLl i_ Illh 48 60 I 36 24 Davis Legend: I Scheduled Start I Scheduled Finish Actual Progress FIGURE 10.7 Sample Gantt Chart 72 10.2 Gantt Charts 315 Schedule baselined network—The Gantt chart is linked to real-time information, so that all project activities have more than just ES, EF, LS, LF, and Float attached to them They also have the dates when they are expected to be started and completed, just as they can be laid out in conjunction with the overall project schedule Updating and control—Gantt charts allow project teams to readily access project information activity by activity Suppose, for example, that a project activity is late by days It is possible on a Gantt chart to update the overall network by factoring in the new time and seeing a revised project status Many firms use Gantt charts to continually update the status of ongoing activities Gantt charts allow managers to assess current activity status, making it possible to begin planning for remedial steps in the cases where the activity's completion is lagging behind expectations Identifying resource needs—Laying the whole project out on a schedule baseline permits the project team to begin scheduling resources well before they are needed, and resource planning becomes easier Easy to create—Gantt charts, because they are intuitive, are among the easiest scheduling devices for project teams to develop The key is having a clear understanding of the length of activities (their duration), the overall precedence network, the date the project is expected to begin, and any other information needed to construct the schedule baseline, such as whether overtime will be needed Figure 10.8 extends the Project Delta example from the previous chapter to the process of constructing a Gantt chart using MS Project This Gantt chart is based on the information contained in our illustrative example, Project Delta The start and finish dates and length are ascribed to each activity and represented by the horizontal bar drawn from left to right through the network The chart lists the early activities in order from top to bottom The overall "flow" of the chart moves from the top left corner down to the bottom right The baseline schedule is shown horizontally across the top of the page Each activity is linked to indicate precedence logic through the network All activities are entered based on their early start (ES) times We can adjust the network to change the logic underlying the sequencing of the tasks For example, the activities can be adjusted based on the late start (LS) date or some other convention As we continue to fill out the Gantt chart with the complete Project Delta (see Figure 10.8), it is possible to determine additional information from the network First, activity slack is represented by the long arrows that link activities to their successors For example, activity E, with its 60 days (12 weeks) of slack, is represented by the solid bar showing the activity's duration and the lengthy arrow that connects the activity to the next task in the network sequence (activity H) Finally, a number of software-generated Gantt charts will also automatically calculate the critical path, identifying the critical activities as the chart is constructed Figure 10.9 shows the critical path as it is highlighted on the schedule baseline Adding Resources to Gantt Charts Adding resources to the Gantt chart is very straightforward, consisting of supplying the name or names of the resources that are assigned to perform the various activities Figure 10.10 gives an MS Project output showing the inclusion of a set of project team resources assigned to the various tasks It is also possible, as Task Name j Duration A Contract signing days B Questionnaire design days C Target market ID days D Survey sample 13 days E Develop presentation days F Analyze results days Demographic analysis days H Presentation to client days FIGURE 10.8 Dec 21, '0 STMTT FS Dec 28, '08 MT Completed Gantt Chart for Project Delta Jan 4, '09 Jan 11,'09 Jan 18 '09 I Jan 25, '09 063011111211131131/55101A S S 1M 316 Chapter 10 • Project Scheduling Task Name Duration c 21, '08 A_ Contract :sitiniro ••• Than 11,109 ° Jan 4, '09 i Dec 28, '08 TT vCift F G Si •.• M T TF SIM T T iF Jan 18, '09 T IF T i F M T Jan 2`,'09 hA T Fr T • • 1)% B (Due,tionnaire design Target market ID 0% 'Curves :sample E Develop pre,entation F Analyze resuits G Demographic analysis 0% H Presentation to client FIGURE 10.9 Gantt Chart for Project Delta with Critical Path Highlighted the figure shows, to assign the percentage of time each resource is assigned to each activity This feature is important because, as we will see in later chapters, it forms the basis for tracking and control of the project, particularly in terms of cost control Figure 10.10 shows six project team members assigned across the six tasks of another project example Remember that the Gantt chart is based on activity durations calculated with full commitment of resources Suppose, however, that we were only able to assign resources to the tasks at a lesser figure ( say 50%) to account for the fact that we not have the sufficient resources available when they are needed The result will be to increase the length of time necessary to complete the project activities The challenge of resource management as it applies to network scheduling is important and will be covered in detail in Chapter 12 Incorporating Lags in Gantt Charts Gantt charts can be adjusted when it is necessary to show lags, creating a visual image of the project schedule Figure 10.11 is a Gantt chart with some alternative lag relationships specified In this network, activities C (specification check) and D (parts order) are linked with a Finish to Finish relationship that has both ending on the same date Activity E is a successor to activity D and the final two activities, F and F, are linked with a Start to Start relationship Similar to lag relationships in network construction, the key lies in developing a reasonable logic for the relationship between tasks Once the various types of lags are included, the actual process of identifying the network's critical path and other pertinent information should be straightforward Task Name Duration .4 Design to prototype days B Engineering days Specification checks O Parts order E Parts delii/eri,, Dec 21,'08 S I Dec 28, '08 T F TS IS M fftilse T I Jan 4, '09 Jan 11, '09 I :WET F Jan 18, '09 Jan 25, M7TIVViTF S S M T John Smith Sue Bailey days e Cooper John Smith days dai,, s iLSandra Hobbs F Assembly Ian Tinnings FIGURE 10.10 Gantt Chart with Resources Specified Task Name Duration Dec 21, '08 SM1- 11 T F A DE,SIctri tO prOtOtype days El Engineering days C Specification checks :3 days Parts order days E Parts: delivery days F S days FIGURE 10.11 Gantt Chart with Lag Relationships Jan 4, '09 Dec 28, '08 ftiATT1,xr T I F S S M T \lc/ • S ' lan 11 '09 1M : iT IF HSI'S 10.2 Gantt Charts 317 BOX 10.1 PROJECT MANAGERS IN PRACTICE Major Julia Sweet, U.S Army Major Julia Sweet works in a setting where projects are a way of life, even under sometimes hazardous conditions Julia serves as a program manager for an engineer brigade located in central Afghanistan The brigade is responsible for designing all construction projects in Regional Command South (RC-S) and Regional Command East (RC-E) Over 10 months (since 2008) the design management section had designed and gained approval for more than 500 construction projects with a total value of over $1.6 billion Typical projects include waste water treatment plants, living containers/tents, helicopter landing zones, perimeters, and headquarters buildings Julia comes by her interest in projects and project management through years of work in some very different settings Following her college graduation with a degree in chemistry, she first served as an Army engineer in Germany before moving to reserve status and spending 12 years in various project management positions in the pharmaceutical industry, including five years with Eli Lilly, Inc By the end of her career, she had worked her way up to clinical trial operations team leader in research and development, where she was involved in numerous product development projects After she was recalled to active duty, Julia spent the last 15 years serving first as a base camp master planner in Bosnia and now as a program manager in Afghanistan, managing hundreds of projects worth million of dollars With the Army's force buildup in Afghanistan, Julia's responsibilities have grown enormously To provide for the new troops, her most recent groups of projects involve force protection and perimeter buildup for all the new forward operating bases (FOB)/combat outposts (COP) The number one priority for these sites is force protection (i.e., guard towers, defensive positions, and entry control points) In order to protect the workforce and the followon troops, the perimeter must be secure The troop buildup has also put pressure on the Army's engineer brigades in other ways She and her colleagues are developing living/work areas for the thousands of arriving troops As Julia notes, "Not only is there the challenge of figuring out how many troops, what kind of units, how much bed space they need, but the project must also be designed, approved, funded, and built prior to their arrival; the 'flash to bang time' on this is usually measured in weeks There is also the challenge of acquiring real estate and ensuring the location is secure enough to afford local contractors to perform the work." FIGURE 10.12 Major Julia Sweet, U.S Army (continued) 318 Chapter 10 • Project Scheduling How you effectively manage the sheer size and scale of projects that are needed, while working in a combat zone? The challenges and pressure are nonstop For example, these projects require a number of decisions involving security, logistics, financing, and the speed at which construction must be completed "The enemy also has a vote in the situation," Julia observes, "so it is not uncommon to get a project to the point of execution and later have the location moved or to have the entire project scrapped Convoys with construction materials are constantly attacked and the materials are pilfered or blown up and never arrive on the job site Many times construction materials have to be flown into really remote areas Millions of dollars' worth of materials have been destroyed during the last year, and the majority of the items tend to be very hard to replace Financing and speed are also critical as the troops continue to flow, and you simply have to make it happen to ensure the unit's success on the battlefield It sometimes seems to be taken for granted by everyone but the people here on the ground that if the soldiers have a place to work, eat, and sleep they are better able to focus on the task at hand." Julia's work is highly pressurized but very fulfilling The engineers work to quick turnaround schedules and are required to keep a close eye on cost, but still they must find innovative ways to get a host of projects completed; there is always a huge list of other "critical" projects waiting to get started "Doing this job right saves lives Everyone here recognizes that this is much more than 'construction'; our work literally increases the likelihood of the Army's success on the battlefield I love the authority the Army gives to officers like me to just get the job done As a program manager I am responsible for the overall success of the program from start to finish The goal here is to maintain a sense of unity and cohesion on similar projects across the board, especially in terms of operational need, design specifications, and overall cost." _ 10.3 CRASHING PROJECTS At times it is necessary to expedite the project, to accelerate development to reach an earlier completion date The process of accelerating a project is referred4as crashing Crashing a project directly relates to resource commitment The more resources we are willing to expend, the faster we can push the project to its finish There can be good reasons to crash a project Among them: The initial schedule may be too optimistic Under this circumstance, we may schedule the project with a series of activity durations so truncated they make the crashing process inevitable Market needs change and the project is in demand earlier than anticipated Suppose, for example, your company discovered that the secret project you were working on was also being developed by a rival firm Because market share and strategic benefits will come to the first firm to introduce the product, you have a huge incentive to whatever is necessary to ensure that you are first to market The project has slipped considerably behind schedule You may determine that the only way to regain the original milestones is to crash all remaining activities The contractual situation provides even more incentive to avoid schedule slippage The company may realize that it will be responsible for paying more in late delivery penalties than the cost of crashing the activities Options for Accelerating Activities There are three principal methods for accelerating or crashing project activities: Improving the productivity of existing project resources Changing the working method employed for the activity, usually by altering the technology and types of resources employed Increasing the quantity of project resources, including, ersonnel, plant, and equipment Improving the productivity of existing project resources means finding efficient ways to more work with the currently available pool of personnel and other material resources Some ways to achieve these goals include improving the planning and organization of the project, eliminating any barriers to productivity such as excessive bureaucratic interference or physical constraints, and improving the motivation and productivity of project team members Efforts should always be made to find ways to improve the productivity 328 Chapter 10 • Project Scheduling 1) FIGURE 10.21 Completed Project Delta AOA Network t l) 94 FIGURE 10.22 Project Delta Forward Pass Using AOA Network Figure 10.22 shows the forward pass results for Project Delta The nodes display the information concerning ES in the upper right quadrant As with the AON forward pass, the process consists simply of adding duration estimates for each activity moving from left to right through the network The only places in the network that require some deliberation regarding the ES value to apply are at the merge points represented by nodes and Node is the merge point for activity C and the dummy activity represented by the clotted line Because dummy activities not have any value themselves, the ES for node is the largest of the additive paths for activities A — C =11 vs activities A — B = 10 Therefore, we find that the ES at node should be 11 The other merge point, node 6, uses the same selection process Because the path A—C—D—F= 28, which is the largest of the paths entering the node, we use 28 as the ES for node Finally, after adding the duration for activity H, the overall length of the network is 30 weeks, just as it was in the AON network shown in the previous chapter (see Figure 9.20) The backward pass is also similar in procedure to the earlier AON process The backward pass starts at the far right or completion of the network at node and, using the 30 weeks duration as its starting point, subtracts activity times along each path (11 — Dur = LS) When we reach a burst event, such as node or 4, we select the smallest LS from the choice of activities Vius, using Figure 10.23 as our reference, we can begin O ' 11 \ A7 c) I 1) 24 FIGURE 10.23 Project Delta Backward Pass Using AOA Network 10.5 Controversies in the Use of Networks 329 subtracting duration values as we move from right to left in the network The LS values are included in the node in the bottom right-hand quadrant, right underneath the ES values The forward pass allowed us to determine that the expected duration for the project is 30 weeks Using the backward pass, we can determine the individual activity slacks as well as the critical path, similar to the AON process The difference is that the labeling of -ES and LS values lie within the event nodes, therefore it is necessary to examine each activity path to determine the slack associated with it We know, for example, that the ES for activity E is 10 weeks and the duration of the activity is weeks Therefore, when comparing the EF for activity E of 16 weeks with the ES value in node 6c of 28 weeks, we can see that the difference, 12 weeks, is the amount of slack for the activity Likewise, activity G's ES is 11 weeks and its duration is.9 This EF value of 20 weeks is weeks less than the ES for node 6, indicating that activity G's slack is The same- logic can be applied to each activity in the network to determine the critical path and the activities with slack time AOA vs AON Activity-on-Arrow and Activity-on-Node network diagramming are intended to the same thing: create a sequential logic for all activities with a project and once linked, determine the project's duration, critical path, and slack activities One common question has to with the efficacy of one network approach over the other; that is, what are the benefits and drawbacks of selecting either the AON format or the AOA approach? Consequently, in choosing to use either AOA or AON network methods, it is important to consider some of the strengths and weaknesses of each of these techniques The benefits of AON are centered primarily in the fact that it has AON STRENGTHS AND WEAKNESSES become the most popular format for computer software packages, such as MS Project Hence, as more and more companies use software-based project scheduling software, they are increasingly using the AON method for network diagrams The other benefits of AON are to place the activity within a node and use arrows merely as connection devices, thereby simplifying the network labeling These conventions make AON networks very easy to read and comprehend, even for novice project managers The primary drawback with AON networks occurs when the project is very complex with numerous paths through the model The sheer number of arrows and node connections when multiple project activities are merging or bursting can make AON networks difficult to read AOA modeling's greatest benefit lies in its accepted use in certain business fields, such as construction, where AON networks have not yet made significant inroads Also, in the case of large, complex projects it is often easier to employ the path process used in AOA Finally, because the activity and node system is used for projects that have many significant milestones, such as supplier deliveries, AOA event nodes are very easy to identify and flag On the other hand, there is no question that some conventions in AOA diagramming are awkward, most particularly the use of dummy activities Dummy activities are not a simple concept to master and require more training on the part of novice project managers to be able to use them easily Finally, AOA networks can be "information intensive" in that both arrows and nodes contain some important project information Rather than centralizing all data into a node, as in the AON convention, AOA networks use both arrow and nodes to label the network Ultimately, the choice to employ AON or AOA network methodology comes down to the individual's preferences, as well as the external pressures we will face in our work situations For example, if the organization I work for has decided to adopt AON modeling because of the commonly used scheduling software, in all likelihood I will concentrate exclusively on AON network diagramming approaches Regardless of the decision each of us makes regarding the use of AOA or AON, it is extremely important that we all become comfortable with the basic theory and operation of both types of network models AOA STRENGTHS AND WEAKNESSES 10.5 CONTROVERSIES IN THE USE OF NETWORKS Program Evaluation and Review Technique/Critical Path Method (PERT/CPM) is a well-understood and much-employed system for project planning and scheduling Nevertheless, networks are abstract representations of events in which time is reduced to a numerical value They may or may not be drawn to a scale that has a relationship to the ongoing pattern of events Sometimes this abstraction can be misleading In 330 Chapter 10 • Project Scheduling fact, there are several criticisms and caveats we need to bear in mind as we develop project activity networks, including:' Networks can become too large and complex to be meaningful Many projects are large and hugely complex For example, the creation of an operating system for personal computers, construction of a sports arena, or development of a drug are all projects that can easily contain thousands of steps or individual activities Many projects extend over years, and estimation of activity duration can become general guesses at best As a result, when working with networks for large-scale or long-term projects, it is necessary to find ways to simplify the activity network calculations One rule of thumb for large projects is to try to simplify network logic and reduce it to the most obvious or meaningful relationships Rather than showing every possible path through the network and every activity sequence, a "meta-network" that only shows the key subroutines or network paths can be created These subroutines can be further broken down by the project manager or administrator responsible for their completion, but the overall project network is streamlined to include only the most general or relevant project activities A variably scaled time frame is another option for long-term projects For example, activities scheduled to occur within the first nine months may be listed with durations scaled to the number of days necessary to complete them Activities scheduled between the first and second year may be listed on the network with a scaling of weeks or even months, and activities included in the network beyond the second year may only be listed with durations indicated by months Faulty reasoning in network construction can sometimes lead to oversimplification or incorrect representations Problems frequently occur when organizations attempt to manage their projects on the basis of these multiple layers of activity networks Information going to different levels in the organization is often not easily understood or translatable between levels because they not share a common project schedule Hence, it is important that when simplifying a project network, steps must be taken to ensure that information is not lost through oversimplification or the creation of multiple networks with no integration processes Complex schedules often require a combination "top-down, bottom-up" approach to controlling project activities Top-down control means that there is a tiered system for project schedules At the top is the most basic summary information, as in the case of simply listing work packages or summary "roll ups" of numerous individual tasks While much easier for top management to understand, this top-tier summary network does not give them a basis for understanding the actual development of the project because they are not privy to the status of individual tasks On the other hand, project managers or those responsible for portions of the project need more "bottom-up" information to allow them to maintain hands-on control of the portion of the project network for which they are responsible Project personnel need specific, lower tier activity network information to allow for optimal scheduling and control Top management opts for top-tier summary information that aggregates and simplifies the schedule For example, Figure 10.24 shows a simplified idea of the tiered system for schedules Top management would receive aggregated information from the top tier, middle-level management (such as department heads) would get slightly more detailed information based on activities relevant to their departments or functions, and at the bottom, the project team would employ the full, detailed, and specific project schedule Networks are sometimes used for tasks for which they are not well suited Network activities are not useful for all scheduling challenges Companies will sometimes try to adopt project network scheduling to accommodate other uses within their organizations Suppose, for example, that a manufacturing organization were having problems with its production scheduling Under the mistaken notion that PERT can work just as well for manufacturing operations as it does for project planning, managers may mistakenly decide to employ PERT in situations for which it is not suited In fact, project network scheduling methodologies are an important technique in project management; they not represent a panacea for all scheduling problems that organizations face Networks used to control the behavior of subcontractors have special dangers Many projects involve the use of subcontractors When the "prime contracting" organization employs multiple subcontractors, the common mistake is requiring them to develop independent activity plans without reference to or understanding the planning of other subcontractors with whom they may need to 10.5 Controversies in the Use of Networks 331 P Tier One—Top Tier Two—Middle Tier Three— Bottom FIGURE 10.24 Tiered System of Project Schedules interface If a firm is using multiple subcontractors, two important principles are needed to guide their use of networks First, all subcontractors must be privy to the prime contractor's overall network, which includes the schedules for each "sub." This way, subcontractors can make scheduling decisions not based on assumptions, but on clear knowledge of the plans of other subcontractors The second principle is to work to merge the networks of all subcontractors using a common set of network techniques, time-frame scaling, and so forth It is important that the network be a mutually accessible document, and that is most likely to occur if all subcontractors are equally aware of the rules governing network creation There is a strong potential for positive bias in PERT estimations used in network construction Research has demonstrated that most activity estimations using PERT methods lead to overly optimistic activity duration estimates PERT analysis is based on probabilistic time estimates that, if unreasonably determined, can lead to inaccurate and misleading project schedules The logic that drives duration estimates and the development of the PERT network must be demonstrated as reasonable for PERT scheduling to be meaningful Conclusions Activity network development is the heart of the project management planning process It requires us to make reasonable estimates of activity durations, and it expects us to develop the logic for activity sequencing and use this information to create meaningful project schedules It is only through the careful analysis of the steps in project scheduling that we can turn project concepts into working realities Scheduling allows us to determine the answers to the truly significant questions of project management: What needs to be accomplished? When does it need to be accomplished? How can it be accomplished? The scheduling techniques you select are not nearly as important to the final success of your projects as is your commitment to performing these operations carefully, methodically, and honestly The schedule is our roadmap showing the route we must take to complete the project successfully The care with which we create that map and the manner in which we follow it will go far to determining whether or not we will be successful in running our projects 332 Chapter 10 • Project Scheduling Summary Apply lag relationships to project activities Examples of developing network logic include determining how precedence relationships apply to each project activity; that is, activities follow one another in a common manner in which the predecessor's early finish becomes the successor activity's early start, or are other relationships specified? Among these alternative relationships, referred to as lag relationships, are: finish to start, finish to finish, start to start, and start to finish Construct and comprehend Gantt charts An alternative method for developing the project network other than the use of PERT diagrams is Gantt charts Gantt charts offer an important advantage over the early PERT diagrams in that they link the activities to a project schedule baseline based on actual calendar dates Thus, we can see not only which activities had to occur in what order, but when they were scheduled to begin and end In recent years, Gantt charts have begun to be used in conjunction with PERT charts, particularly with most project scheduling software Understand the trade-offs required in the decision to crash project activities When it has been determined that the project must be accelerated, either due to changes in the external environment or due to top management or customer pressures, a method known as project crashing is employed Crashing directly links all activities to their respective costs and allows us to calculate the cost for each day we choose to accelerate the project The decision of whether or not to crash can therefore be directly linked to the cost implications for crashing, allowing project managers to make an informed decision on time/cost trade-offs Develop activity networks using Activity - on - Arrow techniques Although AON network diagramming has become the more popular method, for many years AOA network diagramming was the technique of choice and is still widely applied in several project settings, such as construction AOA networks and their unique properties, including the creation and use of dummy variables, are discussed in detail in the chapter The steps necessary to construct an AOA network and its advantages and disadvantages over AON notation are also examined Understand the differences in AON and AOA and recognize the advantages and disadvantages of each technique The chapter concludes with a critical review of some of the controversies found in the development and use of network diagrams for project scheduling The chapter lists several drawbacks or concerns in diagramming, including: ( ) networks can become too large and complex to be meaningful, (2) faulty reasoning can lead to oversimplification or incorrect representations, (3) they can be used for tasks for which they are not well suited, and (4) they have special dangers when used to control subcontractor behavior Key Terms Activity (also called task) (p 311) Activity-on-Arrow (AOA) (p 324) Activity - on - Node (AON) (p 324) Arrow (p 324) Backward pass (p 328) Crashing (p 318) Critical path (p 315) Dummy activities (p 326) Early start date (ES) (p 312) Event (p 324) Float (also called slack) (p 313) Forward pass (p 329) Gantt chart (p 313) Lag (p 311) Late start (LS) (p 315) Merge (p 327) Node (p 324) Program Evaluation and Review Technique (PERT) (p 329) Serial activities (p 312) Successors (p 312) Task (see activity) (p 312) Solved Problems 10.1 Crashing Project Activities Suppose you are considering whether or not to crash project activities in order to expedite your project You have calculated the costs per activity for both normal and crashed options These are shown at the top of the following page a Which activities are the most likely candidates for crashing (i e., which are the most cost effective to crash? b Refer back to Figure 10.23 Using the critical path from this activity network, consider A-C-D-F-H as the critical path and assume all other paths are less than a fully crashed A-C-I)-F-H Prioritize the candidates for crashing How does the activity network change the decision rule? SOLUTION Remember that the formula to calculate crashing costs is based on the slope between the normal and crashed costs of each activity: Slope = crash cost — normal cost normal time — crash time Discussion Questions Crashed Normal Activity Duration Cost Duration A days $ 2,400 days Cost $ 3,600 B days 3,500 days 5,000 C days 3,000 days 3,800 D days 2,700 days 4,500 E days 800 days 1,500 F days 1,200 days 2,100 G days 2,400 days 4,200 days 4,500 days 7,000 H Total costs Crashing Costs (per day) A $ 600 $31,700 $20,500 Using this equation, we can create a table showing the crashing costs per day: Activity 333 Crashed Normal Duration Cost $1,500 days $2,000 3,500 days 5,000 days 6,800 days 7,500 days 2,500 days 6,000 E days 4,200 days 5,400 F days 2,000 days 2,700 Activity Duration Cost A days B days C D B 750 C 800 D E F 1,800 450 SOLUTION G 600 H 2,500 a What is the cost per day to crash each of the activities? The formula for calculating crash costs is: 700 Slope = a Prioritizing crashing choices, the most cost effective activities to crash are: (1) activity F, (2) activities A and G, and (3) activity E b The choices for crashing should be prioritized first by those that are on the critical path In this example, the critical path is made up of activities A - C - D - F - H Therefore, the first activity to be crashed would be activity F, followed by activity A Because neither activities G or E is on the critical path, crashing them will not reduce the project length but will add to the overall costs 10.2 Cost of Crashing a Project Consider the following project activity table, identifying each activity, its normal duration and cost, and expedited durations and costs: a What is the cost per day to crash each of the activities? b Assuming they are all part of the critical path, which activities should be crashed first? crash cost - normal cost normal time - crash time The crashed costs for each activity are: Activity A $500 Activity B $1,500 Activity C $700 Activity D $1,750 Activity E $1,200 Activity F $700 b Assuming they are all part of the critical path, which activities should be crashed first? We would crash in order from the least expensive activity to the most In this case, the first choice for crashing is activity A ($500), followed by activities C and F ($700) The last activity we would consider crashing is activity D ($1,750) The total time we can save in crashing all activities is days at a total additional cost of $8,100 Discussion Questions Please give examples of circumstances in which a project would employ lag relationships between activities using: a Finish to start b Finish to finish c Start to start d Start to finish The advantage of Gantt charts lies in their linkage to the project schedule baseline Explain this concept 334 Chapter 10 Project Scheduling What are the advantages in the use of Gantt charts over PERT diagrams? In what ways might PERT diagrams be advantageous? Under what circumstances might you wish to crash a project? In crashing a project, we routinely focus on those activities that lie on the critical path, not activities with slack time Explain why this is the case Explain the concept of a dummy variable Why are they employed in AOA notation? Why is there no need to use dummy variables in an AON network? What are some of the advantages in the use of AOA notation as opposed to AON? Under what circumstances does it seem better to apply AON methodology in network development? Explain why networks used to control the behavior of subcontractors have special dangers Problems Develop the network activity chart and identify the critical path for a project based on the following information Draw the activity network as a Gantt chart What is the expected duration of the project? Activity A B C D E F G H Expected Duration Predecessors days 10 days days day days A A B, C 10 days 14 days days 12 days days Normal A D, E F Activity Duration A Activity Duration A B A C A D B, C B Cost days $1,000 days $2 , 000 days $2,500 days $2,500 $1,200 $7,000 days $ 800 D days $3,500 days days $ day $5,000 days $2,000 days $3,000 10 days $5,000 days $6,300 H, I B Duration days F Predecessors Crashed Cost C G Consider a project with the following information Construct the project activity network using AOA methodology and label each node and arrow appropriately Identify all dummy activities required to complete the network 500 a Calculate the per day costs for crashing each activity b Which are the most attractive candidates for crashing? Why? When deciding on whether or not to crash project activities, a project manager was faced with the following information Activities on the critical path are highlighted with an asterisk: Normal Crashed F D Activity G C A $ 5,000 weeks $4,000 weeks H E, F, G B* 10,000 weeks 3,000 weeks C 3,500 weeks 3,500 week D* 4,500 weeks 4,000 weeks weeks Activity Duration ES EF LS LF A 3 B 10 C 10 10 D 10 13 10 13 E 13 12 17 F 13 17 13 17 10 12 15 17 17 22 17 22 H You are considering the decision of whether or not to crash your project After asking your operations manager to conduct an analysis, you have determined the "precrash" and "postcrash" activity durations and costs, shown in the table below (assume all activities are on the critical path): Slack Cost Duration Extra Cost Duration E* 1,500 weeks 2,500 F 7,500 weeks 5,000 weeks G* 3,000 weeks 2,500 weeks H 2,500 weeks 3,000 weeks a Identify the sequencing of the activities to be crashed in the first four steps Which of the critical activities should be crashed first? Why? Case Study 10.2 b c d What is the project's critical path? After four iterations involving crashing project activities, what has the critical path shrunk to (assume all non-critical paths are [...]... dummy activities do not have any duration value attached to them A FIGURE 10. 20 Partial Project Delta Network Using AOA Notation 328 Chapter 10 • Project Scheduling 1) FIGURE 10. 21 Completed Project Delta AOA Network t 4 l) 94 FIGURE 10. 22 Project Delta Forward Pass Using AOA Network Figure 10. 22 shows the forward pass results for Project Delta The nodes display the information concerning ES in the upper... crash H is higher ($2,000) Thus, crashing activity E by 1 day will increase the project budget from $22,950 to $24,700 The total costs for each day the project is crashed are shown in Table 10. 3 Legend FIGURE 10. 14 iNctivity Duration Fully Crashed Project Activity Network 322 Chapter 10 • Project Scheduling TABLE 10. 3 Project Costs by Duration Duration Total Costs 27 days $22,450 26 days 22,700 25... (ed.), The Project Management Institute Project Management Handbook San Francisco, CA: Jossey-Bass, pp 396-424 4 Gray, C F and Larson, E.W (2003), Project Management Burr Ridge, IL: McGraw-Hill 5 Shtub, A., Bard, J F., and Globerson, S (1994), Project Management: Engineering, Technology, and Implementation Englewood Cliffs, NJ: Prentice-Hall; Navarre, C and Schaan, J (1990), "Design of project management. .. 20 22 24 26 28 10 Duration (Dilv-,) FIGURE 10. 15 Relationship Between Cost and Days Saved in a Crashed Project The fully crashed project network is shown in Figure 10. 14 Note that the critical path is unchanged through fully crashing all activities The association of costs to project duration is graphed in Figure 10. 15 As each project activity has been crashed in order, the overall project budget increases... new equip FIGURE 10. 25 Partial Gantt Chart for ABCups, Inc Project (Left Side) May ; 4512 419 4)26 Sr•5 710 ' 5e17 5 ,24 FIGURE 10. 26 June Ft31 AUClUat 6 ,7 bfl 4 6021 6f h 7F 7.PI Partial Gantt Chart for ABCups, Inc Project (Right Side) 16 an 8,0 339 340 Chapter 10 - Project Scheduling Plantinpr dbl.) rogue TeohnMal appro val Deirmine ade , •.• • • •, ,•• imanth equipment FIGURE 10 21 4- Iamb wit/... mark, liquidated damages no longer factor into the cost structure TABLE 10. 5 Project Costs over Duration Project Duration (in days) Direct Costs Liquidated Damages Penalty Overhead Costs 57 $32,000 $5,000 $11,400 54 33,500 3,000 10, 800 $48,400 47,300 51 35,500 1,000 10, 200 46,700 48 38,500 9,600 48 ,100 -0- Total Costs 324 Chapter 10 • Project Scheduling 55 Total co sts 45 — - 1 iirect costs 35 Cost (tIlotisitil(ls)... project management systems from top management' s perspective," Project Management Journal, 21 (2) Critical Chain Project Scheduling Chapter Outline PROJECT PROFILE Canada's Oil Sands Recovery Projects INTRODUCTION 11.1 THE THEORY OF CONSTRAINTS AND CRITICAL CHAIN PROJECT SCHEDULING Theory of Constraints Common Cause and Special Cause Variation 11.2 CCPM AND THE CAUSES OF PROJECT DELAY Method One: Overestimation... Business e, Engineering Projects Englewood Cliffs, NJ: Prentice-Hall; Hulett, D (1995), "Project schedule risk assessment," Project Management Journal, 26(1), pp 23-44; Lock, D (2000), Project Management, 7th ed Aldershot: Gower; Oglesby, P., Parker, H., and Howell, G (1989), Productivity Improvement in Construction New York: McGraw-Hill 3 Cooper, K G (1998), "Four failures in project management, " in J K... the risk to the project' s schedule because delays in any critical activities will delay the completion of the project (5) c—Allowing for paint to dry before beginning the next activity is an example of a lag relationship occurring between activities 338 Chapter 10 • Project Scheduling INTEGRATED PROJECT Developing the Project Schedule Develop an in-depth schedule for your initial project based on... transferred to the firm's project management group Joe was excited because he realized that project management was typically the career path to the top in BCC, and everyone had to demonstrate the ability to "get their feet wet" by successfully running projects Joe had just left a meeting with his superior, Jill, who assigned him project management responsibilities for a new construction project the company