Construction delays chapter six delay analysis using bar chart schedules

Construction delays chapter six delay analysis using bar chart schedules Construction delays chapter six delay analysis using bar chart schedules Construction delays chapter six delay analysis using bar chart schedules Construction delays chapter six delay analysis using bar chart schedules Construction delays chapter six delay analysis using bar chart schedules Construction delays chapter six delay analysis using bar chart schedules Construction delays chapter six delay analysis using bar chart schedules

Delay Analysis Using

Bar Chart Schedules

Later in this book, we will explain how to perform a delay analysis when

a detailed Critical Path Method (CPM) schedule was created as the nal as-planned schedule for the project However, many projects arescheduled using a bar chart schedule (bar chart) For projects with manyinterrelated activities, a bar chart is not as desirable as a CPM schedule,because a CPM schedule records and preserves the relationships amongthe activities However, a meaningful and accurate delay analysis can still

origi-be performed using a bar chart With any schedule, as the level of detailand the quality of information decrease, the delay analysis becomes moresubjective Therefore, a delay analysis that is based on a bar chart requiresthe analyst to guard against assumptions that favor one outcome or anotherand to work to be as objective as possible This chapter describes how adelay analysis is performed when the project schedule is a bar chart.There is nothing inherently wrong with scheduling a project with a barchart Bar charts were in use long before the Critical Path Method was evercreated As some professionals are quick to point out, the Empire StateBuilding was scheduled with a bar chart and not a CPM In fact, a detailedbar chart can provide almost as much information as a CPM schedule

Fig 6.1is a simple bar chart for the construction of a bridge Though

it does not contain a significant number of activities, it does show thegeneral sequence of work for the construction of the bridge Using thissimple bar chart as a starting point, the project manager could easilydefine each activity in more detail

Fig 6.2 is a more detailed bar chart of the project depicted in

Fig 6.1 This more detailed bar chart more clearly defines the contractor’sproposed work plan In this bar chart, each major activity is broken downinto the work on the respective piers and spans, providing the contractorand owner with a more detailed illustration of the plan for construction.With very little effort, the project manager or project scheduler canmodify the bar chart in Fig 6.2to show the interrelationships among theactivities, as shown inFig 6.3

109 Construction Delays Copyright © 2018 Trauner Consulting Services, Inc.

Using this schedule as a foundation, a CPM schedule for the projectcould be produced with little effort.

Unfortunately, most bar charts for projects do not contain as muchdetail as that inFig 6.3, and often not even as much as the bar chart in

Fig 6.2 In general, most bar charts suffer from the following majorshortcomings that diminish their usefulness as a management tool andtheir effectiveness in measuring delays:

• Lack of detail—too few activities for the amount and complexity ofthe work

• No indication of the interrelationships among the activities

• No definition of the critical path of the project

Obviously, these weaknesses hamper the ability of the analyst

to perform a delay analysis, but they do not make it impossible If nothingelse, the bar chart is helpful in that it defines the plan for constructing theproject, and it can be used as the basis for an analysis of delays

DEFINING THE CRITICAL PATH

The first step in analyzing a bar chart is to define the critical path.Every project has a critical path, including a project that was scheduledwith a bar chart The following definitions illustrate this point

Figure 6.1 Simple bar chart example.

BASIC CRITICAL PATH METHOD

In CPM scheduling, the drafter of the schedule prepares a logic ornetwork diagram As presented in Chapter 2, Float and the Critical Path,once durations are assigned to the activities in the network logic diagram,the critical path can be calculated It is a purely arithmetic process

Figure 6.2 Example 1 detailed bar chart example.

The definition of the critical path is the longest path of work activities throughthe network diagram that forecasts the date when the project will finish The proj-ect cannot finish until every path of work has been completed Whetherthe critical path is defined in a CPM schedule or a bar chart, everyproject has a series of interrelated activities that will control the projectcompletion date.

Figure 6.3 Example 1 detailed bar chart example with logic relationships.

Also, the only way to delay the project is to delay an activity on the ical path of the project In understanding this concept, it is essential to rec-ognize that the critical path of a project is dynamic In this manner, delays

crit-to noncritical activities that persist will cause the critical path crit-to shift crit-to thepath containing that activity and, thus, will then delay the project

IDENTIFYING THE CRITICAL PATH ON A BAR CHART

Because we know that a critical path exists in a bar chart schedule,the delay analyst should first identify this critical path The analyst mustreview the bar chart in detail for obvious conclusions about the sequence ofwork These conclusions may be based on project documentation thatmight clarify the thought process that went into creating the bar chart ordefining the planned work sequence Documentation that can be helpfulincludes the contract, which may dictate staging or phasing, the pre-bid orpreconstruction meeting minutes, internal contractor or subcontractor docu-mentation, project correspondence exchanged before the bar chart was pre-pared, and any other documentation that might shed light on the how theproject team approached the planning and scheduling of the project

Practical knowledge of the type of project and the physical tion requirements is also necessary to reach a reasonable conclusionregarding the project’s critical path For example, to analyze a bar chart of

construc-a high-rise structure, the construc-anconstruc-alyst mconstruc-ay need to know thconstruc-at interior finishesusually are not planned to start until the building or a portion of thebuilding is “dried-in” or “watertight,” that a common sequence of theprogression of trades is from the bottom up, and that it is common fortrades to follow behind one another as the building progresses upward,instead of waiting until the preceding trade has finished all of its work inthe tower

Given the variations in possible work sequences, analysts should resistthe temptation to interpret the bar chart schedule based solely on theirown experience Just because a contractor has performed work in a par-ticular sequence in the past does not mean that the contractor on theproject being analyzed has planned to perform the work the same way.Unless the bar chart is extremely brief, analysts should be able to gleanthe best indication of the overall plan and sequence of activities to

determine the critical path using the bar chart as the primary indicator ofthe project team’s plan for execution of the project, rather than analystsproposing their own version of a plan.

Referring to Fig 6.3, we can define the critical path for the samplebridge project The critical path starts with the mobilization activity, with

a duration of 2 weeks This is obvious, since no other activity is scheduled

to occur during this period We show this first critical activity inFig 6.4

Figure 6.4 Identification of initial critical path activity.

The next two activities on the schedule are the clear and grub activityand the piles at Pier #1 In reviewing the sequence of activities, the clearand grub activity is related to the abutment and approach work Theabutment and approach work is scheduled to finish well before the end ofthe project and does not appear to be related to the schedule of activitiesfor bridge construction The analyst can determine from the contract thatthe approaches are to be constructed using asphalt paving, but the bridgedeck is to be paved with concrete Consequently, there is no physical rea-son to coordinate the concrete placement for the bridge with theapproach construction The only possible relationship might be the need

to move the concrete placing equipment onto the bridge superstructure.However, because the schedule reflects that the deck work is to startbefore workers complete either of the approaches, the analyst concludesthat the equipment can be moved onto the bridge independently of theapproach work Therefore, it appears that the abutment/approach path isnot on the critical path for the project

Therefore, the critical path must be through the piles and piers Whenviewing this bar chart, the analyst sees that the work is “stair-stepped”through the specific activities for each pier Thus, after the piles at Pier

#1 are completed, the piles at Pier #2 can start While the piles at Pier

#2 are being driven, the pile cap at Pier #1 is concurrently constructed.Based on the graphic representation, the critical path appears to followthese activities (shown inFig 6.5):

Thus, the overall critical path from the bar chart (Fig 6.6) is:

• Mobilization

• Piles, Pier #1

• Pile Cap #1

• Curbs & Sidewalks, Span #3

• Curbs & Sidewalks, Span #4

• Punch list

The analyst could reach a similar conclusion working with the lessdetailed bar chart alone (see Fig 6.1) This would, however, require thatthe analyst make more assumptions about the work on the separate piers

As was noted in the preceding discussion, contemporaneous tion can help the analyst define the contractor’s planned sequence inmore detail The less detailed the bar chart, the more assumptions arerequired by the analyst to determine the project’s critical path

documenta-QUANTIFYING DELAYS USING BAR CHART SCHEDULES

The process of quantifying delays using a bar chart is similar to theprocess that is described later in this book when a CPM schedule is avail-able To start the process, the analyst must prepare a detailed as-built dia-gram that shows as specifically as possible when the project work wasactually performed Fig 6.7 is the as-built diagram for the West StreetBridge project Once the as-built has been prepared, the analysis can pro-ceed As the as-built diagram (Fig 6.7) shows, the mobilization activitystarted on schedule (the first day of Week 1) and finished on schedule (bythe end of Week 2) The remaining activities, however, did not proceed

in the same manner as the as-planned schedule had predicted

As the as-built diagram (Fig 6.7) shows, the pile driving at Piers #1,

#2, and #3; the pile caps at Piers #1 and #2; and Pier Column #1 wereaccomplished as-planned in 3 weeks immediately following the mobiliza-tion activity However, the clear and grub activity did not proceed asplanned, but started 2 weeks late and finished in the 1-week plannedduration If the previous conclusions concerning the critical path werecorrect, the delay to the start of clearing and grubbing should not haveresulted in a delay to the project To check this conclusion, the analystcan “update” the bar chart as of the end of Week 5, as shown inFig 6.8

As can be seen in Fig 6.8, the project is still on schedule, but theabutment and approach work has been delayed, or “pushed out” in time,because of the delay to the clear and grub activity As expected, there is

no delay to the critical path The adjusted schedule (Fig 6.8) shows theas-built condition for the first 5 weeks of the project and the adjusted as-planned activities for the remainder of the work

Based on the as-built information, the analyst decides to update theschedule as of the end of Week 11 The as-built diagram (Fig 6.7) showsthat the abutment and approach work has not yet begun and that the piercap work also has not yet begun Pier Columns #1 and #2 were com-pleted on schedule Pier Column #3, however, took 1 week longer tocomplete than planned The adjusted schedule for Week 11 is shown in

Fig 6.9

Figure 6.7 As-built diagram.

Based on the updated and adjusted schedule presented inFig 6.9, theanalyst concludes that the project is now 5 weeks behind schedule Thedelay was caused by the late start of Pier Cap #1 work, which wasplanned to start at the beginning of Week 7, but actually started at thebeginning of Week 12 Although Pier Column #3 was late in finishing and

Figure 6.8 Week 5 update, no delay.

was on the original critical path, once the Pier Cap #1 activity did not start

on time, the critical path shifted solely to the pier cap work Pier Column

#3 activity was effectively given float by this shift in the critical path.Next, the analyst decides to update the schedule at the end of Week

15 This point is chosen because the activities along the bridge pier and

Figure 6.9 Week 11 update, 5-week project delay.

deck path continued in accordance with the adjusted schedule, but theabutment and approach work did not By tracking the two activities thatare precedent to punchlist, specifically the curbs and sidewalks of Span

#4, which are currently driving the punchlist activity, and the paving ofApproach #2, it appears that the critical path shifts in the middle of Week

15 The schedule updated for the end of Week 15 is shown inFig 6.10

Figure 6.10 Week 15 update, no additional project delay.

As shown inFig 6.10, from the end of Week 11 to the end of Week

15, there was no additional delay, despite the fact that the abutment andapproach work continued to be delayed

To test the previous observation that the critical path shifts in the dle of Week 15, the analyst updates the schedule at the end of Week 16.The schedule updated for the end of Week 16 is shown inFig 6.11

mid-As can be determined from Fig 6.11, for the first half of Week 16,the bridge pier and deck path continued to be the driving activity of thepunchlist work, while the abutment and approach path continued to con-sume its last half-week of float Because the pier cap work was progressing

as planned, there was no additional delay for the first half of the week.Then, the abutment and approach work path became longer than thebridge pier and deck path and, as the longest path, the abutment andapproach work became critical Because this path of work continued to

be delayed for the remainder of Week 16, by the end of the week, theproject had been delayed an additional half-week As a result, by the end

of Week 16, the project had been delayed a total of 5.5 weeks

Next, the analyst decides to update the schedule at the end of Week

18 This point is chosen because the as-built schedule indicates that theabutment and approach work actually started at this time The scheduleupdated for the end of Week 18 is shown inFig 6.12

Because the project had been delayed 5.5 weeks as of the last update,the additional delay since that update is 2 weeks The activities on thebridge pier and deck path were not delayed further since the last update.Instead, the additional 2-week delay was the result of the continued lack

of progress on the abutment and approach path

Next, the analyst decides to update the schedule at the end of Week

31, which is the time that the as-built schedule shows that the projectactually completed The schedule updated for the end of Week 31 isshown inFig 6.13

As shown in Fig 6.13, no additional delay was experienced duringthe completion of the project At the completion of the analysis, all proj-ect delays have been identified As a final check, the analyst ensures thatthe total net delay identified during the analysis equals the number ofdays that the project was completed late

This example follows the conceptual approach to analyzing delays lined in Chapter 5, Measuring Delays—The Basics The exact methodused to perform an analysis and the accuracy of the results depend on thelevel of detail of the as-planned schedule and of the available as-builtinformation