FIGURE 8-8 Computer Printout of Sewer Line Activities Only (Sort of Activities List by Code Digit #I Equal to One).

Transcription

1 It****t**.**.****..****t " ACTIVITY SCHEDULE ** *t***************tt*.*t***** PROJECT: SEWER AND WATER LINES SCHEDULE FOR SEWER LINE ACTIVITIES ONLY '* PAGE 1 ** ACTIVITY SCHEDULE ACTIVITY NUMBER ACTIVITY DESCRIPTION DURA- EARLY EARLY LATE LATE TOTAL FREE TION START FINISH START FINISH FLOAT FLOAT C 20 SURVEY SEWER LINES 4 4APR2002 9APR2002 4APR2002 9APR C 30 EXCAVATE FOR MANHOLES 3 10APR APR APR APR C 40 INSTALLMANHOLEFORMWORK 5 15APR APR APR APR PLACE CONCRETE MANHOLES 5 22APR APR MAY MAY C 60 TRENCH SEWER LINE 10 22APR2002 3MAY APR2002 3MAY STRIP MANHOLE FORMWORK 2 29APR APR MAY MAY C 80 LAY SEWER PIPE 15 6MAY MAY2002 6MAY MAY INSPECT MANHOLES 1 27MAY MAY2002 3JUN2002 3JUN REMOVE TRENCHING EQUIPMENT 2 27MAY MAY MAY2002 3JUN C 110 BACKFILL SEWER TRENCH 6 27MAY2002 3JUN MAY2002 3JUN *r********************t*.**.*"******t*t*****..*** END OF SCHEDULE... FIGURE 8-8 Computer Printout of Sewer Line Activities Only (Sort of Activities List by Code Digit #I Equal to One).

2 ... *+ BAR CHART **... PROJECT: SEWER AND WATER LINES SCHEDULE FOR SEWER LINE ACTIVITIES ONLY ** PAGE 1 " BAR CHART ACTIVITY DESCRIPTION DURATION 1APR APR APR MAY MAY2002 7JUN JUN C 20 SURVEY SEWER LINES 4 *XXX C 30 EXCAVATE FOR MANHOLES 3 *XX C 40 INSTALL MANHOLE FORMWORK 5 "XXXX 50 PLACE CONCRETE MANHOLES 5 Xxxxx *---- C 60 TRENCH SEWER LINE 10 *XXXXXXXXX 70 STRIP MANHOLE FORMWORK 2 xx *- C 80 LAY SEWER PIPE 15 'XXXXXXXXXXXXXX 90 INSPECT MANHOLES 1 x----* 100 REMOVE TRENCHING EQUIPMENT 2 xx--*- C 110 BACKFILL SEWER TRENCH 6 *XXXXX FIGURE 8-9 Computer-Generated Bar Chart for Sewer Line Activities Only. WORK DAYS CALENDAR DATES 1APR APR APR MAY MAY2002 7JUN JUN2002

3 160 PROJECT MANAGEMENT FOR ENGINEERING AND CONSTRUCTION TABLE 8-5 CALCULATIONS FOR PROJECT COSTS PER DAY ON AN EARLY START BASIS TOTAL PROJECT DURATION = 94 WORKING DAYS TOTAL PROJECT COST = $147, Activities In progress Project costlday Cumulative project cost % Cost Act. 10 IS I, I,,I Act , 9,,.,, Act. 30 9, 0, u, 9, Act. 40 8,,,,,,, 99,,,, 9, Act. 50 Act. 60 9, 8,,, 3,,,, Act. 60 Act. 70 Figure 8-10 is a computer printout of the daily distribution of costs for the calculations illustrated in Table 8-5. A similar analysis can be performed for other resources, such as labor and equipment. For example, a daily distribution of labor-hours, similar to Figure 8-10, can be used to detect periods of time when the need for labor is high or low. The project manager and his or her team can detect this problem early and appropriately adjust the project plan or acquire additional personnel if needed and available. A tabular format of the distribution of costs on an early start, late start, and target basis is presented in Figure The target scheduled costs are average values between the early and late start schedules. The right hand two columns of Figure show the percentage-cost and percentage-time values for the target schedule. As shown in the figure there is a non-linear relationship between the time and cost for a project. The cumulative cost graph for a project is commonly called the S-curve, because it resembles the shape of the letter "S." The early, late, and target cumulative distribution of costs can be superimposed onto one graph to form the envelope of time

4 **************t.*t**t*~********* ** COST EVERY DAY HISTOGRAM *' *********************"*"***+ttt PROJECT :SEWER AND WATER LINES DISTRIBUTION OF PROJECT COSTS BASIS: EARLY START ** PAGE 1 ** - For all activities - FIGURE 8-10 Computer Printout of Daily Distribution of Costs for Sewer and Water Lines Project.

5 162 PROJECT MANAGEMENT FOR ENGINEERING AND CONSTRUCTION... " W LY COST SCRWlLE '.... PROd0X: SAlW AND Sam LINES.. DAILY COST SCHEDULE FOR ALL ACTMTIES.' DAILY DISTRIBUTION OF COST WR ALL ACTMTIBS -Y START - LATE START - TARGET '* START DATE: 1 APR ZOO2 FINISH DATE: 8 Am ZOO2 I I mm I DAY I PAPLY START I LATE START I TARGET SCRWlLE I ULBrrnR I I I DATE I COSTIDAY CWWIATIVE I COSTIDAY CWWIATTVB I COSTIDAY CmRWLTrVB %TIME %COST I I COST I COST I COST I I FIGURE 8-11 Computer Printout of Daily Costs for All Activities of Sewer and Water Lines Project. over which costs may be distributed for the project (reference Figure 8-12). This graph links two of the basic elements of a project, time and cost. The third element, accomplished work, must also be linked to time and cost. Chapter 9 discusses linking accomplished work to the S-curve. The type of reports presented in this section are typical examples of the reports that can be obtained from the many computer software programs that are available.

6 CUMUL,ATIVE COST % COST % % - ^_ % % % APR APR MAY JUN JUL AUG 2002 FIGURE 8-12 lllustrat~ve S-Curve for Cumulative Cost Curve on an Early Start, Late Start, and Target Basis. The only input data that a project manager must prepare, to obtain the described analyses, are shown in Figure 8-6. RESOURCE ALLOCATIONS FOR DESIGN Efficient utilization of resources is critical to successful management. The primary resource during design is the work-hours of the design team. The project manager depends on the design team to create design alternatives, produce drawings, and write specifications for the proposed project. To properly coordinate all aspects of the design effort, the project manager must ensure the correct expertise is available when needed. Ge'nerally, design team members are assigned to the project by their respective home departments. Since each designer is often involved in several projects at the same time, the project manager must develop a resource allocation plan for each project. The plan should then be distributed to each design team member's home department to ensure that each resource will be available when needed. The project manager can resource load the project plan to include the number of work-hours required for each design discipline. The resource plan is similar to the cost distribution analysis presented earlier in this chapter, except work-hours are

7 164 PROJECT MANAGEMENT FOR ENGINEERING AND CONSTRUCTION used in place of dollars of cost. Thus, the resource plan is simply a histogram of work-hours versus time for each design discipline. The project manager should provide the resource plan for each project to the design team's manager. The design managers can then integrate the resource plans of all active projects into their department's demand for technical expertise. This is necessary to ensure adequate resources are available for the projects when required. RESOURCE ALLOCATIONS FOR CONSTRUCTION During the construction phase, the primary resources are labor, materials, and equipment. The correct quantity and quality of material must be ordered and delivered to the job-site at the right time to ensure efficiency of labor. Equipment to be installed in the project often requires a long lead time from the fabricator. Thus, the project plan should include material and equipment required by the construction work force. Labor represents a major cost of construction. The labor force on the job operates construction equipment and installs the materials. A resource allocation plan is required to ensure high efficiency and productivity during construction. The project manager can resource load the project plan to include the number of work-hours required for each craft of construction labor. The resource plan is a histogram of work-hours versus time, similar to the cost distribution analysis presented earlier in the chapter. The construction plan shows the desired sequence of work. However, to be workable, the plan must also show the distribution of resources, such as the required labor for each craft on the job The demand for labor should be uniformly distributed for each craft on the project, to prevent irregularities. The resource plan can be used as a tool to ensure a relatively uniform distribution of labor on the project. Figure 8-13 is a simple bar chart for a project, showing each work activity, number of crews, and number of people in the crew for all labor in the project. The lower portion of Figure 8-13 shows irregularity in the distribution of workers per day during the middle of the project. Figure 8-14 illustrates the same project as Figure 8-13, except Activity F is started one day later and Activity H is started two days earlier. The lower portion of Figure 8-14 shows a relative uniform distribution of labor by making these two minor adjustments in the project plan. A similar analysis can be made for each craft of labor to ensure uniform distribution of workers on the project. A resource allocation for a particular craft typically has a flat appearance on the graph, whereas a resource allocation for all crafts typically has a bell-shaped graph as shown in Figure PROGRAM EVALUATION AND REVIEW TECHNIQUE (PERT) In the Critical Path Method of scheduling projects, the duration of each activity is usually defined with a reasonable degree of certainty. For most projects the type and amount of work is known, which enables the project manager to establish the approximate duration for each work activity. For example, the time to produce

8 drawings may be four weeks, the time to perform a soil investigation to gather and test soil samples may be two weeks, or the time to erect forms for concrete may be three days. Using the CPM, the assignment of one duration to each activity provides a deterministic process for the start and finish dates of each activity and a single finish date for the entire project. For some projects it may be difficult to estimate a reasonable single duration for one or more of the activities in the project schedule. There may be a range of durations that may apply to a particular activity, which makes it difficult to select just one duration to assign to the activity. The Program Evaluation and Review Technique (PERT) method of scheduling uses three durations for each activity and the fundamental statistics to determine the probability of a project finishing earlier or later than expected. Although the PERT method is not used extensively in engineering and construction projects, it provides valuable information for assessing the risks of a schedule slippage of a project. The PERT method uses an arrow network diagram to show the logical sequence of activities in a project, whereas the CPM uses a precedence diagram as discussed in preceding sections of this book. In a PERT diagram, activities are represented by arrows with circles at each end of the arrow. The circles are called events that represent an instant in time. The circle at the beginning of the activity represents the start of an activity, and the circle at the end of the arrow represents the finish of the activity. The major difference between the PERT method and CPM is the estimation of durations of activities. PERT is applicable for projects where there is a high degree of uncertainty about how long any given activity will take to complete, where even the most experienced manager can give only an educated guess of the estimated time, and that guess is subject to a wide margin of error. Using PERT there are three durations that are assigned to each activity: a = optimistic time b = pessimistic time m = most likely time The optimistic time is the shortest possible time in which the activity could possibly be completed, assuming that everything goes well. There is only a very small chance of completing the activity in less than this time. The pessimistic time is the longest time the activity could ever require, assuming that everything goes poorly. There is only a very small chance of expecting this activity to exceed this time. The most likely time is the time the activity could be accomplished if it could be repeated many times under exactly the same conditions. It is the time that it would take more often than any other time. The most likely time is the time the manager would probably give if asked for a single time estimate. It is important to note that the optimistic time and the pessimistic time may not deviate the same amount from the most likely time. In simple mathematical terms, a and b may not be symmetrical about m.

9 . 166 PROJECT MANAGEMENT FOR ENGINEERING AND CONSTRUCTION Activity Duration Numbers Workers Work Day of Project Number in Days of Crews in Crew A B C D E F G H I J K Totals FIGURE 8-13 Irregular Distribution of Labor. Number of Workers 3838 per Day

10 CHAPTER 8: PROJECT SCHEDULING 167 Work Day of Project Actii Duration Number Workers Number in Days of Crews in Crew A B C D E F G H I J K Totals Number of Workers per Day FIGURE 8-14 Distribution of Labor after Starting Activity F Two Days Later and Activity H Two Days Earlier.