This paper was first published in the Canadian Journal of Civil Engineering, Vol. 21, 1994 pp 939-953, under the title "A Pragmatic Approach to Using Resource Loading, Production and Learning Curves on Construction Projects". It has been modified only to the extent necessary to make it presentable in web page format.

Published here October, 2001.

Abstract | Introduction | Resource Loading | S-curves | What can be Learned?
Productivity Improvement | Learning vs. Experience | Original Theory | Two Approaches
Illustration | Issues | Conclusions | References | Appendix 1 | Appendix 2 

Progress S-curves (output)

As might be expected, the foregoing factors have a considerable impact on total production especially as represented by the more familiar output or progress S-curves.

A complete determination of the project status and projections to final completion for management action can perhaps best be tracked by an integrated cost/schedule system or technique known as "Earned Value and Performance Measurement" (Kerzner 1989). The earned value, i.e. the Budgeted Cost of Work Performed (BCWP), is determined at regular intervals during the course of the project. At the same time, the Actual Cost of Work Performed (ACWP) is also determined, and both are compared to the baseline plan which is the Budgeted Cost of Work Scheduled (BCWS). By presenting these results graphically as S-curves, the variances in cost and schedule can readily be seen, and by analyzing the results relative to the baseline plan S-curve, estimates can be made of anticipated variations at completion. The key elements of the technique are shown in Figure 3.

Figure 3 - Earned value and performance measurement

Figure 3: Earned value and performance measurement

The technique is especially useful on projects involving a large number of significant activities by different trades and/or under conditions which change during the course of the work. There are, however, several weaknesses in the approach (Meredith 1985). Cost data must be collected which reflects the actual progress of the work, work in progress must be measurable and it must be measured. Consequently, this form of tracking requires significant additional effort or qualified dedicated staff to collect reasonably reliable data. This is particularly true where large purchases of off-site equipment may involve staged payment assessments.

Since the results are at best estimates of work-in-hand and the final results are estimated projections, the technique is not usually considered worth the effort on most projects. The exceptions are large complex projects, or projects on which this approach is required under the terms of the contract. When the technique is adopted, an essential element in its successful use is a realistically shaped baseline plan S-curve.

A better strategy for tracking progress is to identify the major critical activities on site that are measurable and plot those S-curves as surrogates for the whole job or stages of the job. Figure 4 shows three S-curves[2] illustrating different major activities. To facilitate comparison they are shown plotted as percent progress against percent time.

Figure 4 - Three examples of progress S-curves
Figure 4: Three examples of progress S-curves

Curve (a) shows progress on a 5560 pipe pile driving contract lasting 137 working days. Curve (b) shows the cumulative progress on a 180,000 cu. yd. bulk excavation contract lasting 15 weeks. Notice the progressive addition of plant as the work opens up in the beginning, and the subsequent removal of plant as the availability of work runs out towards the end. Curve (c) shows progress on a 7-month civil contract as reflected by the approved monthly measurement progress billings.

Figure 5 shows measured progress on a 42,000 cu. yd. structural concrete activity of 16-months duration in Ontario, Canada. This curve is interesting because it clearly shows the slow down in progress over the winter months. The original data indicates that the virtual cessation of activities due to cold weather was only two-and-a-half months. However, due to the S-curve effects just before and after the cold weather cessation, the total impact of this condition was closer to three-and-a-half months. In the preparation of the original construction schedule, this situation could have been reasonably foreseen and an appropriate adjustment made to the "standard" S-curve profile.

Figure 5 - Placing of formed structural concrete. Total concrete = 31 900 m3; total time = 16.5 months

Figure 5 - Placing of formed structural concrete.
Total concrete = 31 900 m3; total time = 16.5 months
***  Resource Loading (input)

2. From the author's personal records of progress tracking.
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