Annex C- SAMPLE TIME MONITORING BASED ON WEIGHTAGE CONCEPT (S-CURVE)
C-1 GENERAL
To summarize the status of various activities of a construction project a single common measurement parameter, namely, project metric, is required. One of the simple solutions for this is by assigning a pre-agreed percent weightage for all the activities of the project.
The weightages of all activities are summed up and plotted as a cumulative planned curve which is usually in the shape of English alphabet ‘S’. This S-curve plotted for planned and actual metric may be used as an efficient tool for time monitoring. S-curve can be prepared at all levels of WBS and each work element of the project can be individually monitored and status summary prepared. The S-curve prepared at total project level is a weighted summation of all the sub-activities in the work breakdown structure. S-curve is a useful MIS tool for time monitoring which depicts pictorially the status of an updated schedule of the project, the tool is useful for decision-making during the time control.
C-2 PROCEDURE FOR S-CURVE PREPARATION
For allocation of weightages to various works packages within a project, the following three criteria are to be considered:
a) Criticality/importance of work package,
b) Tentative tendering cost, and
c) Level of effort required.
Within the works package weightages are further distributed to each progress phase of work totalling up to 100 percent, that is,
a) Design : X percent (say 5 percent)
b) Procurement : Y percent (say 40 percent)
c) Construction : Z percent (say 50 percent)
d) Testing and : T percent (balance 5 Commissioning percent)
The distribution is standardized across all the work packages in a project.
The weightages are further distributed within the above four phases across activities on vertical scale.
Following distribution criteria are to be considered:
a) Level of efforts/skill level of tradesman required for implementation.
b) Based on sub-critical path within a works package driven by its own intermediate completion milestone.
c) For procurement activities, lead time for delivery and availability in the market.
Weightages are assigned (total 100 percent distributed on horizontal scale) to different work phases of each
activity.
Table 1 to Table 4 give a sample distribution of weightages to different phases across vertical and
horizontal scales for a work package.
Against each activity in Tables 1 to 4 BOQ unit is chosen as a progress representative. The baseline schedule from time planning process determines the distribution of the metrics on the project timeline.
The timescale for metrics distribution and curve plotting can be month, week or even days depending on the nature of project and level of monitoring required for the project.
C-2.1 Identification and Monitoring Procedure Standardization
As the project progresses, the actual performance of works packages and its activities are tracked against its planned
value as given in Table 5 and a new actual S-curve is plotted along with its baseline S-curve (see Fig. 13).
The reasons for deviation can be ascertained by drilling down to lower levels in WBS of the project. This
analysis becomes input for time control and decision making for mitigation.
The time control procedure in 6.3 determines revised plan and activities metrics for future activities. The weightage distribution is reworked for future activities of the project and plotted in dotted line as a forecast curve. If the actual progress is behind the baseline and if it is possible for the backlog to be recovered either before or by the baseline completion time this is deemed as ‘catching up’, and the distribution plotted for this is called the catch-up curve (see Fig. 14).
