W13_Reginald Nwachukwu_Analysis of Critical Path for the Construction of 27.0m Length Precast Box Culvert

1. Problem Definition or Opportunity Statement:

To identify and analyse the CRITICAL PATH (S) for the construction of 27.0m length precast box culvert

In continuation of the scheduling task by the schedule team discussed in the weekly blog post  http://bistro12.blogspot.com/2013/03/w12reginald-nwachukwuscheduling-270m.html the lead scheduler have further asked me to identify and analyse the CRITICAL PATH(S) necessary to accomplish the construction of the precast box culvert. He further instructed that management have approved only 18 WD workdays so as to move the construction team to another site. Table 1-1 below shows the Activity List and the relationships/logic and durations.

Table 1-1  Activity List with Relationships and Durations

2. Development of Feasible  Alternatives:

To develop feasible alternatives necessary to identify and analyse the critical path in the PDM network model developed for the construction of the precast box; four generally acceptable methods for critical path analysis were adopted as alternatives to optimise the PDM Schedule. These alternatives or methods includes:

(a.)  Lowest Total Float
(b.) Negative Total Float
(c.) Longest Path
(d.) Longest Path Value Method

For brevity, only the Least Total Float method have been applied to the schedule model using the following:

(i) Date & Float Constraints
(ii) Calender Date

3. Development of  Outcome for Each Alternative:

The schedule model is subject to analysis by constructing the ADM model and the original path duration for the schedule. Later, the various constraints were applied to the schedule model to evalute their impacts on the completion dates and the critical path(s).

Figure 1 - 1 ADM network model for the construction of precast box culvert.

Figure 1 - 2 PDM Original Path Duration with No constraints applied to the network model 

Figure 1 - 3 PDM network model with 4 Date Constraints applied to the network model

Figure 1 - 3 PDM network model with 3 Date Constraints applied to the network model

Figure 1 - 3 PDM network model with IMPOSED DATE applied to the network model

4. Selection of Acceptable Criteria:

Criteria used to selection the path(s) that are critical to completing the construction precast box will be based on the Least Total Float method where activities with least total float are selected as been on the critical path. Though this method does not give complete solution to identifying and analyzing CP, but it does provide insight into CP identification and analysis. Here, activities with the LEAST TOTAL FLOAT are construed to be on the CRITICAL PATH.

5. Analysis and Comparison of Each Alternative:

Analyzing and comparing the possible outcomes from step 3, the CRITICAL PATH remain the same irrespective of the different types of constraints applied to the network model and the IMPOSED DATE constraint only introduced NEGATIVE FLOAT for the Clear Site activity (-2 Days); but the CP remain same.

6. Selection of Preferred Alternative:

The preferred alternative is maintain the identified CRITICAL PATH ( B - E - F - G - J - K - M ) which remain unchanged after applying date constraints due to material delivery or minimum no of days necessary for concrete to gain strenght before loading it ( for base slab take 3DAYS).

7. Performance Monitoring and Evaluation of Results:

The performance of the network model will be monitored by establishing the changes or other constraints that might impact the completion date and results obtained from the performance can be further evaluated to reflect the TRUE representation of the activities necessary to complete the precast culvert.

References:

1. Humphreys G.C. (2002) Project Management Using Earned Value (2nd Edition) pp. 143 - 144 Orange CA Humphreys & Associates

2. AACE International (2012) Skills and Knowledge of Cost Engineering (5th Edition Revised) pp. 13.3-13.7  AACE International Morgantown W.V. 

3. AACE International (2008) Planning and Scheduling Professional certification Guide (First Edition Revised) pp. 143-145  AACE International Morgantown W.V. 

4. AACE International Recommended Practice No. 49R-06 (2010) Identifying The Critical Path pp. 4 - 8 AACE International Morgantown W.V.