Project Scheduling Analysis Using the Precedence Diagram Method (PDM) Case Study: Surabaya’s City Outer East Ring Road Construction Project (Segment 1)

The project acceleration by the Crash Program is one of the ways that is often used to make time and cost efficiency on an ongoing project. Acceleration of project completion time will affect the efficiency of equipment and labor productivity. In the case study of the Surabaya Outer East Ring Road Project Construction Segment 1, a project that has the potential to be accelerated is discussed in order to obtain efficiency values in terms of time and cost, Project acceleration by means of the Crash Program using the Precedence Diagram Method (PDM) method to determine the value of efficiency. This project uses resources, in this research the software used is Microsoft Project 2016. The research method used is to design network planning, find the critical path for each job, determine the work that has the potential to be accelerated, calculate the crash cost in additional working hours. and work shifts, calculating direct costs and indirect costs for each activity that changes due to changes in the duration of implementation, calculating the cost slope. Application of the Crash Program in the work of Asphalt Concrete Surface Layers (AC) thick 5 cm in the project will have an impact on increasing the time efficiency previously planned from 180 working days to 175 working days and efficiency with the difference in project costs of Rp. 18.313.935,8 with a ratio of 0,997 between the PDM method compared to the cost of the contract value calculated using the crashing project method.


Project Definition
Project activities can be interpreted as one of the temporary activities that take place in a limited period of time, with the allocation of certain resources intended to carry out tasks whose objectives have been clearly outlined. The task can be in the form of building factories, making new products or conducting research and development [6].

Project Management
Project management can be interpreted as the application of management functions in a project activity in other words it is an activity that regulates the course of activities in project implementation for all project stages [7].

Network Diagram Method
There are several types of network analysis methods that can be used in project time scheduling, including [8]

PDM (Precedence Diagram Method)
According to [9] the advantage of Precedence Diagram Method (PDM) compared to CPM is that PDM does not require fictitious / dummy activities so that network creation becomes simpler. This is because different overlapping relationships can be made without increasing the number of activities [10]. In PDM there are also known constraints. One constraint can only connect two nodes, because each node has two ends, namely the beginning or beginning = (S) and the ending or finished = (F). So here there are four types of constraints [11], namely: 1. Constrain finishes to start -Finish to Start (FS) This constraint provides an explanation of the relationship between the start of an activity and the completion of an earlier activity. Formulated as FS (i-j) = a which means the activity (j) starts a day, after the activity that preceded it (i) is completed.

Constrain start to start -Start to Start (SS)
Provide an explanation of the relationship between the start of an activity with the start of an earlier activity. Or SS (i-j) = b which means an activity (j) starts after b days the previous activity (i) starts. Such constraints occur if before the previous activity is completed 100% then the activity (j) may start after a certain part of the activity (i) is finished. 3. Constrain finishes to finish -Finish to Finish (FF).
Provide an explanation of the relationship between the completion of an activity with the completion of the previous activity. Or FF (i-j) = c which means an activity (j) is completed after c days of the previous activity (i) are completed. This kind of constraint prevents the completion of an activity from reaching 100% before the previous activity has finished (= c) days. 4. Constrain start to finish -Start to Finish (SF) Explain the relationship between the completion of the activity and the start of the previous activity. Written by SF (i-j) = d, which means that an activity (j) is completed after d days of the previous activity (i) begin.

Calculation of Precedence Diagram Method (PDM)
Activities in the Precedence Diagram Method (PDM) are described by a rectangular symbol because the location of the activity is in the node section, often called Activity On Node (AON). The activities in PDM are represented by an easily identifiable symbol, a common form that is often used is seen in Figure 2

Metode Crashing
Crashing Project is an action to reduce the overall duration of work after analyzing alternatives available from the network. Aims to optimize work time with the lowest cost. Often there are trade-offs in crashing, i.e. exchange of time and costs. This can be illustrated in the form of a time-cost graph ( Figure 3).

Fig 3. Relation Graph between Time and Cost in Normal Condition
In a crashing project, there are two time components, namely: a. Normal Time, i.e. completion of activities under normal conditions, b. Crash Time, which is the shortest time that is most likely to complete the activity. From these two components, we can get the Total Acceleration Time, with the equation: Total Acceleration Time = Normal Time -Acceleration Time While the cost component in a crashing project is divided into three, namely: a. Normal costs, which are direct costs to complete activities in normal conditions, b. Crash Cost, which is the direct cost to complete an activity in the shortest time condition that is most likely to complete a n activity.
From these two components, we can get the Total Acceleration Cost, with the equation: c. Total Acceleration Fees = Acceleration Fees -Normal Costs d. Acceleration Cost per Time Unit (Slope), i.e. direct costs to complete an activity in the shortest time condition in the smallest time unit specified, using the equation: e. Acceleration Cost per Unit (Slope) = Total Acceleration Cost ÷ Total Acceleration Time To do a crash on a project, there are steps to complete it, namely: a. Draw a network diagram for each event, b. Calculate the total acceleration time, the total acceleration fee, and the acceleration cost per unit time for each event, c. Determine the critical path and the length of the project, d. Select the activity on the critical path that has a minimum acceleration rate, and reduce the time the activity is as much as possible e. Update all time activities, if the desired time limit has been reached, then stop. If not, repeat step 3.

Alternative Addition to Working Hours (Overtime)
Crashing by adding work hours will affect the efficiency of the project. Productivity for these alternatives can be calculated using formulas. Daily Productivity = Volume Normal Normal Duration (1) Productivity / hour = Daily Productivity ÷ Normal Work Hours (2) Productivity after crash = Daily productivity + (Total Overtime Time × Productivity / hour ×%) From the daily productivity value after the crash, the duration of the project completion can be sought after the acceleration (crash duration) Crash Duration = Volume ÷ Productivity after Crash (4) The amount of the crash cost can be calculated using the equation below.

Method
The collection of data or information obtained from the relevant agencies, namely the contractor and the supervisor of the Surabaya,s City Outer East Ring Road Construction Project (Segment 1). There are two types of data needed for this research, first is primary data in the form of interviews with resource persons and direct observations in the field and the second is secondary data including S curve data and recapitulation of project cost calculations and variable cost data including the list of Budget Plans (RAB), list of material prices and wages as well as a daily report on the number of workers and Shop drawing. After the data from the project is collected, the first step that must be done in this research is to compile network planning, starting from determining the number of work activities, then determining the duration of each work, determining which activities precede, which activities follow and which activities can be carried out in the same time and put it in the Microsoft Project to find out the critical path of the work. After the network planning is arranged, the next step taken is to do Crashing analysis by determining the total acceleration time, the total acceleration cost and the total acceleration cost per unit time (cost slope), the calculation of the three is only done on the activities that are passed by the critical path. Activities that will be crashed are activities that have the longest duration and are allowed to be accelerated, after the crashing process, network planning is reorganized with the duration of the crashing (the latest duration).

Results and Discussion
Project data used in preparing new project scheduling consists of Workbreak Down Structure (WBS) data, project duration or Time Schedule curve S, and work item analysis. These data are not directly used for scheduling new projects but are analyzed first so that they can be effectively applied to each method.

Critical Trajectory of Project Activities
Project data used in preparing new project scheduling consists of Workbreak Down Structure (WBS) data, project duration or Time Schedule curve S, and work item analysis. These data are not directly used for scheduling new projects but are analyzed first so that they can be effectively applied to each method.

Fig 1. Activities that are in the Critical Path
After knowing the activities that are on the critical path, the next stage is to determine what work allows acceleration, namely work that has a long duration and can do overtime work. After calculating the coefficient of workers in the analysis as well as the volume of work, the work on the critical path that can be accelerated is the Asphalt Concrete Surface Layers (AC) thick 5 cm so that it can speed up the implementation time from 180 days to 175 days.

Crash Project
The calculation of the crash project or acceleration of the project is done by overtime work done by workers, so that it is closely related to the wages received by each worker. In this crash project, the activities carried out to accelerate the duration are activities that have a long duration and allow acceleration to be carried out on critical paths, namely the Asphalt Concrete Surface Layers (AC) tb. 5 cm with the initial work duration of 28 days. The project duration calculation uses the PDM approach, ie with a total project planning time of 180 days with a value of IDR 44.239.157.158,40. The crash project activity of Asphalt Concrete Surface Layers (AC) tb. 5 cm can be seen as follows:

Determine Project Indirect Costs
To calculate the optimal cost with the acceleration duration of 5 working days, we must know the indirect and direct costs of the project. Costs for construction projects are known as Budget Plans (RAB) and Implementation Budget Plans (RAP). These RAB and RAP have differences, especially in the information provided from the two documents. In the RAB the information obtained is the cost required to complete each work item. While in the RAP the information obtained is the costs required for each project resource, namely material, labor, and equipment. Formulated the RAB and RAP in the construction project are as follows: 1. From the project data obtained a Cost Budget Plan (RAB). The actual project cost is in the form of an Implementation Budget (RAP), assuming that the contract value (RAB) includes the Contractor's profit and also a general overhead of 8,5%. In mathematical form can be written as follows: To calculate overtime work for Asphalt Concrete Surface Layers (AC) thick 5 cm, then the worker's overtime / hour of work must be known.  Where, x = the cost of the Precedence Diagram Method y = cost of Implementing Initial Schedule If = < 1, then the project implementation using PDM scheduling will be more profitable.
Based on the results of the above analysis, it can be seen that acceleration using the PDM method by using the help of Microsoft Project software to identify critical paths can reduce the time of execution of work to 175 days of efficiency which is calculated based on the ratio of Crash Project cost comparisons using PDM with RAP costs less than 1 which can it was concluded that the implementation using the PDM method was more profitable.