Critical Chain Project Management (CCPM)

Critical chain project management (CCPM) is a project management methodology that helps you monitor essential resources and prioritize dependent tasks—so you can complete projects as efficiently as possible. If your team is looking to carefully monitor the usage of resources, critical chain project management is a good strategy to keep track of those resources.

The history of critical chain project management

Dr. Eliyahu M. Goldratt developed the concept of CCPM in 1997. CCPM relates very closely to one of Dr. Goldratt's other theories—the theory of constraints. The theory of constraints helps you identify key bottlenecks or limiting factors standing in the way of your project's completion. The idea is that every project has one main constraint and this constraint has the ability to disrupt the entire project by breaking the weakest chain. Read: The beginner’s guide to the theory of constraints

The critical chain method vs. the critical path method

These two forms of project management are very similar but have one major difference. The critical path method focuses on the single string of concurrent tasks required to complete a project. While other tasks may need to be completed, the critical path highlights all of the tasks that are absolutely necessary for the project's completion. This form of project management can help teams identify the most optimal workflow to create an efficient project timeline. Any tasks that are not part of the critical path are relegated to a lower priority. Project health is dictated by whether or not certain critical tasks are completed by a certain time.

The critical chain method also focuses on task dependencies, but it also considers the resources needed to complete a project. Because there are so many unknown variables that can contribute to resource constraints, the critical chain method builds resource buffers (excess resources to act as a barrier) into the project timeline. Unlike the critical path method, which only focuses on when tasks are completed, the critical chain method dictates project success by how quickly resource buffers are consumed. If your team hasn't used any resource buffers, your project is progressing successfully.

The components of a critical chain

There are three main parts of a critical chain: the critical path, the feeding chain, and resource buffers.

The critical path

The critical path is the longest sequence of dependent tasks that need to happen to complete a project. In other words, it’s all of the tasks that are absolutely necessary for a project’s success, laid out in the order in which they need to be completed. In the critical chain method, it’s important to understand that there are different levels of dependencies. The critical path holds the main level of dependencies, or project critical tasks, and if a task doesn’t affect the critical path, they are delegated to a different path, also known as the feeding chain.

The feeding chain

The feeding chain is a secondary chain of dependent tasks that need to run concurrently with the critical path. Each feeding chain eventually merges with the critical path. This is because the string of events in the feeding chain only affects one of the tasks on the critical path. The feeding chain needs to run at the same time as the critical path to prevent any delays within the critical path.

Let’s take a look at the critical path and the feeding chain in a simple example. Say you’re planning a work party. Your critical path looks like this:

• Decide on a theme
• Send out party invites
• Find a venue
• Host event

While these are still steps to the critical path, there are some tasks in a feeding chain that must happen in tandem with the critical path. For example, before sending out party invitations, the team needs to decide who to invite. Before hosting the event, they need to purchase decorations according to the theme, and set up the event. These are all examples of tasks that are in a feeding chain.

The resource buffers

Buffers are safeguards built into the resources of the critical chain to ensure a project runs smoothly. Like bumpers in a bowling lane, these buffers are designed to give projects extra wiggle room in the event that something doesn't go according to plan.

There are three types of buffers commonly used in the critical chain project management methodology:

• Project buffers: The extra time that's placed between the final task and the end of the project. Adding an extra chunk of time before the expected due date gives team members a chance to catch up on any outstanding project tasks they couldn’t get to earlier.
• Feeding buffers: The extra time that's placed between the feeding chain (also known as the non-critical chain) and the critical chain. Adding this buffer into the timeline prevents any delays from the feeding chain affecting the critical chain.
• Resource buffers: These are literal resources you set aside in case the critical chain is in need of extra supplies—like extra team members to have on hand, additional equipment, or help from a third-party.

4 steps for using the critical chain project management process

If you’re new to using the critical chain project management process, try these four steps to get you started.

1. Identify the critical path first

When you're using the critical chain method, the critical path is the spinal cord of your entire project. It's the entire basis of planning, so figuring out what individual tasks make up that core chain is extremely important.

2. Determine the exact amount of resources your project requires

In this instance, resources can refer to the amount of time your team members need, the actual products and tools your team uses to create the end result, or the actual workers needed to complete a task.

If you can, estimate how many resources you'll need to complete this project. Estimate how many people it will take to complete a specific task on the critical chain, and approximately how long it will take them. Do this for every task laid out on the critical chain. Based on these calculations, do you have enough resources to complete this project?

If you have any known resource constraints, such as team members leaving due to vacation, you can plan around those constraints. This is one of the major benefits of using the critical chain methodology—the bulk of the project planning happens before the project even begins. Read: Your guide to getting started with resource management

3. Place your buffers

Once you determine the required resources for the critical path and feeding chains, it’s much easier to identify where to place buffers and how much time or resources your buffers should include. This will give you an opportunity to calculate the buffers you should build based on the requirements you’ve already calculated when creating the critical path. When a project manager is handling buffer management, they can help maintain resource availability and prevent any bottlenecks.

4. Keep team members focused

Multitasking is your team’s worst enemy. When your team members have to switch between different projects or different tasks, their focus can become fragmented and it can be harder for them to produce work at their typical quality and speed.

To ensure your team members can stay on track with the project schedule, don't assign one person too many different tasks. If you keep them oriented on one project or one task, they're more likely to stay focused. Ensuring team members aren't working on too many different projects at once can also help prevent context switching, which can lead to stress and burnout.

Critical Chain Project Management in literature

The Review of Critical Chain Project Management (CCPM) Conference Paper · July 2019

CCPM bases on Theory of Constraints (TOC) created a revolution in project management, so that traditional methods of project management, such as PERT, GERT, and the CPM are now less widely used. CCPM application is important to the project manager in that regard it provides the project manager with unique facilities for project planning and control. This article reviews CCPM studies from 1997 to 2018.

Introduction

According to TOC, the five factors of the inherent uncertainty of the time of activities, student syndrome, Parkinson law, multiplicity, and lack of concentration of resources are mentioned as the main reasons for the failure of the projects(Goldratt, 1997). The Jewish physicist E. M. Goldratt, in TOC, tries to solve the problem in a real system throughout five basic steps to define system constraints, ensuring maximum output for the bottleneck of the system, the coordinating of all the components of the system to the bottleneck, the creation of a beat based on the bottleneck, and monitoring the above steps, if failure to solve the bottleneck problem and repetition of the mentioned steps(Goldratt, 1997).

CCPM was also formed based on TOC in 1997(Cox & Schleier, 2010). Due to the importance of buffer sizing in CCPM, so far, different methods have been proposed to determine the project, feeding, and resource buffer size(CHAKOSARI & Chaharsooghi, 2019a). The evaluation of methods for determining the buffer size in CCPM shows the strengths and weaknesses of each method in practice(CHAKOSARI & Chaharsooghi, 2019b).

Review of CCPM studies within 22 years ago

CCPM based on TOC was introduced by E. M. Goldratt in 1997(Goldratt, 1997). Newbold described CCPM through a practical example(Newbold, 1998). Leach introduced CCPM as an innovation in the project management(Leach, 1998). Ehresman also reviewed the studies in CCPM(Ehresman, 1998). Cabanis-Brewin also explained the principles of CCPM based on TOC(Cabanis-Brewin, 1999). Simpson and Lynch, while investigating on the organizational communication, suggests the use of CCPM based on TOC to avoid multi-tasking phenomenon(Simpson & Lynch, 1999a). Simpson and Lynch, during interviews with project CCPM experts, investigated the critical factors in project success in CCPM(Simpson & Lynch, 1999b). Leach, investigates the relationship between project performance and the use of CCPM, based on a better performance indicator over time, cost, and project scope(Leach, 1998).

Duncan, while explaining the principles of CCPM, reviewed CCPM in accordance with the project management standard of PMBOK(Duncan, 1999). While researching the application of TOC in project management, Michael and Elizabeth Umble, suggest the use of CCPM for the success of project management(Umble & Umble, 2000). Schuyler, while outlining CCPM, has simulated CCPM through Monte Carlo simulation method(Schuyler, 2000a). In another study, Schuyler optimized the decisions of the project plan, based on the division, the network structure of activities, resources and the start time of each activity(Schuyler, 2000b).

Rand conducted a review of the studies until 2000 in the field of CCPM(Rand, 2000). Pritchard investigated the issue of risk management in CCPM(Pritchard, 2000). Piney provided a mixed model of project management using the critical path and critical chain methods(Piney, 2000). Peterson et al. investigated on CCPM of Earned Value Management (EVM) in CCPM(Peterson & Filiatrault, 2000). In another study on the risk management in CCPM, five model behaviors were suggested including: preservation of estimates; commitment time management of implementation of activities against the estimated time of implementation; initiating activities as early as possible; managing key resources (Constraints Management); and multi-tasking of resources; in which the appropriate response to them can reduce the risk(Filiatrault & Peterson, 2000).

Yeo and Ning, while studying the disadvantages of Engineering, Procurement, and Construction (EPC) projects, proposed a supply chain and CCPM through research in the area of CCPM integration and supply chain in EPC projects(Yeo & Ning, 2001). 3 Steyn proposes CCPM as a new tool for project management(Herman Steyn, 2001). Pitagorsky, while studying the average rate of 40-60% of project failures, considers CCPM to be a scientific approach to reduce resource constraints in the project and thus to improve the trend of the progress of the project(Pitagorsky, 2001). Leach, while outlining CCPM, has investigated the quality of project risk management with a CCPM approach(Leach, 2001). Kendall et al. believe that the use of CCPM approach, in that it improves the performance of the project management organization, is also a success of the project(Kendall, Pitagorsky, & Hulett, 2001). Steyn, while studying the theoretical applications in project CCPM, considers the application of project risk management and project cost management with CCPM approach to be more in projects(H. Steyn, 2002).

Cerveny et al. consider CCPM to be a comprehensive solution for aligning the quality and quantity methods of project management(Cerveny & Galup, 2002). According to Taylor et al., considering the possibility of eliminating the negative effects of uncertainty over the time and cost of activities in CCPM, the conditions for strategic budgeting of the project are proposed using CCPM(Taylor & Rafai, 2003). Spoede et al., while explaining the principles and outlining CCPM benefits, explain critical chain schedule in four main steps: the definition of the critical chain, the support of the critical chain, the creation of a Drum Buffer Rope (DBR) based on the critical chain, and the avoidance of resource contentions(Spoede & Jacob, 2003). Sood and Brigham, in their research, while exploring CCPM, mention CCPM as the best method for project management and resource management(Sood & Brigham, 2003). According to the Raz et al., CCPM is not able to meet all of the project CCPM needs, such as project management processes, despite of the benefits of implementation, such as reducing the time and cost of implementing project activities(Raz, Barnes, & Dvir, 2003).

Ramgopal, while explaining the difference in risk and uncertainty and their importance, investigated CCPM and project's uncertainty management(Ramgopal, 2003). In 2004, E. M. Goldratt later wrote a book entitled "THE GOAL", in which he described a CCPM method in the form of a story(Goldratt & Cox, 2004). In addition to explaining the principles of the dynamic systems, Sonawane investigated on the application of the dynamic systems in CCPM, to develop project management of a modern construction project(SONAWANE, 2004). Miranda, in response to the uncertainties involved in the development of software projects, due to the probable activities and the need to redirect the project, during the implementation time, proposed a combination of CCPM and Incremental Development (ID), in the implementation of software projects(Miranda, 2004). Lee et al. used the combination of CCPM and dynamic systems to solve multifunctional problems and resource contentions in software projects(LEE & MILLER, 2004). Lee considers it essential the use of CCPM to run software projects, given the uncertainty surrounding the project activity(Lee, 2004).

As a result of Darren and Miller's research at the Naval Maintenance Center, it was concluded that TOC and CCPM of about 99 percent of operation lines of the Navy's Maintenance Center resulted in improved performance at this Center(Darren & Miller, 2004). Brokman et al., while explaining the project planning and control processes and the principles of CCPM, and presenting the history of the inventory of the Project Management Office (PMO), suggests the use of CCPM in scheduling complex projects in terms of execution(Brokman, Kfir, & Pilovsky, 2004). In a research project entitled "Project Scheduling," from theory to practice, Herroelen addressed the issue of project scheduling, including project activities, with prerequisite relationships and resource constraints(Herroelen & Leus, 2005). 4 Casey, in his research, while explaining the principles of CCPM, mentions CCPM as an innovative approach in managing project scheduling(Casey, 2005). Davis et al., have used training and facilitation in the implementation of CCPM in the project, taking into account the resource constraints(Davis, Samanlioglu, Stanfield, & Davis, 2006). Dass et al. have conducted survey evaluation for the duration of the project on the schedule of the project portfolio by allocating resources by TOC(Dass & Steyn, 2006). In a case study in the aviation industry,

Best has paid attention to case CCPM applications in various projects(Best, 2006). Yang, while comparing the traditional planning and scheduling techniques, such as PERT and CPM, examined the application of CCPM in construction projects(J.-B. Yang, 2007). Rabbani et al. presented an innovative method for project scheduling under resource constraints in random networks using a critical chain approach(Rabbani, Ghomi, Jolai, & Lahiji, 2007). Shen et al., explored the agile and CCPM in scheduling of the project(Shen & Chua, 2008). While reviewing the studies conducted until 2008 on the project management, Prabhakar, reviewed CCPM research in a part of his research(Prabhakar, 2008). Blackstone et al. carried out CCPM simulation based on uniform, triangular, and exponential distribution to assess CCPM efficiency, and found positive CCPM impacts over time and cost of project implementation(Blackstone, Cox, & Schleier, 2009). Balakrishnan explores the application of project management software for critical chain analysis(Balakrishnan, 2009).

Shi et al., while presenting the amount of CCPM use, suggested the use of CCPM in portfolio management of construction projects(Shi, 2009). Sarapinas et al., while explaining TOC, introduced the application of TOC in project-oriented organizational structures(Sarapinas & Sudžius, 2009). Peng et al. presented the modified critical chain and optimization model based on the optimal CCPM model, as well as the issue of project scheduling under resource constraints(Wuliang Peng & Jin, 2009). Bevilacqua et al. investigated the critical chain and risk analysis in the perishable industries(Bevilacqua, Ciarapica, & Giacchetta, 2009). Simpson, while stressing the importance of implementing a project quickly and with the ability to predict the activities of a project, considers the periodic update based on the definition of the project baseline and the periodic report of the program as an important issue(Simpson, 2010). In order to improve the performance of a system in a cross-sectional manner, it is possible to improve the system in a cross-sectional manner easily by detecting and solving the constraints(Cox & Schleier, 2010).

Zhao et al. investigated the innovative use of CCPM for project planning and control under resource constraints and uncertainty(Zhao, You, & Zuo, 2010). After 10 years of the birth of TOC, Startton reviewed the studies on TOC and CCPM(Stratton, 2010). Robinson et al.(Robinson & Richards, 2010), also in another study(Paper, 2010), explained CCPM, reviewing the research on the critical chain and CCPM. Reyck et al. investigated the effective planning of the project using the appropriate planning tools such as CCPM, using the Agile software(Reyck, 2010). In his research, Doyle described the principles of CCPM, providing examples using simulation tools in CCPM(Doyle, 2010). Sharon et al. while comparing project management and engineering management systems, have applied TOC and critical chain in system management(Sharon, Weck, & Dori, 2011). Gupta reviewed the studies conducted until 2011 on TOC and critical chain(Gupta, 2011). Tsou et al., using the analytical approach, presents a TOC-based model for solving the problem of project scheduling, which the performance of each scheduling strategy using simulation techniques parameters can be evaluated(Tsou, 2012). Yang, while explaining CCPM, uses a fuzzy triangular numbers to implement CCPM method during a sample accounting project(Y. Yang, 2012).

Toulasi et al., while presenting a review article, focused on TOC(Tulasi, Rao, & Tirupati, 2012). 5 Prestin et al., in their research, tried to reduce Work In Process (WIP), using network analysis and critical chain, in production space(Prestin & Bingman, 2012). Peng et al. analyzed the project risk scheduling, using the chain of events method, in the form of aerial terminal project(Wei Peng, Shen, & Liu, 2012). Mitra et al. provided lesson learned on the implementation of major projects in Saudi Arabia in the form of an article(Mitra & Tan, 2012). DEAC et al. went on to study quantitative project management techniques and CCPM reviews as a modern project planning technique(DEAC, VRINCUT, & BRANZAS, 2012a). In a review article, HALL has studied on recent developments and study opportunities in the field of project management(HALL, 2012). Grant, while reviewing CCPM history, has, at a glance, explained the status of CCPM in the field of project management(Grant, 2012). In his research on qualitative project CCPM techniques, DEAC et al. presented a modern approach to project management using CPM(DEAC & VRÎNCU, 2012).

According to DEAC et al., project CCPM and CPM are similar in terms of time reserve creation, but the amount and location of assignment of precautionary periods varies in each of the methods(DEAC, VRINCUT, & BRANZAS, 2012b). A number of Chinese researchers, while exploring CCPM, have proposed a method for improving multi project management in the critical chain(HUANG, LI, CHUNG, HSU, & Chih-Hung TSAI, 2013). Cooper, while introducing CCPM, in his research, introduces a condition for improving the focus and predictability of project goals in the use of CCPM methodology(Cooper, 2013). The researchers believe that like monitoring and continuous control of a project in CCPM, the choice of service provider in the supply chain can also be carried out(Wei & Ying, 2013). Huang et al., while explaining the principles of CCPM as well as the strategy and tactic trees, conducted a study to improve management of projects portfolios using CCPM(HUANG et al., 2013). DEAC et al. provided comprehensive software using the qualitative techniques of CCPM in the Romanian market(DEAC, VRINCUT, & PAUN, 2013). DEAC et al., in their research on comprehensive CCPM Software in the Romanian market, investigated the compatibility of Microoft Project (MSP) Schedule Software components in CCPM(DEAC et al., 2013).

According to DEAC et al., the requirements for successful implementation of CCPM steps in the organization, as well as how to manage the project portfolios by CCPM, has an important role in the efficient and effective management of the project(DEAC & VRÎNCU, 2013). According to Kirpes, the use of CCPM can commit the project obligations in a timely manner and within the framework of the projected budget(Kirpes, 2014). Anantatmula et al., while explaining CPM, mentions CCPM as a revolution in project management(Anantatmula & Webb, 2014). Zhang et al., while persuading experts to innovate in project management, and introduce competitive advantages and efficiency of CCPM, will use this approach by experts in projects to increase the efficiency of the project(M. Zhang & Jin, 2014). Warchalowski et al., acknowledge that CCPM has significant effects on improving the time between implementation of operations, timely delivery of output, the high efficiency of project resources, as well as increased project profits(Warchalowski & Patrick, 2014).

Yung et al. in order to solve the problem of scheduling multi-project resources in managing a research and development project in the automotive industry presented a multi-project scheduling system based on the intuitional and critical chain of activities based on priorities(S. Yang & Fu, 2014). The American researchers, while reviewing the history of research on project CCPM and TOC of constraints, which forms the basis of CCPM, provide statistics on the number of articles published in various areas of project management, including TOC between 1999 and 2013(Johnson, Creasy, & Fan, 2015a). Parker et al. described the benefits of using TOC and several other theories in strategic planning(Parker, Parsons, & Isharyanto, 2015). 6 Zhang et al. have conducted a research on dynamic monitoring and effort-centered project control using software that is based on risk management determinants(J. Zhang, Shi, & Diaz, 2015). The degree of understanding the planning and scheduling theory in construction projects and the case study of the Omani construction projects has been evaluated by AlNasseri et al(AlNasseri & Aulin, 2015).

Three researchers, while studying a number of articles on TOC that is the foundation of CCPM, concluded that the number of articles published in TOC since 2010 has been reduced(Johnson, Creasy, & Fan, 2015b). In a research, while exploring and explaining the principles of CCPM, it is recommended to use the benefits of CCPM for project planning and control(Jayaraman, 2016). In a research, practical application of CCPM and Scrum, which is the software development framework of the Agile Thinking Methodology series, in the flexible management of multiple projects has been addressed(Almeida, Souza, & Produção, 2016). Several researchers have researched on the comparisons of traditional planning methods, such as CPM and PERT, with CCPM for information technology projects and related software development, and provided significant benefits to CCPM use(ALMA, COŞKUN, & UĞUR, 2016). Fan, in the computer simulation, distinguishes between the traditional method of CPM and the new method of critical chain(Fan, 2016). Using CCPM of the total duration of project implementation in railway projects of India dropped by 3%, which would certainly reduce the total cost of the project, which is a very significant result of the project(Sarkar & Babu, 2016).

Pawiński et al. have implemented the scheduling problem under resource contention by considering CCPM constraints on a computer in the internal network environment as well as a personal computer(Pawiński & Sapiecha, 2016). EVM in project control and during a specific project has been examined and, at the end of the research, the use of EVM has been proposed in CCPM(Nkiwane, Meyer, & Steyn, 2016). Goto et al. conducted research on a solution to the problem of project resource contention using a genetic algorithm in CCPM(Yokoyama & Goto, 2017). Goto et al., using the Max Plus Linear model under the name of MPL, presented the leading managerial framework of CCPM, focusing on projects with probable time and limited resources under the title CPM-MPL(Yokoyama & Goto, 2017). Two researchers, while pointing out the importance of improving project management in companies to improve the company's performance, recommends the use of CCPM to experts(Apaolaza & Lizarralde, 2017). Apaolaza et al., in a case study, explaining the principles of CCPM, described the importance of implementing a new project management method and the need for fundamental changes in management of companies to achieve efficient and effective management(Apaolaza & Lizarralde, 2017).

In a research, the combination of repetitive and non-repeat scheduling methods has been devoted to the unique application of these scheduling methods, and a new scheduling method for repeatable projects has been introduced based on the combination of linear scheduling and CCPM(Salama, Salah, & Mosel hi, 2018). Poshdara et al. used a multi-objective probabilistic method for optimal time allocation of buffer sizing, based on an optimization approach with a target search method, including practical results and decision-maker preferences(Poshdara, Gonzálezb, Rafteryb, Orozcoc, & Cabrera-Guerrerod, 2018). In the present study, while introducing an optimal approach to determining the buffer size in CCPM by maximizing the buffer strength determined in project scheduling, the effective measures to determine the buffer size in CCPM, such as network complexity, flexibility, criticality, and buffer strength was studied(Ansari, Makuib, & Ghoddousia, 2018).

Hammad et al. developed a framework for estimating, allocating, and managing precautionary times, using TOC and techniques of Earned Schedule Management (ESM) method, which somewhat overcomes the negligence of CPM(Hammad, Abbasi, & Ryan, 2018).

Problem in the recent literatures

In studies conducted so far in the field of CCPM, the optimal solution for planning using CCPM has not been investigated. A significant part of the delays in the projects is due to the lack of sufficient knowledge of the planning team and, consequently, the lack of precise sequencing of activities, the lack of precise estimation of the time and cost of implementing activities. The tool for detecting and correcting planning errors in CCPM was envisaged under Fever Chart (FC), but unfortunately, in none of the studies on CCPM, FC was investigated in the planning phase.

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