The problem they want to solve is the relationship between construction period and cost in the project. They study how to take correct measures to shorten the construction period and increase the cost as little as possible. 1957 On May 7, a meeting was held in Newark, Delaware, and it was officially decided to start the development of new planning technology. Kelly borrows the concept of linear programming to solve the problem of automatic calculation of project plan. Simply put, it is to determine the duration of each activity and the logical relationship between activities, and automatically calculate the duration of the project after inputting it into the computer. For computer computing, Kelly uses nodes such as I and J to represent the logical relationship between activities.
One of the problems encountered at that time was that DuPont's management did not understand Kelly's method. In order to make others understand the principle of the method used, Kelly drew a chart to explain the work done by the computer. The diagram represents activities with arrows and the logical relationship between activities with nodes. This is the earliest arrow diagram (ADM).
As mentioned above, Kelly and Walker's initial research aims to solve the relationship between project duration and cost. Therefore, the methods originally proposed by Kelly and Walker also include the cost planning method, that is, the corresponding cost of each activity is loaded to get the cost of the whole project, so that the cost related to the schedule can be analyzed. This method is not much different from the present method. However, under the circumstances at that time, it was difficult for the project to collect fees and break them down into various activities. Therefore, for a long time, the critical path method was mainly used for schedule planning and control. Kelly and Walker also put forward the method of resource loading and allocation, and of course there are the same problems as cost analysis. Despite these problems, on July 24th, 1957, they had made a simplified example called "The Works of George Fisher", which included 6 1 activities, including 8 time limits and 16 virtual tasks. When they first developed this method, they called it Kelly-Walker method, and the key line in the plan was called the main chain.
According to Kelly and Walker's papers and other related books, they conducted three experiments to test Kelly-Walker method. The first experiment was in1957 65438+February, and DuPont set up a testing team to test this new planning method. A traditional planning team independently planned a chemical equipment project with a value of100000 USD. The members of this test team did not participate in the development of Kelly-Walker method, but they received 40 hours of training before starting the test. The plan of this project begins with the completion of the preliminary design. When preparing the plan, they first break down the whole project into smaller work packages, and then break down these work packages into activities. Project * * * has 800 activities, including 400 construction activities and 65,438+050 procurement and design activities. According to the records, the biggest advantage of Kelly-Walker method in this project is that great changes have taken place during the implementation of the project. Compared with the traditional planning method, Kelly-Walker method is easier to update the plan, and its workload is only 65,438+00% of the original plan. In addition, it can accurately predict the labor force when the design information is only 30%, and can accurately identify the key procurement work. 1958, they conducted the second experiment, aiming at a chemical equipment project worth 20 million dollars. According to the paper published by Kelly and Walker in 1959, the main advantage of this experiment is that it can easily include the design scheme.
However, one of the most mentioned experiments now is their later experiment of maintaining equipment. In this project, they used Kelly-Walker method for analysis and planning, which reduced the equipment maintenance time by 25%. 1959, Kelly and Walker*** published a paper entitled Critical Path Planning and Scheduling. In this 25-page paper, Kelly and Walker not only explain the basic principle of critical path method, but also put forward the methods of resource allocation and balance and cost planning. The principle of the method we use today is not different from the method proposed by Kelly and Walker in principle.
However, the development of critical path method is not smooth. After the change of DuPont's leadership, this technology is no longer used, and Remington Rand also thinks that this technology has little future.
Mochili Partnership, founded by Dr. Mochili and Kelly, has played an important role in the development of critical path method. In the early 1960s, under the leadership of Kelly, the company conducted a lot of training and promotion of critical path method.
At the same time, another technology that plays an important role in the development of critical path method (CPM) is the plan evaluation and review technology (PERT) developed by Polaris Company of the US Navy. On June 1955,165438+1October 17, the US Navy Polaris Project established a special project management office (SPO) to manage its fleet ballistic missile project, and the person in charge was Admiral Raborn. During 1956 and 1957, they studied various existing project management technologies. 1in the autumn of 957, they came into contact with the planning management technology developed by DuPont, which played an important role in their development of PERT. 1958 65438+ 10, SPO studied the feasibility of realizing planning and control on computers. 1958 65438+ 10, on October 27th, SPO formally set up a team to develop PERT technology. About one year later, PERT technology became an operational technology, including program evaluation and review technique. Interestingly, at 1959, this special project management office (SPO) of Polaris Project held a reception to introduce their new technology, hoping that the participants could give more opinions. Kelly and Walker are invited. At the meeting, they found that the PERT developed by SPO is exactly the same as the Kelly-Walker method of the main chain in principle, and the critical path mentioned by SPO. When they came back, they decided to change the name of their method to critical path method. In the early 1960s, PERT developed rapidly. According to statistics, by 1964, there were more than 1000 kinds of references and papers about PERT. By 196 1 year, various similar methods based on PERT appeared, such as PERT/Cost, PERT-Ramps (resource allocation &: Multi-project schedule), map, scan, TOPS, PEP, TRACE, LESS and PAR, etc. Among them, PEP method allocates Gantt chart activities by logical relations, which is a graphic output method commonly used by planning software. 1962, when the then US Secretary of Defense McNamara drafted the decree, he pointed out that the coexistence of the plan review law and the critical path law would easily lead to confusion, and all departments of the Ministry of National Defense would use the plan review law (PERT) in the future, which was a major blow to the advocates of the critical path law at that time. However, in the subsequent development, the critical path method (CPM) gradually took advantage, and the actual use was the plan review method. Even so, the essence of many so-called plan review methods (PERT) is actually the critical path method (CPM). For example, the NASA-Porter method used by NASA at that time was actually the critical path method (CPM).
Whether it is the critical path method (CPM) or the plan review method (PERT), the arrow line method (ADM) is used at first, and then the arrow line method is mainly used for a long time. It wasn't until 1970s that PDM became popular, but ADM was still widely used. After 1990s, Primavera Company of the United States developed its Windows version of planning management software, and only used leader diagram (PDM) as its computing platform, which fundamentally changed this situation. Since then, the leader chart (PDM) has become the main method used by people, while the arrow chart (ADM) is rarely used. John W. Fondahl of Stanford University played an important role in the development of early PDM, and was the authority of non-computer critical path method in the early 1960s. In 196 1, an article entitled "non-computer approach to critical path method in construction industry" was published. In this paper, he elaborated the leading graph system, and thought it was an effective method to draw the critical path manually, because it was very expensive to run CPM with a computer at that time. As a member of Stanford University 65438-0958, Fondahl was commissioned by the US Navy to study ways to improve production efficiency. One of the most important achievements was this paper, which sold 20 thousand copies at that time.
According to the flow chart method used in practice, Fondahl proposed to use nodes to represent activities and connecting lines to represent the logical relationship between activities. This paper discusses the simplicity of flow chart and the possibility of reducing manpower input by manual calculation. At the same time, the paper also discusses the problem that the cost is inversely proportional to the construction period. After that, Stanford University continued to study the manual progress update of PDM, and published the related technical report in 1964.
Although Dr. Fondahl strongly emphasized that his proposed method is manual calculation of critical path method, H.B Zachry Company began to study the application of leading graph method in computers in 1962. 1in March, 963, they jointly conducted this research with IBM, and then formed IBM's planning software, named "Project Control System (PCS)". This system is also the first software to introduce time interval (LAG) into planning. Although the leading graph method was first applied to mainframes, it was later widely used in the software of minicomputers and personal computers. This trend makes the dominant chart (PDM) gradually become the main method, and the dominant chart (PDM) basically becomes the only method used abroad, while the arrow chart (ADM) is only used occasionally in teaching and training. The development momentum of program evaluation and review technique (PERT) once overwhelmed the critical path method (CPM), but now it is rarely used.
Although the United States has developed critical path method (CPM) and program evaluation and review technique (PERT), other countries such as Europe and Britain have also developed some similar project management technologies, but there are few records about these technologies.
Critical Path Method (CPM) was originally developed for project management. However, in the process of development, it has gradually played an important role in contract claims and dispute settlement of engineering projects. The earliest lawsuit involved the requirement of using the critical path method (CPM) in 1972 (appeal of Min Mar Builders, Inc., GSB CA No.3430, 72-2 BOA). In this case, the court rejected the contractor's claim because the contractor did not use CPM, because the crossplot it used could not show whether the specific activity was critical or not. After that, the critical path method (CPM) has gradually become a necessary method in the claim for construction delay, and has gradually formed many professional analysis methods, and even many people specialize in the analysis of construction delay.