What Is a Network Diagram?

Network planning (Network planning) is a graphical model, shaped like a network, so it is called a network diagram. The network diagram is composed of three factors: jobs (arrows), events (also called nodes), and routes.

According to China's "Technical Regulations for Engineering Network Plans" (JGJ / T 121-99), the types of engineering network plans commonly used include:

1.Double code network plan

2. Single code network plan

3. Double-coded time-scale network plan

4. Single code time-scale network plan

It can be divided into positive and non-positive types according to the expressed logical relationship and time parameter.

First, the elements of the network diagram

Any task or project is composed of some basic activities or work, and there are

1. There must be no cyclic route in the network diagram, otherwise the processes that make up the loop will never end and the project will never be completed.

2. There can be multiple arrow lines entering a node, but there can only be one arrow line between two adjacent nodes. When the relationship between multiple activities needs to be expressed, it is necessary to add a node (Node) and a dummy activity (Dummy activity) to represent it. As shown in Figure 1:

Application of network diagram in construction

With the rapid development of modern science and technology, the continuous improvement of management levels, the ever-expanding scale of construction, the methods of planning and production management must be scientific and modernized.

First, draw the preliminary work

1. Detailed construction procedures

According to the specific conditions of each construction unit, refer to the relevant quotas to determine the construction time of the sub-projects. Construction engineering production has its own objective laws, as well as the laws of construction technology and technology. It follows the continuity of the construction process,

Key process

The key process is the process with the smallest total time difference in the network plan.

If the network parameters are calculated according to the calculation period, the total time difference of the key processes is 0;

If the network parameters are calculated according to the planned duration, then:

When Tp = Tc, the total time difference of key processes is 0;

When Tp> Tc, the total time difference of key processes is the smallest, but greater than 0;

When Tp <Tc, the total time difference of key processes is the smallest, but less than 0.

Tp is the planned duration and Tc is the calculated duration.

Key line

The key line is the line connected by the key processes, that is, the line with the longest total length in the network diagram.

(1) Determine the key line according to the key process: First determine the key process, and the line composed of the key process is the key line.

(2) Determine the key line according to the key node: Where the earliest time of the node is equal to the latest time, or the difference between the latest time and the earliest time is equal to the difference between the planned duration and the calculated duration, the node is called a critical node. The nodes on key lines must be key nodes, but the lines formed by key nodes are not necessarily key lines. Therefore, the key lines cannot be determined by the key nodes alone. When a key node is connected to multiple key nodes, its connection arrow line must be discriminated one by one based on the principle of the largest path.

(3) Determine the key line according to the free time difference: The free time difference of the key process must be the smallest, but the process with the smallest free time difference is not necessarily the key process. If the free time difference of all processes is the smallest from the start node, along the direction of the arrow to the end node, the line is a critical line, otherwise it is a non-critical line. ^[2]