Network graphics and network models as a graphic representation of the project implementation

Network graphics

Network Advantages

1. Establishes the entire set of links between individual works.

2. The work identifies the duration of the construction of facilities or their complex (work the critical path)

3. Provides a visual representation of the technological and organizational sequence of work.

4. Conditions are created to predict the progress of construction. With various deviations from the schedule, it is possible to predict the further course of construction and determine its likely duration.

5. The construction management is able to focus the main attention and effort on the works, the performance of which at the moment determines the date of commissioning of the objects, and take measures to ensure timely completion of the work.

6. It is not required to draw up a network schedule many times when conditions change on the construction of facilities, if the technological organizational charts of work execution adopted during the development of the schedule remain unchanged

7. In the process of drawing up the calculation of the network schedules, the performers of the work are actively involved (from the master to the head of the construction organization), which makes it possible to use the experience of a large number of specialists

8. Network schedules allow the use of computer technology.

Basic concepts and elements of network graphics

The complex of works that make up the construction process is usually called a project in network planning and management. A project can be represented by an object or a part of it, a complex of ZiS, an annual program of the organization. A graphical depiction of the process of project implementation with an indication of the organizational and technological relationships between the works is called the network model . A network model with calculated time parameters is called a network diagram . The structure of the network model that determines the interdependence and location in the drawing of works and events is called its topology . The basis of building a network model consists of 3 basic concepts:

- Job

- Event

- Way

Work - the production process for which you want to spend time and resources (personnel, tools and objects of labor, finance).

Work is a process leading to the achievement of certain results. On the network graph is depicted as a solid arrow. Under it often indicate the name of the work, above the arrow - the duration. The concept of work includes waiting (it takes time, but does not require resources).

Between individual works there may be a dependency, which is shown by a dotted arrow.

An event is the result of the completion of one or several works that is necessary and sufficient to start subsequent works. The event is not a process, it takes place instantly, does not require time and resources, is depicted as a circle, which indicates the number of the event

Events that have no previous work - the original .

By the number of completed processes they are qualified for single-purpose and multi-purpose.

Path - continuous work sequence in the network.

Its length is determined by the sum of the limits of its constituent works. There are several ways in the network graph; any path from the end to the end is called the full path (1,4,7; 1,2,5,7).

All network paths have a certain duration; comparing them, they highlight the path of the maximum length; this path is usually called critical .

Basic rules and techniques for building network models

In the formed network model, each work must have a specific content and exact physical volume, be carried out in a certain technological sequence. Therefore, before building a network, it is necessary to establish a range of works and for each of them identify the work that must be completed before the start of this work, work that can be started after the completion of this work and work that can be performed in parallel with the execution of this work.

Building a network is possible from beginning to end, from end to beginning, or from intermediate events in both directions.

When building network models to correctly display the relationship between works, the following rules must be observed:

1. arrows must be directed from left to right; work, as a rule, should be depicted as horizontal lines to avoid complicating the network topology and to eliminate unnecessary intersections

2. It is not allowed to repeat event numbers; when depicting works performed in parallel with common initial and final events, intermediate events are introduced for this purpose and the dashed arrows indicate the interrelation of works

not correct right

3. Work, expectation and dependence should have their own cipher in the form of the number of their initial and final events

4. If work b, c and d can be started after partial completion of work A should be divided accordingly into parts: a1, a2, a3 ... Moreover, each part of work A is considered an independent work and has its preceding and subsequent events

five. If prior to starting work with, it is necessary to carry out previous work a and b, and to start work d to finish work a, then an additional dependency is introduced into the network model

6. If at the end of work a you can start work b and at the completion of work with c work d, and work e can be started only after work a and c, then on the network model this is depicted using two dependencies

7. The network model should not be closed cycles, tails and dead ends.

must not be

8. When enlarging network models, a group of works can be depicted as one work, if this group of works has common initial and final events and the work is assigned to one executor (brigade, sector, construction organization). If there are incoming and outgoing jobs in a group, you must save entry and exit events The duration of such an enlarged work is equal to the duration of the longest journey from the initial to the final event of this group of works.

one.

2

false dependence

right

Calculated parameters of network models

ti - j - duration of the work in question

tj - k - the duration of the subsequent work

th - I - the duration of the previous work

Ti - j ph - early start of work ij

Ti - j ro - early termination of work ij

Ti - j mon - late start of work ij

Ti - j on - late completion of work ij

Ri - j - total reserve time ij

ri - j - private (free) reserve of work time ij

The early start of work Ti - j ph is the earliest possible start time due to the performance of all previous works and equal to the duration of the maximum way from the initial event to the initial event of the work in question

Ti-jro - the earliest possible deadline for work or the end of work started in the early period

Ti - j ph = Ti - j ph + ti - j

Ti-jpn - the latest date to start work, at which the duration of the critical path does not change

Ti-j mon = t cr - ti-j

Ti-jpo - the latest acceptable deadline for the work at which the duration of the critical path does not change

Ti - j by = min Tj - k mon

Ri-j - total reserve time of work ij - the maximum amount of time to which you can transfer the beginning of this work or increase its duration without changing the length of the critical path

Ri - j = Ti - j according to - Ti - j po = Ti - j mon - Ti - j pn = Ti - j according to - Ti - j pn - ti - j

ri-j - private time reserve ij - the maximum amount of time to which you can transfer the start of this work or increase its duration without changing the early start of subsequent work

ri - j = tj - k ph - ti - j po = tj - kj ph - ti - j ph - ti - j

The calculation of network schedules is made in order to determine the duration of the critical path and the time reserves for work not lying on the critical path. The critical path has no time reserves. Calculation of networks, if the number of events is less than 200, it is convenient to maintain on the schedule itself. With more events, a tabular method is used or a computer is used.

First, calculate the early parameters (start) in each event from left to right. Put down the maximum value of the incoming work.

The return stroke is calculated late completion of work included in the event. When several papers are included, the minimum value is set. Events in which the right sector is equal to the left one are on the critical path, and the critical path itself indicates the lower sector.

Ri - j / zi - j

The total reserve is calculated by subtracting from the right sector of the subsequent event the value of the left sector of the previous event and the operating time.

The private reserve is determined by subtracting from the left sector of the subsequent event the value of the left sector of the previous event and the duration of the operation.

Tabular calculation

At the beginning, work codes and their duration are written out from each event in a clockwise sequence number, considering the dependence for work with zero duration.

At the beginning, the early parameters are determined by calculation from top to bottom. Late parameters are determined by calculation from the bottom up, and the late completion of previous work is equal to the late start of subsequent work.

The works in which the early beginning is equal to the late start and (for testing) the early ending is equal to the late ending are on the critical path.

To determine the total reserve, a late start - an early start

To determine the private reserve, the early start of the subsequent work is the early end of the current work.

Tabular calculation