Construction Management
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| Aspects of Construction Management |
Introduction
The construction management deals with the management in which group of people of different categories work together, to execute the project economically without affecting the quality in a well planned and organised manner. It is very essential for the following factors:
1. To check up the wastage of material and labour.
2. To complete the work in the shortest possible time.
3. To have less construction cost.
4. To improve the quality of work by using modern construction equipments.
Functions of Construction Management
The aim of construction management is to facilitate the execution of work in a planned and efficient manner as per design and specifications within the prescribed time limit and with the greatest possible economy in construction cost. In order to achieve this, the construction management should have the following functions:
1. Planning : It is an administrative process which translates the policy int5o a method of achieving the desired objective. Each work should be planned with respect to the manner of execution of the work, urgency of work and the availabity of resources.
2. Organising : The type of organization depends upon the type and volume of work as well as the method of execution. An organization set up should be kept simple and balanced.
3. Directing : The object of directing is that each employee should know exactly what he is supposed to do, how and when to do.
4. Controlling : In a construction work, the following are the main aims of controlling:
(a) To keep a watch over the physical progress of each activity of the work.
(b) To control the quality of work.
(c) To control the expenditure on each item of work.
(d) To control the use of machines.
5. Co-ordinating : The co-ordination is necessary so that proper information is made available at proper time to the correct person. The proper planning, design and execution of the work is called modular co-ordination.
Classification of Construction Work
The construction work may be classified as follows :
(a) Light Construction : It includes the works with light structural members, light foundations and light timber members. The construction of residential and commercial buildings, schools, villages and city roads, small water supply and sewage works, ware houses and light industrial sheds are considered as light construction.
(b) Heavy Construction : It includes heavy structural members on massive foundations. The construction of tunnels, bridges, oil pipe lines, railways, air ports, dams, thermal and hydroelectric power generation plants, atre considered as heavy construction.
(c) Industrial Construction : It includes all the construction work related to industries producing commercial products. The construction of refineries, fertilizers, chemical plants and steel mills are considered as industrial constructions.
Construction Stages
The following are the various stages in every construction work :
1. Conception
2. Study and evaluation
3. Design, drawings and estimates
4. Specifications
5. Contractor realization
6. Procurement of materials
7. Construction and supervision
8. Utilisation and maintenance
Construction Team
It may be noted that a construction work can not be completed by a single person. It requires a team of workers with their specific duties. The construction team includes owner, engineer, architect, designer and contractor or builder.
The conception of idea for any construction work is the responsibility of the owner. He is both financer and the beneficiary of the work.
The engineer is a professional man and responsible for the economic and safe design and construction of the work under his supervision. The field of activities of an engineer includes designing, drawing, estimation, approval of construction plans by the local authority, tendering, supply of material as per contract, control and inspection of quality and progress of work done by the contractor, measurement of work done and payment of it. The engineer is also consulted by the architect regarding design, estimation etc.
The contractor is responsible for the material not supplied by the owner, organising, planning and execution of the work as per given drawings and specifications laid down in the contract.
Resources in a Construction Project
The resources in a construction project are made up of the following things :
1. Money which is the first and foremost item required for any construction project.
2. Plant equipment and machinery required for the construction project.
3. Construction materials such as cement, bricks, steel etc.
4. Skilled and un-skilled manpower.
Construction Planning
It may be defined as a rational, sequential and appropriate way of direction the construction activities. It is an administrative process which translates the policy into a method of achieving the desired goal .
The construction planning may be classified as follows:
1. Pre-tender Planning : The pre-tender planning is the planning undertaken by the contractor after receipt of tender notice and before submitting a bid for the tender for the proposed work. The pre-tender stage of construction requires the following :
(a) Selection of site
(b) Acquisition of land
(c) Finalization of designs
(d) Preparation of estimate
(e) Availability of material, labour, machinery and equipment
2. Post-tender Planning : The aim of post-tender planning is to organise all aspects of construction work so that the work may proceed without any problems causing delay. The post-tender stage of construction consists of the following :
(a) Assessment of work
(b) Assessment of expenditure during execution
(c) Detailed requirement of machinery and equipment
(d) Necessary requirements of men, material, machines and finances at various stages
(e) Finalisation of accounts
3. Technical Planning : The technical planning is carried out for the preparation of detailed drawings, estimate, planning resources and initiating procurement action.
Construction Scheduling
It is a mechanical process for setting up the sequential order of the various operations in a construction project by fixing the dates of starting and completing each operation of the work. In order to prepare a construction schedule, the following data is required :
1. Number of operations
2. Number of activities
3. Output of labour
4. Number of field workers
Organisation
The organization is a group of people which works under an executive leadership. It divides the work and responsibilities of the employees. It establishes a relationship between authority and responsibility and controls the efforts of groups. The organization is a step towards the achievement of established goals. The following are the various types of organizations :
1. Line Organization : It is also called military type of organization because it resembles to olden military organization. Sometimes it is also called as the scalar type since it has straight flow of authority within a single unit. It is the simplest form of organization in which responsibility of each individual is fixed, discipline is strong and quicker decisions are taken. The disadvantage of this organization is that it overloads a few key executive and encourages dictatorial way of working. The line organization is suitable for small construction works such as a private residential building.
2. Functional Organisation : This type of organization was introduced by F.W. Taylor. In the functional organization, the quality of work is better, wastage of material is minimum and specialized knowledge and guidance to individual worker is provided. This type of organization is suitable for large sized construction works.
3. Line and staff organization : This type of organization possesses practically all the advantages of both the line and functional organizations. In the line and staff organization, the quality of work is improved, and there is less wastage of material, man and machine hours. The expert advice from specialist staff executives can be made use of. This type of organization is preferred for medium sized construction works.
Principles of Organisation
In order to have effective organization, the following basic principles should be followed :
1. Span of management
2. Unity of command
3. Delegation of authority
4. Unity of assignment
5. Division of work
6. Separation of work
7. Job definition
8. Contact
9. Ultimate authority and responsibility
Methods of Planning and Scheduling
The methods of planning and scheduling the construction of a project are as follows :
1. By Charts such as bar charts or Gantt chart and milestone charts.
2. By network technique such as programme evaluation review technique (P.E.R.T.), critical path method (C.P.M.) and line of bolana system (L.B.S.).
This methods are discussed as follows :
Bar Chart or Gantt Chart
The bar chart or Gantt chart was developed by Henry Gantt for planning and scheduling the methods of construction. This chart is a graphical representation of various activities involved in a construction work. It consists of two co-ordinates. The horizontal ordinate or bar represents the various activities involved in a construction work and the duration of times required for completion of the activities. The vertical abscissa or bar represents the respective jobs to be performed. The length of bar indicates the duration of activity or job for its completion. The various activities are shown parallel to each other along ordinates.
Since the various activities are shown by a number of parallel ordinates or bars, therefore it is called a bar chart. The duration of the activities are represented from the left to the right Each bar is divided longitudinally into two portions. The top portion indicates the progress of completion of the activity and the bottom portion indicates the duration of the activity.
The use of bar chart is very popular in construction departments because of the following advantages :
(a) It is very simple to prepare and interpret.
(b) Each item of work or activity is shown separately.
(c) It is very easy to compare the progress and original schedule.
(d) It is easy to know the time for the resource of activities.
(e) The modifications to the chart, if required, can be carried out easily.
Notes :
1. The process of calculating the resource requirement of a project is known as resource aggregation.
2. In a bar chart method, the sequence of activities is not clearly defined.
3. The critical activities can not be shown by bar charts.
Milestone Chart
A milestone chart is a modification of a bar chart. In this chart, the key events are shown on respective bars. Each event is numbered and an explanatory note is provided with it. These key events are known as milestones. These charts are restricted to small projects only.
Network Planning and Scheduling
Now-a-days, necessity for better planning and scheduling is increasing due to the increasing complexity of large projects. It is very essential for the success of any project that time schedules and objectives of various operations should be defined in a project. The network analysis helps designing, planning, co-ordinating, controlling and in decision making in order to accomplish the project economically in the minimum available time with the limited available resources. The net work techniques were developed from the milestone chart and bar chart. These conventional planning methods, because of their inherent limitations could not be utilized for planning large and complex projects. There are number of network techniques, but the most important are critical path method (C.P.M.) and programme evaluation review technique (P.E.R.T.).
Terms used in Network Planning Methods
A network is a schematic representation of the entire project, consisting of number of number of activities. These activities are joined together in such a way as to form an integrated network, as shown in Fig. 1.
The following terms are commonly used in network planning methods :
1. Activity : Every project consists of a number of job operations or tasks which are called activities. An activity is shown by an arrow and it begins and ends with an event. An activity consumes time and resources. An activity may be performed by an individual or a group of individuals.
The activity may be classified as critical activity, non-critical activity and dummy activity. The activity is called critical if its earliest start time (EST) plus the time taken by it, is equal to the latest finishing time (LFT). A critical activity (e.g. A, C or E) is marked either by a thick arrow or by two lines as shown in Fig. 1.
The non-critical activities have provision (float or slack) so that, even if they consume a specified time over and above the estimated time, the project will not be delayed. In Fig. 1, B and D are non-critical activities.
When two activities start at the same instant of times (like activities C and D), the head events are joined by a dotted arrow and this is known as dummy activity as shown by F in Fig. 1. The dummy activity does not consume time and resources.
2. Event : The event is a specific instant of time which makes the start and the end of an activity. The event consumes neither time nor resources. It is represented by a circle and the event number is written within the circle, as shown in Fig. 1.
3. Critical Path : It is that sequence of activities which decide the total project duration. It is formed by critical activities. In Fig.1, 1-2-4-5 is the critical path. A critical path consumes maximum resources. It is the longest path and consumes maximum time. A critical path has zero float or slack.
4. Slack or Float : The slack is with reference to an event and float is with respect to an activity. In other works, slack is used with PERT and float with CPM but in general practice, they may be used interchangeably. The slack or float represents the difference between the earliest completion or finish time and the latest allowable time. The slack or float may be positive, negative or zero.
When the slack or float of an activity is positive, then it represents a situation where extra resources are available and the completion of project is not delayed.
When the slack or float of an activity is negative, then it represents that a programme falls behind schedule and additional resources are required to complete the project in time.
When the slack or float of an activity is zero, then the activity is critical and any delay in its performance will delay the completion of whole project.
The slack or float may be total float, free float, interfering and independent float.
The total float is the time available for an activity performance minus the duration of activity. It may be defined as the difference of the latest finish time (LFT) and earliest finish time (EFT). It is also equal to the difference of latest start time (LST) and earliest start time (EST).
The free float is defined as the earliest start time (EST) of its successor activity and the earliest finish time (EST) of the activity in question.
The interfering float is the difference between the total float and free float of an activity.
The independent float is the excess of minimum available time over the required activity duration.
Notes :
(a) The earliest possible time at which an activity may start is called earliest start time (EST).
(b) The sum of the earliest start time (EST) of an activity and the time required for its completion , is called earliest finish time (EFT).
(c) The latest possible time at which an activity may start without delaying the completion of the project, is called latest start time (LST).
(d) The sum of the latest start time (LST) of an activity and the time required for its completion, is called latest finish time (LFT).
Critical Path Method
The critical path method (CPM) is a network technique to deal with large and complex projects. It was first used by Morgan R. Walker in 1957. It helps in ascertaining time schedules, makes better and detailed planning possible, encourages discipline and provides a standard method for communicating project plan schedules and to time and cost performance.
Programme Evaluation Review Technique (PERT)
The programme evaluation review technique (PERT) is a project planning and control technique. It is an event oriented technique. It provides an approach for keeping planning up-to-date. It provides a way for management to require that planning be done on a uniform and logical basis. It permits management to foresee quichly the impact of variations from the plan. The Programme evaluation review technique is applied for long-range planning, installation of machinery, research and development of products and marketing programmes and advertising programmes. The PERT analysis is based upon the following three time estimates :
(a) Optimistic or best time : It is the shortest possible time in which an activity can be completed if everything goes exceptionally well.
(b) Most probable or likely time : It is the time in which the activity is normally expected to complete under normal contingencies.
(c) Pessimistic or worst time : It is the time which an activity will take to complete in case of difficulty. It is the longest of all the three time estimates.
If to = Optimistic or best time,
tn = Most probable or likely time, and
tp = Pessimistic or worst time.
Then
the probabilistic time (tm) for completion of an activity is given
by
