Essencials of Engineering Drawings in construction industry, Classification of Civil Engineering Drawings

Engineering drawing is a language in which the ideas of designers, engineers or draughtsmen are expressed in a manner that is clearly understood by the technician or person concerned with the job. A detailed drawing or a sketch is made of a particular job for completion, manufacture or construction. It is the best possible way to prepare a concise record of the numerous architectural, civil, electrical and mechanical engineering works in a manner that can be readily understood and translated into reality by people whose duties commence when the designer and draughtsmen have finished their work.



Engineering drawing is normally the starting point in a long chain of events which finally results in the production, manufacture or construction of a job required by some section of the community.



Civil Engineering drawing is both an art and science of representing civil engineering objects on paper. It is a universal graphic language by means of which the size, shape and construction of civil engineering objects can be represented clearly and accurately on a piece of paper. It is the language of engineers and through this an engineer conveys his thoughts, ideas and design to others on paper. The workman then executes the work in the field according to these drawings.



If there is an error in any drawing at any stage, it is carried over in practical execution, which results in a great loss of time, money and labour. It is therefore necessary for the engineer/technician to acquire a good working knowledge of engineering drawing. This knowledge of drawings enables him to express, execute and record the size, shape and other information necessary for the construction of various jobs such as bridges, flyovers, roads, buildings etc.


Classification of Civil Engineering Drawings

Civil engineering drawings are classified as:

• Tender Drawings

• Contract Drawings

• Working Drawings

• Completion Drawings

Tender Drawings

It is necessary for an engineer to decide the extent of preliminary design to be carried out at the briefing/report stage. Detailed design at this stage would be a waste of time as the project scheme might be changed completely depending upon the final selection of a particular alternative. Once formalities are over and the project proposal has been cleared, an engineer must prepare a set of engineering drawings called 'Tender Drawings'. Tender drawings together with the other tender documents, bills of quantities, specifications etc. describe the project scheme to the contractor so that he can price the construction work accordingly.

In the case of small projects, design work at preliminary stage may be sufficiently detailed depending upon the experience and background of the designer. In such cases, tender drawings, contract drawings, working drawings and perhaps even the completion drawings may be the same. However, in the case of large projects, these drawings are prepared at various stages of execution.



Tender drawings are the first evidence of the project scheme regarding type and quality of the work involved and hence these are prepared by engineers with great care and with particular attention to drafting and presentation for clarity and case of understanding. The contractor is concerned with the clarity and logical expression of engineering details.



Tender drawings are prepared to various scales using conventions and concepts of engineering drawing for production, manufacture and construction etc.


Contract Drawings

The engineer can carry on with the detailed design only after the completion of tender drawings. During the tendering stage, contractors will be busy in interpreting the tender drawings and preparing their bids. Sometimes a contractor may be skilled in a particular method of construction that is different from the one shown in the tender drawings. He may submit a tender based upon his speciality even though it proposes a modification in the original design envisaged in the tender notice. If the contractor's price is competitive and the engineer agrees with his proposals, modified drawings will have to be prepared. Once the contractors have submitted their tenders, the engineer will have to evaluate and compare these in regard to the contract price and to see whether the proposed constructional methods are suitable and economical or not. On the basis of the engineer's report, the owner will accept one of the tenders and a legally binding contract document will then be prepared and signed, of which the contract drawings form a vital part If tendering has been straight forward and without any alternative proposals, the contract drawings will he the same as tender drawings. If alternate proposals have been accepted, new or additional drawings will have to be prepared by the owner's engineers according to the accepted tender proposals and alternatives.

Contract drawings are printed on good quality paper and are provided with cloth backing to withstand handling and long storage.

Working Drawings

The working drawings fill the gaps in constructional details not reflected in tender drawings. As the name itself indicates, working drawings are used for working, manufacturing, constructing or building purposes and must therefore represent the engineer's final decisions and design details. Changes in drawings hereafter can be expensive, particularly when construction work has already commenced.



In case of small projects, tender drawings may contain most of the constructional details. If changes are small, technical staff at site can often cope with them. However, for large projects with only outline drawings at the tender stage, the drawing office will have-to prepare detailed working drawings. In case working drawings lack finer design/construction details, notes and instructions are incorporated on the drawings to facilitate construction and avoid delays.


 Completion Drawings

Completion drawings are also called `Record' or 'As-built' drawings. In any project, it is unlikely that construction will be carried out exactly as per the working drawings. There are bound, to be certain variations, additions or alterations due to unforeseen site conditions and advancements in technology. Howsoever small the variations, additions or alterations might be, these are recorded on a set of drawings called `Completion', `Record' or 'As-built' drawings.



For large projects, where each phase may take months to be completed and is worth billions of shillings, the `Record' drawings should be prepared simultaneously as the work proceeds. For small works, `Record' drawings may be prepared upon completion of the work. The variations are marked on the set of drawings in red ink/pencil.



Interpretation of Engineering Drawings

An engineer reads and interprets many more drawings then he produces himself. In fact, his own drawings are the result of a close study of other drawings. The various architectural and engineering drawings are prepared so that they may be read clearly without any fear of misinterpretation and confusion. For proper interpretation of engineering drawings, the engineer must have knowledge of the following:

• Scales

• Symbols

• Projections

• Line work