August_1966 — Page 88

A series of cantilever frames in box beam construction. The steel posts are not propped but are hung from the free end of the cantilever and were not grouted until initial deflection under dead load had occurred. The tubes take an external lightweight fenestration

consider that a certain system is based on size of panels which perhaps is not exactly that which is wanted in one or two isolated positions and the tendency here is to say "well, this is only one panel, it will not matter if this panel is made slightly different."

This thinking progresses to a point where, if one is not very careful indeed, nearly every panel made is a variant on the standard panel first considered, and this must be avoided at all costs for the system to be truly workable.

A workable system is one that uses a minimum number of separate com- ponents and it should be possible to manufacture these components in the workshop completely separate from one another without any cross refer- ence to the completed building. Only in this way can one be sure of ob- taining the ultimate in prefabrication. and this is sometimes difficult to achieve in the ordinary workshop where the carpenter, by reason of his years in the trade, will himself at-

tempt to make slight modifications to ensure that one piece fits into another.

Here is the first major rule in any prefabricated system the produc- tion of the parts must follow exactly that shown on the designer's drawing. and no attempt whatsoever should be made by the individual craftsman to improve or alter the section on which he is working.

It therefore becomes obvious that timber prefabrication should only be undertaken under the guidance of properly qualified persons with experi- ence in this sort of work. It is most essential that the manufacturer, in as- sociation with the designer, should en- ter the picture of any proposed plan- ning at the very earliest stage so that the extent and nature of what is pos- sible to be economically achieved in the field of prefabrication is fully un- derstood by the customer prior to any planning or drawings being prepared.

When the drawings are prepared before consideration of the method of manufacture, this invariably leads to

Light delta wing frame using the box beam system

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the prefabrication designer trying to arrange a module within the overall requirements of the drawings produc- ed and this can only end in an un- satisfactory answer.

The question arises: "Why pre- fabricate?" Prefabrication is not the answer to every problem and where time, money and site conditions are such that the building can be built by conventional construction, there is very little need to consider prefabrica- tion. However, prefabrication is de- finitely the answer for speed, but only when properly evaluated at an early stage of the job, where the site access is difficult and where suitably skilled labour is not available or where a de- gree of demountability is desired.

Demountability

A properly designed modular sys- tem prefabricated building, by virtue of its basic design should be demount- able but, if complete demountability is required as a definite part of the planning, care and attention must be given since slight modifications of the methods of putting the building to- a maximum re- gether will ensure covery of parts which may not neces- sarily be so for a prefabricated unit intended to remain permanently on one site.

If

A factor in the speed of mounting an operation using a prefabricated structure is that it is possible for buildings to be manufactured in the factory, virtually at the same time as the customer is seeking his site. the modular system is a good one, the general characteristics of the buildings required are known and it should be possible to completely manufacture buildings without reference to the site whatever, except in terms of access and size of components.

Consideration of transportation of the prefabricated parts should always be taken into account in the initial planning and this can be done with most systems without a great deal of difficulty.

Unfortunately, due to the require- ments of certain authorities, very often the system of prefabrication is included in a contract which is put out to tender, and therefore nothing whatsoever can be done until the suc- cessful tenderer is chosen. Invari- ably, this represents a considerable loss of time and detracts to some ex- tent from the advantages of pursuing a thinking associated with prefabrica- tion.

Site time of any job can be halved if it is possible to give the prefabrica- tor his instructions well before the granting of the main contract. There is still logically, a saving in time, even if the prefabricator is instructed at the commencement of the main con- tract, because invariably there is a large amount of site preparation, levelling and concrete work to be per- formed and, during this time, the pre- fabricator can get ahead with his buildings.

However, if the thinking is pre- fabrication, the whole of the job

Far East Architect & Builder August, 1966