Mitchell's Structure & Fabric Part 1

J S Foster

• Publisher: Routledge
• Year: 2013
• eBook ISBN: 9781317904304
• Edition: 7
• Topic: Technology & Engineering
• Subtopic: Construction & Architectural Engineering
• Index: Technology & Engineering

A new edition of the best selling title in the prestigious Mitchell's Building Series. This book is the first of a two volume set which provides a complete and thorough treatment of the principles and techniques used in the design and construction of a building. This new edition has been thoroughly updated to bring it into line with recent changes in British Standards and developments in construction techniques while retaining the comprehensive approach for which it is renowned.

1
The nature of buildings and building

This chapter explains the function of a building and the nature of the building process, and introduces the basic forms of building structure.

Buildings exist to meet a primary physical human need – that of shelter. Shelter for man, his goods, his animals, and all the mechanical and electrical equipment he requires for his present-day existence. To this need, the whole development of building technology and building techniques is related. In addition to meeting this physical need, buildings and well-related groups of buildings may also satisfy man’s desire for mental and spiritual satisfaction from his environment. To achieve this, buildings must be well designed as well as efficiently constructed.

1.1 The function of a building

A shelter is basically a protection from the elements and the function of a building is to enclose space so that a satisfactory internal environment may be created relative to the purpose of the particular building. That is to say, the space within the building must provide conditions appropriate to the activities to take place within it, and be satisfactory for the comfort and safety of any occupants. Thus, the space will be designed in terms of size and shape, and in terms of environmental factors, such as weather and noise exclusion, and the provision of adequate heat, light and air. The fabric of the building must be designed to ensure that any standards in respect to these are attained.

1.1.1 Functional requirements

The building fabric can be seen, therefore, as the means by which the natural or external environment may be modified to produce a satisfactory internal environment and for this reason it has been called the environmental envelope. In fulfilling this function the building and its parts must satisfy certain requirements related to the environmental factors on which the design of the spaces within it is based.¹ These functional requirements are the provision of adequate weather resistance, thermal insulation, sound insulation, light and air. In addition, adequate strength and stability must be provided together with adequate fire protection for the occupants, contents and fabric of the building (see figure 1.1). The importance of any of these will vary with the particular part of the building and with its primary function, but some indication of their relation to the various parts is given in table 1.1. More detailed discussion of this will be found in the following chapters.

1.2 The nature of building

Building is concerned with providing in physical form the ‘envelopes’ to the spaces within buildings and it has been a primary activity of man throughout history. It is now, to a large extent, an erection process in which the products of other industries are assembled – a complex process, more so than for most other products, both organisationally and technically, involving on most jobs many trades and many different operations, the majority of which are carried out on site and subject, therefore, to the hazards of weather.

1.2.1 Building as an organisational process

Organisationally the building process is concerned with the rational and economic use of the resources for building activity – men, materials, machines, money – in order to produce buildings in the quickest and most economic manner. Practically the building process involves two broad and related activities – design and production. The design

Figure 1.1 Functional requirements of the building fabric

process is concerned with the size, shape and disposition of the spaces within the building and defined by its fabric and with the nature and form of the building fabric and its services. The production process is concerned with the nature and sequence of the operations that are involved in the erection of the building fabric and through which the resources for building are deployed.

The design of the building largely determines the nature and sequence of the building operations. These in turn will determine the methods that can be adopted in carrying out the operations, and the operational methods will determine the manner in which the building resources can be deployed. Thus there is a significant relationship between the design of the building and the use of the

Table 1.1 Functional requirements of elements of construction

building resources. The possibility of the rational and economic use of these resources is, therefore, latent in the building design and the implications of every design decision in respect of this must be exposed at the design stage to ensure that such a rational use of resources can be made at the production stage. Such an exposure is often difficult because of the separation existing, in general, between designer and constructor. The former, being divorced from actual production activity, is not sufficiently aware of the operational significance of many of his decisions; the latter, being divorced from the design process, is not always able to relate his production knowledge and skill to design decisions at a sufficiently early stage. This weakness in the industry has been recognised and attempts to overcome it have been made in building education and in various ways in practice, which include negotiated contracts that bring in the contractor at an early stage, and design and build contracts offered by the contractor or, sometimes, by the architect, and, in the field of building components, the more recent practice referred to in section 2.1.5 of early collaboration between the designer and the component manufacturer.

1.2.2 Building as a technology

In the past, a limited number of available materials resulted in a limited number of structural forms and methods of construction which, after a long period, became fully developed and standardised in practice. These could be, and were, then used on an empirical basis established on their proved performance in use. This is no longer possible nor, indeed, has it been for a long time.

Significance of materials The introduction of new materials, which is now a continuing and expanding process, with properties and characteristics differing from those of the traditional materials, requires the rapid development of new building techniques and new forms of structure appropriate to the nature of these materials. At the same time it is necessary to develop a better understanding of the older materials so that they may be used more efficiently and effectively. Demands on the building industry require an increase in the productivity of the building process which, among other things, may necessitate the development of new techniques. Traditional building materials are bulky and heavy and, therefore, relatively difficult to handle on site and expensive to transport. This has encouraged the search for new, lighter materials which will fulfil the same or even greater range of functional requirements than the old. Such problems and many others such as these cannot be solved with the aid of empirical knowledge but require a scientific approach as a basis of investigation and development. For this reason building, of necessity, has been to a large extent transformed from a craft-based industry into a modern technology with its repository of knowledge based on scientific principles applied to the problems of building, and using scientific methods of investigation and research.

Building construction That part of building technology dealing primarily with the design of the fabric of buildings and the manner in which it is put together is known as building construction and draws, in particular, on the sciences of materials and structure, on the environmental sciences and on building economics. In the past this subject was concerned exclusively with the traditional forms of known and proved performance that could continue to be used in precisely the same way, with the same materials, to provide the same performance. For reasons already given, this is no longer a reasonable approach. New materials with new properties, new performance standards required to be met by the fabric, and the need for greater productivity and economy in building all make it essential that the subject be dealt with as a technology and be considered as a part of the whole field of building technology.

The environmental requirements of the internal spaces set the performance standards of the building fabric and the attainment of these standards sets the practical problems in fabric design. The task of solving these problems is largely that of selecting materials, components and structures that will meet these performance standards in the most economical way. The designer must know the limits within which his choices must be made in terms of the properties of his materials, of structural principles and of the economics of the end result, and these he will derive from building technology.

The architect, however, in trying to meet performance standards also seeks architectural significance for his buildings. This he must do through the fabric, for it is this that defines and gives character and form to the spaces within it. The building form develops from the functional requirements of the building as a shelter, the materials of which it is built, the type of construction used for the fabric and the methods used in its production. The architect, therefore, makes choices in these spheres not only in the light of the required performance standards but also in the light of the architectural end he seeks.

Choice of materials The choice of materials for the building fabric and the manner in which they are used depends to a large extent upon their properties relative to the environmental requirements of the building and upon their strength properties. The strength the fabric of the building must possess in order to function as an ‘environmental envelope’ is derived from materials of appropriate strength used in accordance with known structural principles. Thus, an appreciation of building construction and the ability to devise new forms of construction is developed from a knowledge of materials, an understanding of structural principles and the overall behaviour of structures under load.

Green materials In addition to consideration of the requirements of the internal environment of a particular building, as referred to above, consideration is now being given in the choice of materials to their impact on the wider local and global environments, in terms of their possible detrimental effect on resources, energy and health throughout the life of the materials. This takes into account such matters as how long a material will last and whether or not it can be recycled or reused, and how much energy is expended in the whole process of producing from the basic material one that is ready for use; the effect on a locality by, for example, mining operations to win the basic material; the effect on a wider scale of pollution caused by the processing and production of a material; and the effect of these on the health of those involved in its production and use. Some materials have a smaller detrimental impact than others in some or all of these areas and are called ‘green’ materials, the use of which leads to ‘green’ construction. (Reference should also be made to MBS: External Components, section 1.1, on this topic.)

Building is no longer limited to a number of standardised techniques based on the use of a few well-known materials, but involves an understanding of the properties and characteristics of an increasing number of materials, of structural principles and of building economics so that existing techniques may be used more efficiently and new forms of construction may be developed for the solution of environmental and structural problems. For purposes of current practice, and as illustrations of the ways in which performance standards are met by the component parts of buildings produced by current techniques, it is necessary to study current methods of construction such as those discussed in this series.²

Buildability Section 1.2.1, ‘Building as an organisational process’, considers the traditional separation of building designer and building constructor. This can lead to some disharmony and communications difficulties between the two parties, particularly as the established approach to procurement is by competitive tendering. It almost guarantees that the architect and the constructor have no previous working relationship. At worst, there is no common ground for a mutual understanding.

Communications may be improved where the client engages a design and build partnership. With this contractual relationship the designer, specifier and building manager are within one organisation, but the designer still needs some perception of the practicalities of construction. This concept has become known as the ‘buildability’ factor; the process of ensuring that building design, specification of materials, elements of construction and associated details are not conflicting and incompatible with the method of construction. A very simple example is ensuring that overall window and door sizes are dimensionally co-ordinated to standard sizes of masonry units. This reduces time consuming and visually unacceptable cutting of bricks. Buildability does require knowledge of ...

Table of contents

• Cover
• Title
• Copyright
• Contents
• Acknowledgements
• Preface to seventh edition
• Foreword
• 1 The nature of buildings and building
• 2 The production of buildings
• 3 Structural behaviour
• 4 Foundations
• 5 Walls and piers
• 6 Framed structures
• 7 Roof structures
• 8 Floor structures
• 9 Fireplaces, flues and chimneys
• 10 Stairs
• 11 Temporary works
• Index