The Construction of Buildings 3 [antikvár]

INTRODUCTION Bungalows, single storey offices, single storey schools and single storey farm buildings with permanent internal partitions are commonly built with loadbearing walls and partitions supporting timber roofs of short span, that is up to 7.5. The construction and details of such buildings are based on knowledge gained empirically, that is by trial and error, over many centuries by the craftsmen, builders and architects engaged in their construction. Only in recent years have analytical scientific principles been deduced for the elements of these simple structures and only then in the main because new materials and constructional systems were being used in lieu of traditional materials and systems employed since man first began to build. Mathematical and static design knowledge is little used in calculating the dimensions of the structure of simple loadbearing wall and timber roofed buildings. The rewards of such calculation are so small in saving of material that it is cheaper to use oversize wall, floor and roof structural members. The introduction of space or central heating made it possible to warm whole buildings, which no longer required solid divisions between rooms to contain heat from single open fires and exclude draughts from colder, less used parts of the building. Without the solid load-bearing division between rooms new medium and long span floors and roofs had to be developed. Large concentrations of people employed in manufacturing processes and the heavy equipment they operated called for medium and long span roofs with few internal supports for the roof. Traditional building systems employing loadbearing walls and partitions with short span timber or concrete roofs could not fulfil the need for open long span structures. Of recent years the wish of the majority for more leisure and a greater degree of physical comfort has greatly increased the cost of traditional systems of building. It is becoming more and more wasteful to employ men in laying small units of clay one on another or to split, shape and lay obdurate stone or saw, plane, gouge and chisel coarse sections of timber. It is plain that the parts of buildings will increasingly be manufactured in factories utilising mass production techniques in the fabrication of whole walls, floors and rooms, which will merely need connecting on site. Already standard components for schools are largely used, standard factories, sheds and farm building are everywhere to be seen and before long pre-fabricated standard parts of houses will be in general use. This volume describes the roofing and walling systems at present available for use mainly in single storey structures. The systems described are generally employed in the construction of factories, warehouses and places of assembly. They can and will be used in the construction of houses once the deeply entrenched notion of a house being a separate private rectangular box of traditional form becomes so expensive as to be beyond the means of all but the very rich. Single storey structures: Roofing systems may be classified according to their span as short span, that is up to 7.5, medium span, that is between 7.5 and 25.0 and long span that is over 25.0, and where these terms are used in the following pages they refer to the range of spans set out above. A broad division of the roof systems to be described is:— (1) Lattice truss construction (2) Portal frame construction (3) Shell construction. (1) Lattice truss construction: In this system triangular or rectangular frames of small section metal or timber, supported by columns spaced at 3.0 to 7.5 carry metal or timber secondary members (purlins) which in turn support the roof and its covering. The three most commonly used forms of lattice construction are illustrated in Fig. 1. In this system of construction the roof and its covering are presumed to add nothing to the strength or rigidity of the supporting lattice frames.