Structural Drawing

In this connection the investigations carried out by the Bureau of Standards in Washington, D.C., and by various professional bodies have proved most valuable, the results of such investiga tions—conducted under practical and exhaustive conditions—being incorporated in the various building codes when approved and accepted by the responsible and representative professional in stitutions.

Reinforced Concrete.

The adoption and development of construction in reinforced concrete has followed the lines com mon to steel work, since the theoretical basis is almost identical, and the production of suitable specifications and regulations has been the product of similar efforts. Reinforced concrete buildings are usually of the framed type of construction, consisting of pil lars and beams, as in steel work, but with the wall and floor panels continuous between columns and beams, so that the con crete enclosing the reinforcing steel is continuous and the structure is monolithic in character. All the intersections of beams and columns are thus rigid connections and the rigidity of such struc tures is one of their main features. In recent years the study of elasticity has been closely followed in its application to rein forced work, where the straining of one member is definitely communicated through the rigid continuation to the adjoining members. Hence the designer of reinforced concrete must have an unusually thorough structural training if he is to comprehend and provide successfully for all the variations of stress to which a reinforced structure is subject. The development of the theory of indeterminate structures involving rigid connections has been a natural consequence. A later type of construction dispenses with beams and uses slabs and mushroom-headed pillars.

Reinforced concrete reached an established position as a con structional method in England when a joint committee, under the auspices of the Royal Institute of British Architects, considered and reported on the subject, first in 1907 and later in 1911. The report gave advice and guidance upon this form of construction in the absence of local regulations. As early as 1900 American engineers had developed the technique of reinforced concrete to a high degree.

In 1915 the London County Council, using the authority vested in them under the clauses of the L.C.C. (General Powers) Act 1909, made regulations for the control of buildings erected in reinforced concrete. While, in view of later developments and scientific investigation, these regulations are seen to be faulty, they were accepted at the time as a real help to the architect, builder and engineer, because at that time there was little gen eral recognition of the more intricate problems involved in its use. The regulations include data for the practical design of beams, slabs, columns, foundations and walls, and a specification of materials and minimum strengths under test. These regulations now are in need of revision, because of the great advance in knowledge concerning this work. In the United States various changes have been made in the early rules with the result that more adequate requirements are in force.

Owing to the experience gained in actual design and construc tion and to the greatly extended investigations which have been conducted into the properties of this new material, reinforced concrete appears not only low in maintenance cost, but is of satisfactory permanence. In addition it possesses fire-resisting

qualities. Contradictory data, however, indicate that more knowl edge of the action of concrete under various conditions is neces sary before definite conclusions can be drawn. Owing mainly, perhaps, to the severely classical character of the normal archi tectural training, concrete cannot be said _to have attained the same pre-eminence as a material for architectural expression as it has in construction. However, some interesting, though perhaps exceptional, schemes have been produced by the so-called "modernist" architects and structural designers. (See also CON CRETE and REINFORCED CONCRETE.) Structural Engineer and Architect.—It is recognized that structural engineering developed in its initial stages as a special ized branch of civil engineering, and its most prominent develop ments took place in connection with those pioneering ventures of mankind in the furtherance of which the skill and ability of the civil engineer is of paramount importance. Later developments, however, especially in countries where industrial and commercial conditions are now more stable, have resulted in establishing con ditions in which the work of the structural engineer is, in nature and quality, much more closely related to that of the architect. It follows, therefore, that as a knowledge of the theory and prac tice of structural engineering becomes more established and wide spread, it will become more difficult to distinguish clearly between the work of the architect and that of the structural engineer in regard to the design and construction of tall fireproof buildings.

There are at present, in all countries, numbers of architects who have prepared themselves to undertake responsibility both for architectural design and structural engineering in relation to all the forms of building in which they practise, the combination being most frequently found in Continental countries. In Great Britain, where the private architectural practice still predominates, the employment of a structural engineer as a consultant, or as a specialist, appears to be the normal procedure. In view of the general recognition of the advantages of specialization, and of the difficulties inherent in scientific construction, there is little doubt that the structural specialist will remain a distinct and important person among those who are responsible for the design of future buildings.

Building Skyscrapers in the United States.

The great demand for tall buildings that started at the end of the last century produced a new form of organization to handle their construction. In the past the work was done on a divided contract where work was parcelled out to various contractors who worked under the supervision of the architect who had designed the building. Then, due to the magnitude and complication of the work and the overburdening of the architect, the general con tractor appeared, who was prepared to undertake the building of a skyscraper under a general contract in which he agreed to deliver the completed building on a given date. The contractor became a promoter, a financier, a buyer of materials, a large employer of labour, and principally an organizer who could com bine all building trades and functions under a centralized manage ment. The architect usually, therefore, became responsible only for architectural and structural design.