Structural Drawing

STRUCTURAL DRAWING: see DRAWING, ENGINEERING. STRUCTURAL ENGINEERING. The term structural engineering came into accepted use in America during the 19th century, in relation to the particular branch of civil engineering which was concerned with bridge building. At a later date the term came to be used more frequently in connection with the great development of steel-framed and reinforced concrete build ings in that country, and it is mainly in this connection that the term has been accepted and used throughout the world.

From the brief survey in this article of the development of structural practice, it will be seen that the most fundamental change has not been in the use of mild steel, or, in fact, in the use of any relatively new material, but in the intelligent applica tion in the design of structures of a rapidly extending knowledge of mechanics and of the scientific use of constructional materials. Hence there is a general tendency to give a wider significance to the term structural engineering and to set no arbitrary limits either to the materials employed or to the nature of the structures in which they are embodied.

Structural engineering embraces the design and construction of all those vital structural parts of buildings, and other substantial erections, in which a knowledge of the strength and nature of the materials used and of the relevant principles of the science of mechanics are the controlling factors. See also the articles on ARCHITECTURE and BRIDGES : CONSTRUCTION.

Early Development of Structural Practice.

While the more modern developments of structural engineering have been largely coincident with and dependent upon parallel developments in the production and use of iron, steel and Portland cement, the development of the science of mechanics and of the theory of elasticity have occupied a much longer period of time. Until the middle of the 18th century constructional practice of all kinds had been chiefly governed by the common traditions accepted in the various crafts. This practice was subject to the losses, faults and checks to which knowledge so acquired and held is peculiarly liable. The high state of development of the science of stereotomy or jointing of stone work should, however, be noted, particularly as applying to stone arches, vaults and domes. It arose out of the construction needs of the great cathedrals of the Middle Ages. The great era of bridge building, which may be said to have been initiated by the erection of the second bridge over the Thames at London by the French engineer Labelye in 1749, and by the suc cessful completion of William Edwards' third bridge at Pontypridd in 1755, continued for the remainder of that century, and may be credited with the establishment of a new era in constructive ability and knowledge. At later dates notable bridges were erected by

Robert Mylne, Telford and Rennie, which carried this aspect of structural design to an advanced stage.

Use of Cast Iron.

In England in 1755, the use of cast iron in construction had been advocated by Smeaton, and by the end of the century much experience had been acquired in the production of a uniform and reliable material and in the possibilities of its use in buildings. The most striking use of the metal probably oc curred in the construction of arched bridges, where cast-iron vous soirs were employed in the place of stone; the first bridge of this kind was completed at Coalbrookdale in 1776. (Much confidence was shown in this type of bridge construction and Rennie pre pared designs for a cast-iron bridge of 450 ft. span over the Menai straits.) At a still later date the cast-iron units were made in longer sections and bolted together, so that they were called upon to resist tensile forces and the sections of the ribs approximated to cast-iron beams of curved outline.

Meanwhile, the use of cast-iron in the construction of factory buildings in the north of England was developed, first in columns to support timber beams, and later in the substitution of cast-iron beams for timber. At the commencement of the 19th century, a building was designed by Boulton and Watt and erected in Man chester, in which cast-iron beams were supported on cast-iron columns, while the floors consisted of brick arches supported on the bottom flanges of the beams and brought to a level surface by rough concrete. Buildings of this type were erected with little change for a long period. The principles underlying this form of construction were at first little understood, but such men as Fair bairn, Tredgold and Hodgkinson assisted in the establishment of sound principles; their work was based upon extensive experi ments, mainly upon the use of cast-iron in beams, and their pub lished results proved of great benefit to architects and builders.