The use of steel construction in the erection of large buildings is the natural consequence of the conditions imposed upon owners of property lying within sections of large cities, and the result of the introduction of new materials and devices. Apart from the aesthetic considerations to which has been due the construction of spires, towers, domes, high roofs, &c, the form and height of buildings have always been largely controlled by a practical consideration of their value for personal use or rental. The cost of buildings of the same class and finish is in direct proportion to their cubic contents, and each cubic foot constructed is commercially unprofitable which does not do its part in paying interest on the capital invested. Until the latter half of the 19th century, these considerations practically limited the height of buildings on city streets to five or six storeys. The manufacture of the wrought-iron “I” beam in 1855 made cheaper fire-proof construction possible, and, with the introduction of passenger lifts (see Elevators; Lifts or Hoists) about ten years later, led to the erection of buildings to be used as hotels, flats, offices, factories, and for other commercial purposes, containing many more storeys than had formerly been found profitable. The practical limit of height was reached when the sectional area of the masonry of the piers of the exterior walls in the lower storey had to be made so great, in order to support safely the weight of the dead load of the walls and floors and the accidental load imposed upon the latter in use, as to affect seriously the value of the lower storeys on account of the loss of light and floor space. This limit was found to be about ten storeys. Various devices were successively made to reduce the size of the exterior piers. Iron or steel as a substitute for wood for constructive purposes was long thought to be fire-proof or fire-resisting because it is incombustible, and for this reason it has not only replaced wood in many features of building construction but is also used as a substitute for masonry. In time, however, it was realized that iron by itself is not fire-proof, but requires to be protected by means of fire-resisting coverings; but as soon as satisfactory forms of these were invented their development progressed hand in hand with that of iron and steel forms and combinations.
Buildings in steel are either of ” skeleton ” or ” cage ” construction. These terms may be defined as follows: In ” skeleton ” construction the columns and girders are built without proper or adequate inter-connexion and would not be able to carry the required weights without the support afforded by the walls; or, as in more recent construction, the walls are self-supporting and the other portions of the building are carried on by the skeleton steel work. The construction consists of a complete and well-connected framework of iron or steel capable of carrying not only the floors but the walls, roof, and every other part of the building, and efficiently constructed with wind bracing to secure its independent safety under all conditions of loading and exposure, all loads being transmitted to the ground through columns at predetermined points. In America under this system the walls can be built independently from any level, but in England the requirements of the building acts as to the thickness of walls prevents the general use of this form of construction.
“Cage” construction consists of a complete and well-connected framework of iron or steel capable of carrying not only the floors but the walls, roof, and every other part of the building, and efficiently constructed with wind bracing to secure its independent safety under all conditions of loading and exposure, all loads being transmitted to the ground through columns at predetermined points.
Post time: Nov-07-2022