The Crystal Palace buildings, erected by Paxton for the 1851 Exhibition in Hyde Park, were not usually claimed as one of the early examples of iron-framed buildings, yet the structure was re markable in having foreshadowed and established a principle adopted in the modern steel building, in which the walls do not transmit any important portion of the structural load to the foundation. It was, however, the developments which took place in America at a later date which were to influence most markedly the progress of this form of construction throughout the world. In the year 1883, during a period of unusual building activity in Chicago and following an extensive fire in that city, W. L. B. Jenney designed a building of 1 o storeys that is the forerunner of all high buildings. Afterwards two storeys were added, making the building 12 storeys, proving the soundness of the original calculations. This building, the Home Insurance building, is the first of all skyscrapers. It was finished in 1885. While it is true that L. S. Buffington, a young architect in Minneapolis, had thought of steel skeleton structures as early as 188o, it remained for Mr. Jenney to put the problem to practical test. There is, however, some controversy regarding who should get credit for the first skeleton construction building.
Skeleton Construction.—The Home Insurance building was designed with relatively thin outer walls, the dead load of which is placed on a framework of iron concealed inside the masonry and used to transmit the weight to the foundation. The frame work was made of cast iron columns, and wrought iron I-beams, the beams being bolted to the columns with angle iron brackets. At the suggestion of the Carnegie-Phipps Steel company, rolled Bessemer steel beams, then being first produced, were used above the fifth floor. Cast-iron columns were used to the top since plates and angles of steel, of which the later steel columns were built up, had not yet been rolled. The term skeleton construction was later applied to all buildings of this type. Besides the de velopment of the steel framework, the elevators, the use of Port land cement, another factor of great importance in the creating of skyscrapers was the invention of hollow tile in 1871 by Balt haser Kreisher, which solved both the dead-weight and the fire protection problem.
The advantages to be derived from the erection of high build ings on city sites were rapidly recognized both by the land-owner and the building-owner ; site values were enormously increased and much greater accommodation became available on f restricted area. The adoption of skeleton construction also led to speedier erection, since, on the completion of the steel framing, the build ing of walls and the construction of the floors could proceed simultaneously on several floor levels.
As confidence in the type of building increased, higher and yet higher structures were erected, and since most of them were rela tively slender and were frequently built on sites that afforded poor foundations, the use of piles and of the caisson—already adopted by the bridge builder to ensure sound foundations—increased and developed. Improved practice in the construction of foundations became fundamentally important in the further growth of this type of building, and many ingenious and effective developments occurred, including combined foundations for two or more col umns, and also cantilevered foundations, by means of which the actual foundation construction for the external or boundary col umns could be kept within the limits of the site. (See article on FOUNDATIONS.) Protection from Fire.—Early experience showed the very complete destruction by fire of iron and steel buildings in which the distortion of the framework, under the effects of excessive heat, resulted in the collapse of the metal framework and walls. The importance of fire protection is now generally recognized and the vital parts of steel buildings are required to be protected by terra-cotta, hollow tile, cement concrete or other fire-resisting materials. In America a definite limit of height is generally set by the building regulations for the control of non-fireproof buildings, but if adequate and ample fire-protection of the structural fabric is provided in the permanent construction, no arbitrary limit is set to the height in some American cities; in others there are height limitations. It is necessary, however, to provide, for all high build ings efficient warning, fire-checking and fire-fighting equipment, such as stand-pipes and extinguishers, especially at heights be yond the scope of the local fire-fighting equipment. The work of the various Fire Assurance companies and, more recently, the effective research and investigations of the National Board of Fire Underwriters, has influenced fire-protection, assisted in the im provements of constructional methods, and helped to render these improvements rapidly effective. In Great Britain, structural prac tice and consequent building developments have been somewhat different from those of America. Very high buildings have not been favoured for a variety of reasons which are referred to else where in this article. One of the arguments that was used in the past against high buildings was the difficulty of dealing with fires at great heights. Experience in America, however, has proved that adequate provisions can be made to meet such emergencies.