STEEL SKELETON CONSTRUCTION, a form of building construction by which the loads and stresses are transmitted to the foundation by a framework of metal or re-enforced concrete, with girders at each story supporting the walls enclosed. It represents one of the greatest devel opments in building from the earliest days of architecture. It proves the solu tion to the problem that arose from the concentration of population in a confined area and it was only natural that the idea should first take shape in what was des tined to become the most congested area, in respect to volume of business interests and number of people, in the whole world. The height of buildings had al ways been determined by consideration of security, utility and cost, and until the advent of the steel skeleton six or seven stories were regarded as nearly as far as the builder could go. In the seventies the rising value of real estate set prop erty owners seeking for a plan of raising more revenue from their investments, and gradually buildings rose until a height of 10 and sometimes 12 stories. The huge quantities of masonry called for in these lofty buildings set property owners and builders under the necessity of seeking out devices that would enable them to economize in mate rial and in the ground occupied. Piers were made thinner and columns were put up to receive the ends of the beams and girders and so relieve the piers of the weight of floor. Finally, in 1889, it was found that the thickness of the piers could be reduced still further by taking from the piers the weight of the walls and placing the four walls on girders set between the wall columns at every floor level. It was thus that the princi ple underneath Steel Skeleton Construc tion was revealed. It relegated stone to a subsidiary relation in construction. The essential part of the building became a firmly bound framework of steel able to support not merely the floors and roof, but the walls, interior and external, to gether with every other part of the building, and constructed on lines suffi cient to withstand every condition of wind and weather. In the new type of
building the ancient thick supporting walls are known no more. The walls no longer carry loads; they serve merely as a clothing or curtain to the powerful frame of steel which carries the building upward.
The first iron girders and beams used in the United States came from Europe about 1840 and their value in the con struction of buildings began to become apparent from that time on. Iron beams were used in the floor construction of Cooper Union in New York City in 1860, and steel beams began to be manufac tured in 1885. As soon as the principle of steel skeleton construction was per ceived steel came to be used throughout the entire building, though cast iron con tinued to be used in some buildings for columns and bases. As steel grew con tinually stronger and cheaper a great impetus was given to building con struction all over the country, and build ings of great width and height now rose in the course of as many months as formerly it would have taken years for their construction. The height of buildings is now only limited by its relation to the foundation and the service capable of being rendered by a proper system of elevators propor tionate to the area of floor space. The amount of space saved by the thinning of the walls has been large. Many build ings are now built in which the amount of stone used is negligible. Even in the central business quarters of large cities the buildings are not a few which are apparently made up of steel and glass. Where formerly a building of 10 stories was regarded as risky, now buildings of over 40 stories are regarded as a mod erate development. A building can now be erected at the rate of one story every three or four days, and as the frame directly supports the walls at each story it is not an uncommon sight to see the upper part of a building inclosed by walls while the lower part continues to reveal only the steel frame.