Page:Collier's New Encyclopedia v. 09.djvu/96

LEFT STEEL SKELETON CONSTRUCTION 70 STEELYARD 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. The members of the steel skeleton are completed in their construction at the mill and are assembled and riveted to- gether on the site of the proposed build- ing. Angles, plates, channels and other rolled sections are built up into girders and columns. As much as is possible of the riveting is done at the mill, the rest being attended to at the site of the build- ing. In order to distribute the weight of load columns, bases or bearing plates are placed between the column and its foun- dation. The columns may be of steel or cast iron, hollow circles or hollow squares or H shapes being in use where the strength is sufficient as being the most economical. Slabs or arches of terra- cotta or concrete laid between steel I- beams make up the floor construction. The floor area is determined by its di- vision into units of from 15 to 20 or more feet, according to the size of the rooms required. Single or double gfird- ers, built up or riveted, placed between the columns, hold up the ends of the floor beams. In high and narrow skele- ton buildings cantilever girders are some- times called for to distribute the weight evenly over the footings. The great height of steel buildings in relation to the area of their site has likewise made methods of wind-bracing necessary, the systems employed being sway-bracing, knee-bracing, and portal-arch bracing, the aim in each case being to hold the steel frame in its several parts more securely to its foundation. While the ad- vantages derived from steel skeleton con- struction are many and obvious, there are some disadvantages. There is always the liability to corrosion in the metal frame, while the danger to life and limb from their great height and the concen- tration of population made possible has been often illustrated. While they repre- sent a tremendous development in the art of building, they are erected for con- venience rather than for endurance or beauty, though in this latter respect numerous improvements have been made in late years. This disadvantage may be lessened by new rules and devices, but steel skeleton construction has be- come a necessary adjunct to our material civilization, and greater development may be looked for in the near future. STEELTON, a borough in Dauphin co., Pa., on the Susquehanna river, the Penn- sylvania canal, and the Philadelphia and Reading, and the Pennsylvania railroads; 3 miles E. of Harrisburg. It contains electric railroads, a National bank, and daily and weekly newspapers. Here are the extensive plant of the Pennsylvania Steel Company, a flour mill, shirt fac- tory, planing mill, and brick works. Pop. (1910) 14,246; (1920) 13,428. STEELYARD, a balance or weighing machine consisting of a lever with un- equal arms. It is of two kinds. The common steelyard, or Roman balance, is formed by suspending the article to be weighed from the end of the shorter arm, or placing it in a scale depending there- from and sliding a determinate weight along the longer one till an equilibrium is obtained. The longer arm is so grad- uated that the figure opposite to which the weight rests indicates the weight of the article at the extremity of the shorter arm. The second form is the