THE SKYSCRAPER

Evening Post, Volume CVII, Issue 148, 27 June 1929, Page 18

THE SKYSCRAPER

HOW IT CAME INTO . BEING THE ADVANTAGES OF STEEL

Two decades ago there were very few buildings in the world exceeding ten stories. This limit to height was imposed by the huge foundations necessary to support tall structures.

Prior to the twentieth century sis stories were the limit o£ the buildings. People would not walk up more than six flights of stairs, and as the elevator had not yet been perfected, tall buildings were impracticable. When lifts made their appearance the height of structures in the large towns increased gradually, until 12----story buildings were to be found in many cities (says the Cape "Times"). It was here that the foundation factor cropped up. The great foundations required to support the masonry of buildings of over 12 stories rendered their construction prohibitive. The walls at the base of a 40-story skyscraper would have to be 30ft thick, tapering gradually as they went up. Thirty years ago the use of steel in the construction of buildings was practically unknown. The weight of a floor of offices had to be supported by the walls of the floor below, and columns of concrete took up a large portion of the lower floors. It was only the few top stories which provided a reasonable amount of unrestricted space. Supporting columns of steel were then introduced, and buildings were designed on the principle of the human body —a skeleton of steel taking the place of bones, and masonry the place of flesh. The outline of the construction of a modern skyscraper provides scope for the skill of architects and builders engaged in this highly specialised branch of building. THE FOUNDATIONS. To get down to bedrock foi- the laying of foundations is the aim of the. engineers. Massive concrete pillars are sunk into the ground until they rest upon solid rock. To these are bolted the steel columns upon which the strength of the building depends. The columns are naturally larger at the bottom of the building than elsewhere, but in comparison with the supports of a non-steel building, this taper is hardly perceptible, being about two inches for every, four floors. The steel columns- and girders have to support the entire weight of the building. No weight rests on the brick or stone work, with which'the gaps are filled up, and each space between the columns and girders ia treated as a separate unit. One of these sections, may.be. removed aj: any time without causing strain to the building. The filling in of these gaps may be started-on any .flooF,,and. the- bottom floors can, if desired, be left to the last. In buildings constructed entirely of masonry, windows were restricted in arize, by reason of there having to be sufficient masonry to support the weight of the floors above. The steel framework of the skyscrapers permits large windows' being let in wherever necessary. The steel work ia protected from rust and corrosion by tar and tar-paper, and with these absolutely waterproof girders there is no chance' of water becoming pocketed between the masonry and the steel work. As the expansion and contraction of steel and masonry are necessarily different, a means of counteracting the movement had to be devised. A special flexible cement, which allows for contraction, was used with great success. The fact, furthermore, that the walls are divided into numerous small sections tends to check the expansion and contraction of the building. Were the whole wall to be built in one solid- piece, the contraction would be more noticeable than it is. when made up of small sections. FLEXIBLE STRUCTURES. A feature of the buildings constructed of steel"columns is that they give to the stress of the wind and other factors which cause .movement of. the building. Masonry structures, aimed at stability more than strength, and as soon as any excessive strain was imposed upon them cracks appeared, which considerably weakened a section of the wall and caused a menace to the crowds in the streets below. It is stated that the top 'of the Woolworth Building moves as much as two inches owing to expansion. Should a skyscraper collapse, the onus rests upon the architects* - who designed the building, but i£ they can prove that the contractor has not carried out their instructions in regard to materials and specifications, the loss has to be borne jointly by the architects, consulting engineers, contractors, and sub-contractors. It isl only in America that skyscrapers are permitted. Buildings many hundred feet high may be built in most American cities, subject to certain conditions. In London and Paris no buildings are allowed to be over 100 feet' in height, the restrictions inj Paris being even more severe than in London.