STEEL & CONCRETE BY JEANNA MOËLL
STEEL & CONCRETE BY JEANNA MOËLL
© Bonnier AB 2022 Text: William H. Birkmire 1893. © Photography: Jeanna Moëll Image Editor: Jeanna Moëll. Captions: Jeanna Moëll Layout: Jeanna Moëll Printed: Malmö University, Malmö 2022 ISBN: 91-89204-27-1
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The method of skeleton construction has been developed by the use of iron and steel in the erection of fire-proof buildings, and it seems to have solved the problem of economizing space in the lower floors of high and narrow buildings. In the ordinary methods of building, the higher the wall the thicker it must be at its lower parts, but the lower stories are the most valuable; yet it is in these that the greatest area of a valuable lot must be surrendered to enormously thick walls. Therefore, every foot gained on the inside measurements increases the availability of the structure. In the buildings where the skeleton construction is used throughout, heavy masonry walls are not known, and what appears to be such in the finished state is simply a veneer of some fire-proof material, yet the frame of the building is not a mere heap of beams and columns; but as one example after another is erected we find that the details and connections are being carefully studied, and the whole braced and anchored so completely that the metal construction may be raised, hundreds of feet from foundation to roof without the aid of any masonry – a great metal structure, strong in its own strength, not only to carry the direct loads which may be placed upon it, but also to resist all lateral strains to which it may be subjected. The architectural appearance of our large cities is being rapidly altered by this new system. It imposes no new conditions on the architect, except as to the engineering of the metal frame; and in a few years, with the skill already displayed in treating these problems, many new designs will be brought forth, notwithstanding the great height to which they are built. The skeleton construction consists in the use of cast-iron, wroughtiron, or wrought-steel columns in the side-walls, connected longitudinally at the floor levels with beams, lattice or compound riveted girders supporting the thin curtain walls 12 to 20 inches in thickness; in addition the weight of the floors are transmitted to the longitudinal girders and columns, so that the latter support the entire building. The thin curtain walls are generally built of brick, and extend from the top of any wall girder to the underside of the next story girders, extending a sufficient distance outside to cover the girders and columns with masonry, and continue in this manner to the top of the building. When the first examples of the skeleton construction were completed many questions were raised, and no doubt there exists in the minds of many at the present time that the greater expansion of one material over another might work some trouble. Events have proven that the temperature of this climate from the greatest cold to the greatest heat exerts no appreciable effect, especially while the metal is covered with masonry or some fire-proof material. The first examples of the skeleton construction in buildings were those erected with cast-iron columns. Cast-iron at the time of their erection, and no doubt is at the present time, produced more quickly and cheaper than wrought-iron or steel columns, and these were two very important factors in the problem.
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The constructors and producers of cast-iron advocate its use only as the material for the columns inclosed in the walls. They claim also that the oxide of iron paint so commonly used for coating iron soon dries out, leaving a coating of dry, broken scale or powder. Between the columns and the outer air are only a few inches of brick or some fire-proof material, through which dampness soon finds its way. In wrought-iron, they claim that rust honeycombs and eats entirely through the metal. Mild steel rusts faster than wrought-iron at first, then slower. Castiron, on the contrary, slowly oxidizes in damp situations; rust does not scale from it, and the oxidation when formed is of much less dangerous kind, extending only a little way into the metal to about the thickness of a knifeblade, and then stops for good. Cast-iron of goodly thickness offers a far better resistance to fire, or fire and water combined, than wroughtiron or steel. The experiments undertaken by Prof. Bauschinger, of Munich, in reference to the safety of cast-iron columns when exposed to the action of great heat are quoted. ”Having arranged some cast and wrought iron columns heavily loaded, exactly as they would be if supporting a building, had them gradually heated; first, to three hundred degrees, next to six hundred, and finally to red heat, then suddenly cooling them by a jet of water, just as might happen when water is applied to extinguish a fire. “ ”The experiment showed that the cast-iron columns, although they were bent by the extreme heat and exhibited transverse cracks when cold water was applied, yet they supported the weight resting on them; while the wrought-iron columns were bent before arriving at the red heat, and were afterwards so much distorted by the water that the restraightening them was out of the question; in fact, if supporting a real building, they would no doubt have utterly collapsed under the weight they had to sustain. “ If the brick-work or fire-proofing which surrounds the wall or interior columns can be depended upon as a protection for the metal against the effects of fire and water, the above experiment would lose its weight against the use of wrought-iron or steel. The objection to wrought-iron or steel on account of rusting may seem more real, and yet we have seen pieces of wrought-iron beams, anchors, etc., taken from very old walls unharmed by rust. There is, however, considerable distrust of cast-iron in high and narrow building, especially in relation to the connections with the floor and wall girders. Brackets and lugs are apt to break suddenly and completely, but with wrought-iron and steel will bend a great deal without breaking, and that rivets are stronger than bolts. To this objection it can be said that the brackets and lugs, instead of being cast with the columns, can be put on with angle-knee connections, drilled holes in the columns and with any number of bolts, which in a great many of our high buildings has proven entirely satisfactory, where lateral bracing is not required.
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