Data Employed in the Calculation for the FORT DEARBORN BUILDING, Chicago. 6 Weight of Partitions=20 Pounds per Square Foot of Floor, area to be added. Live Load on Beams taken at 70 Pounds per Square Foot-Partition Fibre Stresses in Beams for Dead and Live Loads=16,000 Pounds per Square inch. 64 66 125 The President: The papers which have been read are now open for discussion as the third number in this series, as indicated to you. Mr. George B. Post, of New York, who has had more experience than any other man in this or any other country in the tall structures which are under discussion, will be the next gentleman to speak to you. Mr. Post: Mr. President, It is with very great hesitation and considerable diffidence that I respond to your invitation in this case, particularly in view of the very flattering way in which you have introduced me. Still more so, because my views upon the subject are quite radical and because I am very apt to say, when I get to my feet, what I feel, without regard to consequences. I am afraid before I get through I shall get myself in a scrape. Still, that can't be helped. I listened with very great interest to Mr. Hastings' paper on the subject of the principles of designs of buildings, and most heartily agree with him in all the views which he has expressed. It is my opinion that a high building— that an office building of twelve, fifteen, sixteen or twenty stories in height, on an average-sized lot, as a problem in design can only be considered as a tower, and the principles of design which govern the construction of towers are naturally and with propriety applied to the designs of such buildings. A building which is two or three times in height its horizontal length has nearly the proportions of a tower, and no matter what we do in our design is practically, when completed, a tower. With regard to the artistic possibility of building a city of towers tangent to each other, which would be the result if the building of tall buildings is not checked by legislation, in the city of New York, I think it will be deplorable. Imagine the Campanile of St. Marks, the Giralda and a dozen other campaniles placed side by side, tangent to each other where would be the effect of the tower? But I think this thing will cure itself. After a few years the nuisance on our narrow streets of the tall building will become so great that their height must be limited by law. Within the last few weeks only, I saw reports of experiments in France with regard to the microbes of typhoid fever, the statement being that in one or two hours, when exposed to sunlight, they died; but lived for days when deprived of sunlight and in the dark. I do not propose to go to any extent into this question of the sanitary condition of the city in case tall buildings were constructed or what effect it would have on the value of property. I think the result would clearly be disastrous. I look confidently to the time that legislation (in the city of New York at least, where our streets are about thirty-five feet wide on an average in the lower part of the city) will restrict the height of buildings. The second paper which has been read has treated of the mechanical question of the construction of such buildings and has assumed, broadly, that if the steel cage can be protected from fire that the building will be indestructible. It is my positive opinion, formed after considerable study of the subject and consultation with the best engineers that I could get hold of, that the life of many of the buildings constructed with steel cages will be but short. They will last longer than I will, but I believe that there are men in this room who will live to see the necessity of taking down many of these buildings, or else of resorting continually to most radical systems of repair in construction. In my individual experience I have taken out from a building a number of wrought iron beams which had been thirty-five years encased in solid brickwork; not in plaster or hollow blocks as we are building at present, but with eight inches of brick work around them and leveled up to the floors with concrete. These beams had possibly been subjected on one side to occasional small quantities of live steam, as they formed the ceiling over a well-conducted engine room; a room containing printing presses. Very many of these beams were entirely destroyed by rust. You could take them and break them, in this way, with your finger. And, as far as I know, it is impossible, unless the utmost care is used with paint or asphaltum, to protect a great system of steel or iron construction so that it will not be assailed by rust-so that we can surely protect it, in all its parts, from corrosion. All structural metal, all metal rolled from plates of metal, from piles, as they are technically called in the mills, as is the case with wrought iron, is laminated in its structure. When attacked by rust, the laminae split off from the surface, constantly exposing new surfaces to the action of moisture or gases, the cause of corrosion. Of course, the steel not being rolled from piles is less affected than iron by corrosion-less seriously affected. I suggest to you, gentlemen, if the cage construction as it is at present used-the cage construction of posts and girders, carrying walls between them, the posts and girders being incorporated in the walls-is to be used of 'necessity, that cast iron columns and Hutchinson girders, locked to the cast iron columns by a mechanical joint without steel or iron rivets or bolts, will make a cage construction which will be reasonably free for a very long period from the dangerous effects of corrosion. Individually I believe, although I never very carefully investigated the subject, that I was the first person to use anything approaching to the steel cage. Some fourteen years ago, I think it was, I built the tower of the Produce Exchange with a wrought iron and cast iron combined cage, filling in the panels with brickwork, but covering it on the outside with cast iron plates in the form of pilasters and string-pieces and cornices, so that it could be examined and the structural work could be painted if necessary. I have built a great many buildings that were reasonably tall; one of them three hundred and fifty feet high, I believe, (the World Building), to the top of the dome; but I never have used a cage enclosed in solid mason work. I never have dared to. I have always built the cage detached inside, anchoring the walls to it, so that the cage in case of corrosion, could be painted or repaired. I presume that I will get myself into a hornet's nest by making this statement, but as I have been called upon I think it my duty to express my opinion and express it without reserve and without hesitation. I don't know that I have anything to say upon the subject more, of very great interest, but will leave the matter to the discussion of others. The President: The first work of the sort which I ever had my attention called to was a building in Chicago, with cast iron columns and wrought iron girders and floor beams and the entire structure was embedded in the masonry. Major Jenney was the architect, and I will call on him next in this discussion. Mr. Jenney: In regard first to the durability of steel. Now, all that Mr. Post has said is undoubtedly correct; there are plenty of examples, I know, where steel or iron have perished under certain conditions. On the other hand, there is in Chicago to-day a piece of steel that was dug out of old Rome-deep in the ground-certainly five hundred years old; under the obelisk in Central Park was found a piece of iron, when it was taken down to bring here, that dated back perhaps a thousand years; you all remember that in India there is a column made of lumps of wrought iron, that is about twenty feet in the ground, that has stood there from eight hundred to a thousand years. So that there are plenty of examples of long-enduring, well-behaved steel, as well as those that behaved badly. How are we to know exactly whether we are going to get the well-behaved? I won't say. In regard to fire-proofing: It is said in Chicago, since the fire in the Athletic Club, that we don't need to be protected against fire half as much as we do to be protected against the fire department. In the Athletic Club it so happened, when that fire took place, that they had put all the interior finish in the entire building-the flooring, the doors, etc., and there was a lot of combustible material all stacked up in one room in the very best possible way to burn. It took fire, and it was well under way, the terra-cotta flooring at a white heat, almost, when the fire department arrived, throwing cold water upon t, causing instantaneous contraction, and a good deal of it flew off. If the fire department would let the fire-proof buildings alone and let the fire within them burn out, and confine themselves to preventing the fire from spreading, the damage would be materially less. We have found by experiments that have been made that the soft porous terra-cotta resists the combination of fire and water better than the hard terracotta fire-proofing and I saw some very good results from a fire-proofing made of expanded metal or wire laths wrapped around in layers, filled in with one of the cement plasterings-the Acme or the Adamant-one layer under the other, which was subjected for a considerable time to as great a heat as we could make with a mass of pine wood, maple wood, etc., piled up against it; then the hose turned on and all of the surface was disintegrated. Still, it all stood there and would have protected cast-iron or wrought-iron perfectly well. In the ordinary office building our internal fire-proofing is quite sufficient. You can take all the material in any one room that you could gather, and set fire to it and lock the door and go home and come back the next day, and the fire would not have got out of that room. Something quite similar actually happened in the building I am in, in Chicago-the Home Insurance Company's building. A man in shutting down his desk as he was going home, set fire, accidentally, to a box of parlor matches, turned away and locked the door without ever noticing it and went off. When he came back the next day his desk was burned up-and possibly a chair and something else of that sort—but the fire had never been discovered. From the outside it is a more difficult problem. If there is a building close up and the fire raging in it, and the heat blown by the wind directly on the face of the building, it will be more or less injured; but as we put our steel columns eight inches back from the lot line, and if we protect with terrra-cotta, which is the best material-terra-cotta, you know, is made into shapes that lap around the steel; we send our steel diagrams to the terracotta manufacturers with our details, drawing the iron on it; at the same time we draw the terra-cotta, draw also the anchors by which the terra-cotta is tied back to the steel-that is all filled up with masonry-all this would be disintegrated on the outside; the construction will not be injured. In the case of a warehouse where there is a quantity of very combustible material that will produce a hot fire, something more must be done; one way that has been suggested seems to me feasible, of putting on two fire-proofings: first in the ordinary way, anchoring it on as well as possible; then the next, wrapped around in little channels, perhaps filled in on top with plaster—that is, two entire coatings. The outer coating will be injured, under intense heat, but the inner one will be protected by the outer coating so as to protect the steel. |