fully. Some were left rough so that they could be carved. As with the steelwork, every piece bore a number which designated the particular spot it was to occupy; even the terra-cotta pieces were numbered. It impressed me greatly to find that every piece of the wall was accounted for, and my respect for the architect went up a hundredfold. It seemed almost like keeping count of the very hairs on one’s head.
When we got down to the ground floor, Mr. Hotchkiss saw us out to the sidewalk. He seemed to enjoy answering our questions, and we had by no means asked him all we wished to, yet.
“Are n’t you ever going to reach the height limit of these tall buildings? I should think they would soon be too heavy for their foundations.”
“Not at all; not at all,’ said Mr. Hotchkiss, looking around for an illustration. Then he fumbled in his pockets and pulled out a small bolt. Unscrewing the nut, he measured it, and found that it was a scant inch square.
“That ’s less than one square inch, eh?”
We nodded assent. Then he placed the nut on the ground and stood on it. “There, now I am subjecting the ground to a greater strain than is this whole building.”
We looked at him incredulously. “Yes, I weigh 210 pounds. Two hundred and ten pounds on one square inch makes how much per square foot? Reckon it up.”
Will had his note-book and pencil out in a jiffy, and started figuring. “Fifteen tons per square foot,” he announced presently.
“That ’s it. The building regulations of this city do not allow a weight of more than fifteen tons per square foot on the foundations. A foolish regulation, in my estimation, based on the idea that concrete would crush under a heavier load than that; but the kind of concrete we have nowadays, thoroughly reinforced with steel, will stand a far greater pressure. You can see for yourselves how ridiculously light the load is when you figure it down to square inches. Why, many a fat woman who picks her way across a muddy street on her French heels, exceeds the limit of the building code for pressure on the earth.”
“But I can’t believe,” I protested, “that a big building like this puts a strain of only 210 pounds on the ground. Do you mean to say that if you cut a sliver out of this wall from top to bottom and only an inch thick by one inch wide, it would not weigh more than 210 pounds?”
“Well, not exactly that. If your sliver were cut out of one of the steel columns, it would weigh six or seven times as much as that, and if it were cut out of the elevator-shaft, it would be as light as air. You must remember that very little of this building is solid all the way up. At the bottom of the columns there is a foot piece that spreads the weight over a large area of concrete. There are sixty-nine concrete piers under this building. It is a regular centipede, with concrete legs all over that stand on rock 120 feet below the sidewalk. Some of those legs are twenty feet in diameter. You will find that there are quite a few square inches in the foundation supports of this building. Altogether the finished structure is going to weigh something like 100,000 tons, with an allowance of 20,000 more for wind-pressure. That is n’t very much when you consider the size of the building. If you could throw the finished building into the ocean, it would float, provided the doors and windows did not leak, and, what is more, fully five sixths of the building would project out of water. Oh, we have n’t reached the height limit by any means. Somebody has figured out just how tall a building could be erected on a plot 200 feet square without violating the building code. He estimated that the building would be 150 stories high, reaching 2000 feet in the air; and it would weigh 516,500 tons. It would cost $60,000,000, and it would be required to stand a wind-pressure of 6000 tons. As a matter of fact, it would take something like 50,000 tons of wind-pressure to upset the structure. Of course, a building like this would not stand on concrete legs, but would have a single solid foundation pier 200 feet square, running down to bed-rock. If the steelwork could be erected directly on the rock without any concrete between, no doubt permission could be obtained to add a few more stories on top. Up-town they don’t have to bother with deep foundations as we do.”
“Did you really have to dig down 120 feet for the foundation for this building?” asked Will.
“Why, certainly we had to. You know how it was done, don’t you? What! never heard of caisson work? Well, there is a treat in store for you. Five blocks down Broadway, they are sinking some caissons now for a twenty-five-story building. You go down there and ask for Jim Squires. He is a personal friend of mine. Hand him this card, and he will show you all there is to show. I ’ll have to be going now. Glad to have met you, boys. So long.”
We shook hands with him, thanked him, and apologized for all the trouble we had given him.
“You ’re quite welcome,” he called, as he moved off. “And if you have any more questions to ask, drop in at the office any time around noon, and ask for Dick Hotchkiss.”
To be continued.
Vol. XL.—52
