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When we approach New York by river or bay, we see in the view of the high buildings of Manhattan Island a picture which has no parallel in the cities of the world. Our first impression of the height and magnitude of these architectural marvels is strengthened as we wander through the downtown streets, and passing from one shadowy canon into another make our way between the tremendous cliffs.
The New York sky scrapers constitute one of the most impressive and interesting features of the city.
The high building is distinctly a modern and wholly American creation. It has grown out of the concentration of business and the ever-insistent demand for business office room in the closely congested business centers.
The skyscraper provides business opportunity for a thousand, two thousand, ten thousand, where without it there would be room only for as many hundreds. Two factors have made it possible —the passenger elevator, which gives immediate access to the upper stories, and the steel cage system of construction, which enables the architect to design his building to any desired height.
The steel cage is a framework of steel beams, bolted together with hot rivets. In effect it is a bridge set on end. The walls are simply weather shields, fastened to it. Under the old system the walls supported the floors; in the new buildings, the walls serve merely as curtains to shut out the weather, and are themselves supported by girders which project at the levels of the floors.
The steel frame goes up first, and the walls are put on afterward; sometimes the upper stories are walled in before the lower ones. Under the old system of supporting walls, buildings were limited to eight or ten stories; the steel cage goes up twenty and fifty stories, and the architects tell us that there are no mechanical obstacles to buildings of too stories. With steel beams and steel ceiling arches, concrete floors and stone and metal stairways, the structures are considered to be fireproof.
Wonderful as New York sky scrapers appear to us as we see them towering in the air, some of the greatest engineering achievements in their construction are below the ground, in the foundations contrived to sustain the prodigious superstructures. The foundations go down to bedrock, in some instances more than too feet below the surface. As the architect went to the bridge engineer to build his steel cage, so he has adopted the bridge engineer's pneumatic caisson system of pier sinking.
Of all the New York sky scrapers, the caisson for high building foundation work was first adopted in the MANHATTAN LIFE INSURANCE BUILDING, on Broadway, near Exchange Place, in 1894. The weight of the structure was calculated at 2I,600 tons; the pressure exerted upon the foundation by the force of the wind acting upon the sides of the building and tending to overturn it was calculated at 2,400 tons; and the weight of the furniture and the human beings who would occupy it was reckoned at 7,000 tons more—making a total weight of 31,000 tons, or 62,000,000 pounds to be carried by the foundations. To provide a foundation that would sustain this immense weight, the architects sunk their caissons down to bedrock, 55 feet below the surface. As each caisson descended, a brick pier was built up on it. When bedrock was reached, the rock was leveled inside the caisson, and the chamber was filled with concrete, so that caisson and masonry formed one solid pier resting on bedrock and rising to the surface of the ground. There were fifteen of these great piers.
The foundation of the AMERICAN SURETY BUILDING, at Broadway and Pine street, were sunk in the same way to bedrock 79 feet down. Our illustration, from the Scientific American, shows the caissons resting on the bedrock, the piers on the caissons, and the columns on the piers. Here, too, is an ingenious cantilever device, which may be seen in the right-hand pier, for distributing toward the center a portion of the weight of the outer walls.
This was the record price for Broadway real estate until the plot on the south corner of Broadway and Wall street was sold in 1906. The American Surety has twenty-one stories, with a height of 308 feet. The statues on the front are by J. Massey Rhind. There is, by the way, a curious circumstance in relation to the cornice, which at the height of 308 feet projects beyond the building line and trespasses upon the air space which belongs to the Schermerhorn Building next door. When the trespass was discovered, the Astors, who own the Schermerhorn, threatened to put up a skyscraper, which would of course cut off the south light and air of the American Surety Building; the matter was adjusted by the American Surety Company taking a ninety-nine years' lease of the Schermerhorn Building.
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