Concrete Standpipes.

Concrete Standpipes.

It is interesting to know that the first standpipe erected in this country was that at Little Falls, N, J., in 1899. To date there have been fifty-three built in this country and abroad. Of these, thirteen have been erected in New England, which would indicate that engineers and water companies here have more faith in this type of construction than in any other part of the world. The Aberthaw Construction Company have built two large standpipes and a tank, the smaller, 40 feet in diameter and 70 feet high, at Westerly, R. I., and the largest at Attleboro, Mass., 50 feet in diameter and 100 feet high to water level The Attleboro standpipe was designed on the basis that the hoops take the entire load with a unit stress in the steel of 13,500 pounds per square inch In order not to have the bars too close together, 1 1/2 inch diameter bars were used in two rows, from the bottom of the standpipe to a height of 61 feet. From 61 to 81 feet a single row of 1½ inch diameter bars were used. From 81 to 100 feet the bars were 1 1/8 inch diameter. In the upper fifteen feet of the height, the section of steel was kept constant, although the hoop stresses from the water were constantly diminishing to the top. This was done to provide for possible stresses caused by the formation of ice in the standpipe. The walls of the standpipe started with a thickness of 18 inches at the bottom and tapered to a thickness of 8 inches at the top. In order to space the reinforcing bars an exact distance apart, 4-inch channels with ⅜-inch punched holes through both flanges were used. The channels were set upright at intervals of about 15 feet, center to center, a ¼-inch rod was passed through the holes, and the hoops were rested directly on the ends of these 1/4-inch rods, which were then bent tip to secure the hoop firmly. From the height of 61 feet to the top. 3-inch channels were used for spacers. The floor of the standpipe was 12 inches thick and met the wall with a curve whose radius was 5 feet. The top surface of the floor was reinforced with 1/4-inch surface twisted bars, 6 inches on centers each way. The foundation consisted of a slab about 18 inches thick but under the walls of the standpipe the depth of this slab was increased to 4 feet for the width of 5 feet. A concrete curb, 3 feet high and 12 inches thick was built around the outside at the bottom. A gate-house enclosing various valves was erected at one side and access to the interior of the standpipe could he obtained through a passage in the same. The roof was Guastavino tile dome, suitably ventilated. The method used in splicing the ends of the bars together may be of interest. These bars were obtained long enough so that three would reach entirely around the circumference with a lap of 40 diameters at each joint. Two wore loop clips were then used at each splice to insure the bars being held firmly together. By actual test at the Watertown Arsenal these clips alone were found sufficient to secure the full working stress of the bare bars. From our experience with this standpipe and the one we erected at Westerly later, I believe the addition of considerably vertical reinforcement in the lower 8 or 10 feet of the standpipe wall would assist very materially and perhaps entirely obviate the formation of a horizontal crack in the lower few feet of a standpipe. The walls under water pressure must increase in circumference. At the bottom of the standpipe, however, this increase in diameter cannot take place owing to the rigid connection of the wall with the floor. It is apparent then, that unless precautions are taken, either by the use of very iow stresses in the hoops or by the addition of vertical steel bars, there may be a distinct movement back and forth on some joint in the standpipe. That this movement is present is further indicated by the fact that when a standpipe has been kept full of water for some time the leakage through these joints almost entirely disappears, but on emptying and refilling the standpipe the little dams formed have apparently been broken down as the leakage again occurs as vigorously as at first. In the Westerly standpipe we endeavored to take care of this by increasing the amount of steel. At the lowest foot the stress is 6,000 pounds per square inch. This stress was increased 1,000 pounds for each foot in height, until we reached a maximum stress of about 12,500 pounds per square inch. No vertical steel, however, was used, and on filling the standpipe w’e found that with a maximum head of water that a small line of dampness occurred in a horizontal joint about 3½ feet above the floor of the tank. This damp place was nearly 30 feet long. Quite different methods were used in erecting the Attleboro and Westerly standpipes. In the ease of the former, a large tower of pine timbers, properly braced, was erected. On the top of this were placed two bull-wheel derricks. Concrete was handled in a bottom dump bucket, swung to the position desired by the derricks, dumped in boxes and shoveled into the wall. Wooden forms were used. At the Westerly standpipe, the plant consisted of a simple concrete mixer fed by wheelbarrows. The mixed concrete was delivered to an ordinary elevator, hoisted to a hopper erected on the elevator tower where it was dumped, and from which it was fed into wheelbarrows and shoveled into place. Steel forms were used.

*Abstract of paper rend before the Boston Society of Civil Engineers by Leonard C. Wason.

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