The viaduct from Long Key is 2 miles long and passed through water having a depth ranging from 13 to 20 feet. The floor of the Gulf is of coral. To construct a pier, about 30 piles would be driven in with their tops projecting up from the floor. A cofferdam would be sunk to include them and a seal of concrete 1 yard thick be placed. The water could now be pumped out and the form concreted. The reinforcement would, of course, be put in place before depositing this concrete. The pier would then be allowed 3 weeks to mature. The concrete was mixed with fresh water to avoid the effect of sea water on the steel. Corrugated bars were used in reinforcing the walls and the 184 arches. High water is 31 feet below the top of this structure, so that the track is well protected from the waves.
It may surprise some, but concrete has actually been used as the chief material in the construction of boats. A reinforced concrete boat was built thirteen years ago for use on the River Tiber in Italy. Not only the hull
but posts and roof of the structure above deck were of concrete. This house boat was 67 by 21 feet. Another Italian boat is the Liguria, a barge in actual service. It is 57 by 18 feet and is rated at 150 tons. The Gretchen is an American example of the stone boat. She has sailed over long distances on the Atlantic and was reputed as comparatively a rapid sailer in a heavy sea. Her reinforcement was a multitude of small rods. This boat drew 14 feet of water and was 65 feet long and had a beam measurement of 16 feet.
Concrete is an obvious material for coal pockets, especially because of its fireproof character. A further advantage is the avoidance of a large maintenance charge. At Charlestown (Boston), the Lehigh & Wilkes-Barre Coal Company had been expending about $1,000 yearly on repairs upon a coal pocket. This has now been replaced by a concrete structure having a capacity of 10,000 tons. It has a depth of 24 feet, and has a length of 182 feet and a width of 92 feet. It is founded upon 750 Simplex concrete piles. If wooden piling had been used, the amount of excavation thus necessitated would have been very considerable because it would have been necessary to cut them off 10 feet below the surface in conformity with the building laws. Moreover, about 2,000 wooden piles would have been required because of the limit of ten tons’ bearing capacity per pile. With the concrete piles, however, the footings for the columns were constructed with but little excavation. The columns, side walls, girders, beams, floors—pretty much everything except the roof—were of reinforced concrete. When a full load of coal is filled in on the floor, the weight per square yard is 18 tons.
A similar application is to the construction of grain elevators. Reinforced concrete has been used at Baltimore in two important buildings of this kind and also in the case of a third at Buffalo. The question of fire is here very important. The grain elevator of the Pennsylvania
Railroad at Baltimore is the largest of the three and is constructed to hold 1,000,000 bushels. There are 53 cylindrical bins having a common height of 79 feet. There are four rows of eight each. The remaining twenty-one bins occupy spaces in between, three rows seven in a row. The set of 32 have the larger size and measure 24.2 feet in internal diameter. The walls are 8 inches thick and have both vertical and circumferential reinforcement. The vertical reinforcement is round bars of 1⅜-inch diameter. The circumferential reinforcement consists of interlaced flat bars. By a patented device the bins were cast in sections. This mold would be attached to the heavier vertical reinforcement and jacked up as needed.
It is unnecessary to emphasize the fact that concrete while economical is not cheap. So that when large masses are used, it is advisable to reduce the expense by using what may be called “pudding stones.” At McCalls Ferry a large dam and adjoining power house span the Susquehanna River. This is a tremendous application of concrete. However, pudding stones were very properly employed in the construction of the great dam. Here steel was employed not so much to reinforce but to supply frames for the molding surfaces. Great pelican cranes of steel were also employed to handle the concrete, etc. The face of the dam is a double curve and thus required a precise mold. Sections of the dam, 40 feet in length, would be constructed to alternate with open spaces of the same length. When it was desired to close such open spaces, a great steel apron would be let down on the upstream face. Concrete could then be laid in the open space.
In all the applications of reinforced concrete with which our attention has so far been occupied, the case has either been one of well-recognized practice or closely related to such practice—with the possible exception of concrete barges. There are two other lines of engineering
application in which it is very desirable to employ concrete, but where we are scarcely entitled to regard its use as anything more than experimental. Reference is made to telegraph poles and cross-ties. If a concrete pole really proves adapted to its service, then we may expect a great reduction in maintenance expense. It is estimated that renewals of wooden poles in the United States cost yearly $13,000,000. The prospect of getting a pole which will not need renewal for a long period is certainly attractive. But the actual service is severe. This is due not so much to the load which must be carried as to the horizontal movements under wind pressure. But by using proper reinforcement, it is thought by some, the pole may be made to withstand the horizontal thrusts. Some experiments have been made of a type of pole recommended by the American Concrete Pole Company, Richmond, Indiana. Four vertical rods bound together by wire constitute the reinforcement. Such a pole 7 x 7 inches at the top and 12 x 12 inches at the bottom was tested to destruction. This pole was 30 feet long and had its butt end sunk 5 feet into the ground. The vertical rods were ⅝ inch in diameter and were bound with No. 9 wire. A horizontal thrust or pull at the top of 840 pounds accomplished a deflection of 6 inches. When this was increased to 1,780 pounds, the deflection amounted to 17 inches. When 2,800 pounds pressure was employed, the deflection was 30 inches accompanied by a slight cracking. A deflection of a full yard together with cracking at the ground line resulted from a pressure of 3,640 pounds. When 7,200 pounds pressure was employed, the cracking became bad and the deflection amounted to 60 inches. A cedar pole of the same size was deflected 11 inches by a pull of 840 pounds. With 1,780 pounds, the deflection was nearly a yard (33 inches); and with 2,200 pounds the pole broke about 3 feet from the ground. The problem of the
telegraph pole will probably be solved, if this has not already been done.