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cars. As the wharves rise and fall rigidly with the tides, the ship is always at the same level with the landing stage, which greatly facilitates the handling of cargo.
Similarly, on what has hitherto been an exposed and shelterless coast, a complete sheltered roadstead may be constructed, by means of a floating breakwater out at sea, affording a harbor of refuge, and also protecting the floating wharves and jetties of a commercial seaport. This system will make it possible for railway companies to provide themselves with terminal facilities at any point along a coast, and at a fraction of the cost at which it is now possible to construct harbor works in exposed positions.
Another illustrative example is the steady-floating lighthouse. These can be placed in the deepest and roughest waters,
where hitherto it has been impossible to William E. MURRAY, OF Los ANGELES, CAL.
construct such works, owing to the difficulties in obtaining foundations. They
can be placed at any distance off shore, deadly barrier to an attacking fleet. thus adding greatly to their efficiency, as These would not only be unseen by the shipping can be directed in a course much enemy, but would afford a steady plat- farther away from a dangerous coast. form from which to discharge the tor- The invention is also applicable for pedoes. All would be connected with railroad bridges across deep water, for one another and the shore by telephone coaling stations out at sea along the or telegraph.
routes of mercantile shipping, and for But the invention is just as important floating wrecking platforms wherewith for commercial uses as for coast-defense to raise sunken vessels. Floating hotels purposes. By way of example, let us and sanitariums, hospitals, bath houses, take the Murray steady-floating wharf. and telegraph stations may also be menThere is hardly a harbor or sheltered tioned, just to indicate the wide range of sound along our coast where there are utility possessed by these structures, denot water frontages that cannot be signed to be steadily floated in deep waturned to use for wharfage purposes, the ters, close in shore or far out to sea, and water being too deep for piling to be all immovable and unaffected by the acdriven, and the expense of filling in with tion of the waves and winds. Their rock being prohibitive. Here steady- steadiness makes secure anchoring easy ; floating wharves can be run out, at which for, in the case of a ship, it is the plungships can discharge or load their car- ing and jerking that causes the real strain goes directly into or out of the railroad on the hawsers.
Largest Concrete Bridge
By Guy E. Mitchell
Secretary, National Irrigation Association
JITH the increased use ones, two at each end, making up of concrete as a build- the abutment piers. The total amount ing material, it is not of masonry in the nine arches is at all strange that nearly 13,000 cubic yards. The foundabridge engineers are tions for the piers of this bridge turning to this most were carried down to depths varying bestable and yet flexible tween 20 and 40 feet, to solid rock, where product with which to it could be reached economically, and in construct spans for other cases to hard, rotten rock. It is
travel across rivers estimated that the total weight of this and ravines. To show the confidence structure from its foundation will be these engineers have in concrete, one about 16 tons per square foot. In conneed but look upon the new Connecticut structing the huge arches, a great amount Avenue bridge now nearing completion of lumber was employed in erecting the at Washington, D. C., which is believed "centering.” In this work one and a-half to be the largest concrete bridge in the million board feet of Georgia pine lumworld.
ber was used, this item alone costing in What is now understood to be the largest concrete bridge standing in this country, is the “Big Muddy" bridge on the Illinois Central Railroad. This structure, however, is only one-fifth the size of the Connecticut Avenuebridge; it was built in 1902, and consists of three 140-foot arches, requiring 12,100 cubic yards of concrete.
Compared with the other bridges in this country and in Europe, the bridge at Washington stands in a class alone. Nowhere else has an attempt been made to build so great a number of arches of such great size as in the present case, entirely of concrete, without steel framing to support the mass. Each of the five principal arches is 150 feet in length; and the bridge at its highest point will be 150 feet above the bottom of Rock Creek gorge, which it crosses. The total length of the structure between the abutments, is 1,341 feet, or 21 feet more than a quarter of a mile.
In addition to the five main arches, there will be four smaller
the neighborhood of $50,000. The reached, so that when the forms are foundations for the centering, consisting removed it is believed that there will be of Virginia pine piling, of lengths vary- no distortion of the arches. The estiing from 20 to 50 feet, were forced into mated maximum settlement of the cenplace by an ordinary one-ton drop-ham- tering under its load was three inches. mer falling about 20 feet, until the pene- Only one arch settled to this extent, the tration under a single blow did not ex- others having an average of two and oneceed one-third of an inch. The govern- half inches. The greatest height of any ment engineers who designed the bridge arch above the ground is 150 feet, and estimated that the maximum settlement from this point it will be about 15 feet of an arch under full load would be one- more to the level of the roadway. half inch. This settlement was not quite On account of the settlement in the centering, which could not have been onry to which they are attached. On the prevented in any practical manner, it was sidewalks there will be a suitable condecided to adopt the European system of struction of steel supporting granolithic building up the arches in alternate blocks, footwalks, and a railing, with proper or "non-continuous," so that, after the lamps and posts—all designed to conform alternate blocks were placed, the shrink with the structure. age in the timber was reduced to a min- When the bridge was first considered, imum. When the key blocks were finally plans were received for steel bridges ; in place, the additional settlement caused but the engineers of the District considin each of the five great spans was ap- ered that, as the Connecticut Avenue proximately one-eighth inch. The alter- bridge is designed to adorn one of the nate blocks were ten feet long, measured most important avenues of the national in the direction of the axis of the bridge, capital—about five miles long, extendand were the full depth of the arch (ap- ing from close by the Executive Mansion proximately 6 feet), and the full width to the limits of the District—it would of the structure. (52 feet). Each block, be advisable to erect a bridge of a therefore, contained about 110 cubic monumental character. The portion of yards, and weighed 220 tons. In each Connecticut Avenue within the city limits arch there are sixteen such blocks which contains some of the choicest residences would make the total weight of the five in Washington and also many of the learches 17,600 tons.
A LABYRINTH OF TIMBER FALSEWORK. View of the Connecticut Avenue bridge, Washington, D. C., in course of construction. Note height of arch
as compared with man at base.
gations of foreign countries. Just beyond Sidewalks, each ten feet wide, will be the bridge, on the north, is the Zoölogical carried on brackets projecting from the Park, which attracts thousands of vissides of the bridge at intervals of about itors. Considering the question of econseventeen feet, and secured to the mas- omy, the engineers decided that, since a onry by iron rods run entirely through steel bridge generally is in constant need the structure and fastened to the brackets of repair, and the usual outcome is the on the opposite side. These brackets pro- erection of a masonry or concrete bridge ject about nine feet, and are to be made in its stead, it would be best to erect a of cast iron so as to reinforce the mas- bridge of this class at first.
IT isn't the man with the deep-laid plans
And the smooth and unctuous smile-
That's going to make his pile !
MONTICELLO, HOME OF THOMAS JEFFERSON. In Albemarle county, central Virginia, near Charlottesville. Mr. Jefferson was third President of the United States, 1801-09. He died here, July 4, 1826.
ARLINGTON HOUSE, FAIRFAX COUNTY, VIRGINIA. Located in the midst of the National Cemetery, on the heights opposite Washington, D. C. Once the property of General Washington, it descended to his adopted son, Parke Custis, and was later the home of the Confederate General, Robert E. Lee, who married the daughter of Custis in 1831. It was at one time headquarters of the Union Army in the Civil War.