below the floor beams of the upper deck, and carry their proportion of the load of the bridge. In each land span they were drawn down and clamped to the other three ropes forming a cable. Plate XXXIV, Fig. 2, is a view of the land span of the footbridge, as seen from the Brooklyn anchorage, as it passes through the steelwork of the end span.

The erection of the framework for the upper deck was begun at the center of the main span and carried toward the towers. Plate XXXVII, Fig. 1, is a view of the main span, showing the erection of the upper deck. The material was run down on top of the cable by bridgemen who held each end with a line and ran along the footwalk with each piece, as shown in Plate XXXIII, Fig. 2. When the posts, stringers and floor beams were in place, the 2 x 6-in. flooring was laid over the beams, beginning at the towers and working toward the center. flooring on the land spans was similarly laid. Handrails of g-in. galvanized wire rope were stretched on each side of every footwalk, and secured to the handrail posts with staples.

The

Half way between each anchorage and tower and at three points along the main span were erected frame towers about 12 ft. high. On these were supporting sheaves over which ran a traveling rope.

STORM CABLES.

The four 21-in. storm cables previously described, each about 1700 ft. long, were delivered on reels at the foot of the Manhattan tower. The free end was taken to the top of the tower, passing up the land. side, and crossing over the top toward the river on the sheaves on top of the footbridge saddles. The rope was now drawn across the footbridge in the same way as were the cables for the upper deck. They were laid across the lower deck beams and in such a manner that they could be easily pushed overboard. While in this position a suspender of 1-in. galvanized wire rope was fastened every 40 ft. The other end of the suspender was attached to the foot-bridge cables. The length of each had been regulated by previous calculations, so that when the storm cable became suspended by them it would hang in the form of a parabola.

When all the suspenders were properly connected the cable was lowered overboard by means of blocks and falls at numerous points until it was hung on the suspenders. The two ends were then pulled

in to each tower, and sockets placed upon them. Each was secured to one of the main posts of the tower and screwed up to the proper tension by means of long U-bolts. A view of the main span, with the storm cables and guys in place, is shown in Plate XXXVI, Fig. 2. The footbridge was secured additionally by means of long guy ropes which ran from the main span down to the towers.

Plate XXXVII, Fig. 2, is a view of the completed footbridge as seen from Brooklyn, just back of the anchorage. When the structure was completed, observations were made to determine how near the bridge came to occupying the position for which it was finally intended. The result of the observations showed it to be within a very few inches of the calculated position, which was a great source of gratification to the engineers in charge, as it proved the correctness of the assumptions, the exactness of the intricate calculations involved, and the accuracy of the instrument work.

When the last wire in each main cable had been laid and the last strand adjusted, the usefulness of the upper deck of the footbridge was at an end. The whole of the upper deck work was then removed, the flooring being transferred to the lower deck and the other timber work being kept on the span, so as not to change the loading and consequently the position of the bridge. The upper cables were tied to the lower ones by long U-bolts, so as to make each carry a proportion of the load.

The work of putting on the cable bands and cable covering, and hanging the suspenders, can now be completed from the lower deck of the bridge.

The expectations of what the footbridge would accomplish have not been over-estimated, for it has permitted a saving of much time made the work safer, and afforded a means of building the cables as nearly perfect as it is within human possibility to do. The erection of such a bridge may be usually considered a very hazardous occupation, but in this case not a single accident occurred.

Reference to cable making, except in explanation of the functions of the footbridge, has been purposely omitted in this paper, as that is a subject in itself.

AMERICAN SOCIETY OF CIVIL ENGINEERS.

INSTITUTED 1852.

PAPERS AND DISCUSSIONS.

This Society is not responsible, as a body, for the facts and opinions advanced in any of its publications.

A PROPOSED NEW TYPE OF MASONRY DAM.

Discussion.*

By Messrs. GEORGE H. PEGRAM, J. BREUCHAUD and A. V. ABBOTT.

GEORGE H. PEGRAM, M. Am. Soc. C. E.-The form of dam pro- Mr. Pegram. posed by the author aims at a saving of masonry, but its main advantage seems to be in the marked increase in overturning resistance shown in his table of comparisons with the Wegmann forms. It also has the advantage claimed by the author of greater stability against the upward pressure of water leaking under the dam.

The type proposed seems susceptible of very neat calculations, but this is not an important consideration in dams of magnitude.

The Pioneer Electric Power Company, of Ogden, Utah, of which the speaker was Consulting Engineer, studied the question of a 100-ft. dam for the Ogden River, and some of the results are given in a paper by Henry Goldmark, M. Am. Soc. C. E.†

At the time the speaker's attention was called to the matter, the company had prepared designs for the ordinary gravity section and also for a steel dam with a vertical face, and it was suggested that in any dam where the weight of masonry is reduced the up-stream face should be inclined so as to use the weight of the water, and it is thought that this suggestion might apply to the form submitted by the author of the paper under discussion.

In the case of the Ogden Dam the walls of the cañon are so pre

*Continued from August, 1902, Proceedings. See April, 1902, Proceedings, for paper on this subject by George L. Dillman, M. Am. Soc. C. E.

+ Transactions, Am. Soc. C. E., Vol. xxxviii, pp. 290 and 302.

Mr. Pegram. cipitous that a diversion of the river seemed a serious question, and the location of a city at the mouth of the cañon made it especially desirable to design a dam which would be as absolutely safe as due considerations of cost would permit. The speaker suggested that a form be tried having isolated piers connected by arches with impervious faces, a form of which is given in Mr. Goldmark's paper; the objects to be accomplished being:

Mr. Breuchaud.

Mr. Abbott.

1. The construction of piers independently, thus avoiding the necessity of a diversion of the river;

2. The securing of an impervious face to the dam;

3.-The avoidance of uplifting pressure by water that might leak under the dam;

4. The ability to get a better class of masonry by building it in smaller masses than in the ordinary dam;

5.-Less total cost.

Cracks in concrete are apt to be long, and hard to stop, and therefore the necessity of a steel plate on the up-stream face. Large steel plates, at the time, could have been bought at a trifle more than one cent per pound, and the speaker proposed a design having isolated piers of triangular form with an up-stream slope of 30°, 11 ft. thick, and spaced 23 ft. in the clear, the up-stream face being a continuous steel plate corrugated with radii of 7 ft. over the piers' ends and 14 ft. between the piers, the up-stream toe to be enclosed in a wall of concrete, 15 ft. thick and 25 ft. high, enclosing horizontal angle-irons riveted to the steel plate to assist by its weight in resisting the overturning effect.

J. BREUCHAUD, M. Am. Soc. C. E.-It is somewhat difficult to give an off-hand estimate of the cost of the masonry in the author's dam as compared with that in a dam of the ordinary section; but the speaker believes the cost would be greater, because it would require a high grade of work, with deep, close-cut beds and joints, to ensure anything like a reasonable degree of water-tightness in such a thin wall as that proposed.

A. V. ABBOTT, M. Am. Soc. C. E.-The speaker has had little experience in the actual construction of masonry dams, but has had considerable in the endeavor to construct masonry in such a manner as to make it completely water-tight; and so it appears to him that the points made by Mr. Pegram are exceedingly well taken.

There are two aspects of engineering: One, the theoretical point of view, and the other, the adaptation of the design indicated by theory to practical conditions. There appears to be little doubt that a dam or other structure intended to enclose water could be designed with a more economical section, upon the principles developed in this paper and discussion, than according to the ordinary methods. Doubtless there would be a considerable saving in the

actual quantity of masonry; but when the problem is presented of Mr. Abbott. making water-tight a structure so thin as would be called for if the principles of this paper were followed out, a very difficult problem is introduced, and one for the solution of which quantity of masonry rather than strength of construction is required. It also seems that the subdivision of a dam into a number of buttresses, as is demanded by the plan proposed in the paper, is likely to introduce such a complication of stresses as will make accurate determination thereof, even theoretically, an exceedingly difficult problem, and one which is entirely incapable of solution under ordinary practical conditions.