26

THE MEMPHIS BRIDGE.

any flow of water between the piers. The hexagonal concrete block wasmade of Louisville cement concrete; Portland cement was used everywhere else in the small piers.

Piers 44, 45 and 46 are also shown on Plate 57. They have pilefoundations, the piles being enclosed in a block eight feet high of Louis-ville cement concrete surmounted by eight feet of Portland cement con-crete, above which they are built of limestone masonry. The limestoneused in these piers is from southwestern Missouri; it is an inferiorstone having bad crowfoot seams, but it was thought that in this posi-tion, where it was away from the river, it would prove durable. Arecent examination shows that this confidence was misplaced; the stonealready is weathering badly, and it would have been much wiser to haveused Bedford stone, the cost of which would have been less.

The details of the ironwork are given on Plate 58. They requirebut little explanation. All the bracing of the towers was made stiff andwithout adjustment, but the diagonals were calculated as tension mem-bers.

The spans are not divided over the center of the posts but in suchposition that the aggregate weight of the long and shoi't spans shall comeover the axis of each post. Provision for expansion and contraction ismade at the upper (eastern) end of each long girder. The viaduct is ofiron, though soft steel is used in the wide web plates of the girders andin some other unimportant places.

A contract for this material was let to the Pennsylvania Steel Com-pany, but the greater part of the work was manufactured at the shops ofCofrode & Saylor at Pottstown, Pa.

The longer spans of plate girders were made by A. & P. Roberts &Co. of Pencoyd, Pa. They are shown on Plate 59.

The floor system is of the form usually used by the Chief Engineeron permanent structures. It is also shown on Plate 59.

At the east end of the viaduct a plate girder span 60 feet longreaches from the first long span to a timber trestle which forms the high-way approach. This span is shown on Plate 60.

The quantities of the various kinds of material in the viaduct aregiven in the following tables: > ■

i • /■

SUBSTRUCTURE.

Piles, ip work...,...lines) feet 24 040

Concrete in foundations.cubic yards 1 837

" " cylinder Piers 6-27. <> «< j4g

Steel in cylinder shells, Piers 6-11...pounds 34 Q&8

Wrought iron in cylinder shells, Piers 12-27.pounds 48 663

Cast iron in caps..... f ‘ 122 860

Wrought iron in U rods.. “ 31 789

Brick masonry .cubic yards 665

Stone masonry in Piers 44, 45 and 46. “ “ 668

SUPERSTRUCTURE.

Iron and soft steel in towers...pounds 1 482 273

Steel in girders, Pier V-6.. “ 47175

Iron and soft steel in girders on towers. . “ 1 595 262

“ “ “ “ “ “ “ Piers 44, 45 and 46. “ 179 549

Cast iron pedestals and anchor bolts on Piers 44, 45 and 46.. “ 12 023

Total.,. “ 3 816 282

The average amount of metal in the superstructure per lineal foot ofviaduct from Pier Y to the end of the ironwork is 1 448 pounds. If thespecial girders over the St. Louis, Iron Mountain &> Southern and KansasCity, Fort Scott & Memphis Railways be omitted, and also the half spanson either side of these girders and the half spans next to Pier Y, theaverage amount of metal per lineal foot becomes 1 509 pounds.

The first work done on the foundations of the viaducts was on the28th of June, 1890. The small piers were all finished on the 19th ofAugust, 1891. The larger piers (44, 45 and 46) were finished Septem-ber 5, 1891. The earth embankment around these piers was finishedDecember 21, 1891. The ironwork was erected by the company’s ownmen. A traveler which ran on a track placed on the ground was set upat the west end of the viaduct and everything was handled with thistraveler, an illustration of which taken from a photograph is given on theaccompanying plate. The erection of this viaduct was completed on the7th of May, 1892.

The total cost of the viaduct was as follows:

Substructure.

Excavating and Backfilling.

$ 2 740.85

Pile work .

11 351.13

Concrete in Foundations.

12 799.09

Iron work. .......

7 848,90

Brick Masonry, r.

11 448.94

Concrete in Cylinders.

1 356.70

Masonry Piers 44, 45 and 46.

11 427.66

$ 58 974.27

Superstructure.

Iron and Steel...

$112 155.55

Erection....

16 657.63

Painting.-.'..

3 424.81

Floor .

10 793.90

$143 031.89

Total Cost of Viaduct. ..

l

$202 006.16

The average cost of each of the two small piers under one bent ofthe viaduct was $432.57 and that of the masonry piers 44, 45 and 46was $6 392.57.

The cost of viaduct complete, including painting and floor, was$88.19 per lineal foot of gross length. The cost of the floor was $4.71per lineal foot and that of painting $1.50, or $2.07 per ton.

Omitting again the special structures as before the cost per foot ofviaduct, including floor and painting, becomes $84.18.

VI.

APPROACHES. r

The East Approach calls for no special description. It is simply aline of railroad built within the limits of the city, the only structure onwhich is a double track plate girder bridge across Delaware Avenue.Delaware Avenue was depressed to pass under this bridge and aneight inch vitrified sewer pipe laid eastward from the lowest point in thedepression, the street under the bridge being paved with brick; at somefuture date it will probably be expedient to turn this drainage towardsthe river; until this is done special care will be required to keep thedrainage pipe clean.

From the west end of the viaduct to station 181 + 06 the West Ap-proach is built in the form of a timber trestle. Of this 2507 feet are aframed structure on pile foundations and the remaining 605 feet a simplepile trestle. Special care was taken in the selection of the timber forthis trestle. The piles are of oak and the timber is all of long leafsouthern pine. The position, however, is one in which timber decaysrapidly, and the whole trestle ought to be replaced by a solid earth em-bankment before the end of 1898. This will require 310 000 cubic yards,or, if the filling should begin with the year 1894, an average of 62 000cubic yards per year, the estimated cost of which would be $20 000a year, the haul being very long.

From the end of this trestle to the west end of the Approach thetrack is laid on a solid earth embankment, excepting that there is a piletrestle 300 feet long between stations 213 and 217. This trestle willprobably have to be kept open.