16
THE MEMPHIS BRIDGE.
Material.
Labor.
Total.
Total.
Caisson.
$8 594.47
6 414.61811.17
$5 523.072479.16596.80
$14 117.54
8 893.77
1 407.97
$24 419.28
8 645.64
Concrete above chamber.... . .
Concrete in chamber.
Cost, excluding sinking, etc...
$15 820.25
$8 599.03
$24 419.28
Sinking.
Insurance.
$2 310.8795.25
$6 239.52
$8 550.3995.25
Sinking, etc.
$2 406.12
$6 239.52
$8 645.64
Total Foundation ..... $33 064.93
Cylinders. 7 323.77
Total cost of Piek . $40 388.69
The total volume of the foundation is 22 feet by 40 feet by 80 feet,equal to 70 400 cubic feet; so that the cost of the foundation, not includ-ing sinking, etc., was $0,347 per cubic foot, and the cost, including every-thing, $0,470 per cubic foot.
GENERAL.
The total cost of the Substructure of the Memphis Bridge was asfollows:
East Abutment..
Pier A.
Pier B.
Anchorage Pier.,
Pier I.
“ II.
“Ill.
“IV..
“ V.
$11 872.87485.32600.5836 267.79141 035.94309 617.43309 351,92119 367.0140 388.69
Total.$968 987.55
The four large piers (I to IY) are really the only portion of the Sub-structure which are of special interest, and it is desirable to compare thequantities and cost of these piers. The total quantities in the severalpiers are as follows:
Piers.
Timber,
Ft. B.M.
Iron,
Pounds.
Concrete,Cubic Yards.
Limestone
Masonry,
Cu. Yds.
Granite
Masonry,
Cu. Yds.
I.
336 768
187 206
3 079
1 292
1 403
11.
1 560 492
450 187
3 379
2 459
1 738
Ill.
1 085 496
366 967
2 379
2 868
2 002
IV..
266 472
145 147
2 065
1 157
1 604
Total.
3 249 228
1 149 507
10 902
7 776
6 747
The total volume and cost of the several piers are given in the fol-lowing table:
Material.
Pier I.
Pier II.
Pier III.
Pier IV.
Total.
Timber, cubic feet.
28 064
130 041
90 458
22 206
270 769
Concrete, “ “ .
83 139
91 237
64 223
55 751
294 350
Masonry, “ “ .
72 767
113 312
131 492
74 561
392 132
Voids, “ “ .
444
48 145
30 518
714
79 821
Total.
184 414
382 735
316 691
153 232
1 037 072
Cost..
$141 035.94
$309 617.43
$309 351.92
$119 367.01
$879 372.30
Cost per cubic foot.
$0,765
$0,809
$0,977
$0,779
$0,848
This table does not take into account concrete below cutting edgeor clay left in chamber above cutting edge of the several caissons.
This includes the entire cost of everything except the equipment.The original cost of the equipment was kept in a separate account called“ Tools and Machinery,” but the repairs were charged to the several foun-dations on which the equipment was being used at the time those repairswere made. The Tools and Machinery account was subsequently cred-ited with the amounts received from the sale of the plant. The balanceremaining charged to equipment was $30 865.54, of which $23 341.80belongs to the Substructure of these piers, amounting to $0.0225 percubic foot for all the piers. If this is included, the total cost per cubicfoot of all the piers would be as follows:
Pier I.
Pier II.
Pier III.
Pier IV.
Total.
Total cubic feet..
184 414$145 186.62$0,787
382 735$318 231.80$0,832
316 691$316 479.81$0,999
153 232$122 815.87$0,801
1 037 072$902 714.10$0,871
Cost.
Cost per cubic foot.
IV .
SUPERSTRUCTURE.
The Superstructure may be divided into two parts : the ContinuousSuperstructure, which reaches from the East Abutment across the riverto Pier IY, and the deck span, between Pier IY and Pier Y. The Con-tinuous Superstructure covers the whole length of the bridge whichaffects navigation and so came under the requirements of the generalcharter and the findings of the Secretary of War. The deck span is en-tirely west of what was the shore line at the time of my visit to Memphis,
in January, 1886, and of the restored shore line as it will exist when thewest rectification works have had their full effect.
CONTINUOUS SUPERSTRUCTURE*
The plans which were submitted to and approved by the Secretaryof War provided for a channel span 770 ft. long in the clear and twospans 600 ft. each in the clear, these three spans crossing the entire navi-gable river, the long span being next to the Tennessee shore. Adding toeach span the estimated thickness of the piers at low water, the designcalled for one span 790 ft. and two of 620 ft. each, measured betweencentres of piers.
The arrangement which would have been most satisfactory to theengineer would have been three equal spans of about 675 ft. each. If,however, one span of extra length was required, it would have been pref-erable to place it at the centre, making this central span a cantilever struc-ture, the cantilevers projecting from the ends of two heavy side spans.The arrangement required by the War Department, however, placed thelong span next to the east shore, so that if this span was built as a canti-lever span it was necessary to provide an independent anchorage on theMemphis bluff. This course was adopted.
The length fixed for the channel span was 790 ft., or 170 ft. morethan either of the other spans. By projecting a cantilever 170 ft. longfrom Pier I (on the Tennessee shore), the distance between the end ofthis cantilever and Pier IY (on the Arkansas shore) was divided by thetwo other piers into three equal spaces of 620 ft. each. By making thecentral span a fixed span with continuous chords and projecting a canti-lever 170 ft. long from each end of this fixed span, there remained twospaces, each 450 ft. long, to complete the bridge, one of these being be-tween two cantilevers and the other between a cantilever and Pier IV.With this arrangement the bridge would consist of a central span 620 ft.long, of three 170 ft. cantilevers precisely alike, of two 450 ft. spans alsoalike, besides the anchorage span east of Pier I.
In order to simplify construction it was desirable to make the panelsof uniform length throughout, and this required that the panel lengthsshould be common divisors of the lengths of the cantilevers, of the sus-pended spans and of the central span. No such common divisors existedfor 170 ft. and 450 ft.; but by shortening the length of the cantilevers to169 ft. 4£ in. and increasing the length of the suspended span to 451 ft. 8
* This account of the Continuous Superstructure is reprinted, with some very slight changes,from the Transactions of the American Society of Civil Engineers, September, 1893.