Blacksmith Work-- 1 laborer at $2 $0.0086 1 blacksmith at $3.25 0.0141 1 waterboy at $0.75 0.0032 ------- Total per cubic yard $0.4473 Add 75% of cost of administration 0.1388 ------- Total labor per cu. yd. $0.5861
The total cost of each cubic yard of concrete in place was estimated to be as follows:
Per cu. yd.
Ten-elevenths cu. yd. pebbles at $1.085 $0.9864 Ten-twenty seconds cu. yd. sand at $0.00 0.0000 1 26 bbls. cement at $1.77 2.2302 Labor as above given 0.5861 Cost of plant distributed over total yardage 0.8400 ------- Total $4.6427
It will be noted that the sand cost nothing as it was dredged from the trench in which the pier was built, and paid for as dredging. The cost of the plant is distributed over this south pier and over the proposed north pier work on the basis of only 20 per cent. salvage value after the completion of both piers. It is said, however, that 80 per cent. is too high an allowance for the probable depreciation.
~DAM, RICHMOND, INDIANA.~--The dam shown in cross-section in Fig. 89 was built at Richmond, Ind. It was 120 ft. long and was built between the abutments of a dismantled bridge. The concrete was made in the proportion of 1 bbl. Portland cement to 1 cu. yd. of gravel; old iron was used for reinforcement. The foundations were put down by means of a cofferdam which was kept dry by pumping. On completion it was found that there was a tendency to scour in front of the ap.r.o.n and accordingly piling was driven and the intervening s.p.a.ce rip-rapped with large stone. Labor was paid as follows per day: Foreman, $3; carpenter, $2.50; cement finisher, $2; laborers, $1.50. The concrete was mixed by hand and wheeled to place in wheelbarrows. The cost of the work was as follows:
Materials-- Per cu. yd.
204 bbls. cement at $1.60 $1.485 Sand and gravel 0.800 Lumber 0.610 Tools, hardware, etc. 0.445 ------ Total materials $3.34
Labor-- Clearing and excavating $0.96 Setting forms and mixing concrete 1.01 Pumping 0.27 ----- Total labor $2.24 Total materials and labor $5.58
[Ill.u.s.tration: Fig. 89.--Concrete Dam at Richmond, Ind.]
~DAM AT ROCK ISLAND a.r.s.eNAL, ILLINOIS.~--The dam was in the shape of an L with one side 192 ft. and the other side 208 ft. long; it consists of a wall 30 ft. high, 3 ft. wide at the top and 6 ft. wide at the bottom with a counterfort every 16 ft., 26 in all. Each counterfort extended back 16 ft. and was 4 ft. thick for a height of 6 ft. and then 3 ft.
thick. There were 3,500 cu. yds. of concrete in the work, which was done by day labor under the direction of the U. S. Engineer in charge.
The forms consisted of front and back uprights of 810-in. stuff 24 ft.
high, connected through the wall by -in. rods which were left in the concrete. The lagging was 212-in. plank dressed down 1 ins. placed inside the uprights. These forms were built full height in 16-ft.
sections with a counterfort coming at the center of each section. Each section contained 95 cu. yds. of concrete and was filled in a day"s work. The concrete was a 1-4-7 mixture wet enough to quake when rammed.
Run of crusher limestone was used of which 50 per cent. pa.s.sed a 1-in.
sieve, 17 per cent. a No. 3 sieve and 9 per cent. a No. 8 sieve. The concrete was mixed in c.o.c.kburn Barrow & Machine Co."s screw-feed mixer which discharged into 2-in. plank skips 2 ft. wide 5-1/3 ft. long and 14 ins. deep, holding cu. yd. These skips were taken on cars to a derrick crane overhanging the forms and by it hoisted and dumped into the forms.
The derrick was moved along a track at the foot of the wall as the work progressed. The concrete was spread and rammed in 6-in. layers. The men were paid $1.50 per 8-hour"s work and the work cost including footing, as follows:
Item-- Total. Per cu. yd.
Cement $1,500.00 $0.429 Sand 400.00 0.114 Storing and hauling cement 460.00 0.131 Taking sand from barge to mixer 96.00 0.027 Crushing stone 1,450.00 0.414 Mixing concrete 4,825.00 1.378 Placing concrete 1,670.00 0.477 Lumber for forms, etc. 600.00 0.171 Erecting and taking down forms 2,450.00 0.700 ---------- ------ Totals $13,451.00 $3.841
~DAM AT McCALL FERRY, PA.~--The dam was 2,700 ft. long and 48 ft. high of the cross-section shown by Fig. 90 and with its subsidiary works required some 350,000 cu. yds. of concrete. The plant for mixing and placing the concrete was notable chiefly for its size and cost. Parallel to the dam, which extended straight across the river, and just below its toe a service bridge consisting of a series of 40-ft. concrete arch spans was built across the river. This service bridge was 50 ft. wide and carried four standard gage railway tracks besides a traveling crane track of 44 ft. gage. This very heavy construction of a temporary structure was necessitated by the frequency of floods against which only a solid bridge could stand; it was considered cheaper in the long run to provide a bridge which would certainly last through the work than to chance a structure of less cost which would certainly go out with the floods. The concrete service bridge was designed to be destroyed by blasting when the dam had been completed. The method of construction was to build the dam in alternate 40 ft. sections, mixing the concrete on sh.o.r.e, taking it out along the service bridge in buckets on cars and handling the buckets from cars to forms by traveling cranes.
[Ill.u.s.tration: Fig. 90.--Steel Forms for McCall Ferry Dam.]
The concrete mixing plant is shown by Fig. 91. Cars loaded with cement, sand and stone were brought in over the tracks carried on the wall tops of the bins and were unloaded respectively into bins A, B and C, of which there were eight sets. Each set supplied material by means of measuring cars to a 1 cu. yd. Smith mixer. Two sets of cars were used for each mixer so that one could be loading while the other was charging. The mixers discharged into 1 cu. yd. buckets set two on a car and eight cars were hauled to the work in train by an 18-ton "d.i.n.ky." At the work the buckets were picked up by the traveling cranes and the concrete dumped into the forms. Figure 90 shows the construction of the steel forms. Six sets of forms were used. Each set consisted of five frames s.p.a.ced 10 ft. apart and braced together in the planes parallel to the dam, and each set molded 40 ft. of dam. The lagging consisted of wooden boxes 8 ft. wide and 10 ft. long. For the vertical face of the dam these boxes were attached by bolts to the vertical post, for the curved face they were bolted to a channel bent to the curve and held by struts from the inclined post of the steel frame.
[Ill.u.s.tration: Fig. 91.--Concrete Mixing Plant for McCall Ferry Dam.]
In construction the footing and the body of the dam to an elevation of 5 ft. above the beginning of the curve were built continuously across the river; above this elevation the dam was built in alternate 40-ft.
sections. The strut back to the service bridge shown in the lower right hand corner of Fig. 90, shows the manner of bracing the first 30-ft.
section of the inclined post to hold the lagging for the continuous portion. The lagging was added a piece at a time as concreting progressed. The ends of each set of frames for a 40-ft. section were for the isolated sections closed by timber bulkheads carrying box forms to mold grooves into which the concrete of the intermediate sections would bond.
[Ill.u.s.tration: Fig. 92.--Traveler for Concreting Dam, Chaudiere Falls, Quebec.]
The concrete used was a 1-3-5 mixture, the stone ranging in size from 2 to 5 ins. Rubble stone from one man size to ton were bedded in the concrete. The capacity of the concrete plant was 2,000 cu. yds. per day or about 250 cu. yds. per mixer per 10-hour day.
~DAM, CHAUDIERE FALLS, QUEBEC.~--The dam was 800 ft. long and from 16 to 20 ft. high, constructed of 1-2-4 concrete with rubble stone embedded.
The rubble stones were separated at least 9 ins. horizontally and 12 ins. vertically and were kept 20 ins. from faces. At one point the rubble amounted to 40 per cent. of the volume, but the average for the dam was 25 to 30 per cent. The stone was broken at the work, some by hand, but most by machine, all to pa.s.s a 2-in. ring. Hand-broken stone ran very uniform in size and high in voids, often up to 50 per cent.
Stone broken by crusher with jaws 2 ins. apart would run 20 to 30 per cent. over 2 ins. in size and give about 45 per cent. voids; with crusher jaws 1 ins. apart from 98 to 100 per cent. was under 2 ins. in size and contained about 42 per cent. of voids. It was found that if the crushers were kept full all the time the product was much smaller, particularly with Gates gyratory crusher, though a little more than rated power was required when the crusher was thus kept full. This practice secured increased economy in both quant.i.ty and quality of product. The concrete was made and placed by means of a movable traveler shown by Fig. 92. Concrete materials were supplied to the charging platform of the traveler by means of a traveling derrick moving on a parallel track. In placing the concrete on the rock bottom it was found necessary in order to secure good bond to scrub the rock with water and brooms and cover it with a bed of 2 ins. of 1-2 mortar. The method of concreting in freezing weather is described in Chapter VII.
CHAPTER XII.
METHODS AND COST OF CONSTRUCTING BRIDGE PIERS AND ABUTMENTS.
The construction of piers and abutments for bridges is best explained by describing individual examples of such work. So far, in America, bridge piers have been nearly always of plain concrete and of form and section differing little from masonry piers; where reinforcement has been used at all it has consisted of a surface network of bars introduced chiefly to ensure monolithic action of the pier under lateral stresses. In Europe cellular piers of reinforced concrete have been much used. Plain concrete abutments differ little in form and volume from masonry abutments. Reinforced concrete abutments are usually of L-section with counterforts bracing the upright slab and bridge seat to the base slab.
Form work for reinforced abutments is somewhat complex; that for plain abutments and piers is of simple character, the only variations from plain stud and sheathing construction being in the forms for moldings and coping and for cut-waters. For piers of moderate height the form is commonly framed complete for the whole pier, but for high piers it is built up as the work progresses by removing the bottom boards and placing them at the top. Opposite forms are held together by wire ties through the concrete. Movable panel forms have been successfully employed, but they rarely cheapen the cost much. Sectional forms, which can be shifted from pier to pier where a number of piers of identical size are to be built, may frequently be used to advantage. An example of such use is given in this chapter.
Derricks are the recognized appliances for hoisting and placing the concrete in pier work; they are the only practicable appliance where the pier is high and particularly where it stands in water and mixing barges are employed. For abutment work and land piers of moderate height derricks and wheelbarrow or cart inclines are both available and where much shifting of the derricks is involved the apparently more crude method compares favorably in cost.
The methods of placing concrete under water for pier foundations are described in Chapter V, and the use of rubble concrete for pier construction is ill.u.s.trated by several examples in Chapter VI. The following examples of pier and abutment construction cover both large and small work and give a clear idea of current practice.
[Ill.u.s.tration: Fig. 93.--Pier and Cofferdam for a Railway Bridge.]
~COST OF CONSTRUCTING RECTANGULAR PIER FOR A RAILWAY BRIDGE.~--This pier, Fig. 93, was built in water averaging 5 ft. deep. The cofferdam consisted of triple-lap sheet piling, of the Wakefield pattern, the planks being 2 ins. thick, and spiked together so as to give a cofferdam wall 6 ins thick. The cofferdam enclosed an area 1420 ft., giving a clearance of 1 ft. all around the base of the concrete pier, and a clearance of 2 ft. between the cofferdam and the outer edge of the nearest pile. The cofferdam sheet piles were 18 ft. long, driven 11 ft.
deep into sand, and projecting 2 ft. above the surface of the water.
The concrete base resting on the foundation piles was 1218 ft. The concrete pier resting on this base was 713 ft. at the bottom, and 511 ft. at the top. The pier supported deck plate girders. There were 100 cu. yds. of concrete in the pier and base.
The cost of this pier, which is typical of a large cla.s.s of concrete pier work, has been obtained in such detail that we a.n.a.lyze it in detail, giving the costs of cofferdam construction and excavation as well as of mixing and placing the concrete.
Setting up and taking down derrick and platform:
4 days foreman at $5.00 $ 20.00 days engineman at $3.00 2.25 days blacksmith at $3.00 2.25 days blacksmith helper at $2.00 1.50 22 days laborers at $2.00 44.00 ------- Total $ 70.00
Cofferdam-- 7 days foreman at $5.00 $ 35.00 4 days engineman at $3.00 12.00 38 days laborers at $2.00 76.00 1 ton coal at $3.00 3.00 ------- Total labor on 7,900 ft. B. M. at $16.00 $126.00 7,900 ft. B. M. at $20.00 158.00 ------- Total for 58 cu. yds. excavation $284.00
Wet Excavation-- 1.8 days foreman at $5.00 $ 9.00 1.5 days engineman at $3.00 4.50 9 days laborers at $2.00 18.00 ton coal at $3.00 1.50 ------- Total labor on 58 cu. yds. at 57c. $ 33.00
Foundation Piles-- 960 lin. ft. at 10c $ 96.00 4 days setting up driver and driving 24 piles at $20 per day for labor and fuel 80.00 ------- Total $176.00
Concrete-- 100 cu yds. stone at $1.00 $100.00 40 cu. yds. sand at $0.50 20.00 100 bbls. cement at $2.00 200.00 5 days foreman at $5.00 25.00 50 days laborers at $2.00 100.00 5 days engineman at $3.00 15.00 2 tons coal at $3.00 6.00 ------- Total, 100 cu. yds. at $4.66 $466.00
8 days carpenters at $3.00 24.00 2,400 ft. B. M. 2-in. plank at $25.00 60.00 1,000 ft. B. M. 46-in. studs at $20.00 20.00 Nails, wire, etc 2.00 ------- Total forms for 100 cu. yds. at $1.06 $106.00
Summary-- Setting up derrick, etc. $ 70.00 Cofferdam (7,900 ft. B. M.) 284.00 Wet excavation (58 cu. yds.) 33.00 Foundation piles (24) 176.00 Concrete (100 cu. yds.) 466.00 Forms (3,400 ft. B. M.) 106.00 --------- Total $1,135.00 Transporting plant 20.00 20 days rental of plant at $5.00 100.00 --------- Total cost of pier $1,252.00
Regarding the item of plant rental, it should be said that the plant consisted of a pile driver, a derrick, a hoisting engine, and sundry timbers for platforms. There was no concrete mixer. Hence an allowance $5 per day for use of plant is sufficient.
It will be noted that no salvage has been allowed on the lumber for forms. As a matter of fact, all this lumber was recovered, and was used again in similar work.
Referring to the cost of cofferdam work, we see that, in order to excavate the 58 cu. yds. inside the cofferdam, it was necessary to spend $284, or nearly $5 per cu. yd. before the actual excavation was begun.
The work of excavating cost only 57 cts. per cu. yd., but this does not include the cost of erecting the derrick which was used in raising the loaded buckets of earth, as well as in subsequently placing the concrete. The sheet piles were not pulled, in this instance, but a contractor who understands the art of pile pulling would certainly not leave the piles in the ground. A hand pump served to keep the cofferdam dry enough for excavating; but in more open material a power pump is usually required.
The above costs are the actual costs, and do not include the contractor"s profits. His bid on the work was as follows: