Superintendent, 2 days at $5.83-1/3 _Concrete Construction: Methods and Costs

Foreman, 2 days at $4.50 9.00 0.014

Carpenter foreman, 10 days at $5 50.00 0.080

Carpenter, 13 days at $3.20 41.60 0.067

Labor, 49 days at $3.04 148.96 0.241

Labor, 19 days at $2.56 48.64 0.078

------- ------

Total $309.87 $0.498

Summarizing we have the following cost:

Materials--

Cement, 5.6 bags at $0.62 $3.472

Gravel (excavating and screening) 0.421

Hauling gravel and sand 0.223

------

Total, materials $4.116

Labor--

Mixing concrete $0.819

Transporting concrete 0.326

Depositing concrete 1.394

Setting and moving forms 0.498

------

Total, labor $3.037

Grand total $7.153

~COST OF CONCRETE WORK IN LINING NEW YORK RAPID TRANSIT SUBWAY.~--The

costs given here refer alone to the concrete work in constructing the

jack arch and steel beam lining of the original standard subway. Figure

143 shows the character of this construction. Arch panel forms were set

up between the wall beams and hung from the floor beams and filled

behind and above with 1-2-4 trap rock concrete. The form panels were

used over and over and the concrete was machine mixed. Common labor was

paid $1.50 per 8-hour day; foremen, $3; carpenters, $3; enginemen,

$3.50; and masons, $4. The costs cover three sections and are in each

case the averages for the whole section. They are, we believe, the only

itemized costs that have been published for concrete work on this road.

[Illustration: Fig. 143.--Cross-Section of New York Rapid Transit

Subway.]

_Two-Track Subway._--In this section of two-track subway there were

8,827 cu. yds. of foundation concrete and 6,664 cu. yds. of concrete in

wall and roof arches. The two classes of work cost as follows:

Foundations-- Total. Per cu. yd.

Labor mixing $ 4,669 $0.53

Labor placing 5,142 0.58

Materials and plant 211 0.02

Cement, sand, stone, etc. 30,719 3.48

-------- -------

Total $40,741 $4.61

Roof and side walls--

Labor mixing $ 5,444 $0.82

Labor placing 5,623 0.84

Labor setting forms 14,746 2.21

Labor plastering arches 431 0.06

Materials and plant 1,176 0.18

Cement, sand, stone, etc. 23,888 3.58

-------- ------

Total $51,308 $7.69

Averaging the work we have 15,491 cu. yds. of concrete placed at a cost

of $5.94 per cu. yd.

_Four-Track Subway._--On two sections of four-track subway the labor

cost of mixing and placing concrete similarly divided was as follows:

Section A. Section B.

Foundations-- Per cu. yd. Per cu. yd.

Labor mixing $0.97 $0.94

Labor placing 0.96 0.95

Power 0.14 0.16

-------- --------

Total $2.07 $2.05

Roof and side walls--

Labor mixing $0.79 $0.91

Labor placing 0.85 0.94

Labor setting forms 2.01 1.20

Labor plastering arches 0.16 0.23

Power 0.28 0.15

------- -------

Total $4.09 $3.43

[Illustration: Fig. 144.--Traveling Form for Side Walls, New York Subway

Tunnels.]

~TRAVELING FORMS FOR LINING NEW YORK RAPID TRANSIT RY. TUNNELS.~--In

constructing the tunnels under Park Ave. and under the north end of

Central Park for the New York Rapid Transit Ry., traveling centers and

side wall forms were used for the concrete lining. The mixing plants

were installed in the shafts and consisted generally of gravity mixers

charged at the surface and discharging into skip cars running on the

tunnel floor.

[Illustration: Fig. 145.--Traveling Form for Roof Arch. New York Subway

Tunnels.]

The forms used in the Park Ave. tunnel are shown by Figs. 144 and 145;

those used in the Central Park tunnel differed only in details. The

method of work was slightly different in the two tunnels, but was

substantially as follows: Three platforms mounted on wheels were used in

each set and two sets were employed. Ahead came a traveler carrying the

side wall forms, next came a shorter traveler carrying a derrick, and

last came the traveler carrying the roof centers. The arrangement

as operated in the Central Park tunnel is shown by Fig. 146. In the Park

Ave. tunnel the "bridges" were dispensed with, the skips being hoisted

through the open end bays of the derrick car and set directly on the

cars on the center traveler.

[Illustration: Fig. 146.--Sketch Plan of Traveling Forms, New York

Subway Tunnels.]

The traveler carrying the side wall forms was set in position and

blocked, the grade and line being given by the track rails, which had

been set exactly for that purpose. The side wall forms differed slightly

in the two tunnels; those for the Park Ave. tunnel shown by Fig. 144

formed the vertical portion of the wall only so that when the arch

forms, Fig. 145, followed a space A B was left which had to be molded

by separate sector-like forms. The side wall forms for the Central Park

work were constructed as shown by Fig. 147, being curved at the top to

merge into the arch centers. In the Park Ave. work the wall studs were

adjusted in or out by means of wedges and slotted bolt holes. In the

Central Park work the studs A Fig. 145 were hung by ¾-in. bolts from

the pieces B spiked to line onto the cross-braces. The bottom was then

lined up by means of wedges at D. The side wall studs being lined up,

the bottom lagging boards were placed and filled behind by shoveling the

concrete into them direct from skip cars on the adjacent tracks on the

tunnel floor. In this way the side walls were built up to the tops of

the forms.

[Illustration: Fig. 147.--Sketch Showing Detail of Side Wall Forms. New

York Subway Tunnels.]

As soon as the side wall concrete had set the forms were struck and the

traveler was moved ahead and set for another section of wall. The

derrick and roof arch travelers were then moved into position between

the finished walls, and the arch traveler was jacked up and aligned.

Skip cars coming from the mixer were run under the derrick traveler,

where the skips were lifted by the derrick and set on the platform cars

to be run alongside the work. The arch lagging was placed a piece at a

time and filled behind by shoveling direct from the skips. As the crown

was approached the lagging was placed in short lengths and filled in

over the ends, the concrete being shoveled in two lifts; in Fig. 145 the

line C D indicates the position of the shoveling board. The centers

were struck by lowering the jack supported traveler down onto the track

rails.

~COST OF MIXING AND PLACING SUBWAY LINING, LONG ISLAND R. R., BROOKLYN,

N. Y.~--The subway carrying the two tracks of the Long Island R. R. under

Atlantic Ave., in Brooklyn, New York city, has a lining consisting of an

invert arch 12 ins. thick at the center, side walls 4½ ft. thick at

the base and 3 ft. thick at the top, and a roof of jack arches between

steel I-beams 5 ft. apart. The dimensions inside the concrete are 16×20

ft. A 1-8 mixture of cement, sand, gravel and stone was used in the

floor and walls and a 1-6 mixture of the same materials in the jack

arches. A bag of cement was called 1 cu. ft., so that a barrel was 4 cu.

ft. A Hains gravity mixer and a batch mixer were used and careful

records were kept of all quantities.

_General Data._--During 1903, about 13,880 cu. yds. of the 1-8 concrete

were placed, 90 per cent. of which was mixed in the gravity mixer and 10

per cent. in the batch mixer. Of the 1-6 concrete 5,320 cu. yds. were

placed, 85 per cent, of which was mixed in the gravity mixer and 15 per

cent, in the batch mixer.

_Gravity Mixer Work._--During 1903, there were 16,940 cu. yds. of

concrete mixed in gravity mixers, requiring 2,860 days' labor mixing and

4,000 days' labor placing. Wages were $1.50 a day and the cost was 26

cts. per cu. yd. for mixing and 33 cts. for placing, making a total of

59 cts. per cu. yd. During the month of August when 2,800 cu. yds. were

mixed the cost was as low as 24 cts. for mixing, plus 22 cts. for

placing, or a total of 46 cts. per cu. yd. for mixing and placing. The

mixer averaged about 113 cu. yds. per day with a gang of 19 men mixing

and 26 men placing. The average size of batch was 0.46 cu. yd. In 1904,

20,000 cu. yds. were mixed in 190 days, worked with a gang of 19 men

mixing; the gang placing consisted of 25 men. The cost was as follows:

Item. Total. Per cu. yd.

2,950 days labor mixing $ 4,870 24 cts.

4,760 days labor placing 7,300 36 cts.

--------- --------

Total $12,170 60 cts.

During the best month of 1904, the labor cost was 16 cts. for mixing and

29 cts. for placing, or a total of 45 cts. per cu. yd.

_Batch Mixer Work._--During 1903 the batch mixer mixed 2,390 cu. yds. in

970 labor days mixing and 740 labor days placing at a cost of 59 cts.

per cu. yd. for mixing and 55 cts. per cu. yd. for placing, or a total

of $1.04 per cu. yd. During the month of June the cost was as low as 40

cts. for mixing and 30 cts. for placing, or 70 cts. per cu. yd. for

mixing and placing. The wages paid were $1.50 per day and the average

gangs were 11 men mixing and 14 men placing; the average batch mixed was

0.57 cu. yd. and the average output was 35 cu. yds. per day. During

1904, the mixer worked 153 days and averaged 46 cu. yds. per day; the

average size of batch was 0.44 cu. yd. The average gangs were 13 men

mixing and 11 men placing. The labor cost of 7,000 cu. yds. was as

follows:

Item. Total. Per cu. yd.

1,910 days labor mixing $3,175 45 cts.

1,740 days labor placing 2,660 38 cts.

------- --------

Total $5,835 83 cts.

_Haulage._--The costs given comprise in mixing, the cost of delivering

the materials to the mixer, and, in placing, the cost of hauling the

concrete away. A Robins belt conveyor was used to deliver materials to

the gravity mixer and this accounts, in a large measure, for the lower

cost of mixing by gravity. The mixed concrete was hauled from both

mixers in dump cars pushed by men.

_Form Work._--The labor cost of forms for 19,300 cu. yds. of concrete

placed in 1903 was $16,800, or 87 cts. per cu. yd. of concrete. The

total labor days consumed on form work was 6,340 at $2.70 per day. The

total cost of concrete in place for mixing, placing and form work was

$1.46 per cu. yd., not including lumber in forms, fuel, interest and

depreciation.

CHAPTER XVII.

METHODS AND COST OF CONSTRUCTING ARCH AND GIRDER BRIDGES.

The construction problems in arch and girder bridges of moderate spans

are simple, and with the exception of center construction and

arrangement of plant for making and placing concrete, are best explained

by citing specific examples of bridge work. This is the arrangement

followed in this chapter.

~CENTERS.~--The construction of centers is no less important a task for

concrete arches than for stone arches. This means that success in the

construction of concrete arches depends quite as much upon the

sufficiency of the center construction as it does upon any other portion

of the work. The center must, in a word, remain as nearly as possible

invariable in level and form from the time it is made ready for the

concrete until the time it is removed from underneath the arch, and,

when the time for removal comes, the construction must be such that that

operation can be performed with ease and without shock or jar to the

masonry. The problem of center construction is thus the two-fold one of

building a structure which is immovable until movement is desired and

then moves at will. Incidentally these requisites must be obtained with

the least combined expenditure for materials, framing, erection and

removal, and with the greatest salvage of useful material when the work

is over. The factors to be taken count of are it, will be seen, numerous

and may exist in innumerable combinations.

[Illustration: Fig. 148.--Center for 50 ft. Arch Span (Supported).]

[Illustration: Fig. 149.--Center for 50-ft. Arch Span (Cocket).]

Centers may be classified into two types: (1). Centers whose supports

must be arranged so as to leave a clear opening under the center for

passing craft or other purposes, and (2) centers whose supports can be

arranged in any way that judgment and economy dictate. Centers of the

first class are commonly called cocket centers. As examples of a cocket

and of a supported center and also as examples of well thought out

center design we give the two centers shown by Figs. 148 and 149, both

designed for a 50-ft. span segmental arch by the same engineer. The

development of the center shown by Fig. 148 into the cocket center shown

by Fig. 149 is plainly traceable from the drawings. In respect to the

center shown by Fig. 149 which was the construction actually adopted we

are informed that 16,464 ft. B. M. were required for a center 36 ft.

long, that the framing cost about $12 per M. ft. B. M., with carpenters'

wages at $4 per day, and that the cost of bolts and nuts was about $1.50

per M. ft. B. M. With lumber at $20 per M. ft. B. M., this center framed

and erected would cost about $35 per M. ft. B. M. As an example of

framed centers for larger spans we show by Fig. 158 the centers for the

Connecticut Avenue Bridge at Washington, D. C., with costs and

quantities; other references to costs are contained in the index.

A center of very economical construction is shown by Fig. 159, and is

described in detail in the accompanying text. The distinctive feature of

this center is the use of lagging laid lengthwise of the arch and bent

to curve. Another example of this form of construction may be found in a

3-span arch bridge built at Mechanicsville, N. Y., in 1903. The viaduct

was 17 ft. wide over all, and consisted of two 100-ft. spans and one

50-ft. span. Pile bents were driven to bed rock, the piles being spaced

6 ft. apart and the bents 10 ft. apart. Each bent was capped with

10×12-in. timber. On these caps were laid four lines of 10×12-in.

stringers, and 8×10-in. posts 3 ft. apart were erected on these

stringers, and each set of four posts across the arch was capped with

8×10-in timbers the ends of which projected 3 ft. beyond the faces of

the arch. The tops of these cross caps were beveled to receive the

lagging which was put on parallel with the center line of the viaduct,

sprung down and nailed to the caps. This lagging consisted of rough

1-in. boards for a lower course, on top of which was laid 1-in. boards

dressed on the upper sides. Hardwood wedges were used under the posts

for removing the centers. In the centers, forms and braces for the three

arches there were used 140,000 ft. B. M. of lumber. The structure

contained 2,500 cu. yds. of concrete.

Another type of center that merits consideration in many places is one

developed by Mr. Daniel B. Luten and used by him in the construction of

many arches of the Luten type of reinforced concrete arch. The

particular feature of this type of arch is that in shallow streams for

bridges of ordinary span the ends of the arch ring are tied together

across stream by a slab of concrete reinforced to take tension. This

slab is intended to serve the double purpose of a tie to keep the arch

from spreading and thus reduce the weight of abutments and of a pavement

preventing scour and its tendency to undermine the abutments.

Incidentally this concrete slab, which is built first, serves as a

footing for the supports carrying the arch center.

As an illustration of the center we choose a specific structure. In

building a 95-ft. span, 11-ft. 1-in. rise arch bridge at Yorktown, Ind.,

in 1905, the centers were designed so as to avoid the use of sand boxes

or wedges. Ribs of 2×12-in. pieces cut to the arc of the arch soffit

were supported on uprights standing on the concrete stream bed pavement.

The uprights were so proportioned by Gordon's formula for columns that

without bracing they would be too light to support the load of concrete

and earth filling that was to come upon them, but when braced at two

points dividing the uprights approximately into thirds they would

support their loading rigidly and without buckling. The design in detail

was as follows: The uprights near the middle of the span were about 15

ft. long and were spaced 7 ft. apart across the stream and 3 ft. apart

across the bridge. Each upright then was to support a loading of

concrete of 7 ft.×3 ft.×26 ins. and an earth fill 1 ft.×7 ft.×3 ft., or

a total load of about 9,000 lbs. Applying Gordon's formula for struts

with free ends,

f S

P = -------------------

l²

I + --------

125h²

where P is the total load = 9,000 lbs., f is fibre stress for

oak--1,600 lbs., l is length of strut in inches and h is least

diameter of strut in inches, it was found that for a length of 15 ft. a

7×7-in. upright would be required to satisfy the formula, but for a

length of 5 ft., which would result from bracing each strut at two

points, a 4×4-in. timber satisfied the formula. Therefore, 4×4-in.

timbers braced at two points were used for the longest uprights. About

30 days after the completion of the arch the bracing was removed from

the uprights, beginning at the ends of the span and working towards the

middle. As the bracing was being removed the uprights gradually yielded,

buckling from 4 to 6 ins. from the vertical and allowing the arch to

settle about ¼ in. at the crown. This type of center has been

successfully employed in a large number of bridges.

Figure 150 shows a center for a 125-ft. span parabolic arch with the

amount and character of the stresses indicated and with a diagram of the

actual deflections as measured during the work.

[Illustration: Fig. 150.--Center for 125-ft. Span Parabolic Arch with

Diagram of Deflections.]

In calculating centers of moderate span there is seldom need of more

than the simple formulas and tables given in Chapter IX. When the spans

become larger, and particularly when they become very large--over 200

ft.--the problem of calculating centers becomes complex. None but an

engineer familiar with statics and the strengths of materials and

knowing the efficiency of structural details should be considered for

such a task. Such computations are not within the intended scope of this

book, and the design of large centers will be passed with the

presentation of a single example, the center for the Walnut Lane Bridge

at Philadelphia, Pa.

The main arch span of the Walnut Lane Bridge consists of twin arches

spaced some 16 ft. apart at the crowns and connected across by the

floor. Each of the twin arch rings has a span of 232 ft. and a rise of

70¼ ft., is 9½ ft. thick and 21½ ft. wide at the skewback and 5½ ft.

thick and 18 ft. wide at the crown. The plan was to build a center

complete for one arch ring and then to shift it along and re-use it for

building the other arch ring. The centering used is shown in diagram by

Fig. 151. It consists of five parts: (1) Six concrete piers running the

full width of the bridge upon which the structure was moved; (2) a steel

framework up to E G, called the "primary bent"; (3) a separate timber

portion below the heavy lines E I and W' I'; (4) the "main staging"

included in the trapezoid E I W' I', and (5) the "upper trestle"

extending from I I' to the intrados.

[Illustration: Fig. 151.--Center for 232-ft. Span Arch at Philadelphia,

Pa.]

The primary bent consists of four I-beam post bents having channel

chords, the whole braced together rigidly by angles. Each bent is

carried on 1½ ft.×6 in. steel rollers running on a track of 19×½ in.

plate on top of the concrete piers. Between the primary bents and the

main staging, and also between the main staging and the upper trestles

are lifting devices. The mode of operation planned is as follows: When

the center has been erected as shown and the arch ring concreted the

separate stagings under K I and K' I' are taken down. Next the

portions under the lines I E and I' W' will be taken down and

erected under the second arch. Finally the remainder of the center will

be shifted sidewise on the rollers to position under the second arch.

~MIXING AND TRANSPORTING CONCRETE.~--The nature of the plant for mixing

and handling the concrete in bridge work will vary not only with varying

local conditions but with the size and length of the bridge. For single

span structures of moderate size the concrete can be handled directly by

derricks or on runways by carts and wheelbarrows. For bridges of several

spans the accepted methods of transport are cableways, cars and cars and

derricks. Typical examples of each type of plant are given in the

following paragraphs, and also in the succeeding descriptions of the

Connecticut Avenue Bridge at Washington, D. C., and of a five-span arch

bridge.

~Cableway Plants.~--The bridge was 710 ft. long between abutments and 62

ft. wide; it had a center span of 110 ft., flanked on each side by a

100-ft., a 90-ft. and an 80-ft. span. The mixing plant was located at

one end of the bridge and consisted of a Drake continuous mixer,

discharging one-half at the mixer and one-half by belt conveyor to a

point 50 ft. away, so as to supply the buckets of two parallel

cableways. The mixer output per 10-hour day was 400 cu. yds. and the

mixing plant was operated at a cost of $27 per day, making the cost of

mixing alone 6¾ cts. per cu. yd. The sand and gravel were excavated from

a pit 4½ miles away and delivered by electric cars to the bridge site at

a cost of 50 cts. per cu. yd. Two 930-ft. span Lambert cableways set

parallel with the bridge, one 25 ft. each side of the center axis, were

used to deliver the concrete from mixer to forms. The cableway towers

were 70 ft. high and the cables had a deflection of 35 ft.; they were

designed for a load of 7 tons, but the average load carried was only 3

or 4 tons. These cableways handled practically all the materials used in

the construction of the bridge. They delivered from mixer to the work

400 cu. yds. of concrete 450 ft. in 10 hours at a cost of 2 cts. per cu.

yd. for operation.

[Illustration: Fig. 151a.--Cableway for Concreting Bridge Piers.]

Another example of cableway arrangement for concreting bridge piers is

shown by Fig. 151a. The river was about 800 ft. wide, about 3 ft. deep

and had banks about 20 ft. high. The piers were about 21 ft. high. The

towers for the cableway consisted of a 55-ft. derrick without boom,

placed near the bank on the center line of the piers and well guyed and

a two-leg bent placed in the middle of the river and held in place by

four cable guys anchored to the river bottom. A ¾-in. steel hoisting

cable was stretched from a deadman on shore, about 150 ft. back of the

derrick, and followed along the center line of the piers, past the

derrick just clearing it, to the bent in the middle of the river. At the

top of this bent was a 16-in. cable block. Through this block the cable

passed down and was made fast to a weight, consisting of a skip loaded

with concrete until the cable had the required tension, and a pitch of

18 to 20 ft. from center of river to anchor on shore. In order to secure

the required pitch from the shore to the river bent the boom fall of the

derrick was hooked onto the cable at the foot of the mast, and then, by

going ahead on the single drum hoisting engine, was raised to the mast

head. This gave the cable a pitch of 18 to 20 ft. from mast head to top

of bent in river. The carriage vised on the cableway consisted of two

16-in. cable sheaves with iron straps, forming a triangle, with a chain

hanging from the bottom point, to which was attached the 5 cu. ft.

capacity concrete bucket. The concrete was mixed on a platform at the

foot of the mast. When ready for operation the chain on the carrier was

hooked to the bucket of concrete, the engine started, and both bucket

and cable raised, the former running by gravity to the pier. The speed

of descent was governed by the height to which the cable was raised on

the derrick, and as the bucket neared the dumping point the engine was

slacked off and the cable leveled. The bucket was dumped by a man on a

staging erected on the pier form. For the return of the bucket the

engine was slacked off and the weight on the river bent would pull the

cable tight so that the pitch would be toward the shore and the bucket

could run down the grade to the mixing platform, the speed being

governed as before by leveling the cable. When the piers were completed

to the middle of the river the engine and derrick were taken over to

opposite side of the river, the bent being left in the middle, and the

work continued. By using the extreme grade of the cable it was found

that the bucket would run from the platform to the bent (400 ft.) in

less than 35 seconds.

[Illustration: Fig. 152.--Sketch Showing Car and Trestle Plant for

Concreting an Arch Bridge.]

~Car Plant for 4-Span Arch Bridge.~--The bridge had four 110-ft. skew

spans, and a total length of 554 ft. The mixing plant was located

alongside one abutment on a side hill so that sand and stone could be

stored on the slope above. The mixer was set on a platform high enough

to clear cars below. Above it and to the rear a charging platform

reached back to the stone and sand piles. Side dump cars running on a

track on the charging platform took sand and stone to the mixer and

cement was got from a cement house at charging platform level. The

concrete for the abutment adjacent to the mixer was handled in buckets

by a guy derrick. A trestle, Fig. 152, was then built out from the mixer

to the first pier; this trestle was so located as to clear the future

bridge about 20 ft. and was carried out from shore parallel to the

bridge until nearly opposite the pier site, where it was swung toward

and across the pier. The concrete was received from the mixer in bottom

dump push cars; these cars were run out over the pier site and dumped.

When the first pier had been concreted to springing line level, the main

trestle was extended to opposite the second pier and the branch track

was removed from over the first pier and placed over the second pier.

This operation was repeated for the third pier. The last extension of

the main track was to the far shore abutment, where the bodies of the

cars were hoisted by derrick and dumped into the abutment forms. The

derrick was the same one used for the first abutment having been moved

and set up during the construction of the intermediate piers. To

construct the arches a second trestle was built composed partly of new

work and partly of the staging for the arch centers. This trestle rose

on an incline from the mixer to the first pier across which it was

carried at approximately crown level of the arch. The concrete for the

portion of the pier above springing line and for the lower portions of

the haunches was dumped direct from the cars. For the upper parts of the

arch the concrete was brought to the pier track in two-wheel carts on

push cars and thence these carts were taken along the arch toward shore

on runways. When the first arch had been concreted the second trestle

was extended to pier two and the operation repeated to concrete the

second arch.

~Hoist and Car Plant for 21-Span Arch Viaduct.~--The double track concrete

viaduct replaced a single track steel viaduct, being built around and

embedding the original steel structure which was maintained in service.

The concrete viaduct consisted of 21 spans of 26 ft., 7 spans of 16 ft.,

and 2 spans of 22 ft. With piers it required about 15,000 cu. yds. of

concrete. Two Ransome concrete hoists, one on each side of the original

steel structure near one end, were supplied with concrete by a No. 4

Ransome mixer. The mixer discharged direct into the bucket of one hoist

and by means of a shuttle car and chute into the bucket of the other

hoist.

The shuttle car ran from the mixer up an incline laid with two tracks,

one narrow gage and one wide gage, having the same center line. The car

was open at the front end and its two rear wheels rode on the broad gage

rails and its two forward wheels rode on the narrow gage rails. At the

top of the incline the narrow gage rails pitched sharply below the grade

of the broad gage rails so that the rear end of the car was tilted up

enough to pour the concrete into a chute which led to the bucket of the

hoist. The sand and gravel bins were elevated above the mixer and

received their materials from cars which dumped directly from the steel

viaduct.

The hoist buckets discharged into two hoppers mounted on platforms on

the old viaduct. These platforms straddled two narrow gage tracks, one

on each side of the old viaduct parallel to and clearing the main track.

These side tracks were carried on the cantilever ends of long timbers

laid across the old viaduct between ties. At street crossings the

overhanging ends of the long timbers were strutted diagonally down to

the outside shelf of the bottom chords of the plate girder spans. Six

cars were used and the concrete was dumped by them directly into the

forms; the fall from the track above being in some cases 40 ft. The

hoists and shuttle car were operated by an 8½×12-in. Lambert derrick

engine, the boiler of which also supplied steam to the mixer engine. The

concrete cars were operated by cable haulage by two Lambert 7×10-in.

engines.

The labor force employed in mixing and placing concrete, including form

work, was 45 men, and this force placed on an average 200 cu. yds. of

concrete per day. Assuming wages we get the following costs of different

parts of the work for labor above:

Item. Per day. Per cu. yd.

1 timekeeper at $2.50 $ 2.50 $0.0125

1 general foreman at $5 5.00 0.0250

3 enginemen at $5 15.00 0.0750

1 carpenter foreman at $4 4.00 0.0200

12 carpenters at $3.50 42.00 0.2100

1 foreman at $4 4.00 0.0200

8 men mixing and transporting at $1.75 14.00 0.0700

13 men placing concrete at $1.75 22.75 0.1137

1 foreman finishing at $4 4.00 0.0200

4 laborers finishing at $1.75 7.00 0.0350

------ -------

45 men at $2.70 $120.25 $0.6012

It is probable that the carpenter work includes merely shifting and

erecting forms and not the first cost of framing centers. No materials,

of course, are included. It should be kept in mind that while the output

and labor force are exact the wages are assumed.

~Traveling Derrick Plant for 4-Span Arch Bridge.~--The bridge consisted of

four 70-ft. arch spans and was built close alongside an old bridge which

it was ultimately to replace. The approach from the west was across a

wide flat; at the east the ground rose more abruptly from the stream.

Conditions prevented the use of a long spur track and also made it

necessary to install all plant at and to handle all material from the

west bank. A diagram sketch of the arrangement adopted is shown by Fig.

153.

[Illustration: Fig. 153.--Sketch Showing Traveling Derrick Plant for

Concreting an Arch Bridge.]

The track from the west approached the existing bridge on an embankment

25 ft. high. A spur track 175 ft. long from clear post to end was built

on trestle as shown. The cement house and mixer platform were placed at

the foot of the embankment at opposite ends of the spur track. Between

the two the slope of the embankment was sheeted with 1-in. boards and a

timber bulkhead 4 ft. high was built along the toe of the sheeting.

Stone, sand and coal were stored behind the bulkhead on the sheeting. A

runway close to the bulkhead connected the cement house with the mixer

platform, all materials to the mixer being wheeled in barrows on this

runway. A ¾-cu. yd. Smith mixer was set on a platform 5 ft. above ground

with its discharge end toward the stream. Beginning under this platform

a service track was carried across the flat and stream to the extreme

end of the east abutment. This track consisted of three rails, two rails

4 ft. apart next to the work and a third rail 25 ft. from the first. The

4-ft. gage provided for cars carrying concrete buckets from the mixer

and the 25-ft. gage provided for a traveling derrick; 18-lb. rails were

used and they proved to be too light, 40-lb. rails are suggested. The

derrick consisted of a triangular platform carrying a stiff leg derrick

with a 25-ft. mast and mounted on five wheels. The wheels were double

flange 16 ins. diameter and cost $30 each, being the most expensive part

of the derrick. The derrick was made on the ground and took four

carpenters between 3 and 4 days to build. Derrick and 350 ft. of service

track, including pole trestle across the stream, cost between $600 and

$800. The derrick was moved by means of a cable wrapped around one spool

of the Flory double-drum hoisting engine and leading forward and back to

deadmen set at opposite ends of the service track. Cars carrying

concrete buckets were run out on the 4-ft. gage track and the buckets

were hoisted by the derrick and dumped into a ½-cu. yd. car running on a

movable transverse track across the bridge. This transverse track was

necessary to handle the concrete to the far side of the work, the

derrick being set too low and the boom being too short to reach. The

derrick was used to handle material excavated from the pier foundations

and also to tear down the centers and spandrel forms. Some rather

general figures on the cost of this bridge are given by Mr. H. C.

Harrison, the contractor. They are:

Materials: Total.

6,000 bbls. cement at $2.05 $12,300

2,500 cu. yds. sand at $0.80 2,000

5,000 cu. yds. stone at $0.85 4,250

260 M. ft. B. M. lumber at $17 4,420

-------

Total $22,970

Labor:

Cofferdams, excavation and pumping $ 3,000

Forms, falseworks and centers 2,000

Mixing and placing concrete 4,000

Placing reinforcement 400

Removing falseworks, forms, etc. 1,200

One coat pitch and paper 150

Building plant, etc. 2,250

-------

Total $13,000

Mr. Harrison states that including plant cost, delays, floods and

incidentals the cost per cubic yard of concrete was $8 and that

excluding these items the cost was $6 per cu. yd.

~COST OF CONSTRUCTING CONCRETE HIGHWAY BRIDGE, GREENE COUNTY, IOWA.~--The

following is the itemized cost of constructing a reinforced concrete

slab highway bridge, one of several built by the Highway Commissioners

of Greene County, Iowa, in 1906. The figures are given by Messrs. Henry

Haag and D. E. Donovan, the last being the foreman of the concrete gang

doing the work. All bridges consist of 10 to 12-in. slabs reinforced

with old steel rails and of abutments and wing walls reinforced with old

rods, bars or angles selected from junk. This junk metal cost 0.6 cts.

per pound and the rails cut to length cost 1.15 cts. per pound f. o. b.

cars. The work was done by a special gang, the men receiving $1.50 per

day and board. As a rule the footings were made 2 ft. wide and as high

as need be to get above the water and dirt. Before the footing concrete

set steel rods, bars or angles were placed; they were long enough to

reach the height of the wall and 3 to 6 ins. into the slab. The forms

for the abutment and wing walls and for the floor slab were then erected

complete before any more concrete was placed. No carpenter was employed,

every man on the job having been taught to take his certain place in the

work, then, the forms being erected, every man had his particular place

in the work of mixing and placing the concrete. The foreman saw that the

reinforcement was properly placed and watched over the accuracy of the

work generally. The concrete was allowed to set on the centers for from

30 to 40 days; the other form work was taken down after three days and

travel over the bridge permitted after three or four days. The concrete

was mixed wet. The bridge whose cost is given was 22 ft. wide and 16 ft.

span with 2-ft. wing walls.

The foundations are 4 ft. deep and 2½ ft. wide. The walls on top of the

foundations are 7 ft. high, 18 ins. wide at the base, and battered up to

14 ins. at the top for wings and 12 ins. at top for walls. The floor is

22 ft. by 18 ft. and 1 ft. thick. The wheel guard is 12 ins. thick by 14

ins. wide and 32 ft. long. The itemized cost of this bridge, containing

73 cu. yds. of concrete, is as follows:

Materials. Total. Per cu. yd.

70 cu. yds. gravel at 70 cts $ 49.00 $0.6726

10 cu. yds. broken stone at 70 cts 7.00 0.0959

75 bbls. cement at $2.20 165.00 2.2603

7,000 lbs. steel rails at 1.15 cts 80.50 1.1027

1,000 lbs. junk rails at 0.6 cts 6.00 0.0819

200 ft. B. M. lumber wasted at $29 5.80 0.0794

15 lbs. nails at 3 cts 0.45 0.0061

Labor and Supplies:

2 days excavation at $14 28.00 0.3835

¾ day foundation at $14 10.00 0.1369

1½ days building forms at $14 21.00 0.2876

2 days filling forms at $14 28.00 0.3835

Hauling lumber and tools 8.00 0.1096

Hauling cement and tools 18.00 0.2465

Taking off forms 2.30 0.0315

1,000 lbs. coal at $4 per ton 2.00 0.0274

------ -------

Total cost $431.05 $5.9054

In round figures the cost per cubic yard of concrete in the finished

bridge was $5.90. Summarizing we have the following cost per cubic yard

of concrete in place:

Item. Per cu. yd.

Cement $2.26

Steel 1.22

Lumber 0.22

Gravel and stone 0.76

Labor 1.41

Coal 0.03

-----

Total $5.90

The average cost of concrete in place for all the work done in Greene

County by day labor was $6.25 per cu. yd. In the job itemized above the

bank caved in, causing an extra expense for removing the earth. The

gravel used in this bridge was very good clean river gravel.

~METHOD AND COST OF CONSTRUCTING TWO HIGHWAY GIRDER BRIDGES.~--The

following account of the methods and costs of constructing two slab and

beam highway bridge decks on old masonry abutments is taken from

records kept by Mr. Daniel J. Hauer. The first bridge was a single span

15 ft. long that replaced wooden stringers and floor that had become

unsafe; the second was two short spans of a steel bridge that was too

light for the traffic of the road, and it was torn down and moved

elsewhere, by the county authorities. The work was done by contract, and

in each case consisted of building the reinforced floor and girders on

the old masonry walls that were in good condition. While the work was

going on traffic was turned off the bridges, fords being used instead.

Figure 154 shows a sketch of the cross-section of the floor and girders.

In Example I the girders had a depth below the floor of 12 ins. and were

of the same width. In Example II the girders were 14 ins. wide and had a

depth below the floor of 18 ins. The floors on both bridges were 6 ins.

thick. Kahn bars were used for reinforcement.

[Illustration: Fig. 154.--Cross-Section of Concrete Girder Bridge.]

_Example I._--This bridge was but little more than 5 ft. above the

stream, which was shallow and not over 7 ft. wide, unless swollen by

floods. The bottom for several hundred feet on either side of the bridge

was covered with coarse sand and gravel, that had pebbles in it from the

size of a goose egg down. This was taken from the stream by men with

picks and shovels and hauled to the site of the work with wheelbarrows,

and then screened so as to separate the gravel from the sand. As it was

found that the sand was so coarse that it would take more cement than

the specifications called for in a 1-2½-5 mixture, some much finer sand

was bought and mixed with it. For the privilege of taking the sand from

the stream $1 was paid the property owner. This was done to get a

receipt and release from him, rather than as an attempt to pay royalty

on the gravel and sand. This dollar is included in the cost of the labor

in getting these materials.

The cost of materials per cubic yard for the bridge was as given below,

the mixture being as stated above. The cement cost $1.40 per barrel,

delivered at the bridge.

Per Cu. Yd.

Steel $2.50

Gravel and sand .75

Sand (bought) .30

Cement 1.57

-----

Per cubic yard $5.12

It is of interest to note the cost of the gravel and sand, as this

includes the cost of digging it, wheeling it in a wheelbarrow an average

distance of 100 ft., and then screening it and putting it in two stock

piles. The proportion of bought sand used with the creek sand was

one-half.

The old wooden floor and stringers had to be torn down. This was done at

a cost of $1.30 per M. ft. B. M., and furnished 60 per cent. of the

lumber needed for forms. The floor boards were 3-in. yellow pine planks,

and the stringers 6×12-in. timbers, rather heavy, but money was saved by

using them. The 6×12-in. timbers were used for props for the centering.

Additional lumber was bought, delivered at the site of the bridge, for

$20.84 per M. ft. B. M.

In framing and erecting the forms the carpenter had laborers helping

him, he doing only carpenter's work, the laborers carrying and lifting

all pieces wherever possible. The carpenter's work was about 40 per

cent. of the total labor cost, which was as follows per cubic yard of

concrete:

Tearing down old bridge $0.08

Lumber .85

Nails .15

Labor, carpenter .77

Labor, laborers .96

-----

$2.81

The forms were torn down by laborers, with the assistance of a man and

his helper, who were given the boards for this labor and to haul them

away. This reduced this item somewhat, as it only amounted to 20 cts.

per cu. yd.

The cost of the forms per thousand feet board measure was:

New lumber $20.82

Nails 1.44

Labor, carpenter 7.60

Labor, laborers 9.50

Tearing down 2.00

------

$41.36

All the men, including the carpenter, worked 10 hours per day, and were

paid at the following rates:

Carpenter $2.50

Sub-foreman 2.00

Laborers 1.50

A regular foreman was not employed, but an intelligent and handy workman

was given 50 cts. additional to lead the men and look after them when

the contractor was not present.

A gang of six men did the work of mixing and placing, and as the stock

piles were close by the mixing board no extra men were needed to handle

materials. Water was secured from the stream in buckets for mixing. The

mixture was made very wet. The cost per cubic yard for the entire

structure was as follows:

Preparing for mixing $0.04

Cleaning out forms .06

Handling steel .03

Mixing and placing 1.15

Ramming .23

-----

$1.51

The cost of the contractor's expense of bidding, car fare, etc., is

listed under general expense, and gives a total cost per cubic yard of:

Materials $ 5.12

Erecting forms 2.81

Tearing down forms .20

Labor 1.51

General expense 2.00

------

$11.64

_Example II._--For this bridge both the stone and sand had to be bought.

The bridge floor was nearly 14 ft. above the bottom of the stream, which

was shallow. The wages paid were as follows for a 10-hour day:

Foreman $3.00

Laborers 1.50

Carpenters were paid $3 for an 8-hour day and time and a half for all

overtime, which they frequently made.

For the girders a 1-2-4 mixture was used. The cement, delivered at the

bridge, cost $1.21 per barrel, there being 8 cts. a barrel storage and 8

cts. a barrel for hauling included in this. The sand was paid for at an

agreed price per cartload delivered, which averaged $1.34 per cu. yd.

The stone was crushed so as to pass a 1½-in. ring in all directions. It

was delivered at the bridge for $2.75 per cu. yd. This makes the cost

per cubic yard for materials as follows:

Steel $1.41

Cement 2.18

Sand .67

Stone 2.75

-----

$7.01

For the floor a 1-3-5 mixture was used, making a cost for material of:

Steel $1.02

Cement 1.69

Sand .67

Stone 2.75

-----

$6.13

Two-inch rough pine boards were used to make the troughs for the

girders, while 1-in. rough boards were used for the floors. These were

all supported by 3×4-in. pine scantlings. This lumber cost delivered

$17.50 per M. ft. B. M. Carpenters did all the framing, and erected it

with the help of laborers. All the carrying of the lumber was done by

laborers. This reduced the cost of the work, as the laborers' wages

amounted to one-third of the whole cost. As soon as the forms were all

in place, which was before the mixing of concrete commenced, the

carpenters were discharged. The cost per cubic yard for forms was:

Lumber $2.82

Nails .05

Labor, carpenters 1.24

Laborers .62

-----

$4.73

The tearing down of the forms was done entirely by laborers at a cost of

61 cts. per cu. yd.

On concrete work it is also advisable to keep the cost of forms per

thousand feet board measure, so as to have such data for estimating on

new work. The cost per M. ft. on this job was:

Lumber $17.50

Nails .30

Labor, carpenters 7.65

Laborers 3.85

Tearing down 3.80

------

$33.10

The concrete was mixed by hand, water being carried in buckets from the

creek. Ten to twelve men were worked in the gang under a foreman, and

the concrete was wheeled from the mixing board to the forms in

wheelbarrows. The mixture was made wet enough to run. The cost per cubic

yard for the girders in detail was as follows:

Foreman $0.41

Preparing for mixing 0.14

Cleaning out forms 0.07

Handling materials 0.30

Handling and placing steel 0.40

Mixing and placing 0.87

Ramming 0.45

-----

$2.64

The cost of labor for the floor was:

Foreman $0.28

Preparing for mixing 0.08

Cleaning out forms 0.05

Handling materials 0.14

Handling and placing steel 0.08

Mixing and placing 0.87

Ramming 0.36

-----

$1.86

This gives a total cost per cubic yard for the concrete in the girders

in the completed bridge as follows:

Materials $ 7.01

Erecting forms 4.73

Tearing down forms 0.61

Labor 2.57

General expense 1.60

------

$16.52

The cost per cubic yard for the floor was:

Materials $ 6.13

Erecting forms 4.73

Tearing down forms 0.61

Labor 1.86

General expense 1.60

------

$14.93

Included with this is an item for general expense, being expenses of the

contractor in bidding on the work, car fare, and other items of expense

in looking after the contract.

It will be noticed that a record is here given of three different

mixtures and that the labor cost of mixing and placing increases with

the richness of the mixture. This is because it takes a greater number

of batches to the cubic yard. Record has also been given of cost of

preparing the mixing board and other work necessary to start and clean

up each day; also when stock piles could not be arranged close to the

mixing board, of the cost of handling the materials. These items, it

will be noticed, are large enough to be considered in estimating on new

work. The cost of sweeping and cleaning out the forms has also been

listed, as this work is extremely important.

The cost of the reinforcing steel is given in with the materials, but

the labor of handling it and placing it in the forms is listed under

labor. This naturally varies with the amount of steel needed, and with

the Kahn bar it will vary from 10 cts. to 75 cts. per cubic yard, as the

prongs of the bar must be bent into proper position and at times

straightened, when bent in shipment. This cost seems large, but it is

done with the ordinary labor, while with round rods a large amount of

blacksmith work has to be done and a smith and his helper frequently

must place them. The patent bars are all lettered and numbered as

structural steel is, and can be placed under the direction of the

foreman.

One striking lesson can be learned from the forming. It will be noticed

that the cost for common labor for handling and helping to erect the

forms was much larger in Example I than in Example II, although the

bridge was higher in the latter instance. This was caused by the heavy

timber that was used, and equaled an extra cost nearly 50 per cent. of

the price of new lumber. It certainly speaks volumes against the use of

unnecessarily heavy timber for concrete forms.

In bridge work the height of the floor above the stream to some extent

governs the cost of the forms. This is made so by the extra lumber

needed as props or falsework to support the forming, and also by the

fact that men at some height above the ground do not work as quickly or

as readily as they do nearer the ground. For high and long spans a

derrick is sometimes needed for the work of placing the centering.

On these jobs the concrete was made so wet that with the proper tamping

and cutting of the concrete in the forms the surfaces were so smooth

that no plastering was needed.

~MOLDING SLABS FOR GIRDER BRIDGES.~--The bridges carry railway tracks

across intersecting streets; the slabs rest on two abutments and three

rows of columns so that there are two 24¼-ft. spans over the street

roadway and one 10¾-ft. span over each sidewalk. The larger slabs were

24 ft. 3 ins. long, 33 ins. thick and 7 ft. wide; each contained 16¾

cu. yds. of concrete and weighed 36¾ tons. The smaller slabs were 10 ft.

9 ins. long, 17 ins. thick and 7 ft. wide; each contained 3.65 cu. yds.

of concrete and weighed 7.8 tons. The weights were found by actual

weighing. They make the weight of the reinforced slab between 160 and

162 lbs. per cu. ft. The concrete was generally 1 part cement and 4

parts pit gravel. The reinforcement consisted of corrugated bars. The

method of molding was as follows:

[Illustration: Fig. 155.--Arrangement of Tracks and Forms for Molding

Slabs for Girder Bridge.]

[Illustration: Fig. 156.--Form for Molding Slabs for Girder Bridge.]

A cinder fill yard was leveled off and tamped, then the forms were set

up on both sides of two lines of railway track arranged as shown by Fig.

155. The exact construction of the forms for one of the larger slabs is

shown by Fig. 156. The side and end pieces were so arranged as to be

easily taken down and erected for repeated use. About 100 floors were

used and they had to be leveled up each time used as the lifting of the

hardened slab disarranged them. The side and end pieces were removed in

about a week or ten days, but the slabs stood on the floor 90 days,

being wetted each day for two weeks after molding.

The plant for mixing and handling the concrete was mounted on cars. A

flat car had a rotary drum mixer mounted on a platform at its forward

end. Beneath the mixer was a hopper provided with a deflector which

directed the concrete to right or left as desired. Under the hopper were

the ends of two inclined chutes extending out sidewise beyond the

car--one to the right and one to the left--and over the slab molds on

each side. Above the mixer was another platform containing a charging

hopper, and from the rear of this platform an incline ran down to the

rear end of the car and then down to the track rails. A car loaded with

cement and gravel in the proper proportions was hauled up the incline by

cable operated by the mixer engine, until it came over the topmost

hopper into which it was dumped. This hopper directed the charge into

the mixer below; the mixer discharged its batch into the hopper beneath

from which it flowed right or left as desired into one of the chutes and

thence into the mold. The chutes reached nearly the full length of the

molds and discharged as desired over the ends into the far end of the

mold or through a trap over the end of the mold nearest the car.

To the rear of the mixer car came a cement car provided with a platform

overhanging its forward end. Two hoppers were set in this platform each

holding a charge for one batch. Coupled behind the cement cars came

three or four gravel cars. These were gondola cars and plank runways

were laid along their top outer edges making a continuous runway for

wheelbarrows on each side from rear of train to front of cement car. The

sand and gravel were wheeled to the two measuring hoppers and the cement

was handed up from the car below and added, the charge was then

discharged into the dump car below and the car was hauled up the incline

to the mixer as already described. Two measuring hoppers were used so

that one was being filled while the other was emptied, thus making the

work continuous.

The molding gang consisted of 33 laborers, two foremen and one

engineman. This gang averaged 7 of the large slabs per 10-hour day and

at times made as many as 9 slabs. When molding small slabs an average

of 12 were made per day. This record includes all delays, moving train,

switching gravel cars on and off, building runways, etc. The

distribution of the men was about as follows:

Handling Materials: No. Men.

Shoveling gravel into wheelbarrows 9

Wheeling gravel to measuring hoppers 9

Emptying cement into measuring hoppers 2

Handling cement to men emptying 1

In charge of loading dump car 1

On top of cement car 1

Sub-foreman in charge 1

Mixing and Placing:

Engineer 1

In charge of mixer 1

Hoeing and spreading in mold 2

Spading in mold 2

Finishing sides of block 2

General laborers 3

Foreman in charge 1

Total men 36

This gang mixed and placed concrete for 7 blocks or 117¼ cu. yds. of

concrete per day. Assuming an average wage of $2 per day the cost of

labor mixing and placing was 61.4 cts. per cu. yd. or $10.28 per slab.

It is stated that the slabs cost $11.80 per cu. yd. on storage pile.

This includes labor and materials (concrete and steel); molds; loading

into cars with locomotive crane, hauling cars to storage yard and

unloading with crane into storage piles, and inspection, incidentals,

etc. To load the slabs into cars from storage piles, transport them to

the work and place them in position is stated to have cost $2 per cu.

yd. The slabs were placed by means of a locomotive crane being swung

from the flat cars directly into place.

[Illustration: Fig. 157.--Sections Showing Construction of Connecticut

Ave. Bridge.]

~METHOD AND COST OF CONSTRUCTING CONNECTICUT AVE. BRIDGE, WASHINGTON, D.

C.~--The Connecticut Ave. Bridge at Washington, D. C., consists of nine

150-ft. spans and two 82-ft. spans, one at each end, all full centered

arches of mass concrete trimmed with tool-dressed concrete blocks.

Figure 157 is a part sectional plan and elevation of the bridge,

showing both the main and spandrel arch construction. This bridge is one

of the largest concrete arch bridges in the world, being 1,341 ft. long

and 52 ft. wide, and containing 80,000 cu. yds. of concrete. Its total

cost was $850,000 or $638.85 per lin. ft., or $10.63 per cu. yd. of

masonry. It was built by contract, with Mr. W. J. Douglas as engineer in

charge of construction. The account of the methods and cost of

construction given here has been prepared from information obtained from

Mr. Douglas and by personal visits to the work during construction.

_General Arrangement of the Plant._--The quarry from which the crushed

stone for concrete was obtained was located in the side of the gorge at

a point about 400 ft. from the bridge. Incidentally, it may be added,

the fact that the contractor had an option on this quarry gave him an

advantage of some $30,000 over the other bidders. The stone from the

quarry was hoisted about 50 ft. by derricks and deposited in cars which

traveled on an incline to a Gates gyratory crusher, into which they

dumped automatically. The stone from the crusher dropped into a 600-cu.

yd. bin under the bottom of which was a tunnel large enough for a dump

car and provided with top gates by which the stone above could be

dropped into the cars. The cars were hauled by cable to the mixer

storage bin and there discharged. Sand was brought in by wagons and

dumped onto a platform about 50 ft. higher than the bottom of the main

stone bin. A tunnel exactly similar to that under the stone bin was

carried under the sand storage platform. The sand car was hauled from

this tunnel by cable to the mixer storage bin using the same cable as

was used for the stone cars, the cable being shifted by hand as was

desired. Cement was delivered to the mixer platform from the crest of

the bluff by means of a bag chute.

The mixer used was one of the Hains gravity type. It had four drops and

was provided with four mixing hoppers at the top. The concrete was made

quite wet. The proportions of sand and water were varied to suit the

stone according to its wetness and the percentage of dust carried by it.

The head mixer regulated the proportions and his work was checked by the

government inspector. From the bottom hopper the mixed concrete dropped

into a skip mounted on a car.

[Illustration: Fig. 158.--Center for Connecticut Ave. Bridge

(Elevation).]

To distribute the skip cars along the work a trestle was built close

alongside the bridge and at about springing line level. This trestle had

a down grade of about 2 per cent. from the mixer. Derricks mounted along

the centering and on the block molding platform lifted the skips from

the cars and deposited them where the concrete was wanted. The skip

cars were large enough for three skips but only two were carried so

that the derricks could save time by depositing an empty skip in the

vacant space and take a loaded skip away with one full swing of the

boom. Altogether nine derricks were used in the bridge, four having

70-ft. booms and five having 90-ft. booms. These derricks were jacked up

as the work progressed.

[Illustration: Fig. 158.--Center for Connecticut Ave. Bridge

(Details).]

_Forms and Centers._--The forms for wall and pier work consisted of

1-in. lagging held in place by studs about 2 ft. on centers and they in

turn supported by wales which were connected through the walls by bolts,

the outer portions of which were removed when the forms were taken down.

The centers for the five 150-ft. arches were all erected at one time;

those for the 82-ft. arches were erected separately. The seven centers

required 1,500,000 ft. B. M. of lumber or 1,404 ft. B. M. per lineal

foot of bridge between abutments, or 1,640 ft. B. M. per lineal foot of

arch span. The centers for the main arch spans are shown in detail by

Fig. 158; this drawing shows the sizes of all members and the maximum

stresses to which they were subjected from the loading indicated, that

is the arch ring concrete. The centers as a rule rested on pile

foundations. Four piles to each post were used for the intermediate

posts and two piles for the posts in the two rows next the piers.

Concrete foundations, however, were put in Rock Creek and on the line of

Woodley Lane Bridge where it was impracticable to drive piles. As

considerable difficulty was experienced in driving the piles, the ground

consisting mostly of rotten rock, it is thought that it would have cost

less if the contractor had used concrete footings throughout.

Some of the costs of form work and centering are given. The cost of

lumber delivered at the bridge site was about as follows:

M. ft. B. M.

Rough Virginia pine $25

Dressed Virginia pine lagging 23

Rough Georgia, sizes up to 12×12 ins. 33

Rough Georgia, sizes over 12×12 ins. 35

Rough oak lumber 35

The following wages were paid: Foreman carpenter, $3.50; carpenters, $2

to $3; laborers, $1.70, with a few at $1.50. An 8-hour day was worked.

The cost, of formwork is given in summary as follows:

Lagging per M. ft. (used twice):

Lumber at $23 $11.50

Erection 15.00

------

Total cost erected $26.50

Studding and rough boards used in place of lagging per M. ft. (used twice):

Lumber at $25 $12.50

Erection 10.00

------

Total cost erected $22.50

Wales per M. ft. (used six times):

Lumber at $36 $ 6.00

Erection 10.00

------

Total cost erected $16.00

The total cost of the main arch span centers to the District of Columbia

was $54,000 or $59 per lineal foot of arch span, or $37.33 per M. ft. B.

M. The cost of center erection and demolition was as follows:

Erection below springing line per M. ft. $15

Erection above springing line per M. ft. 25

Demolition 5

The salvage on the centers amounted to $11 per M. ft. B. M.

The spandrel arch centers were each used twice and cost per M. ft. B. M.

for

Lumber at $25 per M. ft. $12.50

Erecting at $25 per M. ft. 25.00

Moving at $5 per M. ft. 5.00

Total per M ft. 42.50

_Molding Concrete Blocks._--The bridge is trimmed throughout with molded

concrete blocks, comprising belt courses, quoin stones, chain stones,

ring stones, brackets and dentils. The blocks were made of a 1-2-4½

concrete faced with a 1-3 mixture of Dragon Portland cement and

bluestone screenings from 3/8-in. size to dust. They were cast in wooden

molds with collapsible sides held together by iron rods. Each mold was

provided with six bottoms so that the molded block could be left

standing on the bottom to harden while the side pieces were being used

for molding another block. The molding was done on a perfectly level and

tight floor on mud sills, the perfect level of the molding platform

having been found to be an important factor in securing a uniform

casting. The blocks were molded with the principal showing face down and

the secondary showing faces vertical. The facing mortar was placed

first and then the concrete backing. Care was taken to tamp the concrete

so as to force the concrete stone into but not through the facing. Mr.

Douglas remarks that the back of the block should always be at the top

in molding since the laitance or slime always flushes to the surface

making a weak skin which will develop hair cracks. In this work the

backs of the blocks were mortised by embedding wooden cubes in the wet

concrete and removing them when the concrete had set. These mortises

bonded the blocks with the mass concrete backing. The blocks were left

to harden for at least 30 days and preferably for 60 days and were then

bush hammered on the showing faces, some of the work being done by hand

and some with pneumatic tools.

Some precautions necessary in the molding and handling of large concrete

blocks were discovered in this work and merit mention. In designing

blocks for molding it is necessary to avoid thin flanges or the flanges

will crack and break off; blocks molded with a 2¼ in. flange projecting

1¾ ins. gave such trouble from cracking on this work that a flange 5

ins. thick was substituted. Provide for the method of handling the block

so that dog or lewis holes will not come in the showing faces. Dog holes

can be made with a pick when the concrete is three or four weeks old.

When it is not practicable to use dogs, two-pin lewises can be used. The

lewis holes should be cast in the block and should be of larger size

than for granite; they should not be located too near the mortar faces.

In turning blocks it is necessary to provide some sort of cushion for

them to turn on or broken arrises will result. When the work will

permit, it is desirable to round the arrises to about a 3/8-in. radius.

The following general figures of the cost of block work are available.

Foreman cutters were paid $5 per day; foreman concrete workers $3 per

day; stonecutters $4 per day; concrete laborers $1.70 per day, and

common laborers $1.50 to $1.70 per day. Plain and ornamental blocks cost

about the same, the large size of the ornamental blocks bringing down

the cost. The following is given as the average cost of block work per

cubic yard:

Cement $ 1.95

Sand 0.35

Stone 1.14

Forms, lumber and making 0.80

Mixing and placing concrete 1.50

Dressing 4.73

Handling and setting 2.00

Superintendence, plant, incidentals at 25 per cent. 3.12

Condemnation at 5 per cent. 0.78

------

Total cost blocks in place $16.37

It will be seen that the largest single item in the above summary of

costs is the item of dressing. This was done, as stated above, partly by

hand and partly by pneumatic tools. Hand tooling cost about twice as

much as machine tooling, but its appearance was generally better. The

average cost of tooling the several forms of blocks is shown by Table

XIX. For 42,190 sq. ft. the average cost was 26 cts. per sq. ft. or

$2.34 per sq. yd., or $4.73 per cu. yd. of block work. This tooling was

done by stone cutters, and was unusually high in cost.

_Mass Concrete Work._--All parts of the bridge except the molded block

trim were built of concrete deposited in place. Briefly, the molded

blocks were set first and then backed up with the mass concrete

deposited in forms and on centers. The only features of this work that

call for particular description are those in connection with the main

arch ring and the spandrel arch construction.

The main arch rings were concreted in transverse sections; Fig. 158

shows the size and order of construction of these sections. Back forms

were necessary up to an angle of 45° from the spring line after which

the concrete was made somewhat drier and back forms were not used. After

Sections 1, 2, 3 and 4 had been concreted they were allowed to set and

then the struts and back forms were taken out and the intervening

sections were concreted. The large Sections 6 and 7 were concreted in

five sections each, in order to permit the taking out of the timber

struts supporting the sections above. The concrete in all sections was

placed in horizontal layers as a rule and it is the judgment of the

engineers in charge of this work that this is the preferable method.

TABLE XIX.--SHOWING COST OF TOOLING CONCRETE ORNAMENTAL BLOCKS FOR

CONNECTICUT AVENUE BRIDGE.

===============================================================================

| | Per Superficial Foot of

| Per Cubic Foot. | Showing Face.

+------+-----+------+-----+------+------+------+------

-------------------------+------+-----+------+-----+------+------+------+------

Rail Posts (Cap and Base)| 344| 16.0| 5,500|$0.27| 10.5 | 3,630|$0.41 | 0.66

Moulding under coping | 770| 5.9| 4,560| 0.30| 3.8 | 2,930| 0.47 | 0.64

Dentils between Moulding | 520| 5.5| 2,860| 0.20| 8.0 | 4,160| 0.14 | 1.45

Coping | 494| 61.2|30,220| 0.12| 35.4 |17,490| 0.21 | 0.58

Pedestal (3 courses) | 162| 27.2| 4,400| 0.15| 14.1 | 2,290| 0.29 | 0.52

Rail Posts (Top and Base)| 296| 7.1| 2,100| 0.50| 17.3 | 5,100| 0.21 | 2.43

over Piers (Top and Base)| 248| 22.9| 5,690| 0.17| 26.5 | 6,580| 0.15 | 1.16

-------------------------+------+-----+------+-----+------+------+------+------

Average of above--Totals | 2,834| 19.5|55,330|$0.17| 14.8 |43,190|$0.26 | 0.77

-------------------------+------+-----+------+-----+------+------+------+------

TABLE XX.--SHOWING COST OF MASS CONCRETE WORK PER CUBIC YARD.

[Transcriber's note: Table split]

===========================================================================

Description. | | +--------+------+-------+ |

-------------------+--------+---------+--------+------+-------+-----------+

Class A, in Piers | 1:2:4½ | 150 | 1.65 | 0.39 | 1.08 | 3.12 |

Class A, in Arches | 1:2:4½ | 200 | 1.65 | 0.39 | 1.08 | 3.11 |

--Solid Work | 1:3:6 | 160 | 1.40 | 0.42 | 1.23 | 3.05 |

--Hollow Work | 1:3:6 | 110 | 1.40 | 0.42 | 1.23 | 3.05 |

Spandrel Walls | 1:3:6 | 110 | 1.40 | 0.42 | 1.23 | 3.05 |

Spandrel Arches | 1:3:6 | 200 | 1.40 | 0.42 | 1.23 | 3.05 |

in Abutments | 1:3:6 | 150 | 1.40 | 0.42 | 1.23 | 3.05 |

over Bridge | 1:3:10 | 145 | 0.90 | 0.31 | 1.30 | 2.51 |

-------------------+--------+---------+--------+------+-------+-----------+

===============================================

| Cost of |

| Mixing and Placing. |

Description. +--------+--------+--------+

| | | Total |

| | | Mixing |

| | | and |

| Mixing.| Placing| Placing|

-------------------+--------+--------+--------+

Class A, in Piers | 0.09 | 0.21 | 0.30 |

| | | |

Class A, in Arches | 0.05 | 0.28 | 0.33 |

Class B, in Piers | | | |

--Solid Work | 0.09 | 0.18 | 0.27 |

Class B, in Piers | | | |

--Hollow Work | 0.11 | 0.36 | 0.47 |

Class B, in | | | |

Spandrel Walls | 0.11 | 0.40 | 0.51 |

Class B, in | | | |

Spandrel Arches | 0.07 | 0.26 | 0.33 |

Class B, | | | |

in Abutments | 0.11 | 0.24 | 0.35 |

Class C, Filling | | | |

over Bridge | 0.11 | 0.28 | 0.39 |

-------------------+--------+--------+--------+

=========================================================================

| Cost of Form Work. | |

Description. +----------+-------+--------+-----------+-------------+

-------------------+----------+-------+--------+-----------+-------------+

Class A, in Piers | 0.17 | 0.05 | 0.16 | 0.38 | $3.80 |

| | | | | |

Class A, in Arches | 0.08 | 0.03 | 0.10 | 0.21 | 3.66 |

--Solid Work | 0.17 | 0.05 | 0.16 | 0.38 | 3.70 |

--Hollow Work | 0.77 | 0.25 | 0.64 | 1.66 | 5.18 |

Spandrel Walls | 0.85 | 0.28 | 0.73 | 1.86 | 5.42 |

Spandrel Arches | 0.94 | 0.30 | 0.86 | 2.10 | 5.48 |

in Abutments | 0.10 | 0.03 | 0.12 | 0.25 | 3.65 |

over Bridge | 0.00 | 0.00 | 0.00 | .... | 2.90 |

-------------------+----------+-------+--------+-----------+-------------+

[Footnote G: Add 25% to the cost here tabulated for superintendence,

plant and incidentals.]

Considerable difficulty was experienced in building the large arches

with a concrete block facing on account of the fact that the edges of

the blocks are liable to chip off when any concentrated pressure is

brought on them. In order to permit the ring of blocks to deform as the

centering settled under its load, sheet lead was placed in the joints

between blocks at the points corresponding with the construction joints

between sections of the mass concrete backing. The deflection of the

centers at the crown was a maximum of 3¼ ins. and a minimum of 2½ ins.

TABLE XXI--Detail Cost of Engineering and Inspection for Different

Classes of Work.

Engineering. Inspection.

Kind of Work. Total. Unit. Total. Unit.

Class A, concrete, 23,500 cu. yds $3,055.00 $0.13 $1,762.50 $0.075

Class B, concrete, 36,580 cu. yds 3,658.00 0.10 1,646.10 0.045

Class C, concrete, 2,150 cu. yds 107.50 0.05 53.75 0.025

Class D, concrete, 6,250 cu. yds 1,875.00 0.30 4,687.50 0.75

1,000 M. ft. B. M. centering 1,000.00 1.00 440.00 0.44

Cement, 73,000 barrels 365.00 0.005 730.00 0.01

Earth filling, 50,000 cu. yds 1,000.00 0.02 500.00 0.01

The centering of the main arches was not struck until the spandrel

arches and all the work above the main arches to the bottom of the

coping had been completed. The first and third spandrel arch on each

side of the piers was made with an expansion joint in the crown. To

permit further of the adjustment of the portion of the masonry above the

backs of the main arches, the crown of the middle arch of each set of

spandrel arches was left unconcreted until the center of the main arches

had been struck. It may be noted here that the expansion joints in the

first and third arches were carried up through the dentils and coping,

and observations show that these joints are about 1/8 in. larger in

winter than in summer.

The cost of the mass concrete work is shown in Table XX. These figures

are based on the wages already quoted and the following: Foreman

riggers, $4.50; riggers, $1.50 to $1.75 and $2; skilled laborers, $2;

engineers, $3.50. The detail cost of engineering and inspection is shown

in Table XXI.

~ARCH BRIDGES, ELKHART, IND.~--At the new Elkhart, Ind., yards of the Lake

Shore & Michigan Southern Ry. the tracks are carried over a city street

by concrete arches 40, 60 and 160 ft. long. These arches all have a span

of 30 ft., a height of 13 ft. and a ring thickness at crown of 28 ins.

The reinforcement consists of arch and transverse bars; the arch bars

are spaced 6 ins. on centers 2½ ins. from both extrados and intrados,

and the transverse bars are spaced 24 ins. on centers inside both lines

of arch bars. The proportions of the concrete were generally 1 cement, 3

gravel and 6 stone. The gravel was a material dug from the foundations

and was about 50 per cent. sand and 50 per cent. gravel, ranging up to

the size of pigeons' eggs. The concrete was machine mixed and was mixed

very wet.

The work was done by the railway company's forces, and Mr. Samuel

Rockwell, Assistant Chief Engineer, gives the following figures of cost:

Total. Per cu. yd.

Temporary buildings, trestles, etc. $ 752.33 $0.15

Machinery, pipe fittings, etc. 416.34 0.08

Sheet piling and boxing 1,006.12 0.21

Excavation and pumping 1,619.74 0.33

Arch centers and boxing 3,528.92 0.73

--------- -----

Total $7,323.45 $1.50

Concrete masonry:

Cement 8,860.55 1.84

Stone 1,788.50 0.36

Sand 240.00 0.05

Drain tile 103.03 0.02

Labor 8,091.41 1.68

---------- -----

Total concrete $19,083.49 $3.95

Steel reinforcing rods $ 3,028.39 $0.63

Engineering, watching, etc. 508.40 0.11

---------- -----

Grand total (4,833 cu. yds. concrete) $29,943.73 $6.19

~ARCH BRIDGE, PLAINWELL, MICH.~--The following figures of cost of a

reinforced concrete arch bridge are given by Mr. P. A. Courtright. The

bridge crosses the Kalamazoo River at Plainwell, Mich., and is 446 ft.

long over all with seven arches of 54 ft. span and 8 ft. rise. The arch

rings were reinforced with 4-in., 6-lb. channels bent to a radius of 70

ft. and spaced 1.9 ft. c. to c. The contract price of the bridge was

$19,900.

The concrete was made of Portland cement and a natural mixture of sand

and gravel in the proportions of 1-8 for the foundations, 1-6 for arches

and spandrel walls and 1-4 for the parapet wall. The proportions were

determined by measure; the wagon boxes being built to hold a cubic yard

of sand and gravel. A sack of cement was taken as 1 cu. ft. For

foundations the pit mixture was used without screening; stones over 4

ins. in diameter being thrown out at the pit or on the mixing board. For

the arches and spandrel walls the gravel was passed over a 2-in. mesh

screen on the wagon box. The aggregate for the parapet walls was

screened to 1 in. largest diameter. The concrete was mixed in a McKelvey

continuous mixer which turned the material eight times. The mode of

procedure was as follows: The gravel was loaded upon wagons in the pit

and hauled to a platform at the intake of the mixer. Half of the cement

required in the concrete was then spread over the top of the load in the

wagon box and the whole was dumped through the bottom of the wagon box

onto the platform and spread with shovels. The remainder of the cement

was spread over the mixture and the whole was shoveled by one man to a

second man who shoveled it into the mixer. Water was added after the

mixture had passed about one-third of the way through the mixer. The

mixer delivered the concrete directly into wheelbarrows, by which it was

delivered to the work. The concrete was spread in layers from 2 to 4

ins. in thickness and thoroughly rammed with iron tampers; two men were

employed tamping for each man shoveling. The arches were concreted in

three longitudinal sections, each section constituting a day's work. The

work was done in 1903 and the concrete cost for mixing and placing:

Labor: Per day. Per cu. yd.

13 men at $1.80 $23.40 $0.78

Engine and mixer 5.00 0.17

1 team 3.00 0.10

1 foreman 3.00 0.10

------ -----

Totals for labor $34.40 $1.15

Materials:

0.65 bbl. cement at $2 $1.30

0.9 cu. yd. gravel at $0.50 0.45

-----

Total for materials $1.75

Grand total $2.90

~METHODS AND COST OF CONSTRUCTING A FIVE-SPAN ARCH BRIDGE.~--This bridge

consisted of five elliptical arch spans of 40, 45, 60, 87 and 44 ft.,

carried on concrete piers. The arch rings were 12 ins. thick at the

crowns and 18 ins. thick 5 ft. from the centers of piers and carried

4-in. spandrel walls; there were 1,000 cu. yds. of concrete in the

arches and 600 cu. yds. in the piers. Each arch ring was reinforced by a

grillage of longitudinal and transverse rods.

[Illustration: Fig. 159.--End View of Center for Short Elliptical Arch

Spans.]

_Forms and Centers._--Figure 159 is an end view of the center arch. It

consists of a series of bents, 6 ft. c. to c., the posts of each bent

being 5 ft. c. to c. These posts are made of 2×6-in. Washington fir.

Upon the heads of the posts rest 2×6-in. stringers, extending from bent

to bent. Resting on these stringers are wooden blocks, or wedges, which

support a series of cross-stringers, also of 2×6-in. stuff, spaced 2 ft.

c. to c. On top of these cross-stringers rest the sheeting planks,

which are 1×6-in. stuff, dressed on the upper side, and bent to the

curve of the arch. This sheeting plank was not tongue and grooved, and a

man standing under it, after it is nailed in place, could see daylight

through the cracks. It looked as if it would leak like a sieve, and let

much of the wet concrete mortar flow through the cracks, but, as a

matter of fact, scarcely any escapes. Figure 160 shows a front view of a

bent, and indicates the manner of sway bracing it with 1×4-in. stuff.

Figure 161 shows the outer forms for the parapet wall, or concrete hand

railing, and it will be noted that the cross-stringers are allowed to

project about 3 ft. so as to furnish a place to fasten the braces which

hold the upright studs. The inner forms for the parapet wall are shown

in dotted lines. They are not put in place until all the concrete arch

is built. Then they are erected and held to the outer forms by wire, and

are sway braced to wooden cleats nailed to the top surface of the

concrete arch.

[Illustration: Fig. 160.--Front View of Center for Short Elliptical Arch

Spans.]

[Illustration: Fig. 161.--Form for Parapet Wall for Arch Bridge.]

For the five spans the total amount of lumber in the centers was in

round figures 28 M. ft., distributed about as follows:

Item. Ft. B. M.

1×6-in. sheeting 5,600

2×6-in. longitudinal stringers 2,600

2×6-in. cross stringers 2,600

2×6-in. posts 4,000

3×8-in. sills 1,500

1×4-in. braces 3,000

Outer forms for spandrel walls 4,000

Inner forms for spandrel walls 4,000

------

Total 27,300

The aggregate span length of the arches was 276 ft., so that a little

less than 100 ft. B. M. of lumber was used for centering per lineal foot

of span. The superintendent at $5 per day and five carpenters at $3.50

per day erected the five centers in 18 days at a cost of $400, or a

trifle more than $14 per M. ft. B. M.; the cost of taking down the

centers was $2 per M. ft. B. M., and the lumber for the centers cost $24

per M. ft. B. M. making a grand total of $40 per M. ft. B. M. for

materials and labor. As there were 1,000 cu. yds. of concrete in the

arches and spandrels, the cost of centers and forms was $1.12 per cu.

yd. This form lumber was, however, after taking down, used again in

erecting a reinforced concrete building. Assuming that the lumber was

used only twice, the cost of centers and forms for these five arches was

less than 80 cts. per cu. yd. of concrete.

_Shaping and Placing Reinforcement._--The 60 and 87-ft. spans were

reinforced with 32 1½-in. round longitudinal rods held in place by

½-in. square transverse rods wired at the intersections; the

reinforcement of the smaller spans was exactly the same except that

1-in. diameter rods were used. To bend the longitudinal rods to curve,

planks were laid on the ground roughly to the curve of the arch; the

exact curve was marked on these planks and large spikes were driven part

way into the planks along this mark. The end of a rod was then fastened

by spiking it against the first projecting spike head and three men

taking hold of the opposite end and walking it around until the rod

rested against all the spikes on the curve. It took three men two 8-hour

days to bend 46,000 lbs. of rods. Their wages were $2.50 each per day,

making the cost of bending 0.03 ct. per pound, or 60 cts. per ton. It

took a man 5 mins. to wire a cross rod to a longitudinal rod. With wages

at $2.50 per day the cost of shaping and placing the reinforcement per

ton was as follows:

Item. Per ton.

Bending rods $0.60

Shearing rods to lengths 0.40

Carrying rods onto bridge 0.40

Placing and wiring rods 2.35

-----

Total $3.75

Including superintendence the labor cost was practically $4 per ton, or

0.2 cts. per lb. Altogether 66,000 lbs. of steel was used for

reinforcing 1,000 cu. yds. of concrete, or 66 lbs. per cu. yd. The cost

of steel delivered was 2 cts. per lb., and the cost of shaping and

placing it 0.2 ct. per lb., a total of 2.2 cts. per lb. or 2.2 × 66 =

$1.45 per cu. yd. of concrete.

_Mixing and Placing Concrete._--A Ransome mixer holding a half-yard

batch was used. The mixer was driven by an electric motor. The concrete

for the piers was a mixture of 1 part Portland cement to 7 parts gravel;

for the arches, the concrete was mixed 1 to 5. The gravel was piled near

the mixer, a snatch team being used to assist the wagons in delivering

the gravel into a pile as high as possible. Run planks supported on

"horses" were laid horizontally from the mixer to the gravel, so that

big wheelbarrow loads could be handled. The barrows were loaded with

long-handled shovels, and the men worked with great vigor, as is shown

by the fact that four men, shoveling and wheeling, delivered enough

gravel to the mixer in 8 hrs. to make 100 cu. yds. of concrete. We have,

therefore, estimated on a basis of six men instead of four. The mixer

crew was organized as follows:

Per day.

6 men shoveling and wheeling $12

2 men handling cement 4

1 man handling water 2

1 man dumping concrete 2

2 men handling dump cars 4

2 men handling hoisting rope 4

4 men spreading and ramming concrete 8

1 engineman 4

1 foreman 5

Fuel, estimated 3

---

Total $48

The output of this crew was 100 cu. yds. per day. The concrete was

hauled from the mixer in two small dump cars, each having a capacity of

10 cu. ft. The average load in each car was ¼ cu. yd. Ordinary mine cars

were used, of the kind which can be dumped forward, or on either side.

The cars were hauled over tracks having a gage of 18 ins. The rails

weighed 16 lbs. per yard, and were held by spikes ¼×2½ ins. Larger

spikes would have split the cross-ties, which were 3×4 ins. Only one

spike was driven to hold each rail to each tie, the spikes being on

alternate sides of the rail in successive ties. No fish plates or splice

bars were used to join the rails, which considerably simplifies the

track laying.

[Illustration: Fig. 162.--Trestle for Service Track.]

Two lines of track were laid over the bridge. The tracks were supported

by light bents, the cross-tie forming the cap of each bent, as shown in

Fig. 162. The bents were spaced 3 ft. apart. There were two posts to

each bent, toe-nailed at the top of the tie, and at the bottom to the

arch sheeting plank. Two men framed these crude bents and laid the two

rails at the rate of 150 lin. ft. of track per day, at a cost of 4 cts.

per lin. ft. of track. As stated, there were two tracks, one on each

side of the bridge, but they converged as they neared the concrete

mixer, so that a car coming from either track could run under the

discharge chute of the mixer; Fig. 163 shows the arrangement of the

tracks at the mixer. The part of each rail from A to B (6 ft. long)

was free to move by bending at A, the rail being spiked rigidly to the

tie at A, leaving its end at B free to move. To move the end B, so

as to switch the cars, a home-made switch was improvised, as shown in

Figs. 163 and 164.

[Illustration: Fig. 163.--Arrangement of Service Tracks at Mixer.]

[Illustration: Fig. 164.--Improvised Switch for Service Cars, General

Plan.]

It will be remembered that this bridge was a series of five arches.

There was a steep grade from the two ends of the bridge to the crown of

the center arch. Hence the two railway tracks ascended on a steep grade

from the mixer for about 175 ft., then they descended rapidly to the

other end of the bridge. Hence to haul the concrete cars up the grade by

using a wire cable, it was necessary to anchor a snatch block at the

center of the bridge. This was done by erecting a short post, the top

of which was about a foot above the top of the rails. The post stood

near the track, and was guyed by means of wires, and braced by short

inclined struts. To the top of the post was lashed the snatch block

through which passed the wire rope. Fig. 165 shows this post, P. About

10 ft. from the post P, on the side toward the mixer, another post,

Q, was erected, and a snatch block fastened to it. When the hoisting

engine, which was set near the concrete mixer, began hauling the car

along the track, a laborer would follow the car. Just before the car

reached the post Q, he would unhook the hoisting rope from the front

end of the car, then push the car past the post Q, and hook the

hoisting rope to the rear of the car. The car would then proceed to

descend in the direction T, being always under the control of the wire

rope, except during the brief period when the car was passing the post

Q. Each of the two cars was provided with its own hoisting rope, and

one engineer, operating a double drum hoist, handled the cars. The hoist

was belted to an 8 HP. gasoline engine, no electric motor being

available for the purpose.

[Illustration: Fig. 165.--General Plan of Rope Haulage System.]

[Illustration: Fig. 166. Fig. 167. Details of Haulage Rope Guides.]

Where hauling is done in this manner with wire ropes, it is necessary to

support the ropes by rollers wherever they would rub against

obstructions. A cheap roller can be made by taking a piece of 2-in. gas

pipe about a foot long, and driving a wooden plug in each end of the gas

pipe. Then bore a hole through the center of the wooden plugs and drive

a 1-in. round rod through the holes, as shown in Fig. 166. The ends of

this rod are shoved into holes bored into plank posts, which thus

support the roller. Where the rope must be carried around a more or less

sharp corner, it is necessary to provide two rollers, one horizontal and

the other vertical, as shown in Fig. 167.

When conveying concrete to a point on the bridge about 300 ft. from the

mixer, a dump car would make the round trip in 3 mins., about ¼ min. of

its time being occupied in loading and another ¼ min. in dumping. One

man always walked along with each car, and another man helped pull the

wire rope back.

Including the cost of laying the track and installing the plant, the

cost of mixing and placing the 1,600 cu. yds. of concrete was only 55

cts. per cu. yd., in spite of the high wages paid. However, the men were

working for a contractor under a very good superintendent.

Summing up the cost of the concrete in the arches of this bridge, we

have:

Per cu. yd.

1.35 bbl. cement at $3 $4.05

1 cu. yd. gravel at $1 1.00

66 lbs. of steel in place at 2.2 cts. 1.45

Centers in place (lumber used once) 1.12

Labor, mix and place concrete 0.55

-----

Total $8.17

The cost of the nails, wire, excavation and plant rental is not

available, but could not be sufficient to add more than 10 cts. per cu.

yd. under the conditions that existed in this case.

~CONCRETE RIBBED ARCH BRIDGE AT GRAND RAPIDS, MICH.~--The bridge consisted

of seven parabolic arch ribs of 75 ft. clear span and 14 ft. rise. The

five ribs under the 21-ft roadway were each 24 ins. thick, 50 ins. deep

at skewbacks and 25 ins. deep at crown; the two ribs under the sidewalks

were 12 ins. thick and of the same depth as the main ribs. Each rib

carried columns which supported the deck slab. Columns and ribs were

braced together across-bridge by struts and webs. All structural parts

of the bridge were of concrete reinforced by corrugated bars. The

abutments were hollow boxes with reinforced concrete shells tied in by

buttresses and filled with earth. There were in the bridge including

abutments 884 cu. yds. of concrete and 62,000 lbs. of reinforcing metal,

or about 70 lbs. of reinforcing metal per cu. yd. of concrete. Of the

884 cu. yds. of concrete 594 cu. yds. were contained in the abutments

and wing walls and 290 cu. yds. in the remainder of the structure. (Fig.

168.)

[Illustration: Fig. 168.--Details of Ribbed Arch Bridge.]

_Centers._--The center for the arch consisted of 4-pile bents spaced

about 12 ft. apart in the line of the bridge. The piles were 12×12

in.×24 ft. yellow pine and they were braced together in both directions

by 2×10-in. planks. Each bent carried a 3×12-in. plank cap. Maple

folding wedges were set in these caps over each pile and on them rested

12×12-in. transverse timbers, one directly over each bent. These

12×12-in. transverse timbers carried the back pieces cut to the curve of

the arch. The back pieces were 2×12-in. plank, two under each sidewalk

rib and four under each main rib of the arch. The back pieces under each

rib were X-braced together. The lagging was made continuous under the

ribs but only occasional strips were carried across the spaces between

ribs. This reduced the amount of lagging required but made working on

the centers more difficult and resulted in loss of tools from dropping

through the openings. Work on the centers and forms was tiresome owing

both to the difficulty of moving around on the lagging and to the

cramped positions in which the men labored. Carpenters were hard to keep

for these reasons.

_Concrete._--A 1-7 bank gravel concrete was used for the abutments and a

1-5 bank gravel concrete for the other parts of the bridge. The concrete

was mixed in a cubical mixer operated by electric motor and located at

one end of the bridge. The mixed concrete was taken to the forms in

wheelbarrows. The mixture was of mushy consistency. No mortar facing was

used, but the exposed surfaces were given a grout wash. In freezing

weather the gravel and water were heated to a temperature of about 100°

F.; when work was stopped at night it was covered with tarred felt, and

was usually found steaming the next morning.

_Cost of Work._--The cost data given here are based on figures furnished

to us by Geo. J. Davis, Jr., who designed the bridge and kept the cost

records. Mr. Davis states that the unit costs are high, because of the

adverse conditions under which the work was performed. The work was done

by day labor by the city, the men were all new to this class of work,

the weather was cold and there was high water to interfere, and work was

begun before plans for the bridge had been completed, so that the

superintendent could not intelligently plan the work ahead. Cost keeping

was begun only after the work was well under way. Many of the items of

cost are incomplete in detail.

The following were the wages paid and the prices of the materials used:

Materials and Supplies:

No. 1 hemlock matched per M. ft. $20

No. 1 hemlock plank per M. ft. 17

No. 2 Norway pine flooring per M. ft. 19

No. 2 yellow pine flooring per M. ft. 20

12×12-in.×16-ft. yellow pine per M. ft. 29

12×12-in.×24-ft. yellow pine, piling per M. ft. 27

Maple wedges per pair 50 cts.

½-in. corrugated bars per lb. 2.615 cts.

¾-in. corrugated bars per lb. 2.515 cts.

7/8-in. corrugated bars per lb. 2.515 cts.

Coal per ton $4

Electric power per kilowatt 6 cts.

Medusa cement per bbl. $1.75

Aetna cement per bbl. 1.05

Bank gravel per cu. yd. 0.85

Sand per cu. yd. 0.66

Carpenters per day $3 to 3.50

Common labor per day 1.75

The summarized cost of the whole work, with such detailed costs as the

figures given permit of computation, was as follows:

General Service: Total. Per cu. yd.

Engineering $451 $0.512

Miscellaneous 75 0.084

Pumping: Total 110 days.

Coal at $4 per ton $210

Machinery, tools and cartage 283

Labor 497

----

Total $990

This gives a cost of $9 per day for pumping.

Excavation: Total cost. P. C. Total.

Timber cartage, etc. $ 375 17.6

Tools 69 3.3

Labor at $1.75 1,687 79.1

------ -----

Total $2,131 100.0

Filling 5,711 cu. yds.: Total. Per cu. yd.

Earth $1,142 $0.20

Labor including riprapping 396 0.07

------ -----

Total $1,538 $0.27

Removing Old Wing Walls: Total.

Labor and dynamite $ 346

Tools and sharpening 64

-----

Total $ 410

Hand Rail, 150 ft.: Total. Per lin. ft.

Material $ 278 $1.85

Labor 29 0.19

----- -----

Total $ 307 $2.04

Wood Block Pavement, 296 sq. yds.: Total. Per sq. yd.

Wood block, etc. $ 695 $2.35

Labor 57 0.19

----- -----

Total $ 752 $2.54

Steel, 62,000 lbs.: Total. Per lb.

Corrugated bars, freight, etc. $1,498 2.41 cts.

Plain steel, wire, etc. 75 0.12 cts.

Blacksmithing, tools and placing 438 0.71 cts.

------ ----

Total $2,011 3.24 cts.

Concrete.

Centering: Total. Per cu. yd.

Lumber and piles $ 332 $1.14

Labor 272 0.95

----- -----

Total $ 604 $2.09

Total. Per cu. yd.

Forms $ 3,312 $ 3.75

Concrete 5,532 6.25

------- ------

Grand total $18,113 $20.50

In more detail the cost of the various items of concrete work was as

follows for the whole structure, including abutments, wing walls and

arch containing 884 cu. yds.:

Form Construction: Total. Per cu. yd.

Lumber and cartage $1,547 $1.75

Nails and bolts 129 0.15

Tools 110 0.12

Labor, erecting and removing 1,526 1.72

------ -----

Total $3,312 $3.74

Concrete Construction.

Materials:

Aetna cement at $1.05 $1,218 $1.37

Medusa cement at $1.75 499 0.56

Sand at 66 cts. per cu. yd. 37 0.04

Gravel at 85 cts. per cu. yd. 915 1.04

------ -----

Total materials $2,669 $3.01

Mixing:

Machinery and supplies $ 549 $0.62

Power at 6 cts. per kw. 52 0.06

Tools 22 0.02

Labor 737 0.83

----- -----

Total mixing $1,360 $1.53

Placing concrete $ 609 $0.69

Tamping concrete $ 481 $0.54

Heating Concrete:

Apparatus and cartage $ 47 $0.05

Fuel 96 0.11

Labor 270 0.31

----- -----

Total heating $ 413 $0.47

Grand total $8,844 $9.98

Considering the abutment and wing wall work, comprising 594 cu. yds.,

separately, the cost was as follows:

Forms: Per cu. yd.

Materials $1.20

Labor 1.09

-----

Total $2.29

Concrete:

Materials $2.92

Labor 2.38

-----

Total $5.30

Heating water and gravel $0.70

Grand total $8.29

Considering the arch span, comprising 290 cu. yds., separately, the cost

was as follows:

Forms: Per cu. yd.

Materials $3.70

Labor 3.03

-----

Total $6.73

Concrete:

Materials $3.22

Labor 3.57

Total $6.79

Grand total $13.52

CHAPTER XVIII.

METHODS AND COST OF CULVERT CONSTRUCTION.

Culvert work is generally located on the line of a railway or a highway,

so that the facilities for getting plant and materials onto the work are

the best, and as culverts are in most cases through embankment, under

trestle or in trench below the ground level the advantage of gravity is

had in handling materials to mixer and to forms. Ordinarily individual

culverts are not long enough for any material economy to be obtained by

using sectional forms unless these forms are capable of being used on

other jobs which may occasionally be the case where standard culvert

sections have been adopted by a railway or by a state highway

commission. Various styles of sectional forms for curvelinear sections

are given in Chapter XXI, and centers suitable for large arch culverts

are discussed in Chapter XVII. Figure 169 shows an economic form for box

sections; it can be made in panels or with continuous lagging as the

prospects of reuse in other work may determine. For curvelinear sections

of small size some of the patented metal forms have been successfully

used.

~BOX CULVERT CONSTRUCTION, C., B. & Q. R. R.~--Mr. L. J. Hotchkiss gives

the following data. Box sections of the type shown by Fig. 169 are used

mostly; they range in size from single 4×4-ft. to double 20×20-ft. and

triple 16×20-ft. boxes. These boxes are more simple in design and

construction than arches, and for locations requiring piles they are

less expensive. The form work is plain and the space occupied is small

as compared with arches, so that excavation, sheeting and pumping are

less and the culvert can be put through an embankment or under a trestle

with less disturbance of the original structure. Finally, less expensive

foundations are required.

For small jobs where it does not pay to install a power mixer a hand

power mixer mounted on a frame carried by two large wheels has been

found at least as efficient as hand mixing; more convenient and easier

on the men. The machine is turned by a crank driving a sprocket chain;

it is charged at the stock piles and then hauled to the forms to be

discharged. Local conditions determine the capacity of power mixer to be

used. Difficulties in supplying material or in taking away the concrete

may readily reduce the output of a large machine to that of one much

smaller, and the small machine is cheaper in first cost and in

installation and operation. Where the yardage is sufficient to justify

the installation of equipment for handling the materials and output of a

large mixer it is found preferable to a small one, as the increase in

plant charges is not proportionately so great as the increase in the

amount of concrete handled. Again it may occur on a small job that the

concrete must be taken a long distance from the mixer, that a large

batch can be moved as quickly and as easily as a small one and the time

consumed in doing it is sufficient for the charging and turning of a

large mixer before the concrete car or bucket returns to it. Here a

large mixer, while it may stand idle part of the time, is still

economic.

[Illustration: Fig. 169.--Box Culvert and Form, C., B. & Q. R. R.]

The plant lay-outs vary with the local conditions, as the following will

show. In one case of a culvert located under a high, short trestle the

following arrangement of plant was employed: A platform located on each

side of the approach embankment about 8 ft. below the ties was built of

old bridge timbers. A track was laid on each platform and ran out over a

mixer located on the end slope of the embankment. Two mixers, one for

each platform, were used. From each mixer a track led out over the

culvert form and a track along the top of this form ran the full length

of the culvert. Gravel and sand were dumped from cars onto the side

platforms and thence shoveled into small bottom dump cars, which were

pushed out over the mixer and dumped directly into it. Cars on the short

tracks from mixers to culvert form took the mixed concrete and dumped it

into the distributing cars traveling along the form. The cars were all

hand pushed.

An entirely different lay-out was required in case of a long box culvert

located in a flat valley some 600 ft. from the track. A platform was

built at the foot of the embankment with its outer edge elevated high

enough to clear two tracks carrying 5 cu. yd. dump cars. The sand and

gravel was dumped from cars onto the side of the embankment, running

down onto the platform so that scraper teams moved it to holes in the

platform where it fell into the dump cars. These cars were hauled by

cable from the mixer engine and dumped at the foot of an inclined

platform leading to a hopper elevated sufficiently to let a 1½ cu. yd.

dump car pass under it. A team operating a drag scraper by cable moved

the material up the inclined platform into the hopper, whence it fell

directly into the car to which cement was added at the same time. The

charging car was then pulled by the mixer engine up another incline, at

the top of which it dumped into the mixer. The concrete car was hauled

up another incline to a track carried on the forms and reaching the full

length of the culvert work.

The placing of the reinforcement is given close supervision. When a wet

concrete is used it is found necessary to securely fasten the bars in

place to prevent them being swept out of place by the rush of the

concrete. A method of supporting the invert bars is shown by Fig. 169;

2×2-in. stakes are large enough and they need never be spaced closer

than 6 ft. The longitudinal bars are held on the stakes by wire nails

bent over and the transverse bars are wired to them at intersections by

stove pipe wire. The vertical wall bars are placed by thrusting the

ends into the soft footing concrete and nailing them to a horizontal

timber at the top; the horizontal wall bars are wired at intersections

to the verticals. In the roof slab the stakes are replaced by metal

chairs, or by small notched blocks of concrete.

The form construction is shown by Fig. 169. It is not generally made in

panels, since, as the work runs, the locations of boxes of the same size

are usually so far apart that transportation charges are greater than

the saving due to use a second time. No general rule is followed in

removing forms, but they can usually be taken down when the concrete is

a week old.

The boxes are built in sections separated by vertical joints, one

section being a day's work. The vertical joints are plain butt joints;

tongue and groove joints give trouble by the tenons cracking off in the

planes of the joints. A wet mixture is used and smooth faces obtained by

spading.

~ARCH CULVERT COSTS, N. C. & ST. L. RY.~--The cost of arch culvert

construction for the Nashville, Chattanooga & St. Louis Ry. is recorded

in a number of cases as follows:

~18-ft. Arch Culvert.~--Mr. H. M. Jones is authority for the following

data: An 18-ft. full-centered arch culvert was built by contract, near

Paris, Tenn. The culvert was built under a trestle 65 ft. high, before

filling in the trestle. The railway company built a pile foundation to

support a concrete foundation 2 ft. thick, and a concrete paving 20 ins.

thick. The contractors then built the culvert which has a barrel 140 ft.

long. No expansion joints were provided, which was a mistake for cracks

have developed about 50 ft. apart. The contractors were given a large

quantity of quarry spalls which they crushed in part by hand, much of it

being too large for the concrete. The stone was shipped in drop-bottom

cars and dumped into bins built on the ground under the trestle. The

sand was shipped in ordinary coal cars, and dumped or shoveled into

bins. The mixing boards were placed on the surface of the ground, and

wheelbarrow runways were built up as the work progressed. The cost of

the 1,900 cu. yds. of concrete in the culverts was as follows per cu.

yd.:

1.01 bbls. Portland cement $2.26

0.56 cu. yds. of sand, at 60 cts. .32

Loading and breaking stone .25

Lumber, centers, cement house and hardware .64

Hauling materials .04

Mixing and placing concrete 1.17

Carpenter work .19

Foreman (100 days at $2.50) .13

Superintendent (100 days at $5.50) .29

------

Total per cu. yd. $5.29

It will be seen that only 19 cu. yds. of concrete were placed per day

with a gang that appears to have numbered about 21 laborers, who were

negroes receiving about $1.10 per day. This was the first work of its

kind that the contractors had done. It will be noticed that the cost of

42 cts. per cu. yd. for superintendence and foremanship was

unnecessarily high.

~Six Arch Culverts 5 ft. to 16 ft. Span.~--All these arches were built

under existing trestles, and in all cases, except No. 2, bins were built

on the ground under the trestle and the materials were dumped from cars

into the bins, loaded and delivered from the bins in wheelbarrows to the

mixing boards, and from the mixing boards carried in wheelbarrows to

place. Negro laborers were used in all cases, except No. 5, and were

paid 90 cts. a day and their board, which cost an additional 20 cts.;

they worked under white foremen who received $2.50 to $3 a day and

board. In culvert No. 5, white laborers, at $1.25 without board, were

used. There were two carpenters at $2 a day and one foreman at $2.50 on

this gang, making the average wage $1.47 each for all engaged. The men

were all green hands, in consequence of which the labor on the forms in

particular was excessively high. The high rate of daily wages on

culverts Nos. 1 and 3 was due to the use of some carpenters along with

the laborers in mixing concrete. The high cost of mixing concrete on

culvert No. 2 was due to the rehandling of the materials which were not

dumped into bins but onto the concrete floor of the culvert and then

wheeled out and stacked to one side. The cost of excavating and

back-filling at the site of each culvert is not included in the table,

but it ranged from 70 cts. to $2 per cu. yd. of concrete.

Cost of Six Concrete Culverts on the N., C. & St. L. Ry. & St. L. Ry.

No. of culvert 1 2 3 4 5 6

Span of culvert 5 ft. 7.66 ft. 10 ft. 12 ft. 12 ft. 16 ft.

Cu. yds. of concrete. 210 199 354 292 406 986

Ratio of cement to

stone 1:5.5 1:6.5 1:5.8 1:5.8 1:6.1 1:6.5

Increase of concrete

over stone 16.0% 9.9% 6.3% 12.3% 8.3% 5.3%

Bbls. cement per cu.

yd. 1.02 0.90 1.06 1.01 1.00 1.09

Cu. yds. sand per cu.

yd. 0.43 0.49 0.44 0.46 0.46 0.47

Cu. yds. stone per

cu. yd. 0.86 0.90 0.95 0.89 0.94 0.94

Total days labor

(inc. foremen and

supt.) 702 607 784 726 768 1,994

Av. wages per day

(inc. foremen and

supt.) $1.61 $1.33 $1.59 $1.19 $1.47 $1.46

Cost per cu. yd.--

Cement 2.18 1.94 2.27 1.82 2.11 2.01

Sand 0.17 0.20 0.18 0.18 0.19 0.14

Stone 0.52 0.52 0.47 0.54 0.47 0.58

Lumber 0.88 0.43 0.48 0.43 0.31 0.57

Unload, materials 0.23 0.17 0.18 0.18 0.16

Building forms 1.07 0.33 0.62 0.47 0.72 0.41

Mixing & placing 1.59 1.74 1.69 1.35 1.23 1.26

------ ------ ------ ------ ----- -----

Total per cu. yd. $6.64 $5.33 $5.89 $4.97 $5.19 $4.97

~14-ft. 9-in. Arch Culvert.~--Mr. W. H. Whorley gives the following

methods and cost of constructing a 12-ft. full centered arch culvert 204

ft. long. The culvert was built in three sections, separated by vertical

transverse joints to provide for expansion; the end sections were each

61 ft. long and the center section was 70 ft. long. Fig. 170 is a

cross-section at the center; for the end sections the height is 14 ft. 9

ins., the crown thickness is 1 ft. 9 ins., and the side walls at their

bases are 5 ft. thick. The concrete was a 1-3-6 mixture, using slag

aggregate for part of the work and stone aggregate for a part. The

culvert was built underneath a trestle which was afterwards filled in.

_Mixing and Handling Concrete._--The height of the track above the

valley permitted the mixing plant to be so laid out that all material

was moved by gravity from the cars in which it was shipped until finally

placed in the culvert. Sand and aggregate were received in drop bottom

cars and were unloaded into bins in the trestle. These bins had hopper

bottoms with chutes leading to a wheeling platform, which was placed

between two trestle bents and extended over a mixer placed outside the

trestle. The cement house was erected alongside the trestle at the

wheeling platform level and a chute from an unloading platform at track

level to the opposite end of the house enabled the bags to be handled

directly from the car to the chute and thence run by gravity to the

cement house. Sand and aggregate were chuted from the bins into

wheelbarrows, wheeled about 23 ft., and dumped into a hopper over the

mixer. Water was pumped by a gasoline engine from a well just below the

trestle to a tank on the trestle, whence it was fed to the mixer by a

flexible connection, a valve so regulating the flow that the necessary

amount was delivered in the time required to mix a batch.

[Illustration: Fig. 170.--Section of Arch Culvert, N., C. & St. L. R.

R.]

The mixer was a No. 5 Chicago Improved Cube Mixer, operated by a

gasoline engine; a larger size would have been preferable since a batch

required only two-thirds of a bag of cement which had to be measured

which required the services of an additional man. The mixer was in

operation 194 hours and mixed 7,702 batches (1,217 cu. yds.), or a batch

every 87 seconds, or 6.3 cu. yds. per hour. During the last ten days it

mixed a batch every 78 seconds while running. The best short record made

was 291 batches in five hours, or one batch every 63 seconds, this being

at the rate of 58 batches equal to 9.2 cu. yds. of concrete in place per

hour, or nearly 1/6 cu. yd. per batch. It took about ½ minute to mix the

concrete and about the same length of time to charge and discharge the

mixer.

To convey the concrete from the mixer to the culvert walls a 1 cu. yd.

drop bottom car was used. This car ran on 30-in. gage tracks carried on

a trestle straddling the culvert walls and having its floor high enough

to clear the arch. A track ran lengthwise of the trestle over each

culvert wall, and a cross track intersecting both with turntables ran to

the mixer. Three men handled the car, a round trip to the extreme end of

the trestle being made in about 3 minutes. In the meantime the mixer was

discharging into a small hopper which unloaded into the car on its

return. One only of the three sections, of the culvert was built at a

time, both walls being brought up together. After a point had been

reached about 2 ft. above the springing on both walls, one track was

removed and the other was shifted to the center of the trestle.

_Forms._--There was used in the forms 15,000 ft. B. M. of 2-in. dressed

lagging for face work, 21,000 ft. B. M. rough lumber for back work, and

old car sills for studding. No charge was made for studding except the

cost of loading, the cost of the remaining lumber was $16 per M. for

dressed and $12.50 per M. for rough. A credit of one-third the cost was

allowed for the old material recovered. The total cost of the labor of

erecting the material in forms, bins and platforms was $666. The work

was done by a bridge crew of white men, the average rate of wages per

man, including the bridge foreman's time, being $2.20 per day. In

addition a mason at $3.50 per day and a carpenter at $2.25 per day

worked with the bridge crew in erecting forms.

_Cost._--The cost of the 1,217 cu. yds. of concrete in the culvert was

as follows:

Item. Per cu. yd.

1.08 bbls. cement at $1.72 $1.85

0.47 cu. yd. sand at 30 cts. 0.14

0.25 cu. yd. broken stone at 51 cts. 0.13

0.8 cu. yd. slag at 26 cts. 0.21

Lumber in forms, etc. 0.30

Miscellaneous materials 0.05

Labor, unloading materials 0.11

Labor, mixing and placing concrete 0.42

Labor, building forms 0.55

Labor, not classified 0.18

Labor, excavating 40 cts. per cu. yd. 0.28

Labor, back filling and tearing down forms 0.10

-----

Total $4.32

~CULVERTS FOR NEW CONSTRUCTION, WABASH RY.~--The following data relate to

culvert work carried out in constructing the Pittsburg extension of the

Wabash Ry. in 1903. All the work was done by contract.

_Plant I_: This plant was located on a hillside with the crushing bins

above the loading floor or platform which extended over the top of the

mixer, so that the crushed stone could be drawn directly from the chutes

of the bins and wheeled to the mixer. The sand was hauled up an incline

in one-horse carts and dumped on this floor, and was also wheeled in

barrows to the mixer. The proportions used were 4 bags of cement, 4

barrows of sand and stone dust and 7 barrows of crushed stone. A 7/8-cu.

yd. mixer was used and it averaged 40 cu. yds. per 10-hour day at the

following cost for labor:

Item. Per day. Per cu. yd.

1 foreman $ 3.00 $0.08

3 men charging with barrows 4.50 0.11

1 man attending engine and mixer 2.50 0.06

2 men loading concrete barrows 3.00 0.08

4 men wheeling concrete barrows (100 ft.) 6.00 0.15

4 men ramming concrete 6.00 0.15

4 men wheeling and bedding rubble stones 6.00 0.15

------ -----

Totals $31.00 $0.78

Assuming 1/3 ton of coal per day at $3 per ton, we have 2 cts. more per

cubic yard for fuel.

_Plant II._--At this plant a Smith mixer was used with a loading floor 4

ft. above the ground, this low platform being made possible by having a

hole or sump in which the skip receiving the concrete was set. A derrick

handled the skips between the sump and the work. The batch was made up

of 2 bags of cement, 2 barrows of sand and 4 barrows of stone. The

output was 50 cu. yds. per day of 10 hours at the following cost:

Item. Per day. Per cu. yd.

1 man feeding mixer $1.50 $0.03

1 mixer runner 2.50 0.05

1 derrick engineman 2.50 0.05

2 tagmen swinging and dumping 3.00 0.06

6 men wheeling materials 9.00 0.18

2 men tamping concrete 3.00 0.06

1 foreman 3.00 0.06

------ -----

Totals $24.50 $0.49

The cost of fuel would add about 3 cts. per cubic yard to this amount.

~SMALL ARCH CULVERT COSTS, PENNSYLVANIA R. R.~--Mr. Alex. R. Holliday

gives the following figures of cost of small concrete culvert work

carried out under his direction. The culvert section used is shown in

Fig. 171. This section gives a slightly larger waterway than a 36-in.

cast iron pipe. Eight culverts, having an aggregate length of 306 ft.

were built, using a mixture of Portland cement and limestone and

screenings. Each culvert had a small spandrel wall at each end.

The work was done by a gang of six men, receiving the following wages:

Foreman, cents per hour 27.5

Assistant " " " 17.5

Laborers " " " 15.0

Teams " " " 35.0

Superintendent, 2 days at $5.83-1/3 $ 11.67 $0.018