Cement, including freight and haulage, cost $1.97 per barrel. Limestone
and screenings cost 50 cts. per cu. yd. f. o. b. at quarry. No freight
charges are included in cost of any of the materials except cement. The
cost of the 306 ft. of culvert was as follows:
Item. Total. Per lin. ft. Per cu. yd.
Labor $443.14 $1.45 $3.35
Stone and screenings 78.50 0.25 0.60
Cement 307.53 1.01 2.34
Forms 12.00 0.04 0.09
------- ----- -----
Total $841.17 $2.75 $6.38
[Illustration: Fig. 171.--Small Culverts, Pennsylvania R. R.]
~26-FT SPAN ARCH CULVERT.~--The culvert was 62 ft. long and 26-ft. span
and was built of 1-8 and 1-10 concrete mixed by hand. The wages paid
were: General foreman, 40 cts. per hour; foreman, 25 cts. per hour;
carpenters, 22½ to 25 cts. per hour, and laborers, 15 cts. per hour. The
cost of the concrete in place, exclusive of excavation but including
wing walls and parapet, was as follows:
Per cu. yd.
0.96 bbl. cement, at $1.60 $1.535
1.03 tons coarse gravel, at $0.19 0.195
0.40 tons fine gravel, at $0.21 0.085
0.32 tons sand, at $0.36 0.115
Tools, etc. 0.078
Lumber for forms and centers 0.430
Carpenter work on forms (23 cts. hr.) 0.280
Carpenter work platforms and buildings 0.050
Preparing site and cleaning up 0.210
Changing trestle 0.085
Handling materials 0.037
Mixing and laying, av. 15½ cts. per hr. 1.440
------
Total per cu. yd $4.540
There were 1,493 cu. yds. of concrete in the work. The excavation cost
$463 and the total cost was $7,243.
~COST OF RAILWAY CULVERT.~--The culvert was for a single track railway and
contained 113 cu. yds. of concrete and required 36 cu. yds. of
excavation. The figures are given by C. C. Williams as follows:
Cost of Material.
Kind and Amount of Material. Unit Price. Cost.
Stone, 113.2 tons $.70 $ 79.24
Sand, 46.8 yds. .55 25.74
Cement, 137 bbls. .85 116.45
-------
Total $221.43
Lumber 52.50
Rail and bolts 36.60
-------
Total $ 89.10
Excavation.
Labor, 189 hours at .15 $ 28.35
Foreman, 60 hours at .30 18.00
-------
Total $ 46.35
Concrete.
Labor, 683 hours at .15 $102.45
Foreman, 130 hours at .30 39.00
-------
Total $141.45
Forms.
Carpenters, 313 hours at .225 $ 70.42
Labor, 30 hours at .15 4.50
-------
Total $ 74.92
Handling Materials.
Moving material, 245 hours at .15 $ 36.75
Unloading material, 95 hours at .15 14.25
Foreman, 20 hours at .30 6.00
-------
Total $ 57.00
Superintendence and Office.
Superintendent, 6 hours at .50 $ 3.00
Office 10.00
-------
Total $ 13.00
-------
Grand total $643.25
Proportional Costs.
Per cent.
Cost of Total
Per Yard Cost of
Item. Cost. Concrete. Concrete.
------
Concrete material $221.43 $1.96 7.1
Laying concrete 141.45 1.25 23.6
Lumber 52.50 .46 08.7
Rail and bolts 36.60 .32 06.1
Building forms 74.92 .67 13.3
Handling material 56.90 .50 09.0
Superintendent and office 13.00 .12 02.2
----- ------
Total $5.28 100.00
Excavation 46.35 1.28
-------
Total $643.15
Contractor's Receipts.
113 yds. concrete at $5.95 $672.35
36 yds. excavation at .30 10.80
-------
Total $683.15
Total cost 643.15
-------
Profit, 5.9% of contract price $ 40.00
~12-FT. CULVERT, KALAMAZOO, MICH.~--A portion 1,080 ft. long of a new
channel built in 1902-3 for a small stream flowing through the city of
Kalamazoo, Mich., was constructed as an arch culvert of the form shown
by Fig. 172. The concrete section is reinforced on the lines indicated
by a double layer of woven steel wire fabric. The concrete was
approximately a 1 cement, 6 sand and gravel mixture.
[Illustration: Fig. 172.--Cross-Section of Culvert at Kalamazoo, Mich.]
The centers were built in sections 12½ ft. long of the form and
construction shown by Fig. 173, and a sufficient number was provided to
lay twelve sections of invert and six sections of arch. The arch centers
were arranged to be uncoupled at the crown; this with the hinges at the
quarter points permitted the two halves to be separated and each half to
be folded so that it could be carried from the rear of the work through
the forms still in place and erected again for new work. When in place
the center ribs rested on the side forms which set on the invert
concrete and are braced apart by the hinged cross-strut. This
cross-strut was the key that bound the whole structure together; the
method of removing this key is indicated by Fig. 174. From his
experience with these centers the engineer of the work, Mr. Geo. S.
Pierson, remarks:
"In work of this kind it is very important to have the centering
absolutely rigid so it will not spring when concrete is being tamped
against it and thus weaken the cohesion of the concrete. It is also
important to have the arrangement such that all the centering can be
removed without straining or jarring the fresh concrete. The centers
were generally removed in about three or four days after the concrete
arch was in place."
[Illustration: Fig. 173.--Center for Culvert at Kalamazoo, Mich.]
The invert concrete was brought to form by means of templates, Fig. 173,
and straight edges. The side forms were then placed and braced apart by
the struts and concreting continued to the skewback plane indicated in
Fig. 173. The arch form was then placed; it rested at the edges on the
side forms and was further supported by center posts bearing on boards
laid on the bottom of the invert. A template, Fig. 175, was used to get
the proper thickness and form of arch ring. Outside forms were used to
confine the concrete at the haunches but nearer the crown they were not
required.
[Illustration: Fig. 174.--Hinged Cross Strut for Center for Culvert at
Kalamazoo, Mich.]
Much of the work was done when the thermometer, during working hours,
ranged from 12° to 25° above zero. When the temperature was below
freezing, hot water was used in mixing the concrete and on a few of the
coldest days salt was dissolved in the water. In addition each section
of the work was covered with oiled canvas as soon as completed, and the
conduit was kept closed so far as was practicable to retain the heat.
Concreting was never stopped on account of cold weather.
[Illustration: Fig. 175.--Templet for Arch Ring for Culvert at
Kalamazoo, Mich.]
Account was kept of the cost of all work, and the figures obtained are
given in the following tables:
Labor Force, Materials Used and Progress of Work.
Average progress per day in feet 18.0
Greatest number of feet laid in one day 28
Average number of laborers per day mixing and wheeling 10.04
Average number of laborers per day placing concrete 5
Average number of laborers per day setting up forms 4.57
Cubic yards of concrete mixed and wheeled per day per man 1.96
Cubic yards of concrete placed per day per man 3.54
Cubic yards of concrete per lin. ft. 0.95
Barrels of cement per lin. ft. 1.18
Barrels of cement per cu. yd. 1.24
Proportion of cement to sand and gravel 1-6
Itemized Cost per Lineal Foot.
Sand and gravel $0.42
Cement 2.44
Mixing and wheeling concrete 0.98
Labor placing concrete 0.47
Forms and templates 0.30
Metal fabric 0.39
Setting up forms 0.43
Finishing 0.09
Tools, general and superintendence 0.43
-----
Total per lineal foot $5.95
The cost per cubic yard was thus $6.26. Wages were $1.75 per day.
~METHOD AND COST OF MOLDING CULVERT PIPE, CHICAGO & ILLINOIS WESTERN R.
R.~--During 1906, the Chicago & Illinois Western R. R., Mr. O. P.
Chamberlain, Chief Engineer, built a number of culverts of concrete pipe
with an interior diameter of 4 ft., and 6-in. shells. Fig. 176 shows the
forms in which the pipe was molded. Both forms are of ordinary wooden
tank construction. The inner form has one wedge-shaped loose stave which
is withdrawn after the concrete has set for about 20 hours, thus
collapsing the inner form and allowing it to be removed. The outer form
is built in two pieces with 2×5/8-in. semi-circular iron hoops on the
outside, the hoops having loops at the ends. The staves are fastened to
the hoops by wood screws 1¾ ins. long driven from the outside of the
hoop. When the two sides of the outer form are in position, the loops on
one side come into position just above the loops on the other side, and
four ¾-in. steel pins are inserted in the loops to hold the two sides
together while the form is being filled with concrete and while the
concrete is setting. After the inner form has been removed, the two pins
in the same vertical line are removed and the form opened horizontally
on the hinges formed by the loops and pins on the opposite side. The
inner and outer forms are then ready to be set up for building another
pipe.
[Illustration: Fig. 176.--Form for Molding Culvert Pipe.]
The concrete used in manufacturing these pipes was composed of American
Portland cement, limestone screenings and crushed limestone that has
passed through a ¾-in. diameter screen after everything that would pass
through a ½-in. diameter screen had been removed. The concrete was mixed
in the proportions of one part cement to three and one-half parts each
of screenings and crushed stone. All work except the building of the
forms was performed by common laborers. In his experimental work Mr.
Chamberlain used two laborers, one of whom set the forms, and filled
them and the other of whom mixed the concrete. The pipes were left in
the forms till the morning of the day after molding. The two laborers
removed the forms filled the day before, the first thing in the morning,
and proceeded to refill them. The average time the concrete was allowed
to set before the forms were removed was 16 hours. Mr. Chamberlain
believes that with three men and six forms the whole six forms could be
removed and refilled daily. Based on the use of only two forms with two
laborers removing and refilling them each day, and on the assumption
that a single set of forms costing $40 can be used only 50 times before
being replaced, Mr. Chamberlain estimates the cost of molding 4-ft.
pipes as follows:
2 per cent, of $40 for forms $0.80
1.1 cu. yds. stone and screenings at $1.85 2.04
0.8 bbls. cement at $2.10 1.68
10 hours' labor at 28 cts. 2.80
-----
Total per pipe $7.32
This gives a cost of $1.83 per lineal foot of pipe or practically $7 per
cu. yd. of concrete. The pipe actually molded cost $2.50 per lin ft., or
$9.62 per cu. yd. of concrete, owing to the small scale on which the
work was carried on--the laborers were not kept steadily at work.
The pipes were built under a derrick and loaded by means of the derrick
upon flat cars for transportation. At the culvert site they were
unloaded and put in by an ordinary section gang with no appliances other
than skids to remove the pipes from the cars. As each four-foot section
of this pipe weighs about two tons, it was not deemed expedient to build
sections of a greater length than 4 ft., to be unloaded and placed by
hand. On a trunk line, however, where a derrick car is available for
unloading and placing the pipes, there is no reason why they should not
be built in 6 or 8-ft. sections.
CHAPTER XIX.
METHODS AND COST OF REINFORCED CONCRETE BUILDING CONSTRUCTION.
If we set aside concrete block construction, virtually all concrete used
in building construction is reinforced; plain monolithic or mass
concrete now, as in the past, is one of the secondary building
materials. It is reinforced concrete building construction that is
discussed in this chapter. In no class of concrete work is the
contractor's responsibility for the successful outcome of the work
greater than in reinforced concrete building construction. No degree of
excellence in design can make up for incompetent, careless or dishonest
work in construction. This is true not merely in the general way that it
is true of all engineering construction--it is true in a special way
peculiar to the material. Except for the reinforcing steel, the
contractor for concrete building work has no guarantee of the quality of
any element of his work except his own faithful care in performing every
task that combines to produce that element. The quality of his concrete
depends upon the care with which he has chosen his cement, sand and
stone, and on the perfection with which he has incorporated them into a
homogeneous mixture. The quality of his beam or column, then, depends
upon the care with which the concrete is placed in position with the
reinforcement and with which the supporting forms are maintained until
the member is amply strong to do without support. There is no certainty
of any detail except the certainty that is had by performing every part
of the work as experience has taught that it should be performed if
perfect results are to be attained. We have dwelt thus emphatically on
the responsibility in concrete building work of the contractor for the
reason that in the past it has been upon the contractor that the burden
of failure has been generally shifted.
The construction work of buildings is divided into (1) construction,
erection and removal of forms; (2) fabrication and placing of
reinforcement; (3) mixing, transporting and placing concrete.
CONSTRUCTION, ERECTION AND REMOVAL OF FORMS.
The stereotyped text-book statement that forms must be true to
dimensions and shape and rigid enough in construction to maintain this
condition under all loads that they have to sustain mentions only one of
the factors that the constructing engineer or the contractor has to keep
in mind in designing such forms. His design must be made true and rigid
at the least possible cost for first construction of lumber and
carpenter work; it must be made with the plan in mind of using either
the same forms as a whole or the same form material several times in one
structure; it must be made with a view to convenience in taking down,
carrying and re-erecting the forms the second or third time; and it must
be made with the object in sight of securing the greatest salvage value
either in forms fit for use again or in form lumber that can be sold or
worked up for other purposes.
The general conditions governing the computation and design of economic
form work are discussed in Chapter IX.
~COLUMN FORMS.~--Concrete columns are usually square or rectangular in
section, with, commonly, chamfered or beveled corners. The popularity of
these sections is due very largely to the simplicity of the forms
required. When hooped reinforcement is used, the column section is
always circular or polygonal. Hollow sections, T-section and channel
sections are rarely employed and then only for wall columns.
Column forms should be made in units which can readily be assembled,
taken apart and re-assembled. The number, arrangement and size of the
units are determined by the shape and size of the column and the means
adopted for handling the forms. For square or rectangular columns there
will be usually four units of lagging, one for each side, plus the
number of clamps or yokes used to bind the sides together. Yokes or
clamps will seldom be spaced over 3 ft. apart unless very heavy lagging
is used; 2 ft. spacing for yokes is common. For circular columns two
units of lagging are necessary and this is the number commonly used; the
yokes or hoops are spaced about as for rectangular columns. Metal forms
can be used to good advantage for cylindrical columns. Forms for
polygonal columns are difficult to construct in convenient units. Forms
built complete a full story high and concreted from the top are
essential where wet and sloppy concretes are used. In Europe, where
comparatively dry concretes are employed and where the reinforcement is
commonly placed a piece at a time as concreting progresses, three sides
of a rectangular form are erected full height and the fourth side is
built up as the concrete and metal are placed. This construction is now
less common, even abroad, than it was, since wetter mixtures are coming
to be approved by European engineers to a greater extent now than
formerly. It is a time consuming method and with wet mixtures it has
nothing to recommend it. For lagging 1¼ and 2-in. plank are commonly
used; with yokes spaced 2 ft. apart the lighter plank is amply strong
and reduces the weight of the units to be handled as well as the amount
of form lumber required.
[Illustration: Fig. 177.--Form for Rectangular Column for Factory
Building, Cincinnati, O.]
Column forms should always be constructed with an opening at the bottom
by means of which the reinforcement can be adjusted and sawdust,
shavings and other material cleaned out.
~Rectangular Columns.~--The form shown in section by Fig. 177 was used in
constructing a factory building at Cincinnati, O. Two 2×4-in. studs at
each corner carry the horizontal side lagging boards and are clamped
together by yokes composed of four hardwood corner saddles connected
around the form by a hooked rod with center turnbuckle on each side. No
nails are used in assemblying the parts; the same studding and yokes
serve for several sizes of column, the lagging alone being changed. The
lumber required for studding is 5½ ft. B. M. per foot of column length.
The lumber required for lagging, using 1 in. boards, would be 2-2/3 ft.
B. M. for a 12-in. column, and 2/3 ft. B. M. would be added for every
2-in. increase in size of the column. About 3½ ft. B. M. is required for
each set of four corner saddles. With the studs rabbeted at the mill,
the carpenter work is reduced to the simple task of sawing the boards
and struts to length. The form is taken down by simply unscrewing the
turnbuckles; it can be erected by common labor in charge of one
carpenter to attend to the plumbing and truing-up. The form can be used
over and over and for columns of different sizes without change except
in the length of the lagging boards.
The form shown by Fig. 178 was used in constructing a nine-story
warehouse at St. Paul, Minn.; it is a design which has become almost
standard with a number of large building contractors. In this
construction lagging boards the full length of the column are used and
are held without nails by yokes. The yokes consist of two heads of wood
held together by threaded rods with nuts; between the rods and the
lagging are struts or blocks serving both as spacers and to hold the
lagging to plane and surface. The yoke proper is adjustable to the
extent of the threaded portions of the tie rods. It is to be noticed
that the lagging boards are not connected by battens or cleats,
therefore, two or three widths of stock serve for all ordinary changes
in size of columns and carpenter work is limited to sawing them to
length. Furthermore as the boards are full column length, their salvage
value when removed from the forms is high. Common laborers under a
carpenter foreman can assemble and erect the form. For a 12-in. column
and using 3×4-in. yokes spaced 2 ft. apart and 1¼-in. lagging, this form
requires about 12 ft. B. M. of lumber per foot length of column. The
column form shown by Fig. 226 for the six-story building described in a
succeeding section differs from the one described only in the details
of the yoke construction. In place of the struts between the wooden
heads of the yoke a cleat is nailed across the projecting ends which has
to be pried loose every time the yoke is removed and nailed into place
again every time the yoke is put onto another form; these repeated
nailings soon destroy the yoke heads. This form as constructed requires
about 8¾ ft. B. M. of lumber per foot length of 12-in. column, which is
3¼ ft. B. M. less than is required for the form shown by Fig. 177. The
saving comes entirely in the yoke construction.
[Illustration: Fig. 178--Form for Rectangular Column for Warehouse at
St. Paul, Minn.]
The form shown by Fig. 238 is of the same general type as are the two
just described, the chief difference in detail being in the yoke
construction and in the forming of the lagging boards into a panel or
unit for each side by means of battens. This panel construction makes a
lagging unit which is more convenient to handle, but less convenient to
adapt to changes in size of column. The salvage value of the lumber is
also reduced by the nailing. Assuming 1¼-in. lagging and a yoke spacing
of 2 ft., to permit direct comparison, this form requires 10½ ft. B. M.
of lumber per foot length of 12-in. column as compared with 12 ft. B. M.
for the form shown by Fig. 177 and 8¾ ft B. M. for the form shown by
Fig. 178. As actually constructed with 2-in. lagging the form shown by
Fig. 238 requires about 14 ft. B. M. of lumber per foot length of 12-in.
column.
The French constructor, Hennebique, uses the column form construction
shown by Fig. 179. Three sides of the forms are built full length of
vertical plank and the fourth is built up of horizontal lagging nailed
on a board at a time as concreting progresses. In place of rectangular
yokes, steel clamps of special form are used to hold the lagging in
place. To tear down this form requires drawing the nails in the
horizontal lagging and the knocking loose of the clamps. The vertical
lagging is of necessity connected by battens into panels to make it
possible to hold it in place by the form of clamp used. Assuming 2-in.
vertical lagging with 7/8×3-in. battens every 3 ft., and 7/8-in.
horizontal lagging this form requires about 12 ft. B. M. of lumber for
every foot length of 12-in. column. This form seems to offer no
particular merits to American eyes: there is practically no saving in
lumber over forms with rectangular yokes and the clamp shown, while
adjustable, is not nearly so rigid and secure a bond for the lagging as
is a good yoke.
[Illustration: Fig. 179.--Form Used by Mr. Hennebique for Rectangular
Columns.]
[Illustration: Fig. 180.--Form for Rectangular Column for a Factory
Building, New York City.]
The form shown by Fig. 180 is an extreme example of nailed construction
throughout, no yokes or clamps being used. It was used in constructing a
factory building in New York City. Horizontal lagging nailed to
vertical studs was used for all four sides; three sides were built up
full height and the fourth side was placed a board at a time as
concreting progressed. This form required 7-1/3 ft. B. M. of lumber per
foot length of 12-in. column, which is probably about as low in lumber
as column form construction can be got. The labor of tearing down and
re-erecting the form would be high as also would the waste of lumber.
Nailed forms of this type are rarely used.
[Illustration: Fig. 181.--Form for T-Section Wall Column.]
[Illustration: Fig. 182.--Form for Corner Wall Column.]
The form shown by Fig. 181 was used for molding T-section wall columns
for a power station. It is noteworthy for its section; because of the
provision for molding grooves in the two sides to which the curtain
walls join, and because of the manner in which three of the eight sides
were built up as the concreting progressed. The sides a b c, d e and
f g h were erected in full column units and the sides c d, e f and
h a were erected in sections 2 ft. high as concreting progressed. The
yokes were spaced 2 ft. apart. Using 1¼-in. stuff for yokes and lagging
this form as built required about 16 ft. B. M. per foot length of
column. Except for the beveling of the mold for the curtain wall
recesses, the framing is all plain saw and hammer work.
[Illustration: Fig. 183.--Core Form for Hollow Column.]
A corner wall column form is shown by Fig. 182 and as this was an
example of hollow column work the section of the concrete within the
form is shown. Forms of this shape and of T-section are properly classed
as special form work so that the examples given here are helpful merely
as indicating general methods that may be followed. This particular form
required 15¾ ft-B. M. of 7/8-in. lagging per foot of column length, and,
neglecting the special top frame, about 16 ft. B. M. of "staging" per
foot to support the lagging. The core forms for molding the hollow
spaces in the columns of this particular building are shown in Fig. 183.
The cross pieces or keys carried on the 5/8-in. bolts as pivots are
revolved a quarter turn to slip clear of the slots and permit the sides
to close together and free the core for withdrawal. In many cases the
contractor will find it preferable to use thin sheet metal core molds or
light wooden cores and leave them in place. In one case known to the
authors where hollow wall columns were used as hot air ducts for a
heating system the duct was laid up of one row of bricks, encircled by
the column form and the annular space concreted around the brick duct as
a core. The rare use of irregular columns makes form and core
construction for them a special problem requiring special detailed
estimates in each case. The channel section wall column form shown by
Fig. 230 is a case in point; here the form became practically a portable
mold for duplicating columns as many times as was desired.
[Illustration: Fig. 184.--Form for Large Rectangular Columns.]
As an example of form work for very large columns or pillars that shown
by Fig. 184 is particularly good; it was used for constructing eight
3-ft. square pillars for a water tank tower. The lagging consists of
four panels made by nailing horizontal boards to vertical studs. The
panels are clamped together by rectangular yokes spaced 3 ft. apart.
There are nearly 27½ ft. B. M. of lumber per foot length of 3-ft. column
in this form.
[Illustration: Fig. 185.--Adjustable Form for Rectangular Columns.]
The form shown by Fig. 185 was used by Mr. R. W. Maxton in constructing
a large factory building at St. Louis, Mo., and is notable for the means
adopted for centering the forms and for reducing their lateral
dimensions to fit them for molding the decreasingly smaller columns of
the upper floors. To center the forms the short angles A A are molded
into the concrete so as to project slightly above the tops of the floor
slab. Also the pieces of wood C are molded into the floor slab. The
form is set over the angles and lined up truly by nailing the blocks B
to the blocks C. It will be noticed also that the column mold bears
only at the four corners the lagging being cut away somewhat on each
side so as to afford an opening for cleaning. The lagging for the sides
of the column mold is battened together to form four units or panels
which are held together by iron clamps of the form shown. Lag screws
are used everywhere in place of nails. The notable feature, however, is
the piecing out of the lagging panels with 1-in. strips, one or more of
which can be ripped off on each side to reduce the size of the forms as
the columns grow smaller toward the top of the building.
~Polygonal Columns.~--Forms for polygonal columns require more lumber and
more carpenter work and are less susceptible of ready arrangement into
units than forms for rectangular columns. There is no approach to a
uniform practice in their construction and the few forms shown here are
merely specific examples.
[Illustration: Fig. 186.--Form for Octagonal Column for a Factory
Building.]
The form shown by Fig. 186 was used for interior columns of octagonal
section with hooped reinforcement for a factory building. This form for
a 12-ft. octagonal column 24 ins. across between sides requires
approximately 325 ft. B. M. of lumber. The form shown by Fig. 187 was
used by the same engineer in another building; it is, as will be noted,
in four units coming apart in joints at diagonally opposite corners.
This form for an octagonal column 18 in. across between sides required
about 13 ft. B. M. of lumber per foot of column length, with yokes
spaced 3½ ft. apart.
The form shown by Fig. 188 was used in a large warehouse at Chicago,
Ill. It will be noted from the dotted lines that one yoke clamps the
sides a a, the next the sides b b and so on. This does away with
triangular blocking to hold the corner boards that is used in the form
shown by Fig. 187. Six pairs of yokes were used for each column so that
the yoke spacing was about 2 ft. With 2×6-in. yokes and 1½-in lagging a
form for a column 18 ins. between sides would require some 17 ft. B. M.
per foot of column length.
[Illustration: Fig. 187.--Form for Octagonal Column for Factory
Building.]
[Illustration: Fig. 188.--Form for Octagonal Column for a Warehouse,
Chicago, Ill.]
~Circular Columns.~--Circular columns have been most frequently molded in
steel forms, and these are by all odds the best for general work. Made
in two parts of sheet steel and in sections that are set end to end one
on another a form is obtained which is easy to erect, remove and
transport. Wood forms for circular columns are rather clumsy affairs and
are expensive to construct. Such a form, Fig. 190, is described in the
succeeding section; another is shown by Fig. 189. This form was used
successfully for filling and encasing steel columns for a fireproof
building in Chicago, Ill., and is a favorite circular form construction
in Europe. It is apparent that the hooping needs to be very heavy and
that the form is one that will be hard to handle and rather expensive to
make.
In several instances, where hooped reinforcement has been used, the
hooping has been wrapped with, or made of, expanded metal or other
mesh-+work, and the concrete deposited inside the cylinder thus formed,
without other form work. A six-story factory building in Brooklyn, N.
Y., was built with circular interior columns from 28 ins. to 12 ins. in
diameter, reinforced by a cylinder of No. 10 3-in. mesh expanded metal,
stiffened lengthwise by four round rods 1 in. in diameter for larger
columns to ½ in. in diameter for smaller columns. This reinforcement was
set in place and wrapped with No. 24 ½-in. mesh metal lath, and the
cylinder was filled with concrete and plastered outside. A moderately
dry concrete is essential for such construction.
[Illustration: Fig. 189.--Form for Circular Column.]
The method of molding shells with the hooping embedded described for the
Bush terminal factory work in another section is another way of avoiding
form work of the usual type.
Light steel forms as well as the special construction noted must be
supplemented by staging to hold them in line and to carry the ends of
the girder forms that are ordinarily carried by the column forms. Four
uprights arranged around the column so as to come under the connecting
girders are commonly used; they are set close enough to the column to
hold the form plumb by means of blocks or wedges.
~Ornamental Columns.~--Forms for ornamental columns call for special
design and construction. For many purposes, such as porch and portico
work, the best plan is to mold the columns separately and erect them as
stone columns of like character are erected. Metal forms of various
patterns are made by firms manufacturing concrete block molds and can be
purchased from stock or made to order. Where the column is to be molded
in place form construction becomes a matter of pattern making, the
complexity and cost of which depends entirely upon the architectural
form and ornament to be reproduced. The molding of ornament and
architectural forms in concrete is discussed in Chapter XXIII, and the
two examples of ornamental column form work given here from recent work
indicate the task before the builder.
[Illustration: Fig. 190.--Form for Molding Fluted Cylindrical Column.]
The form shown by Fig. 190 was used for molding in place fluted columns
used in a court house constructed at Mineola, N. Y. The lagging in the
form of staves forms a 24-sided polygon and is held in position by hoops
and yokes. The molds for the flutes were formed by inserting screws from
the outside so as to penetrate the staves and molding half-round ribs of
plaster of Paris over them by means of the simple device shown. To
dismantle the form the screws were removed and the lagging taken down
leaving the plaster of Paris in place as a protection to the thin edges
until the final finishing of the building.
The methods illustrated by Fig. 191 were employed in molding columns in
place for a church at Oak Park, Ill. The bottom portions of these
columns were plain square sections molded in place in square molds. The
top portions were heavily paneled. The four corner segments were cast in
glue molds backed by wood with wires embedded as shown. After becoming
hard they were set on end on the plain column and tied and braced as
shown. The side openings were then closed by wooden forms and the
interior space was filled with concrete. The surface facing for these
columns was bird's-eye gravel and cement, with very little sand, mixed
very dry and placed and tamped with the coarse concrete backing.
[Illustration: Fig. 191.--Form for Ornamental Column for Church at Oak
Park, Ill.]
~SLAB AND GIRDER FORMS.~--Slab and girder construction for roofs and
floors is of three kinds: (1) Concrete slab and steel beam construction
in place; (2) concrete slab and girder construction in place (3)
separately molded slab and beam construction. The third method of
construction is distinct from the others in respect to form work as well
as other details and is considered separately in Chapter XX.
~Slab and I-Beam Floors.~--Centers for floor slabs between steel I-beams
are made by suspending joists from the beam flanges and covering them
with lagging. Frequently the joists and lagging are framed together into
panels of convenient size for carrying and erecting. The construction is
a simple one in either case where slabs without haunches or plain arches
form the filling between beams. Figure 192 shows an arch slab center;
plain hook bolts, with a nut on the lower end, passing through holes in
the joists are more commonly employed. For 1-in. lagging the joist
spacing is 2 ft., for 1½-in lagging, 4 ft., and for 2-in. lagging, 5 ft.
[Illustration: Fig. 192.--Form for Arch Slab Between I-Beams.]
[Illustration: Fig. 193.--Form for Flat Slab Floor Between I-Beams.]
A more complex centering is required where the slab has to be haunched
around the I-beams. The center shown by Fig. 193 was designed by Mr. W.
A. Etherton for the floor construction of the U. S. Postoffice Building
erected at Huntington, W. Va., in 1905. The center consists essentially
of the pieces A (2×4 ins. for spans not exceeding 6 ft.) and the
2×3-in. triggers B, which rest on the lower flanges of the floor beams
and thus support the forms. The trigger is secured at one end to the
piece A by a 1×3-in. cleat C and at the other end by 1×3-in. cleats
D on either side of A, which serve also as supports for the batter
boards E. The six-penny nail F is but partly driven and it is to be
drawn before removing the forms. When the supports of the beams are not
fireproofed the cleats D extend to the bottom of the trigger B, but
otherwise one cleat extends lower to secure the cross-strip G. To
remove the forms, draw the partly driven nail F; knock off the strip
G or loosen it enough to draw the nails in B>; pull the triggers on
one beam, and the forms will drop. If the soffit board H is used it is
necessary first to remove the strip G. For larger beams use the
spacing blocks H as shown; for smaller beams omit the trigger B and
extend A to rest on the flange of the beam, then to remove the form
A must be cut preferably near the beam.
No complete records of the cost of these forms were obtained, but the
following partial information is furnished by Mr. Etherton: Considering
a panel 6 ft. span by 19 ft. long on 15-in. I-beams, the lumber
consisting of 1-in. boards supported by 2×4-in. cross-pieces on 2×3-in.
triggers spread 3 ft. on centers, soffit of beams not fireproofed, it
required one carpenter five hours at 30 cts. per hour to complete the
panel. Figuring from this alone I should say that 10 cts. per sq. yd. is
a fair estimate for carpenter work. In working over the forms for
another floor the 1-in. boards require more time to handle and I should
say that the saving in cost of work over the first floor would be not
over 2 cts. per sq. yd. Two laborers moved their scaffolding and took
down the forms from three completed panels of 13 sq. yds. each in one
hour. Smaller panels require a longer time per yard. Counting for the
proper piling of lumber I should allow one hour for one man to take down
the forms for a 13-sq. yd. panel when conditions are the best. We
contracted with two laborers to remove the forms from the third floor
and roof and pile them in good shape on the ground just outside of the
building for an amount averaging about 4½ cts. per sq. yd., and the men
made but small wages on the contract. The lumber was used on three
floors and the roof, and the best of the 1-in. boards and all of the
2×4-in. and 2×3-in. stuff were used on a second job. For a safe estimate
based on the data secured I should figure the cost of labor and
materials for a three or four-story building about as follows:
Per sq. yd.
Lumber at $20 per thousand 28 cts.
Carpenter work at 30 cts. per hour 10 cts.
Labor tearing down at 15 cts. per hour 4 cts.
-------
Total per square yard 42 cts.
Figure 194 shows an arrangement of centering between steel beams which
is novel in that it provides for molding a slab with girders. The form
was used in building the roof of a locomotive roundhouse. This
roundhouse was of the usual circular form and had a radial width of 80
ft. Each radial roof girder, which was an 18-in. I-beam was carried by
an outside wall pier and three I-beam columns encased in concrete. The
space between main roof girders was spanned by reinforced concrete
girders and roof slab. The center illustrated was employed for molding
the concrete girders and slab, and carries out the idea of making a
stiff and light center for considerable spans of slab without support by
staging. The truss construction of the frames supporting the girder box
will be noted.
[Illustration: Fig. 194.--Form for Slab and Girder Floor Between
I-Beams]
~Concrete Slab and Girder Floors.~--The construction of forms for this
type of floor should be such that the slab centers and the sides of the
girder molds can be removed without disturbing the bottoms of the girder
molds. This permits the beams to be supported as long as desirable and
at the same time releases the greater part of the form work for use
again. It is of advantage also to lay bare the concrete as soon as
possible to the hardening action of the free air. The slabs may be
similarly supported by uprights wedged up against plank caps; no very
great amount of lumber is required for this staging and it gives a
large assurance of safety. It is well also to give the girder molds a
camber or to crown them to allow for settling of the falsework.
The form shown by Fig. 195 was used in constructing girders from 14 to
23 ft. long in a factory building at Cincinnati, O. The sides are
separate from the bottom, being supported at the ends by cleats on the
column form and at intermediate points by struts under the yokes. The
floor lagging is carried by 2×4-in. stringers supported by the yokes.
Uprights set under the bottom plank keep the girder supported after the
sides and slab centers are removed. It will be noted that the form is
given a camber of 1-in. The structural details are evident from the
drawing. The form shows a method of molding a bracket for wind bracing;
a simple modification fits it for molding girders without brackets. A
rough computation gives 10 ft. B. M. of lumber per lineal foot of girder
form as shown.
[Illustration: Fig. 195.--Girder and Slab Form for Factory Building,
Cincinnati, O.]
[Illustration: Fig. 196.--Girder and Beam Forms for Factory Building,
Beverly, Mass.]
The form construction shown in Fig. 196 was employed in building the
slab and girder floors for the United Shoe Machinery Co.'s factory at
Beverly, Mass. In these buildings the main girders cross the building at
20-ft. intervals and midway between the main girders is a bridging beam
also reaching across the building. Floor beams span the 10-ft. spaces
between bridging beams and main girders at intervals of 3 and 4 ft.
Referring first to the main girder form, tall horses are set up at 3-ft.
intervals and connected by stringers laid on the caps. These stringers
carry a cross piece, with a cleat at each end, over each horse. The
bottom boards of the mold rest on these cross pieces and the side pieces
are set up between verticals wedged tight between the cleats. The beam
molds are a modification of the girder molds. The slab centers consist
of panels just large enough to span the openings between beams and
girders and composed of 1-in. boards fastened together by four 1×5-in.
cleats. Except in attaching the quarter round and triangular moldings
for fillets no nailing is necessary in erecting and taking down the
forms.
[Illustration: Fig. 197.--Girder and Slab Form for Concrete Building
Work.]
The form construction shown by Fig. 197 is one used by a large firm of
reinformed concrete builders. The slab centers can be struck and the
sides of the girder mold removed without disturbing the support for the
bottom of the beam. This form runs quite low in lumber, requiring for a
9×12-in. beam box including posts some 9 ft. B. M. per lineal foot of
box. The joists and lagging as shown require about 2 ft. B. M. per
square foot of floor slab. The practice is to give these girder boxes a
camber of ½-in. in 10 ft.
The construction shown by Fig. 198 is designed to provide adjustability,
to enable quick erection and removal and to do away with all nailing.
The construction is as follows: Wooden posts carry at their tops steel
T-beam cross-arms knee braced to the posts by steel straps. The
cross-arms carry the two jaws of a clamp, each consisting of a vertical
plate, and two diagonal braces, slotted so as to slide on the T-beam. A
cut nail or other piece of metal driven into the slots fastens the jaws
on the T-beam. The cross-arms carry the bottom boards of the girder
molds and the vertical plates of the jaws support the side pieces. A
blocking piece slipped between the braces carries the end of the joist
for the floor slab centers. This form is the invention of Mr. W. H.
Dillon and was used in constructing the nine-story, 260×150-ft.
wholesale hardware store Of Farwell, Osman & Kirk Co., St. Paul, Minn.
[Illustration: Fig. 198.--Girder and Slab Form for Warehouse at St.
Paul, Minn.]
[Illustration: Fig. 199.--Girder and Slab Form for Factory Building, New
York, N. Y.]
The form shown by Fig. 199 was used in constructing a factory building
in Long Island City, N. Y., and it is given here chiefly for the purpose
of exhibiting the unnecessary complexity of form work. Comparing this
form with that of nearly any of the preceding designs will bring out
the point. The design, however, was one of the earlier ones to recognize
the advantage of stripping the slab centers and the sides of the girder
boxes without disturbing the bottom plank of the boxes or the staging.
The drawing shows the independent support of the bottom board and side
pieces of the girder mold on the transverse caps of the staging posts.
These posts are 6×8 ins. in section and are spaced from 6 to 8 ft.
apart. Briefly described the bottom board is a single plank from 1 to 3
ins. thick, to which the side pieces are lag-screwed at the bottom. The
side pieces are panels composed of 4×7/8-in. vertical boards nailed to
top and bottom 2×4-in. horizontal timbers. A third horizontal timber
near the top serves as a seat for the ends of the joists carrying the
slab lagging and is braced from the bottom horizontal by vertical
stiffeners. The edge boards of the slab lagging are nailed to the top
edges of the side pieces of the girder mold and the tops of these side
pieces are connected across the trough by strips of board; all the slab
lagging boards except those at the edges of the girder molds are laid
loose. In the building referred to, after the floor concrete had set
about seven days the joists carrying the slab lagging were turned a
quarter over thus dropping the slab form about 2 ins. A few days later
the joists and lagging were taken down and the side pieces of the girder
mold were unscrewed and removed. The bottom board and staging posts were
left in position about three weeks longer and then dropped about 1 in.
by removing fillers from the staging post caps. In another week the
bottom boards and staging posts were taken down. This construction of
form and method of removing it permitted the concrete to be stripped so
that the air could get at it as fast as it was safe to take the support
from any part and at the same time kept the supports in such position
that they form a safety platform in case of collapse. A more important
advantage is that the form timber can be removed as fast as any part of
it is free and used again. Thus the lagging boards and joists and the
side pieces for the girder molds were free for use again about every two
weeks and yet the main supports of the girders were undisturbed until
they were fully a month old.
Other examples of girder and slab forms are shown in the succeeding
sections describing the construction of a six-story building and of a
garage constructed at Philadelphia, Pa.
[Illustration: Fig. 200.--Collapsible Core Forms for Girder and Slab
Floors.]
Another type of slab and girder form construction that deserves brief
mention because of its variation from usual practice and also because of
its extensive use by one prominent builder is shown by Fig. 200. Cores,
or inverted boxes, with four vertical sides and rounded corners, are set
side by side, with ends on stringers carried by the column forms, at
intervals wide enough to enable the beam to be molded between. A plank
resting on cleats on the sides of the cores forms the bottom of the beam
mold. The main girders are molded in similar spaces between the ends of
the cores in one panel and of those in the next panel. To permit the
core to be loosened readily it is hinged; when in place spacers inside
the core keep the sides from closing. These are knocked out, the core
sides close together and the core is removed for use in another place.
Cores similar to these were used in molding the ribbed floor for the
Bush terminal factory building described in a succeeding section. These
cores are capable of repeated use so that while they are somewhat
expensive to frame they give a very low cost of form work when the beam
and girder spacing is arranged largely in duplicate from floor to floor.
It will ordinarily be cheaper to have these cores made to pattern by
regular woodworking shops, and shipped to the building ready to erect.
~WALL FORMS.~--Wall work in modern commercial and manufacturing buildings,
when we come to eliminate windows and wall columns and girders, is
confined very largely to isolated curtain wall panels between windows
and framework. In such buildings, therefore, wall forms consist merely
of wooden panels, one for each face of the wall, constructed to fit the
spaces to be walled up. Where these spaces are duplicated from bay to
bay or story to story the same form panels will serve repeatedly. For
residences and other buildings having greater proportionate area of
blank wall the builder has a choice between continuous forms carried by
staging and movable panel forms.
[Illustration: Fig. 201.--Continuous Form for Wall Construction.]
For one and two-story buildings, with the usual variation in
architectural detail, panel work and window work, the continuous form
has many advantages, and the superior economy of movable panels in
retaining and other plain wall work is by no means always true here. One
good type of continuous wall form construction is shown by Fig. 201. The
gallows frames are spaced about 6 ft. apart along the wall and connected
by horizontal stringers nailed to the uprights or by diagonal bracing.
Each frame may be made up of 6×6-in. posts connected by 2×4-in.
cross-struts and diagonals with bolted connections so that the frame can
be taken down and put together easily and so that the bracing can be
removed as the wall is built upward. The other details of the form work
are shown by the drawing. This construction leaves a clear space for
placing the concrete and the cross pieces give support to runways; it
has been successfully used in a large amount of low building work.
[Illustration: Fig. 202.--Sectional Form for Wall Construction.]
Movable panel forms are of great variety in detail but are generally of
either one or the other types shown by Figs. 202 to 204.
The form shown by Fig. 202 was used in constructing a church at Oak
Park, Ill. For the back of the wall it consists of continuous lagging
held by 2×4 studs. For the face 1×6-in. lagging 12 ft. long was nailed
to 2×4-in. studs to form panels. It will be noted that the ends of the
studs are scarfed so as to interlock in succeeding panels. This
construction also shows a method of supporting the reinforcing bars
inside the form.
The form shown by Fig. 203 was used in constructing a large factory
building, and consisted of two side pieces or panels 3 ft. high and 16
ft. long, the distance between wall columns. For the first course these
were seated on the carefully leveled and rammed ground and securely
braced by inclined or horizontal struts inside and outside of the
building. After the concrete had set for three days the molds were
loosened and lifted until the lower edges were 2 ins. below the top of
the concrete and there they were held by horizontal bolts through their
lower edges and across the top of the concrete by ties nailed across
their tops every 3 ft. and by bracing to the falseworks supporting the
column and floor forms. The cross bolts passed through pasteboard
sleeves which were left permanently embedded in the wall. By starting
the molds level and finishing each course level with their tops no
difficulty was had in keeping the forms plumb and to level as they were
moved upward. This type of form has to be exteriorly braced to staging
or adjacent column forms, etc.
[Illustration: Fig. 203.--Sectional Form for Wall Construction.]
The type of movable panel form shown by Fig. 204 depends for all support
on the wall alone. The sketch shows the form filled ready to be shifted
upward; this operation consists in removing the bottom bolts and
loosening the top bolts enough to permit the studs to be slid upward the
full length of the slots. The lagging boards left free are then removed
and placed on top and the bolts are tightened, completing the form for
another section of wall.
[Illustration: Fig. 204.--Movable Panel Form for Wall Construction.]
[Illustration: Fig. 205.--Sullivan's Plank Holders for Wall Forms.]
A type of wall form construction intended to do away with studding and
bracing is illustrated by Figs. 205 and 206. In both cases metal plank
holders are used in place of studs, and practically the only difference
between the two is in the shape and material of the holders. The mode of
procedure is to work in horizontal courses one plank high around the
wall, removing the bottom plank and placing it on top as each new course
is begun after the first few courses have been laid. Using the
arrangement shown by Fig. 205 in constructing a building 100×54 ft. in
plan and 36 ft. high with 12-in. walls, a height of two 12×2-in planks
was all the form work that was ever necessary at any one time, so that
the amount of form lumber required for the building was 2,464 ft. B. M.
plus 205 ft. B. M. of 2×4-in. flooring strip, or altogether 2,669 ft. B.
M., or 0.24 ft. B. M. per square foot of exterior wall surface, or 6½
ft. B. M. per cubic yard of concrete. This same form lumber with 16
additional plank was then used to construct a building 100×100 ft.×16
ft. high, so that some 3,000 ft. of form lumber sufficed for 17,548 sq.
ft. (exterior surface) of wall or for 617 cu. yds. of concrete in 12-in.
wall, which gives 0.17 ft. B. M. per square foot or 4.8 ft. B. M. per
cubic yard of concrete.
[Illustration: Fig. 206.--Farrell's Plank Holders for Wall Forms.]
~ERECTING FORMS.~--The organization of the erecting gang will depend very
largely on the manner in which the forms have been constructed. If they
have been constructed in sections which go together with wedges and
clamps common laborers with a foreman carpenter in charge to direct and
to line and level the work will do the erecting, but if they have to be
largely built in place carpenters are necessary for all the work except
carrying and handing. There should be at least one foreman for every 15
to 20 men and a head foreman in charge of all form work. The mode of
procedure will differ for every job, but the following general
directions apply to all work in greater or less measure.
Clamps, bolts and wedges and not nails should be used wherever possible
in assembling parts of forms in erection; these devices are not only
quickly and easily applied in erection but they are just as quickly and
easily loosened in taking down forms and they can be loosened without
jarring the concrete member.
Lining girder forms and lining and plumbing column and wall forms is
high-class carpenter work and should be directed by competent
carpenters. A column or girder which is out of line or plumb not only
looks bad but may be required to be removed and corrected by the
engineer. The expense for one such correction will be many times that
which would have been involved by proper care in the first place.
Supports or staging for the forms should be used freely and well braced
in both directions. Uprights should be set on wedges and bear against a
cap piece and on a sill piece to distribute the load.
Erect, line and plumb the column forms first; then erect, line and level
the girder forms and set the girder staging, and finally erect and level
the slab centers and their supports.
Leave the foot of each column form open on one side at the bottom so
that the column reinforcement can be adjusted and connected up and so
that a clear view can be had through the form to detect any object that
may have fallen into the form and become wedged; this same opening makes
it possible to clean the form.
Give the forms a final inspection before concreting to check line and
level, to close open joints and to tighten up clamps and wedges. Finally
clean each form and wet it down thoroughly before placing the
concrete--do this just before placing the concrete.
~REMOVING FORMS.~--Good judgment and extreme care are essential in
removing centers. It goes without saying that forms should never be
removed until the concrete has set and hardened to such strength that it
will sustain its own dead weight and such live load as may come upon it
during construction. The determination of this condition is the matter
that calls for knowledge and judgment. Some cements set and harden more
rapidly than others, and concrete hardens more and more slowly as the
temperature falls. These and other circumstances must all be taken into
account in deciding upon the safe time for removal. Many large
contractors mold a cube of concrete for each day's work and leave it
standing on the finished floor exposed to the same conditions as the
concrete in the forms; examination of this sample block gives a line on
the condition of the concrete in the work and on the probable safety of
removing the forms at any time. In all cases it should be the
superintendent's duty to determine when to remove forms, and he should
satisfy himself by personal inspection that the concrete is in condition
to stand without support. It is also wise at least as a matter of
precaution for the contractor to secure the engineer's or the
architect's approval before removing any formwork.
Care in removing forms is essential for the reason that green concrete
is particularly susceptible to injury from shock or sudden strain. It is
well, therefore, to have a separate gang always doing the work. These
men will in a few days become trained under an experienced foreman so
that they will not only do the work with greater safety but also more
rapidly. This gang should, furthermore, be required to follow a regular
system in its work; a system which may not be departed from without
direct orders from the superintendent. An example of such a system is
outlined below.
The time of beginning this work of removal shall be given by the
superintendent. In warm, dry weather, with other conditions favorable,
removal may be begun after seven days. Then the following schedule may
be followed: At the end of seven days remove the sides of the column
forms. This gives an opportunity to determine the soundness of the
column casting and also serves the further desirable purpose of baring
the concrete to the curing and hardening action of the air. At the end
of 14 days loosen the wedges of the posts supporting the slab centers
and drop these centers a couple of inches: leave the centers in this
position for another day, meanwhile examining the tops of the slabs to
note their condition. Then remove the sides of the beam molds and the
slab centers, replacing the latter with temporary uprights supporting a
plank bearing against the underside of the slab. This precaution is
often neglected and with very little reason considering the importance
of the safeguard thus secured. Ordinarily the shores need not be left in
place more than a week, so that the amount of lumber thus tied up is
small. At the end of three weeks remove the uprights under the beam and
girder molds and strip the bottom plank. In this schedule it is assumed
that the floor is free from any great load and that no unusual loading
is put upon it; if a load of any consequence is to come on the floor the
shores and uprights should be left in place longer. No schedule of
removal can be blindly followed, and that given above is certain only
when the conditions are right and as stated.
FABRICATION AND PLACING OF REINFORCEMENT.
The amount of reinforcing steel used varies from 50 lbs. to 275 lbs. per
cu. yd. of concrete; the highest figure will be had only in very heavy
work and where very heavily reinforced raft foundations are employed,
and the lowest only in one-story buildings consisting of walls and roof.
A fair average is perhaps 150 lbs. per cu. yd. The cost of fabricating
and placing reinforcement will run from 1/3 ct. to 1½ cts. per pound,
but the last figure is exceedingly high; ¾ ct. per pound for fabricating
and placing is a reasonable labor charge.
Contractors frequently have their choice whether the steel shall be
fabricated into frames and placed as units or whether it shall be placed
in separate bars. For girders and columns the difference in cost of the
two methods is not so very great for steel in place when the fabrication
is done in the field. The unit frames cost considerably more than
separate bars to fabricate, but the cost of handling and placing them in
the forms is materially less; on an average the differences balance each
other. Where the frames are made up in regular mills unit frames
generally cost less to fabricate and place than do separate bars. The
use of unit frames in wall and floor slab reinforcement is generally
more expensive than the use of separate bars. The chief gain that comes
from the use of unit frames is the gain due to the certainty that the
reinforcing bars, stirrups, etc., are all there and are properly spaced
and placed.
~FABRICATION.~--Fabrication includes all the work necessary to prepare the
reinforcement ready to place in the forms. It amounts to very little
where separate bar types of reinforcement are used. Plain bending and
shearing operations comprise the whole task. Where the beam or column
reinforcement has to be made up into complete frames which can be
handled and placed as units this task is more complex and considerable
apparatus is essential to rapid and economical work. For this reason it
is wise usually to contract with some metal working shop to assemble and
connect up the various units and to furnish them ready for installation.
In many cases these unit frame types of reinforcement are patented and
the proprietors contract to fabricate and furnish them complete
according to the plans of the engineer or architect. Even where the
frame construction is not so controlled it will be economy generally to
have the fabrication done at regular shops where the necessary tools and
skilled workmen are had. In any case the bars should be ordered cut to
length at the mill so far as possible.
[Illustration: Fig. 207.--Rack for Storing Reinforcing Bars.]
Assuming the fabrication to be done in the field, the mode of procedure
will be as follows: Order the bars or rods to be shipped in bundles of
corresponding sizes and lengths of pieces with each bundle tagged with
its proper shop number or mark. The bundles should weigh about 200 lbs.;
this is a load easily handled by two men and so long as possible all
handling should be done in the original package, for when once broken it
is very hard to get men to carry a full load. As received, the bars of
each size and length should be stored by themselves. For ordinary bars
not having long prongs a rack of the general form shown by Fig. 207
serves the purpose excellently. When a great deal of metal must be kept
stored for some time it is wise to roof over the racks, not only to
protect the metal from rain and snow, but to enable the men to work dry
shod in stormy weather. Usually it will pay to have one man whose sole
duty it is to receive and check all metal and to attend to its
systematic arrangement on the racks; this same man will also direct the
removal of the metal to the shop where it is bent and otherwise worked
up, and can, if he is competent, earn his pay many times over in time
saved all along the line in handling and working up the reinforcement.
The authors have seen enough time wasted in hauling over and rehandling
metal in piles to get at what was wanted to pay for shed, racks and the
wages of a storekeeper several times during a moderate sized job. In
large work provide the storekeeper with a schedule showing the order in
which the metal is wanted for the work so that he can arrange it in that
order and can check up his receipts from the mills and report missing
items in time for the deficit to be made up before some part of the work
has to be stopped because of material missing. System in receiving and
storing the metal is absolutely essential to rapid and accurate work at
the bending and erecting tables.
The work done on the metal consists chiefly of bending. The metal can
usually be bent cold, but for sizes 1½-in. and upward some makes of bars
require heating; this can be done by laying the bars side by side on the
ground and arranging sticks and shavings on top of them in a strip 18
ins. to 2 ft. wide across the portion where the bend is to be. Only
moderate heating is usually required. Ordinary bending is a simple
process and can be done with very simple apparatus. Figures 208, 209 and
210 show frequently used devices, any of which can be made by an
ordinary carpenter. For heavy bars, 1½ and 2 ins., the device shown by
Fig. 210, with its heavy, swinging beam, is particularly efficient. An
example of more elaborate methods is had in the following description of
the processes employed in fabricating girder frames and hooped column
reinforcement for a large factory building. The building was 500×75 ft.,
with six stories and a basement, built for the Bush Terminal Co.,
Brooklyn, N. Y., in 1905. Three longitudinal rows of round columns and
two rows of rectangular wall columns carry heavy longitudinal girders
supporting floor slabs with corrugated undersides as shown by Fig. 211,
which also shows the floor slab reinforcement. About 12,000 cu. yds. of
concrete and 1,000 tons of reinforcing steel were required; hence 167
lbs. of steel were required for each cubic yard of concrete. The floors,
however, were designed to carry a load of 800 lbs. per sq. ft. The
particular feature of interest in this building was the fabrication of
all the column and girder reinforcement into unit frames and cylinders
in temporary workshops on the site.
[Illustration: Fig. 208.--Table for Bending Reinforcing Bars.]
[Illustration: Fig. 209.--Table for Bending Reinforcing Bars.]
[Illustration: Fig. 210.--Table for Bending Reinforcing Bars.]
[Illustration: Fig. 211.--Column and Floor Slab Construction for Factory
Building.]
The circular interior columns, varying from 30 ins. to 12 ins., in
diameter were molded in permanent shells of cinder concrete. The shells
were made in sections about 30 ins. long, with walls 1½ ins. thick,
which were set one on another with mortar joints to form the column
mold. In fabricating the shells the first step was to wind a helix of
steel wire on a collapsible mandrel about 4 ft. long; the mandrel was
set with the axis horizontal and was revolved by hand, the wire being
fed on also by hand and under a slight tension. After the wire helix was
completed it was wrapped with a sheet of expanded metal, the
longitudinal edges of which lapped a few inches and were tied by wire
ties. The expanded metal covering was also wire tied to the helix. Each
of these cylinders of expanded metal and wire was 30 ins. long and
formed the inner mold for making the shell. The outer mold consisted of
a sheet metal cylinder in two parts assembled and supported by wooden
yokes and framework. The two molds were assembled on a plank platform,
one inside the other, and about a common center. The annular space was
then filled with a 1-5 cinder concrete mixed moderately dry so that
while it would exude slightly through the expanded metal mesh it would
not waste to any extent. After from 18 to 24 hours the outer mold was
removed for reuse and the shell was left standing on the molding
platform until safe to handle. The larger shells, 30×30×1½ ins., weighed
about 150 lbs. each.
[Illustration: Fig. 212.--Device for Bending Reinforcing Rods.]
Some 2,000,000 lbs. of plain round steel rods from ¼ in. to 1½ ins. in
diameter were required for reinforcing the concrete. For the main
girders these rods were cut, bent and assembled into frames or trusses
which were placed as units. The main rods were ordered cut to length,
but the stirrup rods were ordered in lengths of 20 ft. and cut to
lengths as required. The rods were brought to the work in carload lots
and were stored according to lengths and sizes in racks under sheds.
Another shed was provided for the steelworkers, who cut and bent the
rods and assembled the girder frames ready for the workmen on the
building. There were about 50 different patterns of frames required.
They were made entirely by hand. For bending large size rods, heavy
compound levers were used; the lighter rods were bent by the device
shown in Fig. 212. The assembling of the trusses was accomplished as
shown by Fig. 213, using the steel framework of the erection shed as a
staging. Across the horizontals of the framework were placed two false
temporary top chord bars marked to the stirrup spacing of the truss
being assembled. On these bars, at the spaces marked, were suspended
stirrups with their lower ends hooked. The lower chord bars were then
suspended in the stirrup hooks and the whole assemblage of bars and
stirrups was then clamped rigid by the lever bars and intermediate
clamps. The loop ends of the stirrups were then bent by special wrenches
to the position shown at _2_, then closed by hammering to the position
shown at _3_, and finally they were wire tied. The process was a simple
one, and by adopting a regular routine the men became so expert that two
of them could complete many trusses in a working day. The contract price
for shaping the steel and assembling it into frames was 1 ct. per lb.;
the cost of the work to the contractor has been stated by Mr. E. P.
Goodrich, Engineer, Bush Terminal Co., to have been about ¾ ct. per lb.
The cost of placing the steel in the building was ¼ ct. per lb.
[Illustration: Fig. 213.--Sketches Showing Methods of Fabricating Girder
Reinforcing Frames.]
~PLACING.~--With unit frame reinforcement the number, size and location of
the bars have been made certain in the shops where the frames are
fabricated so that the erector has nothing to do but to line and level
up the frames in the forms, place such temporary braces as are needed to
hold them true, and make the end connections with abutting frames. Such
frames are usually provided with "chairs" to hold the bottom bars up
from the form so that little bracing or none is required. With separate
bar reinforcement the erector may either place the reinforcement
complete in the form by wire-tying the bars to each other, to temporary
braces or templates and to the forms, or he may insert the various
pieces of reinforcement in the concrete as the pouring advances,
depending on the surrounding concrete to retain them where inserted.
Generally a combination of both methods is employed.
The processes in detail of placing reinforcement are particularized in
several places in other sections; they will differ for nearly every job.
Here, therefore, general rules only will be given.
(1) See that the correct number and size of reinforcing bars, splices
and stirrups are used and that they are spaced and placed strictly
according to the working plans.
(2) Bars must be properly braced, supported and otherwise held in
position so that the pouring of the concrete will not displace them.
(3) Splices are the critical parts of column reinforcement. See that the
bars butt squarely at the ends and are held by pipe sleeves or wired
splice bars; see that the longitudinal rods are straight and vertical;
see that the horizontal ties or hooping are tight and accurately spaced.
When the reinforcement is built up inside the form one side is left open
for the work; ordinarily the column reinforcement will be fabricated
into unit frames, then an opening in the form at the bottom to permit
splicing will suffice.
(4) Take extreme care that beam and girder reinforcement is placed so
that the bottom bars lie well above the bottom board of the mold; use
metal or concrete block chairs for this purpose.
(5) See that the end connections and bearings of beam and girder frames
are connected up and have the bearings called for by the plans.
(6) See that line and level of all bars and of the reinforcement as a
whole are accurate; make particularly certain that expanded metal or
other mesh-work reinforcement lies smooth and straight.
(7) Give all reinforcement a final inspection just previous to pouring
the concrete; this is particularly essential where the reinforcement is
placed some time in advance of the concreting.
MIXING, TRANSPORTING AND PLACING CONCRETE.
A reinforced concrete building requires from 0.2 to 0.5 cu. yd. of
concrete per 100 ft. of cubical volume of the building, assuming walls,
floors and roof to be all of concrete. The amount of concrete to be
mixed, transported and placed is, therefore, large enough, even for a
building of moderate dimensions, to warrant close study of and careful
planning for this portion of the work. A few general principles can be
set down, but as a rule there is one best way for each building and that
way must be determined by individual conditions.
~MIXING.~--Concrete for building work has to be of superior quality so
that no chances may be taken either in the process of mixing or with the
type of mixer employed. Machine mixing and batch mixers should always be
employed. Machine mixing gives generally a more homogeneous and uniform
concrete than does hand mixing and is cheaper. Batch mixers are
generally superior and more reliable than continuous mixers where a
uniformly well mixed concrete is required. The capacity of the mixing
plant is determined by the amount of concrete to be placed and the time
available for placing it. Its division and arrangement is determined by
the area of the work and the type and arrangement of the plant for
transporting the materials and the mixed concrete. The following general
principles may be laid down: Make the most use possible of gravity; it
is frequently economy to carry all materials to the top of bins from
which point they can move by gravity down through the mixer to the hoist
buckets, and where natural elevations or basement floors below street
level permit gravity handling they should be taken advantage of. The
mixing should be done as near the place of concreting as practicable; in
building work this is the point on the ground which is directly under
the forms being filled. It is, of course, impracticable to secure so
direct a route as this from mixer to forms, but it can be more or less
closely approached; using two mixers, for example, one at the front and
one at the rear of a building cuts down the haul from hoist to forms
one-half. Other ways will suggest themselves upon a little thought. In
the matter of the mixing itself, it must never be forgotten that a batch
of concrete without cement which goes into a girder or column will
result in the failure of that member and possibly the failure of the
building. In massive concrete work a batch without cement will not
endanger the stability of the structure, but in column and floor work in
buildings it is certain disaster. Formanship at the mixer is, therefore,
highly important and a cement man who realizes the responsibility of his
task is equally important.
~TRANSPORTING.~--Transporting the mixed concrete is divided into three
operations--delivering concrete from mixer to hoist, hoisting, and
delivering hoisted concrete to the forms. The delivery from mixer to
hoist may be by direct discharge into hoist bucket, by carts or
wheelbarrows, or by cars carrying concrete or concrete buckets. Hoisting
may be done by platform hoists or elevators, by bucket hoists, or by
derricks. Handling from hoist to form may be direct in buckets, by carts
or wheelbarrows, or by cars. These several methods can be worked in
various combinations, and the following examples of plants show such
combinations as are most typical of current practice.
In any system of transportation it is getting the concrete to the hoist
and from hoist to form that eats up the money. Hoisting makes but a
small part of the total transportation cost, and, moreover, the
difference in cost of operation for different hoists is very small. Mr.
E. P. Goodrich states that on three buildings the actual costs for the
hoists installed and removed after the completion of the work were as
follows:
Platform hoist $330
Bucket hoist 465
Derrick 225
In figuring on the form of hoist to be adopted, the capability of the
hoist for general service has to be kept in mind. Platform hoists and
derricks can be used for hoisting form lumber and reinforcing steel as
well as for hoisting concrete, while bucket hoists cannot be so used
except where they may be fitted with special carriages for lumber or
steel. On the other hand, the bucket hoist is usually the quickest
method of hoisting concrete, and it can readily be extended upward as
the work progresses. The last is true also of platform hoists. The use
of derricks necessitates frequent shifting for high work or else the
building of expensive staging to raise the derrick into a position to
command the final height of the building. The probable costs of moving
and extending must be allowed for in choosing the hoist to be used.
Direct discharge of the mixer into the hoisting bucket is, of course,
the ideal manner of transporting the concrete from mixer to hoist, and
this can generally be obtained by planning, particularly where bucket
hoists or derricks are employed. For platform hoists direct discharge is
impossible; it can be somewhat closely approached, however, where
conditions permit car tracks to be laid on the floors being built, so
that a car holding a batch of concrete can be run onto the platform,
hoisted and then run to shoveling boards near the forms that are being
filled. The successful use of such an arrangement of car tracks is
described in Chapter XX, but it was for handling concrete blocks. A
direct discharge from hoisting bucket to forms is frequently possible
where derricks are used for hoisting, but with bucket and platform
hoists, wheeling or carting is necessary.
Where wheeling or carting has to be done either at the bottom or at the
top of the hoist, or at both points, a great factor in the economy of
work is the arranging of the operations in cycles. For example, in
wheeling concrete to forms from a hopper fed by a bucket hoist, arrange
the runways so that each man makes a circuit, passing by the form at one
end and by the hopper at the other end, and goes and comes by a
different route. The speed gained by avoiding confusion and delay saves
many times the additional cost of runways which is small. In fact it is
economy to employ a few extra men to arrange runways and keep them
clean, because of the additional speed thus gained. Good organization
effects more economy than special methods of hoisting as far as the
labor of handling the concrete is concerned.
[Illustration: Fig 214.--Bucket Hoist for Building Work
(Wallace-Lindesmith).]
~Bucket Hoists.~--A bucket hoist construction which has been extensively
used in building work on the Pacific coast is shown by the drawings of
Figs. 214 to 216. Two T-bar guides made in sections connected by
fishplates furnish a track for an automatic dumping bucket hoisted and
lowered by steel cable from engine on the ground to head sheaves as
shown. The sectional construction of the T-bar guides permits the hoist
to be any height desired, it being lengthened and shortened by adding
and taking out sections. The bucket is dumped automatically at any point
desired by means of a tripping device attached to a chute which receives
the contents of the bucket and delivers them to carts, wheelbarrows, or
other receptacle. The hoist is set outside of the building with the
mixer arranged, if possible, to discharge directly into the bucket. By
setting the guide frame in a pit or on blocking any height of edge of
bucket can be secured. The buckets are ordinarily 13½ or 20 cu. ft.
capacity. It is recommended, when greater hoisting capacity is
necessary, to use two hoists set side by side and operated by one cable
in the same manner as double wheelbarrow cages; as the weight of one
bucket counterbalances the weight of the other, the power required for
hoisting is reduced. To adapt this hoist to handling form lumber the
bucket is replaced by the lumber carriage shown by Fig. 216; this
carriage discharges over the head of the mixer and the spring buffer
shown by Fig. 214 is to take the shock of the rising carriage. This
buffer is omitted when concrete only is to be hoisted. In one case this
device has hoisted 520 batches of 12 cu. ft. each to the fourth floor in
8 hours, or nearly 19 cu. yds. per hour. In another case 65 trips per
hour were averaged to the fifth floor with a 12-cu. ft. load each trip;
this is nearly 30 cu. yds. per hour. With the lumber carriage 8 men have
unloaded 14,000 ft. B. M. of 2×10-in. stuff from car to the second floor
and distributed it in 43 minutes. A ½-cu. yd. combination outfit for
concrete and lumber, with 40 ft. of guide track, weighs 1,750 lbs.,
without the lumber carriage the outfit weighs 1,600 lbs. This hoist is
made by the Wallace-Lindesmith Co., Los Angeles, Cal.
[Illustration: Fig, 215.--Wallace-Lindesmith Hoist Bucket in Discharging
Position.]
[Illustration: Fig. 216.--Lumber Carriage for Wallace-Lindesmith Hoist.]
[Illustration: Fig. 217.--Mixer Plant with Gravity Feed from Material
Bins to Hoisting Bucket.]
A popular construction for automatic bucket hoists is that shown by
Figs. 217 and 218 by Mr. E. L. Ransome. The bucket is held upright by
guides at its front and rear edges; to dump it a section of the front
guide is removed at the desired dumping point which allows the bucket to
overturn as shown. A friction crab hoist operated from the mixer engine
runs the bucket. The mixer is located as shown. Figure 218 shows the
foot of the hoist set in a pit with the mixer at surface level, but the
hoist can be set on the surface and the mixer mounted on a platform. In
the latter case a charging bucket, traveling from stock pile up an
inclined track to the mixer platform, is generally used. A hoist like
that illustrated, equipped with a ½-cu. yd. Ransome mixer, will cost
about $1,500 and will deliver 15 cu. yds. of concrete per hour. Mr. F.
W. Daggett gives the following figures of the cost of operation:
Mixing Gang:
Total 1 hr.
1 mixer foreman, also engineer, 25c. $.25
1 man charging mixer, 20c. .20
1 man running hoist, 20c. .20
2 men wheeling sand, 17½c. .35
4 men wheeling and shoveling stone, 17½c. .70
1 man helping up runway, 17½c. .17½
2 men carrying cement, 17½c. .35
Gang Placing Cement:
1 foreman, 25c. .25
9 men wheeling concrete, 17½c. 1.57½
3 men tamping concrete, 17½c. .52½
1 man filling carts, 17½c. .17½
------
Total labor cost per hour $4.75
Fuel, etc. .50
------
5.25
This gives a cost of 35 cts. per cu. yd. for mixing and placing
concrete.
In this particular case the mixer was charged by wheelbarrows.
Frequently the stone and sand bins can be arranged to chute the
materials directly into the charging hopper as shown by Fig. 217. In
place of barrows two-wheeled carts of the type shown by Fig. 12 can be
used. Mention has already been made of operating the charging bucket on
an incline from stock pile to mixer. Such arrangements are described in
Chapter IV.
[Illustration: Fig. 218--Bucket Hoist for Building Work (Ransome).]
In constructing a 9-story store at St. Paul, Minn., the concrete was
hoisted by continuous bucket elevators. A lay-out of the construction
plant is shown by Fig. 219. In the alley near the center of the north
side of the building the surface grade was about 6 ft. above the third
story level. A hopper was constructed at grade and provided with two
chutes running to the basement. These chutes discharged on opposite
sides of a vertical partition separating the sand and stone bins, and by
closing either chute at its top by a suitably arranged deflector plate
either sand or stone could be dumped into the same hopper and chuted to
its proper bin. Cement was brought to the work in cars over the tracks
shown and was wheeled from the cars over runways leading to the charging
platforms near each mixer. Other runways connecting with these platforms
provided for wheeling the sand and stone to the mixers. The runways were
placed at the proper height to permit the barrows to be emptied directly
into the charging hoppers. Two Smith mixers were used, located as shown,
and each discharged through a chute into one of the bucket elevator
boots. There were two elevators which were "raised" two stories at a
move as the work progressed. Each elevator discharged into a hopper
holding 1½ batches, and from these hoppers the concrete was fed into
wheelbarrows and wheeled to the forms. The bucket elevators were carried
no higher than the eighth floor. When this floor had been completed the
hoppers were moved down to the fifth floor and the wheelbarrows were
taken to platform elevators and carried to the remaining floors and
roof. Special 4-cu. ft. wheelbarrows were used for handling the
concrete. A maximum of 155 cu. yds. of concrete was mixed, transported
and placed in a 10-hour day with a gang of 28 men.
~Platform Hoists.~--The common builders' hoist or elevator, operating
single or double platforms or cages, needs no special description. The
wheelbarrow, cart or car containing the concrete is run onto the
platform, hoisted and then run to the forms. The chief advantage of this
device in concrete work is that it will handle all classes of material
without any change of carriage or arrangement, it can thus be used for
handling form lumber and reinforcing steel as well as for handling
concrete.
[Illustration: Fig. 219.--Plan of Concrete Mixing and Handling Plant for
9-Story Building.]
~Derricks.~--The use of derricks for hoisting in concrete building work is
limited by the necessity of supporting them independently of the
structure being built; the formwork or the completed concrete work
cannot be utilized to carry derricks during construction. For low
structures the derrick can be set on the ground, but for high buildings
a supporting tower or staging is necessary. The arrangement of such
falsework can be illustrated best by specific examples.
In constructing a 7-story factory at Cincinnati, O., concrete was mixed
on the ground and hoisted by a derrick with an 80-ft. boom mounted on a
tower 55 ft. high. The derrick was located to one side of the building.
For the lower floors the boom swing covered so large an area that the
bucket was dumped at various places, but for the upper floors it was
found more economical to dump buckets into a hopper from which
wheelbarrows were filled. By this plan less time was consumed in placing
the bucket and no tag rope man was required, as the engineman could
swing the boom to a certain point on the wall which would bring the
bucket directly over the hopper. A Smith mixer discharged directly into
derrick buckets, which rested on a track long enough to hold two
buckets. The buckets were filled and emptied alternately by shuttling
the truck and attaching first one and then the other to the derrick.
In constructing an 11-story and basement office building in New York
City a four-legged tower starting from the bottom of the excavation was
erected at about the center of the lot. It was built of timber and
extended upward as the progress of the work demanded until it overtopped
the roof 11 stories above the street. The tower was square in plan and
was divided into stories corresponding approximately to the several
stories of the building. A floor was constructed in the tower at each
story to be used in storing materials. For hoisting a 75-ft. boom was
swung from each leg of the tower, each boom being operated by a separate
engine and having a nominal capacity of 5 tons. The four booms covered
the whole building area and were kept about two stories above the work
by being shifted upward as the work progressed. This arrangement of
derricks was used to handle the steel, lumber and concrete, the building
being built up around the tower, which was so located that its only
interference with the building structure was in the shape of square
holes left in the floor slabs to accommodate the tower legs.
In constructing an 8-story warehouse covering some three acres of ground
in Chicago, Ill., the derrick plant shown by Figs. 220 to 222 was
installed. Some 7,500 tons of reinforcing steel, 125,000 cu. yds. of
concrete and 4,000,000 ft. of form lumber had to be handled.
Incidentally it is worth noting that there were about 120 lbs. of
reinforcing steel and 32 ft. B. M. of form lumber used per cubic yard of
concrete.
The controlling conditions governing the arrangement and character of
the construction plant were as follows: The building, to be built
entirely of reinforced concrete, was 135 ft. high. Its west front
abutted on the river and its south front on the street; at the north
end there was some ground available for plant and along the east front
there was a strip about 20 ft. wide between the building wall and the
main line tracks of a railway. At best, therefore, the area outside of
the building and available for plant and storage was limited, while
inside the building area the contractor was confronted by the insistence
of the architect that an unbroken monolithic construction be obtained as
nearly as possible, by reducing the floor openings for construction work
to a minimum. The sketch plan, Fig. 220, shows the plant designed to
meet the conditions.
To get the large amount of construction material onto the work a side
track was built along the 20-ft. area on the east side of the building
and another was turned into the area at the north end of the building.
These side tracks handled all construction materials coming onto the
work. Over the first there were built two sets of storage bins for sand
and gravel and all concrete materials brought in in carload lots are
unloaded at these two points, as will be described further on. Lumber
for forms and steel for reinforcement shipped in similar manner were
taken by the second siding to the lumber yard and steel mill at the
north end of the building.
[Illustration: Fig. 220.--Plan of Concrete Mixing and Handling Plant for
Large Warehouse Building.]
The raw materials after being worked up in the mixer plants and the saw
and steel mills were distributed over the work by an industrial railway.
The track system of this railway is shown by the dotted lines; it was
located on the basement floor, with rampes leading to the No. 1 mixer
plant and to the saw and steel mill tracks. The two main lines of track
passed close to or under the elevator and stairway shaft openings in the
several floors. This permitted the derrick buckets, lowered and hoisted
through the shafts, to be loaded directly from the car tracks. All mixed
concrete, forms and reinforcing frames were distributed by this railway
to the several shafts and thence hoisted and placed by the derrick
plant.
[Illustration: Fig. 221.--Derrick for Handling Concrete for Large
Warehouse Building.]
The derrick plant consisted of four derricks arranged as shown by the
circles in Fig. 220. The view, Fig. 221 shows the first derrick
installed and illustrates the general construction quite clearly.
Briefly the derrick consisted of a vertical steel-work tower 10 ft.
square and 85 ft. high, within which operated a steel mast 135 ft. high
and carrying an 80-ft. boom connected just above the tower. The mast was
pivoted at the bottom and had rollers turning against a horizontal ring
inside the tower at the top. It was operated by a bull wheel above the
top of the tower, the turning ropes running down inside the mast to the
foot block and thence horizontally to the operating motor. The topping
and hoisting lines also followed this route. The top of the tower was
guyed by four ropes to anchorages in the basement floor. The boom
commanded a circle 170 ft. in diameter and could lift 150 ft. above the
base of the mast. The derrick was operated by a 25-HP. double drum
electric hoist with a derrick swinging spool; this hoist was set on the
basement floor. It will be noted that the guys are below the bull wheel
so that the boom has a clear swing through a complete circle.
As stated above, four of these derricks were employed. Together they did
not cover the entire building area, but by the use of a derrick bucket
so designed that it could be used as a storage bin for feeding
wheelbarrows, it was found possible to keep the number of derricks down
to four.
This derrick plant possessed several advantages of importance. In the
first place the derricks would handle all classes of material--concrete,
forms, steel frames--equally well and could be transferred from one
class of work to the other with practically no delay. In the second
place, for a large area of the building, they handled the material from
the basement direct to the place it was to occupy in the work, and did
it in one operation. Finally they permitted the handling and erection
of the forms and reinforcement in large units. Thus a column form would
be assembled complete at the mill, moved as a unit by car to the proper
shaft and then hoisted and set in place as a unit by the derrick. Girder
forms, floor slab forms, girder and column reinforcing, etc., could be
similarly assembled and handled. The derricks occupied only the area of
four floor panels, the remainder of the area of each floor was left
unobstructed for the work to be done. No materials or supplies needed be
stored on the floors until they were in perfect condition to accommodate
them, and not then, even, so far as the prosecution of form erection and
concreting were concerned.
The sand and gravel for concrete were brought in by bottom or side dump
gondola cars from pits located about 30 miles out on the Chicago,
Milwaukee & St. Paul Ry. The cars were switched onto the main side track
and unloaded under the bins which straddle this track. A receiving
hopper, with its top at rail level and long enough to permit two cars to
be unloaded at once, received the sand or gravel and distributed it
through twelve gate openings onto an 18-in. horizontal belt conveyor 65
ft. long. This conveyor discharged into a second conveyor, 133 ft. long,
which ran up a 22° incline, extending away from the bins and discharged
onto a third conveyor 117 ft. long, which doubled back on a 22° incline
reaching to and over the top of the bins. This third conveyor had two
fixed trippers and an end discharge to distribute its cargo. All three
conveyors were operated by a 35-HP. motor located at the junction of the
two inclined conveyors, both of which were driven from the same shaft. A
chain belt from the idler shaft of the first incline conveyor to the
driving shaft of the horizontal conveyor operated that unit of the
plant. This belt was operated as a cross belt by reversing alternate
links. No manual labor was required to handle the sand and gravel from
the cars to the storage bins.
The mixer arrangement at the two bins differed. At the No. 1 bins the
mixer was located as shown in Fig. 220, close to the bin. Chutes led
directly from the sand and gravel bins to the charging hopper and the
bags of cement were stacked alongside this hopper. The mixer discharged
either directly into the bucket of the first derrick or into cars for
transportation on the railways. At the No. 2 bins a belt conveyor took
the concrete materials down into the basement to a mixer located close
enough to one of the distribution tracks to permit it to discharge
directly into the cars.
[Illustration: Fig. 222.--Special Concrete Bucket for Large Warehouse
Building.]
The derrick buckets by which the concrete was hoisted and handled to the
work were of special construction. A bucket was desired which would
serve several distinct purposes. It must first be able to hold a full
mixer batch of material, since, with the derrick arrangement, economy in
hoisting necessitated hoisting in large units and also because storage
capacity was required of the bucket for wheelbarrow work. The four
derricks did not command the entire area of a floor; there were corners
and other irregular areas outside of the circles covered by the several
booms over which the concrete must be distributed by barrows or carts.
A bucket large enough to supply the barrows, while a second bucket was
being lowered, charged from the mixer and hoisted, was required. In the
second place, a bucket was required whose contents could be discharged
all at once or in smaller portion at will. Finally a bucket was desired
which could be made to distribute its load along a narrow girder form or
in a thin sheet for a floor slab.
To meet these requirements the bucket shown in Fig. 222 was designed. It
held 42 cu. ft., or about 1.55 cu. yds. of concrete. It had a hopper
bottom terminating in a short rectangular discharge spout closed by a
lever operated under cut gate, which could be opened as much or as
little as desired. To the underside of the bucket there was attached a
four-leg frame in which the bucket stood when not suspended. Ordinarily,
that is within the circles commanded by the derricks, the buckets were
discharged suspended and directly into the forms, the character of the
discharge gate permitting a thin sheet to be spread for floor slabs or a
narrow girder or wall form to be filled without spilling or shock. For
wheelbarrow work outside the reach of the derricks the mode of procedure
was as follows: A timber platform about 3 ft. high and having room for
standing two buckets was set just on the edge of the circle commanded by
the derrick boom. Two buckets were used. A full bucket was hoisted and
set on the platform, with its spout overhanging. This bucket served as a
storage bin for feeding the wheelbarrows while the second bucket was
being lowered, charged and hoisted to take its place on the platform,
and serve in turn as a storage hopper.
~PLACING AND RAMMING.~--A wet concrete is usually used in building work
except on occasions, for exterior wall work and except for pitch roof
work, where a wet mixture would run down the slope. Placing and tamping
are therefore, essentially pouring and puddling operations. The pouring
should be done directly from the barrows, carts, or buckets if possible;
dumping onto shoveling boards and shoveling makes an extra operation and
increases the cost by the wages of the shoveling gang. Where shoveling
boards are necessary, take care that they are placed close to the forms
being filled, as it is wasteful of time to carry concrete in shovels,
even for a half dozen paces. Before pouring any concrete, the inside of
the forms should be wet down thoroughly with a hose or sprinkler, if a
hose stream is not available. The final inspection of forms and
reinforcement just before concreting will have made certain that they
are ready for the concrete, so far as line and level of forms and
presence and proper arrangement of the reinforcement are concerned, but
the concrete foreman must watch that no displacement occurs in pouring
and puddling, and must make certain particularly that the forms are
clean.
In pouring columns it is essential that the operation be continuous to
the bottom of the beam or girder. It is also advisable to pour columns
several hours ahead of the girders. Puddling should be thorough, as its
purpose is to work the concrete closely around the reinforcement and
into the angles of the mold and to work out air bubbles. A tool
resembling a broad chisel is one of the best devices for puddling or
slicing. In slab and girder construction, the pouring should be
continuous from bottom of girder to top of slab. Work should never be
stopped-off at horizontal planes. As in columns, careful puddling is
essential in pouring beams. In slab work, the concrete is best compacted
by tamping or rolling. A broad faced rammer should be used for tamping
wet concrete, or a wooden roller covered with sheet steel, weighing
about 250 lbs., and having a 30-in. face.
Theoretically, concreting should be a continuous operation, but
practically it cannot be made so. Bonding fresh concrete to concrete
that has hardened, though it has been done with great perfection by
certain methods as described in Chapter XXIV, must still be held as
uncertain. Ordinarily, at least, a plane of weakness exists where the
junction is made and in stopping off work it should be done where these
planes of weakness will cause the least harm. Experts are by no means
agreed on the best location of these planes, but the following is
recognized good practice. Work once started, pouring a column, should
not be stopped until the column is completed to the bottom of the
girder. For beams and girders; stop concrete at center of girder with a
vertical face at right angles to the girder, or directly over the center
of the columns; in beams connecting with girders, stop concrete at
center of span, or directly over center of connecting girder; stop
always with a vertical face and never with a sloping face, and never
with a girder partly filled. For slabs; stop concrete at center of span,
or directly over middle of supporting girder or beam; stop always with
vertical joints. If for any cause work must be stopped at other points,
than those stated, the fresh concrete and the hardened concrete must be
bonded by one of the methods described in Chapter XXIV.
~CONSTRUCTING WALL COLUMNS FOR A BRICK BUILDING.~--The columns, 12 in
number, were constructed to strengthen the brick walls of a power
station and were built as shown by Figs. 223 and 224, one at a time. The
staging, 50 ft. high and 4×6 ft. in plan, was erected against the wall
which had been shored, a portion of the wall was cut out and forms
erected and the concrete column substituted for the section of wall
which was removed. The staging was then moved into position for another
column.
[Illustration: Fig. 223.--Section of Rectangular Wall Column.]
Two men, with sledge and drill, cut out the brick work amounting to
about 12 cu. yds. for each column in 15 hours, at a cost of about 70
cts. per cu. yd., including removal to the street. The cost of moving
and re-erecting the scaffolding was $2.94 per each move. The character
of the reinforcement is shown by Fig. 223; it was erected as the
concreting progressed, the main bars being in sections 15 ft. long,
spliced with and distanced by side bars and cross bolts at the splices.
[Illustration: Fig. 224.--Staging and Forms Used in Building Column
Shown by Fig. 223.]
The concrete was hand mixed in 6-cu. ft. batches at the foot of the
column, by three men with a fourth turning over and filling the buckets.
The buckets, 12 ins. in diameter and 16 ins. high, were hoisted by a
pulley line arranged as shown and pulled by a mule driven by a man, at
$1 per day for the mule and $1.50 for the man, the cost of hoisting
being 25 to 40 cts. per cu. yd., depending on the rapidity of the man
inside the form. This man tamped the concrete which was emptied from the
buckets by a man on the scaffolding. Each batch raised the level in the
form 15 ins., and between batches a set of ties for the column rods was
placed by the man during the tamping. It took from 1½ to 2 days to
concrete a column of 12 cu. yds. The concrete was a 1-3.8-5.7 limestone
screenings mixture, mixed wet enough to be easily pushed into the forms
and worked around the reinforcement. The form construction is shown by
Fig. 224. The form for one column required 650 ft. B. M. of lumber, and
on an average, each form was used twice. As a matter of fact, the side
strips and outside braces were used three times, while much of the
7/8-in. sheathing was destroyed by being used once. The lumber for
shoring cost $23 per M. ft. B. M., and the light lumber for forms cost
$18 per M. ft. B. M. All lumber was yellow pine. All labor was negro, at
15 cts. per hour; foremen who worked. 22½ cts. per hour. The cost of the
several parts of the work compiled from records furnished by Mr. Keith
O. Guthrie, engineer in charge, was as follows:
Cost per Cost per
Concrete. column cu. yd.
Lumber for forms $ 4.81 $0.40
Setting up and removing forms 11.32 0.95
Cement, 10.17 bbls. at $2.40 24.40 2.03
Sand, 5.87 yds. at $0.90 5.28 0.44
Stone, 8.75 yds. at $1.35 10.94 0.91
Mixing and wheeling 15.73 1.31
Hoisting by mule with driver 4.80 0.40
Handling bucket on scaffold 2.93 0.25
Tamping inside column 2.93 0.25
Painting with grout 3.89 0.32
Clearing away rubbish 1.97 0.16
Rigging, etc. 2.64 0.21
Tools 0.59 0.05
Moving scaffold 2.94 0.25
Moving mix board and rigging hoist 1.62 0.14
------ -----
Total cost of concrete $96.79 $8.07
Cost per Cost cts. per
Reinforcement. column. lb. of bars.
Iron bars, 1,034 lbs. $20.68 $2.00
Drilling iron bars 1.44 0.14
Setting iron bars in place 1.23 0.12
Bolts for splicing and spacing 3.98 0.40
Wire cross ties at 2½, cts. lb. 1.39 0.14
Labor forming 130 cross ties 1.13 0.11
------ -----
Total cost of iron and steel $29.85 $2.91
Summary of Cost.
Per column. Per cu. yd.
Concrete in place $96.79 $8.07
Steel in place 29.85 2.49
Cutting out and removing brick 8.36 0.70
Shoring floors and roof, labor 5.87 0.49
Ditto for lumber used 3 times 3.44 0.29
------- ------
Total $144.31 $12.04
[Illustration: Fig. 225.--Girder Plan for 6-Story Building.]
~FLOOR AND COLUMN CONSTRUCTION FOR SIX-STORY BUILDING.~--The building was
91×112 ft.; 56 columns spaced 16 ft. apart carried the girder system
shown by Fig. 225, which in turn supported a 3½-in. floor slab. The
walls and partitions were not concrete. The following records were kept
by the authors:
_Forms._--The column forms were built as shown by Fig. 226. The boards
were 1½-in. stuff, surfaced on four sides; the yokes were spaced 2 ft.
apart. The 1×6-in. pieces were nailed to the 2×4's with 8-d. nails with
heads left projecting for easy pulling. The girder forms, Fig. 227,
rested on the column forms and on intermediate posts half-way between
columns. These intermediate posts were 3×4's with 4×4×12-in. head blocks
nailed to their tops and wedges under their bottoms. The girder molds
were 1½-in. stuff, and to the side pieces were nailed 1×4-in. cleats;
the bottom and side pieces were connected by 3/8×4-in. lag screws spaced
28 ins. apart. The floor slab stringers were carried on the 1×4-in.
cleats; they were spaced 28 ins. apart and were not nailed; neither were
the 1×6-in. lagging boards nailed to the stringers. The point to be
noted is the design and construction of the forms so that they could be
put together and taken apart easily. The lumber required for forms for
one floor 91×112 ft., or, say, 10,200 sq. ft., was as follows:
Lumber for columns, ft. B. M. 9,000
Lumber for 10×10-in. beams, ft. B. M. 7,600
Lumber for 5×10-in. beams, ft. B. M. 2,700
Intermediate 3×4-in. posts, ft. B. M. 1,000
Lagging, 1×6-in. boards, ft. B. M. 9,000
Stringers, 3×4 ins., ft. B. M. 4,500
------
Total ft. B. M. 33,800
[Illustration: Fig. 226.--Column Form for 6-Story Building.]
In round numbers, we can say that 34,000 ft. B. M. of lumber were used
for 10,000 sq. ft. of floor area, or 3.4 ft. B. M. per 1 sq. ft. Enough
forms were provided to erect two complete floors; the forms for the
lower floor being removed and erected again for the second floor above,
thus using all the lumber three times. With carpenters at $3.50 for 8
hours, the forms were framed ready for erection for $4 per M. ft. B. M.
The lumber framed ready to erect cost them:
Lumber, cost per M. ft. B. M. $26.00
Labor, framing per M. ft. B. M. 4.00
------
Total per M. ft. B. M. $30.00
[Illustration: Fig. 227.--Girder and Slab Forms for 6-Story Building.]
Since the lumber was used three times, $30 ÷ 3 = $10 is the charge
against each 1,000 ft. B. M. needed to encase the concrete on a floor.
There were nearly 34,000 ft. B. M. per floor, hence the cost of lumber
ready for erection was $340 per floor. There were as shown below, 200
cu. yds. of concrete per floor, so that the cost was $340 ÷ 200 = $1.70
per cu. yd. of concrete for forms ready for erection. It took a gang of
5 men 7 days to tear down and carry up the forms for one floor; hence 5
× $2 × 7 = $70 per floor, or practically $2 per M. ft. B. M., or $0.35
per cu. yd. of concrete for taking down and carrying forms two stories.
It took a gang of 10 carpenters 7 days to erect these forms, which at
$3.50 per day was $245 per floor, or $7 per M. ft. B. M., or $1.20 per
cu. yd. of concrete.
_Concrete._--The amount of concrete per floor was as follows:
Floor slab 3½ ins. thick, 10,200 sq. ft. 110 cu. yds.
Beams, 10×10 ins. 40 cu. yds.
Beams, 5×10 ins. 20 cu. yds.
Columns, 15×15 ins. (average) 30 cu. yds.
-----
Total concrete per floor 200 cu. yds.
A concrete mixer, a hoist and a gang of 14 men mixed and placed the
concrete for a floor in 7 days. At $2 per day for labor this gives 14 ×
7 × $2 = $196, or say $1 per cu. yd. for mixing and placing the
concrete.
_Reinforcement._--In each of the 10×10-in. beams there were 4, 1-in.
round rods, 2 straight and 2 bent, and stirrups of 1/8×1-in. straps
spaced 5 ins. apart at columns and 15 ins. at the center. In each
5×10-in. beam there was half as much steel as in a 10×10-in. beam. The
floor slab reinforcement consisted of ¼-in. rods spaced 5 ins. apart and
2 cross-rods in 7-ft. panel. The column reinforcement consisted of 4
rods averaging 1 in. in diameter. In round numbers the amount of steel
required for each floor was, therefore, as follows:
Lbs. steel rods in 10×10-in. beams 16,200
Lbs. steel rods in 5×10-in. beams 4,000
Lbs. stirrups in beams 3,000
Lbs. steel rods in floor slabs 3,800
Lbs. steel rods in columns 1,400
------
Total pounds steel per floor 28,400
This is equivalent to 142 lbs. of steel per cubic yard of concrete, or
about 1 per cent of the total volume of reinforced concrete was steel.
The steel in the beams was about 3 per cent. It required a gang of 5
laborers 7 days at $2.25 per day, to bend and place the steel for each
floor or $86 for labor on 28,400 lbs. of steel. This is equivalent to
0.3 ct. per lb., or 45 cts. per cu. yd. of concrete.
_Summary of Costs._--Summarizing the figures given we have the following
cost per cubic yard of concrete in floors and columns:
Per cu. yd.
142 lbs. steel at 2½ cts. $ 3.55
1 bbl. cement 2.50
1 cu. yd. gravel 1.10
½ cu. yd. sand 0.55
170 ft. B. M. lumber ready to erect at $10 (1/3 of $30) 1.70
170 ft. B. M. torn down at $2 0.35
170 ft. B. M. erected by carpenters at $7 1.20
Mixing and placing concrete 1.00
Shaping and placing steel 0.45
Superintendence 0.25
------
Total $12.65
~WALL AND ROOF CONSTRUCTION FOR ONE-STORY CAR BARN.~--The barn was 50 ft.
wide and 190 ft. long, divided into three rooms by two transverse
partitions and covered with a 4-in. roof having a pitch of ½ in. per
foot. The main walls were 12 ins. thick and the partition walls 10 ins.
thick. The main room 110 ft. long had four car tracks its whole length
with pits under each and a 6-in. reinforced concrete floor slab between.
The floor girders, one under each rail, were 12 ins. square, each
reinforced by three 1¾-in. rods, and were carried on 12×12-in. pillars.
The total yardage of concrete was 874 cu. yds. divided as follows:
Walls and foundations, cu. yds. 614
Pillars and girders in track pits, cu. yds. 44
Reinforced floors, cu. yds. 55
Roof 160
---
Total, cu. yds. 873
A 1-2½-5 concrete was used for floors, roofs and girders and a 1-3-6
concrete for foundations and walls. There were 26½ tons of reinforcing
steel, or 61 lbs. per cu. yd., or 0.45 per cent. of the volume of the
concrete was steel. The wages paid were: Foreman, $2.50; blacksmith, $2;
engineer, $1.75; laborers, $1.50; two-horse team and driver, $3.67;
one-horse team and driver, $2.92; carpenter, $2.25; carpenters worked 9
hours; all others 10 hours.
_Forms._--Carpenters framed and erected forms and common laborers under
foreman carpenter took them down. Lagging was all 2-in. stuff and
uprights 3×4-in. stuff. Props for roof forms were 18-ft. round timber
procured on the job. They were 6 ins. in diameter at the top and cost 50
cts. each, 91 being used. These props are not included in the lumber
listed below, but their cost is included in the costs given. No record
was kept of the number of times the lumber was used, but as 54,643 ft.
B. M. were bought and about twice this much would be needed to enclose
the concrete if used only once, we will assume that all lumber was used
twice. Including the props there were about 60,000 ft. B. M., or 70 ft.
B. M. per cu. yd. of concrete. The cost of the lumber was $1,520.86, and
the cost of labor on the forms was $1,660.60, so that the cost of forms
was:
Item. Per cu. yd. Per M. ft. Per sq. ft.
Lumber $1.74 $13.50 $0.038
Labor 1.90 14.07 0.041
----- ------ ------
Total $3.64 $27.57 $0.079
If the lumber had been used only once the cost per cubic yard would have
been $5.38, and per M. ft. B. M., $41.07.
_Concrete._--A railway track was run the full length of the building
upon what was eventually the fourth track of the car barn and a Ransome
mixer was set up as close to the track as possible allowing a platform
to be built between it and the track. Cars were brought up to this
platform and the materials handled by wheelbarrows direct from cars to
mixer. Both platform and mixer were moved twice as the work progressed.
The concrete was taken by wheelbarrows on runways to the side walls. For
the roof it was hoisted by a horse by means of a mast having an arm with
a three-quarters swing; the barrows were hoisted direct using a hook for
the wheel and two rings for the handles.
The cost of the concrete for materials was:
1.1 bbl. cement at $1.21, per cu. yd. $1.33
¾ ton sand at 75 cts., per cu. yd. 0.55
Aggregate, per cu. yd. 0.88
61 lbs. steel at 1.9 cts., per cu. yd. 1.15
Lumber, 70 ft. B. M. at $27, per cu. yd. 1.74
-----
Total per cu. yd. $5.65
The cost of labor per cubic yard was:
Forms, per cu. yd. $1.900
Mixing, per cu. yd. 0.210
Placing, per cu. yd. 0.310
Finishing, per cu. yd. 0.143
Handling cement, per cu. yd. 0.017
Handling sand, per cu. yd. 0.104
Handling steel, per cu. yd. 0.270
Handling aggregate, per cu. yd. 0.222
Coal, at $4.25 per ton, per cu. yd. 0.010
Foreman, per cu. yd. 0.133
Teams and laying pipe line, per cu. yd. 0.087
------
Total, per cu. yd. $3.406
Summarizing, we have the following cost per cubic yard:
Concrete materials, per cu. yd. $2.76
Labor mixing and placing concrete 1.01
Forms, materials and labor 3.64
Reinforcement, materials and labor 1.42
Fuel, foreman and pipe line labor 0.23
-----
Total, per cu. yd. $9.06
The cost for handling steel, making stirrups, welding, etc., was $8.90
per ton, or 0.45 ct. per lb.
_CONSTRUCTING WALL COLUMNS FOR A ONE-STORY MACHINE SHOP._--The building
was 53×600 ft.; each side wall consisted of 40 columns of channel
section carried on footings of channel section somewhat heavier than
that of the column. The columns were spaced 15 ft. on centers and each
was 7½ ft. wide so that there were 7½ ft. spaces between columns, which
were filled with 3-in. curtain walls extending 7½ ft. above the floor.
Figures 228 and 229 show the column and footing construction. Each
column contained 125 cu. ft., or 4.63 cu. yds. of 1-3-5 1-in. crushed
slag concrete above the footing and the costs given here relate only to
the columns above footings. In the 80 columns there were 370 cu. yds. of
concrete.
_Forms._--A column form is shown by Fig. 230; it contains approximately
1,000 ft. B. M. of lumber. Ten of these forms were used, so that 10,000
ft. B. M. of form lumber were required for 370 cu. yds. of concrete, or
27 ft. B. M. per cu. yd. of concrete. Each column had a superficial area
excluding ends of about 420 sq. ft., so that 420 × 80 = 33,600 sq. ft.
was the superficial area of all the columns and 10,000 ft. B. M. ÷
33,600 sq. ft. = 0.3 ft. B. M., or, say, 1/3 ft. B. M., of form lumber
was used per square foot of concrete enclosed. The cost of the forms per
1,000 ft. B. M., and, therefore, per form, was:
Lumber, 1,000 ft. B. M., at $31.75 $31.75
Labor constructing form 16.39
------
Total per 1,000 ft. B. M. $48.14
[Illustration: Fig. 228.--Channel Section Wall Column for Factory
Building.]
This gives us a cost per cubic yard of concrete for materials and labor
constructing forms of $480 ÷ 370 = $1.30, and per square foot of outside
wall area of $480 ÷ (146 × 80) = 4.1 cts.
The erection and taking down of the forms, owing to the weight of some
of the pieces, was done by means of special derricks. The footings were
brought to within ½ in. of grade and a tenon form of the exact shape of
the channel section of the column was placed on top and filled with
grout to a depth of 1 in. These tenons served as guides in setting the
column forms, and proved to be much quicker and more accurate than
points.
[Illustration: Fig. 229.--Footing for Wall Column Shown by Fig. 228.]
The forms were assembled on the ground and erected by a 35-ft. A-frame
derrick mounted on wheels. The construction is shown by Fig. 231. This
derrick had a capacity of about 4 tons and carried a Ransome friction
crab hoist driven by a 5 h.p. Meitz & Weiss kerosene oil engine. It was
the practice to set a number of forms before filling any. This enabled
the carpenter gang to be plumbing up the first form while the erecting
gang were setting others. The forms had to be very securely guyed and
braced to withstand the impact of the falling concrete. Very little
trouble was had in keeping them well lined up.
[Illustration: Fig. 230.--Form for Molding Wall Column Shown by Fig.
228.]
Two gangs were employed in assembling forms and a portion of the men in
each gang also shaped and placed the reinforcement and placed and tamped
the concrete in the forms so that no exact division of labor is
possible. The organization of these gangs and the wages paid were as
follows:
Derrick Gang:
1 foreman, at 36 cts. per hour $ 3.94
1 crabman, at 30 cts. per hour 2.70
2 topmen, at 27 cts. per hour 4.86
2 bottom men, at 23 cts. per hour 4.14
------
Total per 9-hour day $15.64
Assembling Gang:
1 boss carpenter, at 47 cts. per hour $ 4.23
2 carpenters, at 36 cts. per hour 6.48
2 carpenters, at 30 cts. per hour 5.40
2 carpenters' helpers, at 25 cts. per hour 4.50
4 men forming and placing reinforcing steel
and rethreading bolts, at 23 cts. per hour 8.28
------
Total per 9-hour day $28.89
------
Grand total $44.53
These gangs assembled and erected the molds and concreted 80 columns in
22 working days, including 2 days lost on account of cold weather, so
that 4 columns were completed per day of 9 hours. We can subdivide the
cost as follows:
Item. Per cu. yd.
Erecting forms and concreting $0.81
Assembling forms and reinforcement 1.56
-----
Total $2.37
Charging the 4 men placing reinforcement and rethreading bolts to
forming and placing reinforcement alone we can figure the cost of
fabrication and erection of reinforcement very closely. There were 160
lbs. of reinforcing steel in each column, hence $8.28 ÷ (160 × 4) = 1.3
cts., was the cost per pound of forming and placing it. This includes
handling.
The stripping of the forms was carried on by another gang using a
derrick similar to the first one described, except it could be of
lighter construction as it had to handle only the separate parts of each
form and not the forms assembled. The derrick shown in Fig. 232 was a
33-ft. A-frame, with wheels at the bottom of each leg. It had a friction
crab hoist driven by an electric motor, both of which were fastened to
the derrick frame between the shear legs.
[Illustration: Fig. 231.--Derrick for Erecting Wall Column Forms Shown
by Fig. 230.]
The operation of stripping required only four men and the crabman. The
outside flat panel was removed first, and left leaning up against the
concrete while the inside trough shaped panel was pried loose and
lowered onto the ground with its inside face uppermost. The side panels
being comparatively light, were stripped without the use of the derrick,
and these panels were assembled on the ground with the inside piece. The
derrick then picked up the outside panel again, and placed it in its
proper place. After the bolts were put in place, the assembled form was
moved on rollers to another point in the line of columns where it was
again erected. The arrangement of derricks for erecting and stripping
forms is shown in Fig. 233.
The gang stripping forms was made up as follows:
1 foreman, at 30 cts. per hour $ 2.70
1 crabman, at 27 cts. per hour 2.43
1 topman, at 27 cts. per hour 2.43
2 bottom men, at 23 cts. per hour 4.14
------
Total per 9-hour day $11.70
[Illustration: Fig. 232.--Derrick for Stripping Wall Column Forms Shown
by Fig. 230.]
This gang of five men stripped 4 columns containing 18.52 cu. yds. of
concrete each day, so that the cost of stripping was $11.70 ÷ 18.52 =
62.7 cts. per cu. yd.
_Concrete._--The concrete was mixed in a No. 2 Ransome mixer and
delivered to the work in Ransome concrete carts. These carts were pushed
along a runway which terminated in a slight incline under the derrick so
that their contents could be emptied into the derrick buckets.
The concrete was hoisted in an 8-ft. bottom dump bucket, using the
derrick described above. It was necessary to stir up the concrete
thoroughly with long-handled slicers as it was being deposited in order
to prevent segregation. This expedient combined with a wet mixture and
tight molds was found to overcome this difficulty very effectually.
The gang mixing and wheeling concrete was made up as follows:
1 mixer foreman and engineer at 27 cts. per hour $ 2.43
4 laborers charging mixer at 18 cts per hour 6.48
4 laborers wheeling concrete at 18 cts. per hour 6.48
------
Total per 9-hour day $15.39
This gang mixed and wheeled concrete for four columns, or 18.52 cu.
yds., hence the cost per cubic yard was 82.6 cts.
With cement at $1.60 per bbl., sand at $1 per cu. yd. and slag at $1.10
per cu. yd. the cost of materials per cubic yard of concrete was $3.
[Illustration: Fig. 233.--Arrangement of Derricks for Erecting and
Stripping Forms.]
Summarizing the above figures we have the following cost per cubic yard
of concrete in place:
Item. Per cu. yd.
Concrete materials $3.00
Reinforcing steel 0.73
Forms, lumber and framing 1.30
Forms, erecting and concreting 0.81
Forms, assembling and reinforcement 1.56
Forms, stripping 0.63
Mixing and wheeling concrete 0.83
-----
Total $8.86
~CONSTRUCTING ONE-STORY WALLS WITH MOVABLE FORMS AND GALLOWS FRAMES.~--In
constructing the walls for an 85×30-ft. factory building at Old Bridge,
N. J., Mr. A. E. Budell made use of movable forms and gallows frames to
construct the curtain walls and columns in one piece. Each side wall was
built its full height in successive 50-ft. lengths by depositing the
concrete between two forms which were moved upward as the concreting
progressed. Fig. 234 indicates the mode of procedure. The form was
raised and lowered by means of two gallows frames fitted with blocks and
tackle. A steel cable, with a trolley affixed, extending from one frame
to the other, provided a convenient mode of hoisting material to the
form, and the gallows frames took the place of ladders for climbing onto
the structure. No scaffolding whatever was used and only one man was
required overhead to dump the buckets and tamp the concrete into place.
[Illustration: Fig. 234.--Gallows Frame Supporting Wall Form Panels for
One-Story Building.]
[Illustration: Fig. 235.--Details of Wall Form Panel for One-Story
Building.]
The two walls were carried up simultaneously, one form being shifted
into place and filled while the other was left in place until the
concrete was sufficiently hard. It was found that 18 hours was amply
sufficient to allow the concrete to set hard, after which the form was
removed and lifted to a higher level. Thus the men were continuously
engaged in lifting and filling first one form and then the other. The
average length of time required to remove, raise and fill one form was 5
to 6 hours. Thus, two forms could be raised and filled almost every day.
The construction of the forms and of the gallows frames is shown by
Figs. 234 and 235. The cost of one set of forms and gallows frames was
as follows:
320 ft. B. M. of 2×10 in.×10 ft. plank at $34 $ 10.88
150 ft. B. M. of 3×4 in.×16 ft. spruce at $33 5.25
135½ ft. B. M. 1×8 in. yellow pine at $30 4.08
335 ft. B. M. 1¼×6 in. spruce at $33 11.05
4 posts 6×8 in.×26 ft. = 416 ft. B. M. at $30 12.48
4 sills 6×8 ins.×16 ft., 2 caps 6×6 ins.×9 ft.,
4 braces 6×6 ins.×16 ft. = 490 ft. B. M. at $30. 14.70
3 pieces 3×10 ins.×20 ft. = 150 ft. B. M. at $30 4.50
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Total lumber (1,996.5 ft. B. M.) $ 62.94
Accessories:
Bolts for trussing, 675 lbs. at 2 cts. $ 13.50
Iron guy rope and clips 7.00
Blocks 8.00
One coil of ¾-in. rope 28.00
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Total accessories $ 56.50
Labor making one outfit:
2 men, 8 days, at $2.75 per 9 hrs. $ 44.00
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Grand total $163.44
This sum covered the cost of forms for one side of the building 85 ft.
long and containing 150 cu. yds. of concrete, hence the cost of forms
was in round figures $1.10 per cu. yd. of concrete. Each cubic yard of
concrete required 1,997 ÷ 150 = 13-1/3 ft. B. M. of form lumber.
The concrete was a 1-2½-4½ mixture. A careful record for 15 days, showed
an average of 2.8 cu. yds. of concrete placed in 6 hours by a gang of
6.3 men. From this we can figure the cost of concrete in place to be
about as follows:
2.8 cu. yds. concrete at $3 for materials $ 8.40
6.3 men 6 hours at 15 cts. 5.67
1 foreman 6 hours at $4 per day 2.00
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Total per cu. yd. $16.07
Thus the cost of concrete in place was $16.07 ÷ 2.8 = $5.73 per cu. yd.
Adding the cost of forms we get $5.73 + $1.10 = $6.83 per cu. yd. as the
cost for labor and materials in constructing forms and mixing and
placing concrete.
[Illustration: Fig. 236.--Detail of Column and Cantilever Column Footing
for Four-Story Garage.]