Chapter XXIV

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~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 ------- 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 ------- Total accessories $ 56.50

Labor making one outfit: 2 men, 8 days, at $2.75 per 9 hrs. $ 44.00 ------- 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 ------ 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.]

Offsets and molding decorations were easily made, although they were quite numerous on the building in question, at least more so than would ordinarily be the case in mill building construction. The offset of 1 ft. at every column was made very readily by sliding wooden shoulder pieces into place on the inner face of the form, which pieces in turn received 2-in. faced planking, the latter being slid into place from above. Thus the entire system was collapsible and small alterations were easily made whenever the form was shifted. Flat surfaces or offsets could be obtained at will by either removing or setting in the shoulder pieces. Molding effects were made on the front face of the wall by tacking molding strips to the form wherever necessary. The entire work was done with common labor and the finished building presented a smooth, homogeneous surface which required very little dressing.

[Illustration: Fig. 237.--Details of Cantilever Girders for Mezzanine Floor for Four-Story Garage.]

~FLOOR AND ROOF CONSTRUCTION FOR FOUR-STORY GARAGE.~--The building was 53×200 ft., and 4 stories high, with provision for 2 additional stories in the design of footings and columns. Two rows of wall columns connected by transverse girders carrying the floor and roof slabs made a comparatively simple construction, except for a mezzanine floor carried on cantilever beams and except for the use of cantilever footings; these two special details are shown by Figs. 236 and 237. The amount of concrete in the building was 1,910 cu. yds., distributed as follows:

Cu. yds.

Footings, reinforced 190 Columns, reinforced 450 Floors and roof, reinforced 1,100 Floor on ground, not reinforced 170 ----- Total 1,910

The amount of reinforcing metal used was 237 tons, distributed as follows:

Item. Tons. Lbs. per cu. yd. Footings 42 442 Columns 20 90 Floors and roof 175 318 --- --- Total and average 237 272

This is equivalent to 2 per cent. of steel in 1,910 - 170 = 1,740 cu. yds.

_Forms._--The total area of concrete covered by forms (1,740 cu. yds.) was 94,000 sq. ft., distributed as follows:

Footings, sq. ft. 4,000 Columns, sq. ft. 20,000 Floors and girders, sq. ft. 70,000 ------ Total, sq. ft. 94,000

For the work 50,000 ft. B. M. of old lumber was used and 170,000 ft. B. M. of new lumber was bought, the cost being as follows:

50 M. ft. B. M. at $13 per M. $ 650 170 M. ft. B. M. at $26 per M. 4,420 ------ 220 M. ft. B. M. at $23 $5,070

This is equivalent to 126 ft. B. M. per cu. yd. of concrete. New forms were made for each floor except the sides of the girder molds which were re-used so far as they would fit, but the roof forms were made from lumber used for the floors. In all no more than 20 per cent of the form lumber was used a second time. In round figures new lumber was required for 80,000 sq. ft. of concrete; this gives a cost for lumber of 6.4 cts. per sq. ft. The construction of the column and floor forms is shown by Fig. 238. A force of 15 carpenters at $4.40 per day under a foreman at $35 per week erected and tore down forms; the carrying was done by laborers at $1.70 per day working under a foreman at $35 per week; carpenters worked an 8-hour and laborers a 10-hour day. Forms for one floor were framed and erected in 8 to 10 days. The cost of forms for 1,740 cu. yds. and 80,000 sq. ft. of concrete and per M. ft. B. M. was as follows:

Item. Per cu. yd. Per sq. ft. Per M. ft. Lumber $2.90 $0.064 $23.00 Framing, erecting and removing. 2.00 } 15.67 } 0.057 Handling lumber 1.10 } 8.70 ----- ------ ------ Totals $6.00 $0.121 $47.37

[Illustration: Fig. 238.--Column and Floor Forms for Four-Story Garage.]

The lumber had a considerable salvage value which is not allowed for in the above figures.

_Concrete._--The concrete was a Portland cement, ¾-in. trap rock mixture, mixed wet in two Chicago Improved Cube Mixers equipped with charging buckets. The mixers were located on the ground floor, one at the rear and one at the front of the building, both discharging directly to a hoist. With a gang of 30 men at $1.70 per 10-hour day under a foreman at $35 per week a floor was concreted in 2 days, the columns being concreted the first day and the floor being concreted the second day. The labor cost for mixing and placing concrete and for fabricating and setting reinforcement was as follows:

Item. Per cu. yd. Mixing and placing concrete $1.95 Erecting and setting steel 2.05 ----- Total $4.00

The cost of concreting includes the cost of granolithic surface for the floor slabs. The girder reinforcement was made up into unit frames and the frames were set as a unit, horses set over the molds being used to suspend and lower them into place. The cost of $2.05 per cu. yd. is equivalent to ¾ ct. per lb. Summarizing, we have the following cost for materials and labor on forms and for labor mixing and placing concrete and reinforcement:

Per cu. yd. Lumber for forms $ 2.90 Labor on forms 3.10 Labor on concrete 1.95 Labor on steel 2.05 ----- Total $10.00

This $10 total does not include the cost of the concrete nor of the steel.

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