Concrete Construction Part 47

[Ill.u.s.tration: Fig. 234.--Gallows Frame Supporting Wall Form Panels for One-Story Building.]

[Ill.u.s.tration: Fig. 235.--Details of Wall Form Panel for One-Story Building.]

The two walls were carried up simultaneously, one form being s.h.i.+fted 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 210 in.10 ft. plank at $34 $ 10.88 150 ft. B. M. of 34 in.16 ft. spruce at $33 5.25 135 ft. B. M. 18 in. yellow pine at $30 4.08 335 ft. B. M. 16 in. spruce at $33 11.05 4 posts 68 in.26 ft. = 416 ft. B. M. at $30 12.48 4 sills 68 ins.16 ft., 2 caps 66 ins.9 ft., 4 braces 66 ins.16 ft. = 490 ft. B. M. at $30. 14.70 3 pieces 310 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 -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 1-2-4 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.

[Ill.u.s.tration: 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 s.h.i.+fted. 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, h.o.m.ogeneous surface which required very little dressing.

[Ill.u.s.tration: Fig. 237.--Details of Cantilever Girders for Mezzanine Floor for Four-Story Garage.]

~FLOOR AND ROOF CONSTRUCTION FOR FOUR-STORY GARAGE.~--The building was 53200 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

[Ill.u.s.tration: 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, -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 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.

CHAPTER XX.

METHOD AND COST OF BUILDING CONSTRUCTION OF SEPARATELY MOLDED MEMBERS.

This chapter deals exclusively with the methods and cost of molding and erecting separately molded wall blocks, girders, columns and slabs. The structural advantages and disadvantages of this type of construction as compared with monolithic construction will not be considered. The data given in succeeding paragraphs show how separate piece work has been done and what it has actually cost to do it in a number of instances.

~COLUMN, GIRDER AND SLAB CONSTRUCTION.~--European engineers have developed several styles of open web or hollow girder and column shapes, but in America solid columns and girders have been used except in the comparatively few cases where one of the European constructions has been introduced by its American agents.

~Warehouses, Brooklyn, N. Y.~--In constructing a series of warehouses in Brooklyn, N. Y., the columns and girders were molded in forms on the ground. For molding the columns, forms consisting of two side pieces and one bottom piece, were used, saving 25 per cent. in the amount of lumber required for a column form, and doing away with yokes and bolts, since only simple braces were required to hold the side forms in place. It was found that the side forms could readily be removed in 24 to 48 hours, thus considerably reducing the time that a considerable portion of the form lumber was tied up. It was figured by Mr. E. P. Goodrich, the engineer in charge of this work, that this possible re-use of form lumber reduced the amount required another 50 per cent. as compared with molding in place. Girders were molded like columns in three-sided forms; the saving in form work was somewhat less than in the case of columns, but it was material. In general, Mr. Goodrich states, the cost of hoisting and placing molded concrete members is higher per yard than when the concrete is placed wet. That is in ma.s.s before it is hardened.

[Ill.u.s.tration: Fig. 239.--Sketch Showing Forms and Reinforcement for Visintini Girder.]

~Factory, Reading, Pa.~--In constructing a factory at Reading, Pa., an open or lattice web type of girder invented by Mr. Franz Visintini and extensively used in Austria was adopted; columns were molded in place in the usual manner with bracket tops to form girder seats. The girders were reinforced with three trusses made up of top and bottom chord rods connected by diagonal web rods; one truss was located at the center of the beam and one at each side. The method of molding was as follows: The trusses were made by cutting the chord rods to length and threading the web diagonals and verticals onto them. To permit threading the web pieces were bent, when rods were used, with an eye at each end; when straps were used the ends were punched with holes. The work was very simple and was done mostly by boys in the machine shop of the company for which the building was being erected. The girders were molded two at a time in forms constructed as shown by the sketch. Fig. 239. A form consisted of a center board, two side boards, two end pieces and the proper number of cast iron cores, all clamped together by three yokes.

Triangular cast iron plates, A, were screwed to the bottom boards for s.p.a.cers. The side, center and end boards were then set up and the end clamps were placed. The cast iron hollow cores, B, were then set over the s.p.a.cers, and the form was ready for pouring. A layer of concrete was placed in the bottom of the mold and the first side truss was placed; the concrete was then brought half way up and the middle truss was placed; concreting was then continued up to the plane of the second side truss which was placed and covered. Cores and forms were all cleaned and greased each time they were used. The cores were removed first by means of a lever device and generally within three or four hours after the concrete was placed. The remainder of the form was taken down in two to four days and the beam removed.

~Kilnhouse, New Village, N. J.~--In constructing a kiln house for a cement works one story columns with bracket tops and 50-ft. span roof girders were molded on the ground and erected as single pieces. The columns by rough calculation averaged about 2 cu. yds. of concrete and 675 lbs. of reinforcement each or about 337 lbs. of steel per cubic yard. The girders averaged by similar calculation 5 cu. yds. of concrete and 2,260 lbs. of steel, or 452 lbs. per cubic yard of concrete. The average weight of columns was thus not far from 41.3 tons and of girders fully 11 tons.

[Ill.u.s.tration: Fig. 240.--Arrangement for Molding Ten Single-Bracket Columns.]