Part 42 (1/2)

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.

[Ill.u.s.tration: 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 s.p.a.ced 3 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 s.p.a.cing was about 2 ft. With 26-in. yokes and 1-in lagging a form for a column 18 ins. between sides would require some 17 ft. B. M.

per foot of column length.

[Ill.u.s.tration: Fig. 187.--Form for Octagonal Column for Factory Building.]

[Ill.u.s.tration: 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 in. in diameter for smaller columns. This reinforcement was set in place and wrapped with No. 24 -in. mesh metal lath, and the cylinder was filled with concrete and plastered outside. A moderately dry concrete is essential for such construction.

[Ill.u.s.tration: Fig. 189.--Form for Circular Column.]

The method of molding sh.e.l.ls 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.

[Ill.u.s.tration: 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 finis.h.i.+ng of the building.

The methods ill.u.s.trated 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 s.p.a.ce 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 coa.r.s.e concrete backing.

[Ill.u.s.tration: 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 f.l.a.n.g.es 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, pa.s.sing through holes in the joists are more commonly employed. For 1-in. lagging the joist s.p.a.cing is 2 ft., for 1-in lagging, 4 ft., and for 2-in. lagging, 5 ft.

[Ill.u.s.tration: Fig. 192.--Form for Arch Slab Between I-Beams.]

[Ill.u.s.tration: 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 (24 ins. for spans not exceeding 6 ft.) and the 23-in. triggers B, which rest on the lower f.l.a.n.g.es of the floor beams and thus support the forms. The trigger is secured at one end to the piece A by a 13-in. cleat C and at the other end by 13-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 s.p.a.cing blocks H as shown; for smaller beams omit the trigger B and extend A to rest on the f.l.a.n.g.e 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 24-in. cross-pieces on 23-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 4 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 24-in. and 23-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.