Concrete Construction Part 42

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 finishing 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.

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 s.p.a.ce between main roof girders was spanned by reinforced concrete girders and roof slab. The center ill.u.s.trated 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.

[Ill.u.s.tration: 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 a.s.surance 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 24-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.

[Ill.u.s.tration: Fig. 195.--Girder and Slab Form for Factory Building, Cincinnati, O.]

[Ill.u.s.tration: Fig. 196.--Girder and Beam Forms for Factory Building, Beverly, Ma.s.s.]

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, Ma.s.s. 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. s.p.a.ces 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 15-in.

cleats. Except in attaching the quarter round and triangular moldings for fillets no nailing is necessary in erecting and taking down the forms.

[Ill.u.s.tration: 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 912-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 -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, 260150-ft.

wholesale hardware store Of Farwell, Osman & Kirk Co., St. Paul, Minn.

[Ill.u.s.tration: Fig. 198.--Girder and Slab Form for Warehouse at St.

Paul, Minn.]

[Ill.u.s.tration: 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 68 ins. in section and are s.p.a.ced 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 47/8-in. vertical boards nailed to top and bottom 24-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.

[Ill.u.s.tration: 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 s.p.a.ces 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 s.p.a.cers 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.