Chapter IX

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~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