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 ⅞-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 ⅝-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.
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.
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.