This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
In constructing columns, the forms are usually erected complete, the full height of the columns; and concrete is dumped in at the top. The concrete must be mixed very wet, as it cannot be rammed very thoroughly at the bottomland care must be taken not to displace the steel. Sometimes the forms are constructed in short sections, and the concrete is placed and rammed as the forms are built. The ends of the bottom of the forms for the girders and beams, are usually supported by the column forms. To give a beveled edge to the corner of the columns, a triangular strip is fastened in the corner of the forms.
Fig. 154A shows the common way, or some modification of it, of constructing forms for columns. The plank may be 1 inch, 1 1/2 inches, or 2 inches thick; and the cleats are usually 1 by 4 inches and 2 by 4 inches. The spacing of the cleats depends on the size of the columns and the thickness of the vertical plank.
Fig. 153. Tongued-anc Grooved Edge.
Fig. 154 B shows column forms similar to those used in constructing the Harvard stadium. The planks forming each side of the column are fastened together by cleats, and then the four sides are fastened together by slotted cleats and steel tie-rods. These forms can be quickly and easily removed.
Fig. 155 shows a column form in which concrete is placed and rammed as the form is constructed. Three sides are erected to the full height, and the steel is then placed. The fourth side is built up with horizontal boards as the concrete is placed and rammed.
Round columns are often desirable for the interior columns of buildings. Fig. 156 shows a form that has been used for this type of column. The columns for which these forms were used were 20 inches in-diameter, and had a star-shaped core made of structural steel. The forms for each column were made in two parts and bolted together. The sides were made of 2 by 3-inch plank surfaced on all four sides, beveled on two, and held in place by the steel bands, which were 1/4 by 2 1/2 inches and spaced about 2\ feet apart. One screw in the outer plank at each band of both parts, together with a few intermediate screws, held the plank in place. The building for which these forms were made was ten stories in height. Enough forms were provided for two stories, which was sufficient, as they could be removed when the concrete had been in place one week. Later these same forms were used in constructing the interior columns of a six-story building. Some difficulty was experienced in removing these forms, owing to the concrete sticking to the plank. But had these forms been made in four sections, instead of two, and well oiled, it is thought that this trouble would have been avoided. Columns constructed with forms as shown in Fig. 156 will not have a round surface, but will consist of many flat surfaces, 2 1/4 inches wide. If a perfectly round column is desired, it will be necessary to cut the surface of the plank next to the concrete to the desired radius.
Forms for octagonal columns can be made in a somewhat similar manner to these just described.
353. Forms for Beams and Slabs.
A very common style of form for beam and slab construction is shown in Fig.
157. The size of the different members of the forms depends upon the size of the beams, the thickness of the slabs, and the relative spacing of some of the members. If the beam is 10 by apart, will support the slab. The sides and bottom of the beams are enclosed by 1 1/2-inch or 2-inch plank supported by 3 by 4-inch posts spaced 4 feet apart.
20 inches, and the slab is 4 inches thick, then 1-inch plank supported by 2 by 6-inch timbers spaced 2 feet
Fig. 155. Form for Column.
Fig. 156. Form for Round Column.
In Fig. 158 are shown the forms for a reinforced-concrete slab, with I-beam construction. These forms are constructed similarly to those just described.
A slab construction supported on I-beams, the bottom of which is not covered with concrete, may have forms constructed as shown in Fig. 159. This method of constructing forms was designed by by Mr. William F. Kearns (Taylor and Thompson, "Plain and Reinforced Concrete").
Fig. 157. Forms for Beams and Slabs.
The construction of forms for a slab that is supported on the top of I-beams is a comparatively simple process, as shown in Fig. 160. In any form of I-beam and slab construction, the forms can be constructed to carry the combined weight of the concrete and forms. When the bottom of the I-beam is to be covered with concrete, it is not so easily done as when the haunch rests on the bottom flange (Fig. 159) or is a flat plate (Fig. 160).
Fig. 158. Forms for Reinforced-Concrete Slab Supported by I-Beams.