Column Forms

Figure 7-35.-Typical beam and girder forms.

Engineering Aid 3 - Beginning Structural engineering guide book
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Figure 7-33.-Method of joining wall form corner. panels at a them off the inner sections of rod with a special wrench leaving the cone-shaped surface holes. The outer sections and the cone nuts may be reused indefinitely. The use of prefabricated panels for formwork has recently been on the increase. These panels can be reused many times, thus reducing the time and labor required for erecting forms on the site. Many types of prefabricated form panels are in use. Contractors sometimes build their own panels from wood framing covered with plywood sheathing (fig. 7-33). The standard size is 2 ft by 8 ft, but panels can be sized to suit any particular situation. Panels made with a metal frame and plywood sheathing are also in common use and are available in a variety of sizes. Special sections are produced to form inside corners, pilasters, and so forth. Panels are held together by patented panel clamps. Flat bar ties, which lock into place between panels, eliminate the need for spreaders. Forms are aligned by using one or more doubled rows of 2 by 4's, secured to the forms by a special device that is attached to the bar ties. Form panels made completely of steel are also available. The standard size is 24 by 48 in., but various other sizes are also manufactured. Inside and outside corner sections are standard, and insert angles allow odd-sized panels to be made up as desired. Large placement Figure 7-34.-Column form. projects requiring mass concrete are often formed by the use of giant panels or ganged, prefabricated forms. Cranes usually raise and place these large sections, so their size is limited only by the available equipment. These large forms are built or assembled on the ground, and their only basic difference from regular forms is the extra bracing required to withstand handling. Special attention must be given to corners when forms are being erected. These are weak points because the continuity of sheathing and wales is broken. Forms must be pulled tightly together at these points to prevent leakage of concrete. Column Forms A typical concrete column form (fig. 7-34) is securely braced by YOKES to hold the sheathing together against the bursting pressure exerted on the form by the plastic concrete. Since the bursting pressure is greater at the bottom than the top, the yokes are placed closer together at the bottom. Notice, in figure 7-34, that on two panels, the 7-21

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