Slipforming Components

Most slipforming operations include the following components.

Jacks

The forms move upward by mean of jacks. Slipform jacks come in a variety of capacities, 3-ton (2.7-Mg), 6-ton (5.4-Mg), 15-ton (13.6-Mg), 20-ton (18.1-Mg), and 22-ton (20.0-Mg). Jacks are placed so they carry approximately the same load, so that not to throw the forms out of plumb. The number of jacks being utilized is controlled by their carrying capacities. There can be fewer higher-capacity jacks or more lower-capacity jacks. Lower-capacity jacks have the advantage of spreading the load over more sup­ports, thereby reducing the strength requirements for the forms and the yokes. On the other hand, the smaller interval between jacks makes it more difficult to place rebar, inserts, and openings. Depending on the jack size and deck loading, the intervals be­tween jacks range between 4 ft (1.2 m) and 9 ft (2.7 m). Using high-capacity jacks and specially designed yokes, the interval be­tween jacks can be increased substantially.

Подпись: Copyright © Marcel Dekker, Inc. All rights reserved.Jacks come with an individually incorporated self-leveling de­vice. In most cases, keeping the jacks level within V2 in. (12.7 mm) is satisfactory. Jacks are pneumatic, electric, or hydraulic. Hydrau­lic jacks are relatively light and compact, easy to install, and quite reliable under almost all conditions. Pneumatic jacks operate very much like hydraulic jacks except that they use air instead of oil. They are considerably larger in diameter and have a tendency to malfunction in cold weather. Electric jacks also have the advantage of being automatically self-leveling, as they are activated by a water-level system running through all the jacks with the water level controlled from a control point. Each jack has its own electric motor which operates an electric arm attached to the jaw system. Electric jacks are larger than the hydraulic jacks and require elec­tric and water connections as well as individual oil reservoirs.

The jacking rods used in slipforming operations are usually 3/4 in. (19.05 mm) pipe, 1V4 in. (31.75 mm) solid rods, or 2V2 in. (63.50 mm) pipe, depending on the design capacity. These rods are com­monly 10 to 20 ft (3.05 to 6.1 m) with their ends drilled to receive a joining screw dowel connecting one jack rod or tube to the next. Jacking rods can be left in the forms and used as reinforcing. Rods are placed inside the forms and are prevented from buckling by the concrete that has already hardened. Since the jacking rods depend on the concrete for stability, it is necessary to support the rods against buckling when they are out of the concrete, such as when the rods go through a door or window opening. As a result, and whenever possible, jacking rods should be placed to miss any repeated wall openings.

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