Formwork(redirected from Form (concrete))
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a group of elements and parts designed to impart the required form to cast concrete or reinforced-concrete structures erected at a construction site. Selection of the type of formwork is determined by the nature of the buildings or structures for which concrete is being poured and the relationship of their geometric dimensions, the production technology used, and climatic conditions.
Movable sectional small-slab formwork is the most common type. It consists of separate panels and hinges for their connection, supporting elements, and fastenings. The panels and supporting elements may be made of wood, plywood, steel, synthetic materials, or various combinations of them. In the production of metal formwork, the panels may be assembled into larger units or three-dimensional modules, with subsequent mechanized assembly and disassembly, which markedly increases labor productivity. Almost any form for concreting structures of foundations, walls (heights of 10–15 m), floors, or roofs may be assembled from elements of movable sectional formwork. When the concrete achieves sufficient strength to permit striking, the formwork is disassembled and shifted to a new position. In concreting at temperatures below 0°C, formwork panels may be heat-insulated or equipped with heaters (thermally active form-work). Electric heaters are usually used. Thermally active form-work was first developed in the USSR (by the engineer I. I. Bogatyrev) and was used in the 1950’s.
Movable sectional large-panel formwork is made from wooden framework panels of high supporting capacity (weight, 150–500 kg) and fasteners. Strengthened ribs of the formwork frame make possible the elimination of supporting elements (interlocks). The rods holding the panels are fastened to steel anchors embedded in the foundation or in previously poured concrete of the structure. Large-panel formwork is assembled and disassembled by means of hoisting mechanisms.
Sliding formwork consists of steel, wooden, or combination panels 1,100–1,500 mm high, fastened together by steel jack frames. Trusses or main beams of the deck, from which the concrete is poured and the reinforcement is installed, rest on the frames. Scaffolding is attached to the frames, making possible initial finishing of the concreted structures. Hydraulic hoists (the most common) or electrical hoists (jacks) mounted on the frames provide simultaneous vertical movement (sliding) of the entire formwork along a concreted structure, thus freeing the hardened concrete. Sliding formwork is used mainly in the construction of walls, reservoirs, silos, pipes, and other structures not less than 12–15 m high.
Lifting formwork (jumpform), which combines the design features of sliding and movable sectional formwork, consists of panels, special fastenings, and devices for removing formwork from the concrete and for moving it vertically. The working deck usually rests on the concreted structure. It is used mainly for the erection of tall structures of variable cross section (pipes or cooling towers). Special self-hoisting mechanisms are used in concreting unique structures (for example, the Ostankino television tower). Construction enclosures are installed to protect against atmospheric precipitation, wind, and low temperatures.
Rolling formwork consists of steel or wooden panels and a frame mounted on dollies or runners. The formwork moves on rails or a guide by means of electric motors or winches. It is used in the construction of structures of considerable length, such as walls, floors, roofs, tunnels, sewers, water conduits, and small dams.
A block form is a three-dimensional structure consisting of steel panels, a frame, fastenings, and devices for removing the panels from the concrete. Block forms are assembled and disassembled by means of hoist mechanisms. They are used mainly for the concreting of free-standing structures, such as foundations and columns.
Nondemountable formwork is used in cases when its disassembly would be cumbersome. It sometimes functions as insulating protection or decorative or special facing of the building or structure. A woven metal mesh, reinforced-concrete and ceramic slabs connected to the main structure by tie beams, and asbestos-cement, steel, or plastic sheets are used as nondemountable form-work.
Mining formwork is a special type of formwork that may be mobile, folding, or sectional. It is designed for the erection of concrete supports of mine workings.
Operations associated with the production, installation, and dismantling of formwork, as well as with the servicing of mechanisms and devices for moving it, are called formwork operations.
REFERENCESSovalov, I. G., and V. D. Topchii. Opalubochnye raboty. Moscow, 1971.
Rukovodstvo po primeneniiu opalubki dlia monolitnykh zhelezobetonnykh konstruktsii, fasc. 1. Moscow, 1972.
V. D. TOPCHII