Formwork
1. Composition of concrete and reinforced concrete works
2. Appointment and arrangement of formwork
3. Components of formwork and formwork systems
4. Formwork requirements
5. Formwork materials
6. Main types of formwork
7. Technology of formwork processes
1. Composition of concrete and reinforced concrete works
The widespread use of concrete and reinforced concrete in modern construction is due to high physical and mechanical properties, durability, good resistance to temperature and humidity influences, the possibility of obtaining specified structures by relatively simple technological methods, the use of local materials in the base (except steel) and relatively low cost.
Expansion of the scope of concrete and reinforced concrete is facilitated by the existing advanced base for the production of prefabricated reinforced concrete. Industrial plants building materials they produce not only ready-made prefabricated reinforced concrete structures, but also formwork sets, reinforcing cages and meshes, ready-mix concrete, dry mixes for mortars and concretes, various additives to concrete mixtures and mortars, with which you can control their physical, mechanical and technological properties.
According to the method of execution, concrete and reinforced concrete structures are divided into monolithic, prefabricated and precast-monolithic.
Monolithic structures are erected at the facility under construction in the design position.
Prefabricated structures are manufactured in advance at factories, combines and landfills, delivered to the facility under construction and assembled in finished form.
In prefabricated monolithic structures, the prefabricated part is produced at factories and landfills, transported and installed at the facility, then the monolithic part of this structure is concreted in the design position.
In industrial and civil construction, the use of monolithic and precast-monolithic reinforced concrete is effective in the construction of massive foundations, underground parts of buildings and structures, massive walls, various spatial structures, walls and stiffening cores, high-rise buildings (including in seismic areas), many other designs. Concrete and reinforced concrete erect all types engineering structures, as well as bridges, dams, tanks, silos, pipes, cooling towers, etc.
The construction of buildings in monolithic reinforced concrete allows optimizing their design solutions, moving to continuous spatial systems, taking into account the joint work of elements and thereby reducing their cross section. In monolithic structures, the problem of joints is easier to solve, their thermal engineering and insulating properties are increased, and operating costs are reduced.
The erection of monolithic concrete and reinforced concrete structures includes the implementation of a complex of interrelated processes for the installation of formwork, reinforcement and concreting of structures, curing of concrete, its stripping and surface finishing of finished structures.
According to the composition of the work performed during the construction of monolithic concrete and reinforced concrete structures, they are divided into:
- formwork, including the manufacture and installation of formwork, stripping and repair of formwork;
- reinforcing, which consist in the manufacture and installation of reinforcement, with prestressing reinforcement, additionally in its tension; - reinforcement works are integral part in the manufacture of monolithic reinforced concrete structures and are absent in concrete structures;
- concrete, including the preparation, transportation and laying of the concrete mixture, the care of concrete in the process of its hardening.
A complex technological process for the erection of monolithic concrete and reinforced concrete structures consists of procurement and assembly and laying (main) processes interconnected by transport operations.
Complex construction process monolithic structures includes:
- procurement processes for the manufacture of formwork elements and formwork forms, reinforcement and the preparation of concrete mix in the factory and at landfills, in specialized workshops and workshops;
- transport processes for the delivery of formwork, reinforcement and concrete mix to the place of work;
- basic processes (performed directly on construction site) for the installation of formwork and reinforcement in the design position, laying and compacting the concrete mixture, caring for concrete during its hardening, tensioning reinforcement (when concreting monolithic prestressed structures), stripping (dismantling) formwork structures after the concrete reaches the required strength.
2. Appointment and arrangement of formwork
Formwork is a temporary auxiliary structure that forms the shape of the product. The formwork is used to give the required shape, geometric dimensions and position in space of the erected structure by laying the concrete mixture in the volume limited by the formwork.
The formwork consists of formwork panels (forms) that provide the shape, dimensions and surface quality of the structure; fastening devices necessary for fixing the design and invariable position of the formwork panels relative to each other during the production process; scaffolding (supporting and supporting devices), providing the design position of the formwork panels in space.
The concrete mixture is placed in the installed formwork, compacted and kept in a static state. As a result of the ongoing chemical processes, the concrete mixture hardens and turns into concrete. After the concrete has acquired sufficient or required strength, the formwork is removed, i.e., stripping is carried out. The processes associated with the installation and fastening of the formwork are called formwork, and those associated with the laying of reinforcing cages and meshes in the formwork are called reinforcing. The processes for dismantling the formwork after the concrete has gained the required strength are called formwork stripping.
3. Components of formwork and formwork systems
At the heart of the effectiveness of any formwork system lies the possibility of its rapid modification in accordance with the requirements of the building site. The lightness of the panels and the ease of assembling the formwork can significantly increase the rate of production of the entire complex of concrete works and reduce the construction period. The manufactured formwork must guarantee the optimal dimensions of the panels, their high strength and rigidity, the quality of the concrete surface in contact with the formwork.
The individual elements of the formwork system are as follows:
- formwork - a form for the manufacture of a monolithic concrete structure;
- shield - a forming element of the formwork, consisting of a frame and a deck;
- frame (frame) of the shield - the supporting structure of the formwork shield, made of a metal or wooden profile, made in a jig, which guarantees the accuracy of the outer dimensions of the manufactured structure;
- shield deck - the surface in direct contact with concrete;
- formwork panel - a large-sized planar formwork element with a flat or curved surface, assembled from several panels interconnected using special units and fasteners, and designed to create the required surface in the specified dimensions;
- formwork block - a three-dimensional, closed or open formwork element of several panels, designed to form the corner sections of a concreted structure, made entirely and consisting of flat and corner panels or panels;
- formwork system - a concept that includes formwork and elements that ensure its rigidity and stability - fasteners, scaffolding supporting scaffolding;
- fastening elements - locks used to connect and securely fasten adjacent formwork panels to each other; couplers connecting opposing shields and other devices in the formwork, combining the elements of the formwork into a single unchanging structure;
- supporting elements - struts, posts, frames, spacers, supports, scaffolding, floor beams and other supporting devices used when installing and fixing the wall and floor formwork, fixing the formwork in the design position and receiving loads during concreting.
Auxiliary elements of formwork systems:
- hinged scaffolds - special scaffolds hung on the walls from the side of the facades using brackets fixed in the holes left during the concreting of the walls;
- roll-out scaffolds - designed to roll out tunnel formwork or ceiling formwork on them during their dismantling;
- opening formers - a special formwork designed to form window, door and other openings in monolithic structures;
- basement - the lower part of a monolithic wall 10 ... 20 cm high, which is concreted simultaneously with a monolithic ceiling. The purpose of the plinth is to ensure the design thickness of the wall and fix the formwork relative to the center (coordinate) axes.
4. Formwork requirements
Any manufactured formwork must meet the following requirements:
- guarantee of the necessary accuracy of the dimensions of the future structure or structure;
- strength, stability and invariability of shape under the action of loads arising in the process of work; all formwork elements count on strength and deformability;
- the density and tightness of the formwork board deck, i.e. the absence of cracks that cause the formation of voids in the concrete, shells as a result of the outflow of cement mortar;
- high quality of surfaces, excluding the appearance of sags, shells, curvature, etc.;
- manufacturability - the ability to allow quick installation and disassembly, not to create difficulties in the installation of reinforcement, laying and compacting the concrete mixture;
- turnover - multiple use of formwork, which is usually achieved by making it inventory, unified and collapsible;
5. Formwork materials
For the manufacture of formwork elements, a wide variety of materials are used. The supporting formwork elements are mainly made of steel and aluminum alloys, which allows them to achieve a high turnover.
For formwork (deck), softwood (pine, spruce, larch), hardwood (birch and alder), waterproof plywood, steel, plastics, metal mesh, reinforced concrete and reinforced cement boards, chipboard (chipboard) and wood-fiber boards are used. (Fibreboard) boards, polypropylene with fillers.
Wood is used for the manufacture of decks in the form of edged and unedged boards with a width of not more than 15 cm, for scaffolding and fastenings - bars ranging in size from 8x10 to 8x14 cm, a bollard with a diameter of 10 ... 14 cm and round timber with a diameter of up to 20 cm.
The advantages of wood are ease of processing, low weight, the possibility of making molds of any shape, and relatively low cost. Disadvantages - warping, swelling, shrinkage, low turnover due to damage due to significant adhesion to concrete. After laying the concrete mixture in the formwork, the side in contact with it swells, and the other under the influence sun rays dries quickly. As a result, warping of wood occurs, its bulging, cement mortar, voids and shells are formed in concrete. Measures to counteract these processes are the use of sheet pile boards, coating the inner surface with various lubricants to reduce the adhesive force of the formwork with concrete.
Waterproof plywood is used only for sheathing. It has a significant turnover, provides high-quality front surfaces of concrete. To increase turnover, it is necessary that the front surface of the formwork is flush with the framing elements of the frame and is constantly lubricated.
Plywood laminated with phenol-formaldehyde coating is used as a sheathing (deck) for monolithic concrete works, formwork turnover is up to 100 times.
Steel is used for the manufacture of all formwork elements.
Sheet steel with a thickness of 2 ... 6 mm is used for the manufacture of decks (plating) of metal formwork.
Profile steel, mainly channel and corners, is used for the frame and support devices, tubular steel is used for the manufacture of inventory load-bearing scaffolding and struts. Bolts, wire and mostly hardware are used for all kinds of fastenings and connections.
Steel formwork provides a smooth surface of the concreted structure, ease of stripping, rigidity, no deformation, significant turnover. It is advisable to use such formwork with at least 50-fold turnover. The disadvantages of metal formwork are high cost, significant weight and high thermal conductivity. However, nowadays metal formwork is increasingly being used due to its high turnover and the resulting smooth and even concrete surface.
Plastics combine the advantages of steel (strength, repeated turnover, the ability not to change under various temperature and humidity conditions) and the advantages of wood (insignificant mass and ease of processing). The disadvantages of these materials are also excluded - the deformability of wood and the corrosion of steel. The low rigidity, increased flexibility, and relatively high cost of plastics make them still poorly competitive with other materials. Plastics are mainly used as thin protective films applied to wood and metal deck surfaces.
Plastic formworks are used, especially those reinforced with fiberglass. They have high strength under static load, chemically compatible with concrete. Formworks made of polymeric materials are characterized by low weight, shape stability and resistance to corrosion. Possible damage can be easily repaired by applying a new coating. The disadvantage of plastic formwork is that their bearing capacity is sharply reduced during heat treatment of concrete with an increase in temperature up to 60 ºС.
Metal meshes with cells up to 5×5 mm are used for the manufacture of mesh and vacuum formwork.
Thin-walled reinforced cement and reinforced concrete slabs are slabs in which the outer side is smooth, and the inner side is uneven, with protruding reinforcement. This allows, when laying in-situ concrete in such a structure, to achieve a high degree of its connection with this type of formwork. This formwork is called non-removable, as it remains in the structure and works as an integral part of it.
Chipboards (chipboards) and wood-fiber boards (MDFs) are located between wood and waterproof plywood in their characteristics, and they are used mainly for decking, less often for fixing the formwork frame.
The turnover of inventory formwork with a deck of boards, chipboard and fiberboard is 5...10 times, formwork made of waterproof plywood is 50...100 times, steel formwork is 100...700 times.
The use of composites with conductive filler makes it possible to obtain heating coatings with controlled modes of thermal action on concrete.
6. Main types of formwork
The formwork is classified according to its functional purpose, depending on the type of concrete structures and, in general view, subdivided:
- for vertical surfaces, including walls;
- for horizontal and inclined surfaces, including ceilings;
- for simultaneous concreting of walls and ceilings;
- for curved surfaces (mainly pneumatic formwork is used).
As a result of practical use in domestic and foreign mass industrial and civil construction, a number of structurally different formworks have been created and successfully used, depending on the characteristics of the structures being built, formwork material, conditions and methods of work, the most widespread of which are the following:
1. Collapsible small-panel formwork made of small panels up to 2 m2 in area and weighing up to 50 kg, from which formwork can be assembled for concreting any structures, both horizontal and vertical, including arrays, foundations, walls, partitions, columns, beams, floor slabs and coverings.
2. Large-panel formwork made of large-sized panels with an area of up to 20 m2, equipped with load-bearing or supporting elements, struts, adjusting and installation jacks, and scaffolding for concreting. It is intended for the construction of large-sized and massive structures, including extended or repeating walls, ceilings of buildings and structures for various purposes.
3. Horizontally movable formwork, the purpose of which is the construction of linear-extended structures with a length of 3 m, solved both in the form of a separate wall (retaining wall), two parallel walls (open collector), and a closed structure, consisting of walls and covering the necessary specified length.
4. Volumetric-adjustable formwork, which has found application in the simultaneous construction of walls and ceilings of buildings. The formwork consists of L- and U-shaped block-sections, the design allows the sections to move inward. Formwork sections are interconnected along the length, forming several parallel rows at once with distances between blocks equal to the thickness of the walls. This allows, after the installation of the formwork, the laying of the reinforcing cages, to simultaneously carry out the concreting of the walls and the sections of floors adjacent to them.
5. Tunnel formwork is designed for the construction of a closed loop of tunnels built in a closed way. At present, tunnel formwork has found wide application for simultaneous concreting of buildings of the corridor system (hospitals, sanatoriums, rest homes, etc.), when using two sets of formwork, external and internal walls and ceilings are continuously installed at once for the entire width of the floor of the building under construction.
6. Climbing formwork is used for the construction of high-rise structures of constant and varying cross-sectional geometry - pipes, cooling towers, bridge supports, etc.
7. Sliding formwork used in the construction of vertical structures of buildings and structures of great height. The formwork is a system consisting of boards, a working floor, scaffolds, jacks, jack rods fixed on jack frames and a control station for lifting the formwork system. Formwork is used for the construction of external and internal walls of residential buildings, stiffening cores, as well as chimneys, silos, cooling towers and other structures with a height of more than 40 m and a wall thickness of at least 25 cm.
8. Block formwork can be used for formwork internal surfaces staircases, elevator shafts, closed cells of the walls of residential buildings, and the outer surfaces of columnar foundations, grillages, arrays, etc.
9. Vertically movable formwork designed for the construction of structures (tower, cooling tower, residential building) or their parts (elevator shaft of a residential building) and individual parts of buildings and structures one floor high (section of an elevator shaft, a spatial closed cell of 4 walls of a building ).
10. Non-removable formwork used in the construction of structures without stripping, with the installation of waterproofing, cladding, insulation, etc. in the process of work. . Currently, fixed formwork is used not only for concreting individual structures, but also for the construction of complete buildings. This became possible when using expanded polystyrene plates 50...150 mm thick with a density of 20...25 kg/m3 as formwork, with high moisture resistance. Fixed formwork consists of prefabricated formwork elements of walls and ceilings, which simultaneously perform the functions of formwork, insulation and sound insulation of walls and ceilings, as well as a base for applying finishing (textured) coatings. For fixed formwork, woven formwork can be used. metal grid, reinforced concrete, armored and asbestos concrete slabs, foam plastic slabs, glass cement slabs, etc. This type of formwork can be used in cramped working conditions and with the economic feasibility of its use.
11. Special formworks do not fall into the nomenclature of the main types, although they often allow the construction of similar structures. This is a pneumatic formwork, consisting of an inflated rubberized fabric, which forms the formwork of the future spatial structure, supporting and load-bearing elements. In the working position, pneumatic formwork is supported by excessive air pressure and it serves for concreting thin-walled structures and structures of a curved shape.
One can also note the non-reversible (stationary) formwork, the purpose of which is to concrete individual places, sections and even structures, for the formwork of which the use of industrial formwork is uneconomical or technically irrational. This formwork is disposable, collected from production waste.
Combined structures are rational, in which the bearing and supporting elements are made of metal, and those in contact with concrete are made of lumber, waterproof plywood, chipboard, and plastic.
7. Technology of formwork processes
The technological process of the formwork device is as follows. Formwork panels are installed manually or by crane and fixed in the design position. After concreting and reaching concrete strength, allowing stripping, formwork and supporting devices are removed and rearranged to a new position.
There are two main types of formwork forms of collapsible formwork: small-panel and large-panel.
Small-panel formwork consists of inventory boards of various sizes with inventory supporting devices and fasteners. The dimensions of the main panels of the unified formwork are, as a rule, subject to one modular size (300 mm in width and 100 mm in height). In small-panel formwork, it is possible to assemble molds for almost any concrete and reinforced concrete structures - walls, foundations, columns, crossbars, flat, often ribbed and coffered floors and roofs, bunkers, towers, etc. The versatility of the formwork is achieved by the ability to connect panels along any edges.
The main and fundamental feature of formwork panels are closed profiles of steel or aluminum frames, which, together with stiffening ribs, also made of closed profiles, create formwork connections that resist torsion loads and at the same time make it possible to simplify installation and horizontal alignment, and when forming high-rise structures improve work safety.
The complete formwork system is designed for the formworking of all horizontal and vertical building structures, starting from the smallest structures. In addition to the closed profile of the shuttering board frames, a shuttering lock is proposed, which provides a quick (just hit with a hammer) and high-quality connection of two adjacent boards horizontally or vertically anywhere in the structural frame. The deck is made of multi-layer waterproof plywood covered with a special powder or other coating that drastically reduces adhesion to concrete. Bushings are welded into the profile of the formwork frames, which are provided for the passage and convenient insertion of tension rods, for the interconnection of opposing formwork panels.
Flat panels of small-panel formwork have an area of up to 1.5 ... 2.0 m2, a weight of not more than 50 kg for the possibility of their manual installation. If there is an assembly crane at the construction site, the panels can be pre-assembled into a formwork panel or a spatial formwork block with an area of up to 15 m2. The technology of work with small-panel formwork is similar to work with large-panel formwork.
Large-panel collapsible formwork includes panels sized 2...20 m2 with increased bearing capacity. The mass of such shields does not have strict restrictions, since they are mounted and dismantled only with the help of lifting mechanisms. In large-panel formwork, panels can be connected to each other along any edges and, if necessary, be completed with small panels of the same system. As in small-panel formwork, the deck can be made of steel sheet or waterproof plywood.
When constructing strip foundations, the formwork is formed from inventory boards, which are interconnected using locks of various designs. In the case of inserts between the panels of additional elements up to 15 cm wide, elongated locks can be used. The transverse dimension of the structure is fixed with temporary struts on the struts and end shields of the formwork. To perceive the lateral pressure of the concrete mixture, the opposite panels are connected with screw ties (strands).
Work on the installation and dismantling of formwork should be mechanized as much as possible. Initially, the formwork panels are assembled into a formwork panel to the full height of the strip foundation and an area of about 20 m2. Shuttering panels are subject to increased requirements for their rigidity and load-bearing capacity.
The panel formwork of stepped glass-type foundations for a column consists of separate boxes installed on top of each other. The boxes, in turn, are assembled from two pairs of shields - "embedded" and "covering", interconnected by screw ties.
Wall formwork consists of modular panels that can be assembled into formwork panels of almost any size and configuration. The frame of the formwork panels is made of a high-precision profile made of aluminum alloys, the cross section of which ensures the installation of a deck made of laminated plywood with a thickness of 18 and 21 mm, the ends of which are structurally protected by the aluminum profile itself and sealant.
The formwork kit also includes struts for installing panels, hinged cantilevered platforms for concreting, locks for connecting panels and screw ties.
Shield frames are made in conductors, which ensure the non-flatness of the surfaces is not more than 1 mm, the difference in the diagonals of the frames is not more than 3 mm. Cracks, burrs and local deviations with a depth of more than 2 mm are not allowed on the shield deck. When fastening a deck made of waterproof laminated plywood on the shield frames, the countersunk head of the screws can protrude onto the plywood plane by no more than 0.1 mm.
Large-panel formwork provides formwork for monolithic structures with a module of 300 mm. The width of ordinary formwork panels is from 0.3 to 1.2 m in increments of 0.3 m, the standard height is 1.2, 2 and 3 m with a weight of panels from 42 to 110 kg.
Large-panel wall formwork consists of formwork panels, scaffolds hung on these panels, bracing struts and bracing elements. Shields in shuttering panels are assembled by means of centering locks. To align the formwork panel in the design position, the formwork is equipped with struts, the screw couplers of which allow you to adjust the installation of the panel in a vertical plane.
The formwork kit may include a compensation element 0.3 m wide and elongated locks, which are used if it is necessary to have inserts from bars up to 15 cm wide in the formwork when concreting non-modular structures.
The formwork kit allows, if necessary, to make corner joints of panels, joints of wall adjoinings, the device of adjunctions-compensators and other possible options for adjoining formwork panels to each other.
For the construction of the outer walls of the building, special scaffolds are provided, which are all-metal brackets with flooring boards and fences.
The formwork panels are unfastened by means of screw ties and nuts that perceive the pressure of the concrete mixture. To organize workplaces at a height during the acceptance and placement of the concrete mix, scaffolds with railings are provided on the formwork, which are hung on the frame of the formwork panels.
When installing and dismantling the formwork at a height along the perimeter and inside the building, the formwork shields must be protected by inventory protective devices.
Formwork panels are made in accordance with a single module, they are universal and interchangeable, the assembly, installation and connection of the panels to each other can be carried out in a vertical and horizontal position. There are holes in the frame ribs for attaching brackets and installing struts.
To connect the shields to each other, locks are used - at least three locks along the height of the shield: two locks - at a height of 250 mm from the bottom and top of the shield, and a third lock - in the central part of the shield. If, when forming the surface, it is planned to lay a horizontal shield on top of previously installed vertical shields, then along the length of the horizontal shield, three lock connections with vertical shields.
During the installation of the struts and hanging of the brackets of the suspended scaffolds, they are fixed through the holes in the ribs of the formwork panels, regardless of the installation of the shield - vertically or horizontally. When mounting the wall formwork with separate panels, two struts are installed for each panel, when mounting with panels - after 2 ... 4 m. Brackets for laying the working floor are fixed to the formwork panels with a step of 1.2 ...
In the process of installing panels and wall formwork panels, according to the risks applied on the ceilings, they are pressed against the concrete base and brought to a vertical position with the help of strut couplers. The accuracy of the installation is checked by a level or a plumb line.
After mounting the opposite panels of the wall formwork, the panels are fastened together with screw ties, placing at least three ties along the height of the shield. Screw ties installed between opposite shields are passed through steel bushings, bushings and cones made of plastic and plastic, the length of which must correspond to the thickness of the concreted wall. The cones protect the openings in the deck from concrete mixture getting into them, the bushings make it easier to pull out the screw ties after concreting during the stripping process.
The shields are fastened by tightening the nuts of the screw ties. To exclude local deformations of the hollow section of the shield frame when tightening the nuts, wide-brimmed washers are used. After the formwork panels are installed, all unused through holes in the formwork must be plugged with special wooden or plastic plugs to prevent concrete from flowing out of these holes during the concreting process.
Shields and panels of external walls are mounted from working scaffolds fixed on the walls of the previous floor. The scaffolding is carried out as follows. When concreting the walls, through holes remain in them from the screw ties of the formwork panels. When installing scaffolds using a mounting crane, bolts for fastening the bottom of the supports of the working scaffolds are passed through these holes, and these bolts are fixed from the inside of the walls with nuts. Thus, the scaffold is tightly pressed against the concreted wall of the underlying floor.
First of all, the panels (panels) of the outer formwork are mounted, they are installed on the working scaffolds, aligned and fixed with the help of struts. Further, from the ceiling, the inner panels (panels) of the formwork are installed, which are sequentially attached to the outer panels during the installation process with the help of screw ties.
Lifting and installation of boards and formwork panels is carried out with a special gripper, fixed on rope slings, at one point (for a separate board) or two points - for a formwork panel.
Wall formwork can be mounted as separate panels or pre-assembled into panels. Assembly of panels from individual panels must be carried out on a specially prepared site in the area of the assembly crane. The length of panels assembled from shields should not exceed 8 m in length.
The dismantling of the wall formwork is carried out with enlarged panels of 5 ... 6 panels. On the panel to be dismantled, the nuts of the screw ties are unscrewed, the ties are pulled out. Then, with the help of struts, the shields are torn off from the concrete. The detached panel is carried by crane to the warehouse for inspection, repair, and, if necessary, lubrication.
Formwork of columns with facets in the plan from 0.2 to 0.6 m is made of panels 0.8x3.0 m with holes for tie rods, which allows you to set the required size of the columns in the plan. The formwork of the columns is equipped with braces for installation, alignment and stripping, as well as suspended scaffolds with railings.
When installing the formwork of columns, initially on a concrete base (floor), mark the place of its installation (risks of geometric axes, edges of the position of the columns). The reinforcing cage to be installed is initially connected to the frame of the underlying column, plastic rings are additionally installed or horizontal rods are welded to the frame at a height of 300 mm from the bottom and top of the columns to provide the necessary protective layer of concrete during concreting.
Initially, two adjacent shields are installed at risks and beacons and secured with struts. The lower supports of the struts are rigidly fixed to the floor and the shields are brought into a vertical position with the help of strut screws. Then the remaining two adjacent shields are installed, which are also brought to a vertical position. Opposite shields are fastened together with screw ties, they are installed four pieces along the height of the shield. Unused openings in the shields must be plugged with special plugs (wooden or plastic) to prevent leakage of the concrete mixture from the cavity. Cantilever scaffolds are installed from mobile towers. They arrange a working flooring from shields with a protective fence made of boards, which will allow you to safely perform work on concreting columns.
Before concreting, the final alignment of the installed formwork and all its fasteners is carried out.
The option of connecting the shields of the columns to each other provides for fastening by means of a clamp consisting of four brackets connected to each other by wedges. The brackets hold the shields in the required design position, providing the required geometric dimensions of the columns.
Slab formwork can be made in two versions: 1) formwork, including a deck made of laminated plywood sheets, mounted on longitudinal and transverse load-bearing beams, mounted on frames with retractable jacks; 2) canteen prefabricated formwork, consisting of a table in the form of a set of frames with support jacks interconnected by longitudinal ties with roller bearings.
Telescopic props up to 3.7 m high, which are a tubular structure consisting of a base part with a jack and a retractable rod, can be used as formwork load-bearing elements. Found the use of telescopic steel racks, consisting of two pipes included in one another. The initial position of the pipes among themselves is fixed thanks to special slots every 10 cm, the amplitude of changes is from 10 to 130 cm. passing into the slot of the upper part of the outer pipe. The pin rests on a nut screwed onto the thread at the top of the outer tube and holds the inner tube in position.
For smooth lowering of the supports (circling) supporting the formwork panels, special devices are used. When using special inventory wood-metal racks, a screw jack is used, and steel telescopic racks - a nut on the screw thread of the outer pipe.
Metal racks with jacking are used with three types of removable heads. The fork head is designed to install one or two main bearing beams in it. The drop head is convenient in that when the concreted structure of the floor is of sufficient strength, it becomes possible to remove some intermediate racks. When a special lever is pressed, the drop head lowers up to 10 cm, while the remaining system of racks and beams supporting the ceiling maintains its position. The third type of head is the supporting head, which supports the formwork system until the formwork is removed. These heads, when the lever is pressed, lower by 1...2 cm, make it possible to visually assess the condition of the system to be stripped, to easily extend the posts and release the formwork-bearing beams. The formwork panels are detached from the concreted structure due to their own weight or using special crowbars.
The large-panel formwork of the slabs consists of support frames equipped with sliding jacks, on which, through the supports available on them, longitudinal and transverse beams are mounted, carrying the deck of laminated plywood. The bearing beams are interconnected by a special bolted connection. The laminated plywood deck is attached to the beams with countersunk head screws. Mounting and dismantling of the formwork is carried out in accordance with the technological map (TC). The formwork may only be dismantled after the concrete has reached the required strength.
Formwork is installed in accordance with technological maps in a sequence depending on its design; at the same time, the stability of its individual elements during installation must be ensured. The location of the load-bearing telescopic racks and frames on the concrete floor also depends on the location of the racks on the previously concrete floor. At the same time, it is necessary to take into account the rate of erection of structures, the rate of curing of concrete floors and walls, the loads acting on the structure at various stages of the construction of the structure, and other technological factors.
The installation site of formwork and scaffolding must be cleared of debris, snow and ice. The surface of the earth should be planned by cutting off the top layer of soil. Pouring soil for these purposes is not allowed.
When installing the formwork, special attention is paid to the verticality and horizontality of the elements, the rigidity and invariability of all structures in general, and the correct connections of the formwork elements in accordance with the working drawings. Permissible deviations during the installation of formwork and supporting scaffolding are standardized.
The use of inventory formwork provides for mandatory lubrication of the board deck. The most common are hydrophobic lubricants based on mineral oils or salts of fatty acids, as well as combined lubricants.
Lubricants reduce the adhesion of the deck to concrete, thus facilitating stripping and, as a result, increasing the durability of the formwork panels. Lubrication is restored after 1 ... 4 turns of the formwork.
When performing monolithic work using removable formwork, it is very important to pay attention to safety (HSE), since human life and health are incomparably more expensive than the product or service provided in any field of activity.
The tasks of safety engineering in monolithic work include:
- exclusion of emergency situations that threaten the life or health of people;
- reduction of injuries and occupational diseases to a minimum.
In order to protect the working personnel, it is not enough to take a number of technical measures related to safety (install fences, warning labels, etc.). Among other things, personnel must be instructed and checked for knowledge of safety rules.
Depending on the nature of the instruction, there are:
- introductory safety briefing;
- primary (conducted directly at the workplace);
- repeated;
- unscheduled (usually carried out if there was an emergency);
- target (before carrying out an uncharacteristic for a particular technological process or a rarely performed operation).
General safety requirements
When arranging the formwork, installing the reinforcing cage, pouring the building mixture and other works typical for monolithic construction using removable formwork, it is necessary to ensure that the condition of the structures is stable. The wall formwork, depending on the height, must be fixed with one- or two-level struts, the scaffold must be securely fixed to the supporting frame of the formwork panels.
Formwork and monolithic work should be carried out by personnel with appropriate qualifications and who have been instructed in safety, under the guidance and supervision of an engineering and technical worker (foreman or foreman).
It is forbidden to place on the formwork for monolithic construction and scaffolding materials, tools and equipment that are not provided for by the project and work technology. Staying on the formwork flooring of people who are not directly involved in monolithic and formwork ah, also forbidden.
Equipment for moving and finding working personnel (scaffolds, ladders, ladders, etc.) must be securely attached to the elements of the removable formwork.
If the construction formwork is mounted in several tiers vertically, then each subsequent tier can be installed only after checking the correctness and reliability of the installation of the previous one.
Only regular elements included in the formwork system kit should be used as removable formwork supports. Fastening the formwork of walls, foundations, ceilings, etc. with the help of auxiliary materials is strictly prohibited.
When assembling the building formwork, all elements that can be adjusted (telescopic props, threaded pins, eccentric locks, etc.) must be tightened or securely fixed.
The quality of the installation and fastening of the removable formwork and scaffolding is checked daily. Any nonconformities found must be corrected immediately.
If work is performed on an inclined surface with an angle of more than 20 degrees to the horizontal, workers must use safety belts.
The formwork system must be stripped in the reverse order of installation. At the same time, it is necessary to take measures against accidental collapse of individual elements of the removable formwork.
If there is a technical possibility, the wall formwork should be dismantled in large modules with their subsequent disassembly into components on the ground.
The construction site must be equipped with fire extinguishing equipment (shield with tools, boxes with sand, fire extinguishers, etc.).
Requirements for building envelopes
All protective barriers erected during formwork installation must meet the requirements of the State Standard 12.4.059-89 “Construction. Inventory safety fences.
When using sliding building formwork, in order to protect personnel from possible falling objects, suspended scaffolding must be protected by a rigid metal canopy along the entire width of the scaffolding.
Vertical openings through which materials, tools and equipment are lifted or lowered must be covered with glazing.
All tiers of purlins and open ceilings must be protected by technological plank or metal decks that are guaranteed to withstand work loads (from the weight of workers, materials and equipment). When pouring concrete, temporary flooring should be removed only in areas that fall within the area carried out in this moment works.
It is necessary to harvest all formwork elements in special workshops or landfills in accordance with the PPR.
The formwork design for the erection of monolithic structures of buildings and structures must have strength and stability when laying the concrete mix.
The formwork, consisting of large-sized panels, should be installed in tiers, with each subsequent tier being installed after fixing the lower one, using mechanisms from reliable working scaffolds or scaffolding. It is forbidden to work simultaneously in two or more tiers along the same vertical.
During the delivery of formwork elements by cranes, it is necessary to ensure that they do not touch previously installed structures or parts thereof.
Panel formwork of columns, crossbars and beams at a height of not more than 5 m above ground level or ceilings can be installed from portable step-ladders equipped with fenced working platforms. At a height of more than 5 m, work must be carried out from inventory scaffolding or scaffolding, which also has a fenced work platform.
The installation of the formwork scaffolds, as well as the installation of the formwork at a height of more than 5 m, must be carried out by trained workers at least 18 years old who have undergone a medical examination, have at least one year of experience in steeplejack work and a tariff category of at least 3rd. The installed formwork of the slabs must have fences around the entire perimeter.
Suspended formwork of reinforced concrete floors of buildings with steel frames should be installed only after the final fixing of the joints of the frame elements. At the same time, such a design of fasteners supporting the formwork is used, which, when laying the concrete mixture, would not allow it to move or sway.
When erecting reinforced concrete walls in a collapsible formwork for workers, it is necessary to arrange decks with protective fences 1.1 m high on both sides every 1.8 m in height.
It is prohibited to store equipment, buckets or hoppers with concrete mix and other materials not provided for by the project on the working floor of the formwork and suspended scaffolding.
Workers must not be allowed to gather on the formwork deck and suspended scaffolding, as this can lead to the collapse of the scaffolding.
To protect workers on suspended scaffolding, along the outer perimeter of the sliding formwork, it is necessary to install peaks with a width not less than the width of the suspended scaffolding located under them.
To prevent people from entering the canopies, they must be separated from the working platform, except in those cases when they serve as a formwork for the eaves of the structure.
On suspended scaffolding, in places where materials are lifted onto the sliding formwork, it is necessary to make a continuous sheathing, and the sites for receiving materials should be equipped with an alarm system to connect the workers receiving the materials with the minder of the lifting winch.
Work at height on the racking of racks for unfastening and building up jacking rods located along the outer contour of the structure, as well as fixing, repairing and partially cutting off the formwork, installing cornices and canopies must be performed using safety belts attached to reliable supports.
At least two workers must build up the jacking rods and install the bracing.
Working floor decks and suspended scaffolding must be systematically cleaned of concrete residues and debris.
It is forbidden to perform work at a height with a wind speed of 15 m / s or more, with sleet, thunderstorm or fog, which excludes visibility within the work front, and the installation of formwork elements with a large windage should be stopped at a wind speed of 10 m / s.
Before concreting structures, each shift checks the condition of the formwork, scaffolding, railings and stairs. Detected malfunctions of the formwork are eliminated before the start of work.
Dismantling of the formwork can only be started with the permission of the foreman or foreman, and in especially critical cases (if the structures are more than 6 m long and thin-walled) - with the permission of the chief engineer of the construction organization.
Before dismantling the formwork of load-bearing structures (columns, beams, girders, slabs), it is necessary to check the strength of the concrete, to establish whether there are any cracks and other defects that could lead to unacceptable deformations or collapse of the structure after the formwork has been removed.
It is forbidden to store materials from the dismantled formwork on the scaffolds, as well as to dump them from the structure. Materials should be immediately lowered to the ground by a hoist, sorted and stacked. At the same time, protruding nails and staples are removed from the boards.
Dismantling of the formwork can be carried out only after the concrete has acquired strength. Before dismantling, it is necessary to establish the absence of loads and defects in work, which can lead to deformation or collapse of structures. When dismantling the formwork, measures should be taken to prevent accidental fall of formwork elements and collapse of scaffolding or scaffolding.
The formwork used for the construction of monolithic reinforced concrete structures is manufactured and used in strict accordance with the project for the production of works. When installing formwork in several tiers, each subsequent tier is installed only after fixing the previous one.
It is not allowed to place equipment and materials on the formwork that are not provided for by the project for the production of work, as well as the presence of people who are not involved in the production of work.
The formwork is dismantled only after the concrete reaches the specified strength with the permission of the work foreman, and for especially critical structures - with the permission of the chief engineer.
Mounted formwork elements are released from the hook of the lifting mechanism only after they are temporarily or permanently fixed.
In the absence of mounting scaffolds, the formwork panels are fixed on the supporting structures and only after that they are torn off from the concrete.
Safe working conditions must be created at the workplace of formworkers. If work is carried out simultaneously on several tiers, the workplaces are reliably protected from above and below in case of falling tools and formwork elements.
In places where formwork elements are stored, the width of the passages must be at least 1 m. Descents into the pits are equipped with stairs with railings.
Formwork panels, elements of scaffolding and fixtures are lifted and delivered to the installation site in packages or special containers by lifting mechanisms, the packages are covered with slings in at least two places. Elements of fasteners and connections (locks, clamps, bands, etc.) formwork is served only in special containers.
When applying lubricants to the formwork with a pneumatic spray, workers must wear goggles, respirators, overalls, gloves and rubber boots.
At the time of concreting, a worker on duty is appointed, who periodically (1 ... 2 times per hour) inspects the formwork and, in case of deformation of its individual elements, supporting racks or other parts, calls the foremen to take measures to correct the defects found. All defects associated with a violation of the structure of the laid concrete mixture can be corrected within 1-2 hours after the laying of the mixture.
During the installation and dismantling of the formwork, safety requirements are observed.
test questions
- What structural elements does the formwork consist of?
- What methods provide an increase in formwork turnover?
- What types of formwork do you know?
- What materials are used to make formwork elements?
- Give diagrams of vertically removed (block) and horizontally removed (tunnel) formwork.
- Give a diagram and explain the principle of operation of a sliding formwork.
- What are the elements of horizontal sliding formwork?
- Give a diagram of the pneumatic formwork device and name the area of its application.
- What are the advantages of fixed formwork and where is it used?
- What is the sequence of erecting the formwork of a stepped foundation?
- In what sequence is the formwork of the strip foundation mounted?
- Give schemes for the dismantling of tunnel-type formwork and the means of mechanization used.
- What is the sequence of sliding formwork installation?
- In what sequence is the sliding formwork dismantled?
- List the means and techniques that reduce the adhesion of concrete to formwork.
- What are the basic rules for safe formwork?
All General requirements safety precautions required in the production of general construction works, also apply to the production of formwork. In addition, a number of special requirements must be met.
The formwork and the scaffolding supporting it must be strong and stable, for which they must be carried out in full accordance with the project.
Permissible loads on the scaffold decks must be established by the technical staff on the basis of the calculation. The weight of materials stacked on decks, the weight of people and vehicles on them must not exceed the permissible loads.
The accumulation of people on the scaffolding decks and on the formwork of the ceilings is not allowed.
The installation of a collapsible formwork at a height of up to 5.5 m from the ground or the underlying floor can be carried out from ladders or portable ladders with a platform with a fence at the top, and at a height of up to 8 m - from mobile carts. At a higher height for the work of formworkers, decks are arranged on the scaffolding.
The decks of scaffolds, scaffolds and step-ladders located above 1.1 m from the ground level or ceiling must be protected by a railing at least 1 m high, consisting of a handrail, one horizontal element and a side board with a height of at least 15 cm. Side boards should be installed on flooring, and fasten the elements of the railing to the racks from the inside. Wooden handrails must be sharpened.
The height of the passages on the scaffolding must be at least 1.8 m. The installed formwork of the slabs must have fences around the entire perimeter.
The condition of all structures of scaffolding and scaffolding, including the condition of connections, fastenings and fences, should be systematically monitored.
The condition of scaffolding and scaffolding should be checked daily before the start of the shift by the foreman in charge of the relevant work area at this facility.
Large-panel panels, formwork and reinforcement-formwork blocks and panels assembled from inventory panels should be installed by cranes in compliance with the following rules: mounted elements must be rigid and their parts must be securely fastened; it is allowed to release the installed element from the hook of the lifting mechanism only after fixing the element with permanent or temporary ties (according to the project) and checking the reliability of fastening.
Dismantling of the formwork can only be started with the permission of the foreman or foreman, and in especially serious cases (for example, in the construction of large spans, with thin-walled structures, etc.) - with the permission of the responsible construction manager. Before dismantling the formwork of load-bearing structures (columns, beams, slabs, etc.), the construction laboratory must check the strength of the concrete. By inspection and tapping, you need to make sure that there are no cracks and other defects that could lead to unacceptable deflections or collapse of the structure when removing the formwork.
It is forbidden to stack materials from dismantling the formwork on the scaffolds. They must be immediately lowered to the ground, sorted and stacked. Protruding nails and staples must be removed from the boards. It is forbidden even for a short time to lay boards or boards with the tips of the nails facing upwards.
All openings left in the ceilings must be securely sealed or fenced after the formwork has been removed.
When working at height, carried out near the outer walls of the structure, workers must be equipped with securely fastened safety belts with carabiners.
See also:
Stroyizdat, 1988. Concrete and reinforced concrete work are one of the main types of construction works, and the professions of a concrete worker and a reinforcing steel worker - mass construction professions.
Concrete and reinforced concrete work are... Production concrete works in dry hot climates... Calendar plan production organization reinforced concrete works ...
Concrete and reinforced concrete work produced in the manufacture of monolithic and prefabricated concrete and reinforced concrete structures. These work consist of the following complex processes: production and installation of formwork...
Chapter X CONCRETE And REINFORCED CONCRETE WORKS. Sealing of butt joints of prefabricated reinforced concrete structures. From the quality of sealing assembly joints reinforced concrete structures depend on the strength of structures ...
the presence of well-known domestic scientific and engineering schools in the field of concrete theory, production technology concrete and reinforced concrete works, calculation reinforced concrete structures
...concrete and reinforced concrete works carried out at all stages of their production, starting with the manufacture concrete mixes and endingQuality of finished concrete and reinforced concrete products largely depend on the composition concrete mixtures and quality of constituent materials.
For small volumes works formwork can be made at the construction site. Concrete and reinforced concrete. Concrete and reinforced concrete work are...
Reinforcing and concrete work carried out in the usual way. In this case, as a rule, all loads from the hardening concrete are transferred to the mounted prefabricated elements. Concrete and reinforced concrete work are...
The final stage of production verification concrete and reinforced concrete works is the control of ready-made structures before the delivery of buildings and structures to the State Acceptance Commission.
Mobility concrete mixes are checked at least twice a shift at the places of its preparation and laying. Each construction company producing concrete and reinforced concrete work must keep a log concrete works.
1. Scope of preparation under reinforced concrete, concrete and buto- concrete foundations are not taken into account by the norms and must be calculated separately.9. Volume works by device reinforced concrete ceilings with liners made of lightweight concrete kakng, hollow ceramic blocks, etc. ...
Concrete and reinforced concrete work are... Production concrete works in a dry hot climate ... Calendar plan for the organization of production reinforced concrete works ...
Depending on the production method works distinguish between monolithic, prefabricated and prefabricated-monolithic concrete and reinforced concrete structures with non-stressed and prestressed reinforcement.
Vibrated concrete laying. Chapter 7 CONCRETE And REINFORCED CONCRETE WORKS... and surfaces concrete, reinforced concrete and reinforced cement formwork - facings must be moistened with water. ...
Organization concrete and reinforced concrete works should ensure the rapid construction of structures. To do this: produce work at least two shifts; reduce time gaps between works different brigades on this capture ...
Concrete and reinforced concrete work are one of the main types of construction works, and the professions of a concrete worker and a reinforcing steel worker are massive.
Technology and organization of construction reinforced concrete structures. Organization Basics concrete and reinforced concrete works.To the contents of the book: Concrete and reinforced concrete work.
High quality assurance concrete and reinforced concrete works performed at negative ambient temperatures, necessitates compliance with certain requirements.
Chapter 7 CONCRETE And REINFORCED CONCRETE WORKS... and surfaces concrete, reinforced concrete and reinforced cement formwork - facings must be moistened with water. ...
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