Safety instructions for monolithic works. Safety rules for reinforcing work; formwork; classification, characteristics, scope of application of formwork. Ensuring safe working conditions during the construction of monolithic floors
Formwork of structures
1. Composition of concrete and iron concrete works
2. Purpose and arrangement of formwork
3. Components of formwork and formwork systems
4. Requirements for formwork
5. Materials for the manufacture of formwork
6. Main types of formwork
7. Technology of formwork processes
1. Composition of concrete and reinforced concrete works
Widely used in modern construction concrete and reinforced concrete are due to high physical and mechanical properties, durability, good resistance to temperature and humidity influences, the possibility of obtaining specified structures using relatively simple technological methods, the use of local materials in the base (except steel) and relatively low cost.
The expansion of the scope of application of concrete and reinforced concrete is facilitated by the existing advanced base for the production of precast reinforced concrete. Industrial plants building materials They produce not only ready-made prefabricated reinforced concrete structures, but also formwork kits, reinforcement frames and meshes, ready-mixed concrete mixes, dry mixes for mortars and concrete, various additives to concrete mixtures and mortars, with the help of which their physical, mechanical and technological properties can be controlled.
According to the method of execution, concrete and reinforced concrete structures are divided into monolithic, prefabricated and precast-monolithic.
Monolithic structures are erected on the site under construction in the design position.
Prefabricated structures are manufactured in advance at factories, combines and landfills, delivered to the site 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 site, then the monolithic part of this structure is concreted in the design position.
In industrial and civil construction, the use of monolithic and prefabricated 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), and many other structures. All types are built from concrete and reinforced concrete engineering structures, as well as bridges, dams, tanks, silos, pipes, cooling towers, etc.
The construction of buildings in monolithic reinforced concrete allows them to be optimized Constructive decisions, move to continuous spatial systems, take into account the joint work of elements and thereby reduce their cross-section. In monolithic structures, the problem of joints is easier to solve, their thermal and insulating properties are increased, and operating costs are reduced.
Construction of monolithic concrete and iron concrete structures includes the implementation of a set of interrelated processes for installing formwork, reinforcing and concreting structures, curing concrete, stripping it and finishing the surfaces of finished structures.
According to the scope of 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;
- reinforcement, which consists of the manufacture and installation of reinforcement, with prestressed 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 preparation, transportation and laying concrete mixture, care of concrete during its hardening process.
Complex technological process for the construction of monolithic concrete and reinforced concrete structures consists of procurement and installation and laying (main) processes interconnected by transport operations.
Complex construction process monolithic structures includes:
- procurement processes for the production of formwork elements and formwork forms, reinforcement and the preparation of concrete mixtures in factories and at landfills, in specialized workshops and workshops;
- transport processes for the delivery of formwork, reinforcement and concrete mixture to the work site;
- basic processes (performed directly on construction site) for installing formwork and reinforcement in the design position, laying and compacting the concrete mixture, caring for concrete during its hardening, tensioning reinforcement (when concreting monolithic pre-stressed structures), stripping (dismantling) formwork structures after the concrete reaches the required strength.
2. Purpose and arrangement of formwork
Formwork is a temporary auxiliary structure that forms the shape of the product. Formwork is used to give the required shape, geometric dimensions and position in space of the structure being built by laying concrete mixture into the volume limited by the formwork.
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 unchangeable position of the formwork panels relative to each other during the work process; scaffolding (supporting and supporting devices) ensuring 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 chemical processes taking place, 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 unfastening of formwork are called formwork, and those associated with the placement of reinforcing cages and meshes into formwork are called reinforcing. The processes of dismantling the formwork after the concrete has reached the required strength are called stripping.
3. Components of formwork and formwork systems
The basis of the effectiveness of any formwork system is the ability to quickly modify it in accordance with the requirements of the construction site. The lightness of the panels and the ease of assembly of the formwork make it possible to significantly increase the rate of production of the entire complex of concrete works and reduce the construction period. The manufactured formwork must guarantee optimal sizes 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 formative 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 metal or wooden profile, manufactured in a jig that guarantees the accuracy of the external 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 connected to each other using special units and fasteners, and designed to create required surface in specified sizes;
- formwork block - a spatial, closed or open formwork element consisting of several panels, intended for formwork of corner sections of a concreted structure, made entirely and consisting of flat and corner panels or shields;
- formwork system - a concept that includes formwork and elements that ensure its rigidity and stability - fastening elements, scaffolding, supporting scaffolding;
- fastening elements - locks used to connect and securely fasten adjacent formwork panels to each other; ties that connect opposing panels in the formwork and other devices that combine the formwork elements into a single, unchangeable structure;
- supporting elements - struts, racks, frames, struts, supports, scaffolding, floor beams and other supporting devices used when installing and securing the formwork of walls and ceilings, fixing the formwork in the design position and bearing loads during concreting.
Auxiliary elements of formwork systems:
- hanging scaffolds - special scaffolds hung on the walls from the facades using brackets fixed in the holes left when concreting the walls;
- roll-out scaffolds – designed for rolling out tunnel formwork or floor formwork along them when dismantling them;
- opening formers – special formwork designed for forming window, door and other openings in monolithic structures;
- base – lower part monolithic wall 10...20 cm high, which is concreted simultaneously with the monolithic ceiling. The purpose of the plinth is to ensure the design thickness of the wall and fix the formwork relative to the alignment (coordinate) axes.
4. Requirements for formwork
Any formwork produced must meet the following requirements:
- guarantee of the required dimensional accuracy of the future structure or structure;
- strength, stability and invariability of shape under the influence of loads arising during the production process; all formwork elements are designed for strength and deformability;
- density and tightness of the formwork panel deck, i.e., the absence of cracks that cause the formation of voids and cavities in the concrete as a result of leakage of cement mortar;
- high quality surfaces, eliminating the appearance of sagging, cavities, curvatures, etc.;
- manufacturability - the ability to allow quick installation and disassembly, not to create difficulties during the installation of reinforcement, laying and compacting the concrete mixture;
- turnover - repeated use of formwork, which is usually achieved by making it inventory, standardized and collapsible;
5. Materials for the manufacture of formwork
A wide variety of materials are used to make formwork elements. The supporting elements of the formwork are made mainly of steel and aluminum alloys, which allows them to achieve high turnover.
Wood is used for formwork (deck) coniferous species(pine, spruce, larch), hardwood(birch and alder), waterproof plywood, steel, plastics, metal mesh, reinforced concrete and reinforced cement boards, particleboard (chipboard) and fibreboard (fibreboard), polypropylene with fillers.
Wood is used to make decks in the form of edged and unedged boards a width of no more than 15 cm, for scaffolding and fastenings - bars measuring from 8×10 to 8×14 cm, a stock 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 ability to produce forms 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 into the formwork, the side in contact with it swells, and the other quickly dries out under the influence of sunlight. As a result, the wood becomes warped, bulges, and leaks out through the cracks. cement mortar, voids and cavities form in the concrete. Measures to counteract these processes are the use of tongue and groove boards, coating the inner surface with various lubricants to reduce the adhesion force of the formwork to concrete.
Waterproof plywood is used only for sheathing. It has significant turnover and ensures high-quality concrete surfaces. To increase turnover, it is necessary that the front surface of the formwork be flush with the framing elements of the frame and constantly lubricated.
Laminated plywood with a phenol-formaldehyde coating is used as cladding (deck) for monolithic concrete work; the 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 (cladding) of metal formwork.
Profile steel, mainly channels and angles, is used for the frame and supporting devices, tubular steel is used for the manufacture of load-bearing scaffolding and struts. Bolts, wire and mainly hardware are used for all kinds of fastenings and connections.
Steel formwork provides smooth surface concrete structure, ease of stripping, rigidity, absence of deformation, significant turnover. It is advisable to use such formwork with a turnover of at least 50 times. The disadvantages of metal formwork are high cost, significant weight and high thermal conductivity. However, nowadays metal formworks are increasingly used due to their high turnover and the ability to produce smooth and even surfaces. concrete surface as a result of its use.
Plastics combine the advantages of steel (strength, multiple turnover, the ability not to change under various temperature and humidity conditions) and the advantages of wood (low weight and ease of processing). The disadvantages of these materials - deformability of wood and corrosion of steel - are also eliminated. Low rigidity, increased flexibility and relatively high cost of plastics make them still little competitive with other materials. Plastics are mainly used as thin protective films applied to wood and metal deck surfaces.
Plastic formworks are used, especially fiberglass reinforced. They have high performance strength under static load, chemically compatible with concrete. Formwork from polymer materials They are distinguished by their low weight, stability of shape and resistance to corrosion. Possible damage can be easily eliminated by applying a new coating. The disadvantage of plastic formwork is that their load-bearing capacity decreases sharply when the concrete is heat treated with an increase in temperature to 60 °C.
Metal mesh with cells up to 5x5 mm is used for the manufacture of mesh and vacuum formwork.
Thin-walled reinforced cement and reinforced concrete slabs- these are slabs with outer side smooth, but the inner one is uneven, with protruding reinforcement. This allows when laying in such a structure monolithic concrete achieve a high degree of connection with this type of formwork. This formwork is called permanent because it remains in the structure and works as its integral part.
In terms of their characteristics, particle board (chipboard) and fibreboard (fibreboard) are between wood and waterproof plywood and are used mainly for deck construction, less often for fastening the formwork frame.
The turnover rate of inventory formwork with a deck made of boards, chipboard and fiberboard is 5...10-fold, formwork made of waterproof plywood is 50...100-fold, steel formwork- 100...700-fold.
The use of composites with a conductive filler makes it possible to obtain heating coatings with adjustable thermal effects on concrete.
6. Main types of formwork
Formwork is classified according to its functional purpose depending on the type of structures being concreted and, in general view, subdivided:
- for vertical surfaces, including walls;
- for horizontal and inclined surfaces, including floors;
- for simultaneous concreting of walls and ceilings;
- for curved surfaces (mainly pneumatic formwork is used).
As a result practical use in domestic and foreign mass industrial and civil construction, they have been created and are successfully used depending on the characteristics of the structures being built, the formwork material, conditions and methods of work, whole line structurally different formworks, the most widespread of which are the following:
1. Collapsible small-panel formwork made from small panels with an area of up to 2 m2 and a weight of up to 50 kg, from which formwork can be assembled for concreting any structures, both horizontal and vertical, including massifs, foundations, walls, partitions, columns, beams, floor slabs and coverings.
2. Large-panel formwork from 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 designed for the construction of large-sized and massive structures, including extended or repeating walls, floors of buildings and structures for various purposes.
3. Horizontally movable formwork, the purpose of which is the construction of linearly extended structures with a length of 3 m, solved both in the form separate wall (retaining wall), two parallel walls (open collector), and a closed structure consisting of walls and a covering of the required specified length.
4. Volume-adjustable formwork, which has found application in the simultaneous construction of walls and floors of buildings. The formwork consists of L- and U-shaped block sections; the design allows the sections to move inward. Sections of formwork are connected to each other along their length, forming several parallel rows at once with distances between blocks equal to the thickness of the walls. This allows, after installing the formwork and laying the reinforcement cages, to simultaneously carry out concreting of the walls and adjacent sections of the floors.
5. Tunnel formwork is designed for the construction of a closed loop of tunnels constructed using a closed method. Currently, tunnel formwork has found wide application for simultaneous concreting of corridor system buildings (hospitals, sanatoriums, holiday homes, etc.), when using two sets of formwork, continuous installation of external and interior walls and floors immediately covering the entire width of the floor of the building being constructed.
6. Climbing formwork is used for the construction of high-height structures with constant and varying cross-sectional geometry - pipes, cooling towers, bridge supports, etc.
7. Sliding formwork used during construction vertical structures buildings and structures of great height. The formwork is a system consisting of panels, a working floor, scaffolding, jacks, jacking rods mounted on jacking 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 stairwells, elevator shafts, closed cells of walls of residential buildings, and external surfaces columnar foundations, grillages, arrays, etc.
9. Vertically movable formwork intended for the construction of structures (tower, cooling tower, residential building) or parts thereof (elevator shaft of a residential building) and individual parts of buildings and structures one floor high (site elevator shaft, a spatial closed cell of 4 walls of the building).
10. Permanent formwork, used in the construction of structures without stripping, with the installation of waterproofing, cladding, insulation, etc. simultaneously during the work. The specificity of the formwork is that after laying the concrete mixture into it, the formwork remains in the body of the structure, forming one whole with it . Currently, permanent formwork is used not only for concreting individual structures, but also for constructing entire buildings. This became possible when used as formwork polystyrene foam boards thickness 50...150 mm with a density of 20...25 kg/m3, with high moisture resistance. Permanent formwork consists of factory-made 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 permanent formwork woven can be used metal grid, reinforced concrete, reinforced concrete and asbestos concrete slabs, foam plastic slabs, glass cement, etc. This type of formwork can be used in cramped work conditions and when economic feasibility its use.
11. Special formworks are not included in the range of main types, although they often allow the construction of similar structures. This is a pneumatic formwork consisting of inflated rubberized fabric, which creates the formwork of the future spatial structure, supporting and load-bearing elements. In the working position, pneumatic formwork is supported by excess air pressure and is used for concreting thin-walled structures and curved structures.
One can also note non-reversible (stationary) formwork, the purpose of which is in concreting individual places, areas and even structures for the formwork of which the use of industrial formwork is uneconomical or technically irrational. This is disposable formwork, collected from production waste.
Combined structures are rational, in which the load-bearing and supporting elements are made of metal, and those in contact with concrete are made of lumber, waterproof plywood, particle boards, and plastic.
7. Technology of formwork processes
The technological process for constructing formwork is as follows. The formwork panels are installed manually or by crane and secured in the design position. After concreting and the concrete reaching a strength that allows stripping, the formwork and supporting devices are removed and moved 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 various standard sizes with inventory supporting devices and fastenings. The dimensions of the main panels of unified formwork are, as a rule, subject to one modular size (300 mm in width and 100 mm in height). In small-panel formwork, you can assemble forms for almost any concrete and reinforced concrete structures - walls, foundations, columns, crossbars, flat, frequently ribbed and coffered floors and coverings, 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 torsional loads and at the same time make it possible to simplify installation and horizontal alignment, and when formworking high-rise structures increase work safety.
The comprehensive formwork system is designed for formwork of any horizontal and vertical building structures, starting with the smallest structures. In addition to the closed profile of the formwork panel frames, a formwork lock is proposed, which provides a quick (a blow with a hammer) and high-quality connection of two adjacent panels horizontally or vertically anywhere in the structural frame. The deck is made of multi-layer waterproof plywood and is covered with a special powder or other coating that dramatically reduces adhesion to concrete. Sleeves are welded into the profile of the formwork frames, which are provided for the passage and convenient insertion of tension rods, for the mutual connection of opposing formwork panels.
Flat panels of small-panel formwork have an area of up to 1.5...2.0 m2, a weight of no more than 50 kg for the possibility of installing them manually. If there is an installation 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 for performing work with small-panel formwork is similar to working with large-panel formwork.
Large-panel collapsible formwork includes panels measuring 2...20 m2 of increased bearing capacity. The weight of such shields does not have strict restrictions, since they are installed and dismantled only with the help of lifting mechanisms. In large-panel formwork, the panels can be connected to each other along any edges and, if necessary, supplemented with small panels of the same system. As in small panel formwork, the deck can be made of steel sheet or waterproof plywood.
When installing strip foundations, the formwork is formed from inventory panels, which are connected to each other using locks different designs. In the case of inserts between panels of additional elements up to 15 cm wide, extended locks can be used. The transverse dimension of the structure is fixed with temporary struts on the struts and end panels of the formwork. To absorb the lateral pressure of the concrete mixture, the opposing panels are connected with screw ties (ties).
Work on installing and dismantling formwork should be mechanized as much as possible. Initially, the formwork panels are assembled into a formwork panel on full height strip foundation and an area of about 20 m2. Formwork panels are subject to increased demands on 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 panels - “mortgage” and “cover”, connected to each other 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 high-precision aluminum alloy profiles, cross section which ensures the installation of a deck from laminated plywood 18 and 21 mm thick, the ends of which are structurally protected by the aluminum profile and sealant.
The formwork kit also includes struts for installing panels, hanging cantilever scaffolding for concreting, locks for connecting panels and screw ties.
Shield frames are made in jigs that ensure surface non-flatness of no more than 1 mm, the difference in frame diagonals is no 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 attaching a deck made of waterproof laminated plywood to panel frames, the countersunk head of the screws can protrude no more than 0.1 mm onto the plane of the plywood.
Large-panel formwork provides formwork for monolithic structures with a 300 mm module. 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 panel weight from 42 to 110 kg.
Large-panel wall formwork consists of formwork panels, scaffolding hung on these panels, bracing struts and bracing elements. The panels are assembled into formwork panels using centering locks. To align the formwork panel in the design position, the formwork is equipped with struts, the screw couplings of which allow you to adjust the installation of the panel in the 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 of bars up to 15 cm wide in the formwork when concreting structures of non-modular sizes.
The formwork kit allows, if necessary, to carry out corner connections panels, joints of wall junctions, arrangement of junction-compensators and others possible options joining the formwork panels to each other.
For the construction of the external walls of the building, special scaffolds are provided, which are all-metal brackets with flooring panels and fences.
The formwork panels are secured using screw ties and nuts that absorb the pressure of the concrete mixture. To organize workplaces at height when receiving and laying the concrete mixture, the formwork provides for mounting scaffolds with fences that are hung on the frame of the formwork panels.
When installing and dismantling formwork at a height along the perimeter and inside the building, the formwork panels must be protected with inventory protective devices.
The formwork panels are made in accordance with a single module, they are universal and interchangeable; assembly, installation and connection of the panels can be carried out in a vertical and horizontal position. The frame ribs have holes for hanging brackets and installing struts.
To connect the panels together, 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 formworking a surface, it is planned to lay a horizontal panel on top of previously installed vertical panels, then along the length of the horizontal panel there should be three locking connections with vertical shields.
When installing struts and hanging brackets for suspended scaffolding, they are secured through holes in the ribs of the formwork panels, regardless of whether the panel is installed vertically or horizontally. When installing wall formwork with separate panels, two struts are installed on each panel; when installing with panels, every 2...4 m. Brackets for laying the working flooring are attached to the formwork panels in increments of 1.2...1.5 m.
During the installation of panels and wall formwork panels along the marks marked on the ceilings, they are pressed against the concrete base and brought into a vertical position using turnbuckles of the struts. The installation accuracy is checked with a level or plumb line.
After installing the opposite panels of the wall formwork, the panels are fastened together using screw ties, placing at least three ties along the height of the panel. Screw ties, installed between opposing panels, are passed through steel bushings, plastic and plastic bushings and cones, the length of which must correspond to the thickness of the concrete wall. The cones protect the holes 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 panels are fastened by tightening the nuts of the screw ties. To avoid local deformations of the hollow section of the shield frame when tightening the nuts, wide-field washers are used. After installing the formwork panels, all unused through holes in the formwork must be plugged with special wooden or plastic plugs to prevent concrete from leaking out of these holes during the concreting process.
Panels and panels of external walls are mounted from working scaffolds fixed to the walls of the previous floor. The scaffolding is mounted as follows. When concreting the walls, through holes remain in them from the screw ties of the formwork panels. When installing scaffolding using an assembly crane, the bolts for fastening the bottom of the supports of the working scaffold are passed into these holes, with inside walls, these bolts are secured with nuts. Thus, the scaffolding is pressed tightly against the concrete wall of the underlying floor.
First of all, the panels (panels) of the external formwork are mounted, they are installed on the working scaffolding, aligned and secured using struts. Next, internal formwork panels (panels) are installed from the ceiling, which are sequentially attached to the outer panels during the installation process using screw ties.
Lifting and installation of panels and formwork panels is carried out with a special grip attached to rope slings, for one point (for a separate panel) or two points for a formwork panel.
Wall formwork can be mounted either as separate panels or pre-assembled into panels. The assembly of panels from individual panels must be carried out on a specially prepared site in the operating area of the installation crane. The length of panels assembled from panels should not exceed 8 m in length.
Dismantling of wall formwork is carried out in enlarged panels of 5...6 panels. On the panel being dismantled, unscrew the nuts of the screw ties and pull out the ties. Then, using struts, the shields are torn off the concrete. The disconnected panel is transported by crane to the warehouse for inspection, repair, and, if necessary, lubrication.
The formwork of columns with plan face sizes from 0.2 to 0.6 m is made from 0.8 x 3.0 m panels with holes for tie rods, which allows the installation required size columns in plan. The column formwork is equipped with struts for installation, alignment and stripping, as well as hanging scaffolds with guards.
When installing column formwork initially on concrete base(floor) mark the place of its installation (risks of geometric axes, edges of the position of columns). The installed reinforcement cage is initially connected to the frame of the underlying column, additionally plastic rings are 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 the concreting process.
Initially, two adjacent shields are installed along the risks and beacons and secured with struts. The lower supports of the struts are rigidly attached to the ceiling and, using the screws of the struts, the shields are brought into a vertical position. Then the remaining two adjacent shields are installed, which are also brought into a vertical position. Opposite shields are fastened together with screw ties; they are installed in four pieces along the height of the shield. Unused holes in the panels must be plugged with special plugs (wooden or plastic) to prevent concrete mixture from leaking out of the cavity. Cantilever scaffolding is installed from mobile towers. They have a working floor made of panels with protective fence from boards, which will allow you to safely carry out work on concreting columns.
Before concreting, final alignment of the installed formwork and all its fastenings is carried out.
An option for connecting column panels to each other involves fastening using a clamp consisting of four brackets connected to each other by wedges. The brackets hold the panels in the required design position, providing the required geometric dimensions of the columns.
Floor formwork can be solved in two options: 1) formwork, including a deck made of sheets of laminated plywood, mounted on longitudinal and transverse load-bearing beams mounted on frames with retractable jacks; 2) table prefabricated formwork, consisting of a table in the form of a set of frames with support jacks, interconnected by longitudinal connections with roller supports.
Telescopic racks 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 load-bearing elements of the formwork. Telescopic steel racks consisting of two pipes entering one another have found application. The initial position of the pipes between each other is fixed thanks to special slots every 10 cm, the amplitude of changes is from 10 to 130 cm. For precise installation of the stand in height (with an amplitude of 10 cm), there are through holes in the inner (retractable) pipe round holes, into which a steel pin is inserted, passing into the slot in the upper part outer pipe. The pin rests on a nut screwed onto a thread at the top of the outer pipe and supports inner tube in a given position.
For smooth lowering of supports (unwinding) supporting formwork panels, use special devices. When using special inventory wood-metal racks, use screw jack, and steel telescopic stands - 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 load-bearing beams in it. The falling head is convenient because when the concreted floor structure has gained sufficient strength, it becomes possible to remove some of the intermediate posts. When you press a special lever, the falling head lowers up to 10 cm, while the remaining system of posts and beams supporting the floor maintains its position. The third type of heads is support, supports formwork system before stripping. These heads, when you press the lever, lower by 1...2 cm, make it possible to visually assess the condition of the system being stripped, easily extend the racks and release the beams supporting the formwork. The formwork panels are disconnected from the concreted structure using their own weight or using special crowbars.
Large-panel floor formwork consists of support frames equipped with sliding jacks, on which longitudinal and cross beams, supporting a deck made of laminated plywood. The supporting beams are connected to each other with a special bolted connection. The laminated plywood deck is secured to the beams using countersunk screws. Installation and dismantling of formwork is carried out in accordance with the technological map (TC). Dismantling of the formwork is permitted only after the concrete has reached the required strength.
The 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 the installation process must be ensured. The location of load-bearing telescopic posts and frames on the concreted floor also depends on the location of the posts on the previously concreted floor. In this case, it is necessary to take into account the pace of construction of structures, the rate at which concrete gains strength in floors and walls, the loads acting on the structure at various stages of construction, and other technological factors.
The installation site of formwork forms and scaffolding must be cleared of debris, snow and ice. The ground surface should be leveled by cutting off the top layer of soil. Adding soil for these purposes is not permitted.
When installing formwork, special attention is paid to the verticality and horizontality of the elements, the rigidity and immutability of all structures as a whole, and the correct connections of the formwork elements in accordance with the working drawings. Permissible deviations when installing formwork and supporting scaffolding are standardized.
The use of inventory formwork requires mandatory lubrication of the panel deck. The most common hydrophobic lubricants are based on mineral oils or salts fatty acids, as well as combined lubricants.
Lubricants reduce the adhesion of the deck to the concrete, thus facilitating stripping and, as a result, increasing the durability of the formwork panels. The lubricant is restored after 1...4 turns of the formwork.
It is best to prepare all formwork elements in special workshops or at training grounds. At the same time, students are prohibited from working on circular or rip saws, and the preparation and cutting of boards using these mechanisms must be performed by professional workers.
When installing formwork elements in several tiers in height, each subsequent tier is performed after the previous one is securely fastened. It is prohibited to simultaneously carry out work in two tiers along the same vertical.
When working at a height of more than 1.5 m (if it is impossible to arrange fencing), workers are provided with safety belts with carabiners and the places where the chain or rope of the safety belt can be securely fastened are indicated.
Panel formwork of columns, crossbars or beams, when installed at a height of up to 5 m above ground or ceiling level, can be installed from portable stepladders equipped with fenced working platforms. At higher heights, work must be carried out from inventory scaffolding or scaffolding that also has a fenced flooring. Construction workers must have a special certificate for the right to carry out steeplejack work.
The installation of formwork parts or self-supporting formwork blocks with a height of more than 5 m must be carried out by professional workers at least 18 years old, who have passed a medical examination, have a category of at least 3 and have at least 1 year of experience in steeplejacking. In this case, the use of safety belts is mandatory.
Fencing is required along the entire perimeter of the installed floor formwork; fencing is also installed when demolition of buildings occurs.
suspended formwork reinforced concrete floors buildings should be constructed with a fastening design that, when laying the concrete mixture, would not allow it to move or sway.
The detachment commander, together with the foreman and the public safety inspector, must check the serviceability of the formwork, the strength of working decks and fences, and the reliability of stairs every day before starting concreting. If any faults are found, they are corrected before laying the concrete mixture.
It is prohibited to store materials not provided for by the project on the working floor of the formwork, and also to allow a crowd of people on it. It is prohibited to store elements of disassembled formwork on scaffolding, as well as to throw them off the structure.
Openings left in the formwork decks must be fenced or covered with strong shields. Protruding nails should be removed from previously used boards. It is forbidden to lay boards or panels with the tips of the nails facing up, even for a short time.
Floorings of scaffolding, scaffolding and stepladders located above 1.1 m from the ground level or ceiling are equipped with a railing with a height of at least 1 m, consisting of a planed handrail, one horizontal element and a side board with a height of at least 150 mm. Side boards should be placed on the flooring, and railing elements should be attached to the posts from the inside. The height of the passages on the scaffolding is left at least 1.8 m. The installed floor formwork must have a fence around the entire perimeter.
Builders performing formwork work must undergo induction and on-the-job training, and appropriate entries are made in the safety logs. construction organizations. Not allowed to perform formwork work builders who do not have the skills to handle carpentry tools and devices. Formwork work must be performed by young men at least 18 years of age.
The formwork used for the construction of monolithic reinforced concrete structures is manufactured and used in strict accordance with the work project. When installing formwork in several tiers, each subsequent tier is installed only after the previous one has been secured.
It is not allowed to place equipment and materials on the formwork that are not provided for in the work project, as well as the presence of people not involved in the work.
The formwork is dismantled only after the concrete has reached the specified strength with the permission of the work manufacturer, and for especially critical structures - with the permission of the chief engineer.
The assembled formwork elements are released from the hook of the lifting mechanism only after they have been temporarily or permanently secured.
In the absence of mounting scaffolds, the formwork panels are secured to the supporting structures and only after that they are torn off from the concrete.
Safe working conditions must be created at the formwork workers' workplace. If work is carried out simultaneously on several tiers, workplaces are reliably protected from above and below in case of falling of tools and formwork elements.
In places where formwork elements are stored, the width of passages must be at least 1 m. Descents into pits are equipped with stairs with railings.
Formwork panels, elements of scaffolding and devices are lifted and delivered to the installation site in packages or special containers using lifting mechanisms; the packages are covered with slings in at least two places. Elements of fastenings and connections (locks, clamps, ties, etc.) of the formwork are supplied only in special containers.
When applying lubricants to the formwork with a pneumatic sprayer, workers must wear goggles, respirators, overalls, gloves and rubber boots.
During concreting, an on-duty worker is appointed who periodically (1...2 times per hour) inspects the formwork and, in case of deformation of its individual elements, supporting posts or other parts, calls a foreman to take measures to correct the detected defects. All defects associated with a violation of the structure of the laid concrete mixture can be corrected within 1...2 hours after laying the mixture.
When installing and dismantling formwork, comply with safety requirements.
Control questions
- From which structural elements what does the formwork consist of?
- What techniques can be used to increase the turnover rate of formwork?
- What types of formwork do you know?
- What materials are used to make formwork elements?
- Provide diagrams of vertically extractable (block) and horizontally extractable (tunnel) formwork.
- Give a diagram and explain the working principle of sliding formwork.
- What elements does horizontal sliding formwork consist of?
- Give a diagram of the pneumatic formwork and name its scope.
- What are the advantages of permanent formwork and where is it used?
- What is the sequence for constructing the formwork of a stepped foundation?
- In what sequence is the strip foundation formwork installed?
- Provide diagrams for dismantling tunnel-type formwork and the means of mechanization used for this.
- What is the installation sequence for sliding formwork?
- In what sequence is sliding formwork dismantled?
- List the means and techniques that reduce the adhesion of concrete to formwork.
- What are the basic rules for safe formwork work?
All General requirements safety precautions required during production civil works, also apply to the production of formwork work. 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 design.
Permissible loads on scaffolding must be established by technical personnel based on calculations. Weight of materials, stacked on floorings, the weight of people on them and Vehicle must not exceed the permissible loads.
Congestion of people on scaffolding and floor formwork is not permitted.
Installation of collapsible formwork at a height of up to 5.5 m from the ground or underlying ceiling can be carried out with ladders or portable stepladders with a platform with a fence at the top, and at a height of up to 8 m - with mobile carts. At higher heights, decking is installed on the scaffolding for the formwork workers to work.
Floorings of scaffolding, scaffolding and stepladders located above 1.1 m from the ground level or ceiling must be fenced with railings 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 attach the railing elements to the posts from the inside.
Wooden handrails must be planed.
The height of the passages on the scaffolding must be at least 1.8 m. The installed floor formwork must have fences around the entire perimeter.
The condition of all scaffolding and scaffolding structures, including the condition of connections, fastenings and fences, must be systematically monitored.
The condition of scaffolding and scaffolding must be checked daily before the start of the shift by the foreman in charge of the relevant area of work 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: the mounted elements must be rigid and their parts must be securely fastened; It is permitted to release the installed element from the hook of the lifting mechanism only after securing the element with permanent or temporary connections (according to the design) and checking the reliability of the fastening. Dismantling of formwork can only begin with the permission of the work manufacturer or foreman, and in particularly serious cases (for example, during construction, for 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 or other defects that could lead to unacceptable deflections or collapse of the structure when the formwork is removed.
It is prohibited to stack materials from formwork dismantling on scaffolding. They must be immediately lowered to the ground, sorted and stacked. Protruding nails and staples must be removed from the boards. It is prohibited to lay boards or panels with the nail points facing upward, even for a short time.
All holes left in the ceilings must be securely sealed or fenced after the formwork is removed.
When working at height, carried out near the outer walls of a 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 concrete and reinforcement workers are mass construction professions.
Concrete And reinforced concrete work are... Production concrete works in dry hot climates... Calendar plan organization of production reinforced concrete works ...
Concrete And reinforced concrete work produced in the manufacture of monolithic and prefabricated concrete And reinforced concrete designs. These work consist of the following complex processes: production and installation of formwork...
Chapter X CONCRETE AND REINFORCED CONCRETE WORKS. Sealing prefabricated butt joints reinforced concrete designs. On the quality of sealing of installation joints reinforced concrete structures depend on the strength of the structures...
the presence of well-known domestic scientific and engineering schools in the field of concrete theory and production technology concrete And reinforced concrete works, calculation reinforced concrete designs
...concrete And reinforced concrete works carried out at all stages of their production, starting with manufacturing concrete mixtures and finishing Quality of ready-made concrete And reinforced concrete products largely depend on the composition concrete mixtures and qualities of constituent materials.
For small volumes works Formwork can be manufactured on 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 hardening concrete are transferred to the assembled 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 the mixture is checked at least twice a shift at the places of its preparation and placement. Every construction organization producing concrete And reinforced concrete work must keep a journal concrete works.
1. Scope of preparation under reinforced concrete, concrete And buto- concrete foundations are not taken into account by the standards and must be calculated separately.9. Volume works by device reinforced concrete floors with liners made of lightweight concrete, hollow ceramic blocks, etc...
Concrete And reinforced concrete work are... Production concrete works in a dry, hot climate... Production organization schedule reinforced concrete works ...
Depending on the production method works distinguish between monolithic, prefabricated and prefabricated-monolithic concrete And reinforced concrete structures with non-prestressed and prestressed reinforcement.
Laying vibrated concrete. Chapter 7. CONCRETE AND REINFORCED CONCRETE WORKS...and the surfaces concrete, reinforced concrete and reinforced cement formwork - facings must be moistened with water. ...
Organization concrete And reinforced concrete works must ensure the rapid construction of structures. To do this you should: produce work at least two shifts; reduce time gaps between works different brigades at this capture...
Concrete And reinforced concrete work are one of the main types of construction works, and the professions of concrete and reinforcement workers are widespread.
Technology and organization of construction reinforced concrete designs. Organization Basics concrete And reinforced concrete works.To the contents of the book: Concrete And reinforced concrete work.
Security High Quality concrete And reinforced concrete works performed at subzero ambient temperatures necessitates compliance with certain requirements.
Chapter 7. CONCRETE AND REINFORCED CONCRETE WORKS...and the surfaces concrete, reinforced concrete and reinforced cement formwork - facings must be moistened with water. ...
Latest additions:
When performing all processes: installation of formwork, reinforcement, concreting and maintenance of concrete, it is necessary to constantly monitor the strength and stability of formwork panels and racks, decking, ladders and fences.
During formwork work:
Simultaneous work in two or more tiers along the same vertical line without appropriate protective devices (flooring, canopies, etc.) is not allowed.
When working at a height of more than 1.5 m (if it is impossible to arrange fencing), workers are provided with safety belts with carabiners.
The permissible loads on the decking are determined by calculation. The total weight of materials, people and vehicles must not exceed the permissible loads.
Congestion of people on scaffolding and floor formwork is not permitted.
Installation of collapsible formwork at a height of 5.5 m from the ground or the underlying floor can be carried out from ladders or portable stepladders with a platform with a fence at the top.
During a thunderstorm and with a wind of more than 6 points (15 m/s), it is prohibited to carry out work from external scaffolding.
Removal of formwork (stripping) is carried out only with the permission of the foreman, and removal of load-bearing formwork (beams, slabs, etc.) - only after a laboratory conclusion on the actual strength of concrete.
During the production of reinforcement works:
Installed reinforcement elements must be secured; they are not allowed to be left unsecured. Knitting or welding reinforcement while standing on tied or welded clamps or rods is prohibited.
You cannot stand on reinforcement and formwork blocks until they are completely installed and secured. Walking on the reinforced floor is allowed only on “passages” (boards) 0.3 and 0.4 m wide installed on trestles; laying boards directly on the reinforcement installed in the design position is prohibited.
Before starting electric welding work, check:
The serviceability of the electric welding machine and the insulation of its body, welding wire and electric motor (for a remote-controlled machine);
- presence and correct grounding of the welding machine;
- absence of flammable materials near the welding site (at a distance of at least 10.0 m from it).
When working with an open electric arc, electric welders need to protect their face and eyes with a helmet-mask or shield with protective glass filters. Light filters are protected from splashes of molten metal or contamination by simple glass.
Workers assisting the electric welder are also provided with shields and goggles, depending on the conditions.
Perform electric welding work under open air prohibited during rain and thunderstorms. Welders working at height must have pencil cases or bags for electrodes and boxes for cinders. Scattering cinders is prohibited.
During the production of concrete work:
When supplying concrete mixture with cranes, the bucket shutter is secured in such a way as to prevent spontaneous unloading. At the time of unloading the mixture, the distance from the bottom of the tub to the surface on which unloading is performed should not exceed 1 m.
When supplying a concrete mixture with a concrete pump, before starting work, it is tested at a hydraulic pressure exceeding 1.5 times the working pressure. The concrete pump is connected by an alarm to the place where the concrete mixture is placed.
A concrete worker should only work with electric vibrators wearing good rubber boots and gloves.
The wires from the distribution panel to the vibrators are enclosed in rubber sleeves; The vibrator body must be grounded at the place of work. Vibrators operate at a voltage of 36...42 V. All temporary electrical networks and connections are carried out by a specialist electrician and are handed over according to a certificate.
Vibrator handles must have shock absorbers. If they are not available, work with vibrators only in vibration-isolating gloves.
You can only work on concrete in rubber boots. The vibrators are turned off during breaks in work, as well as when concrete workers move from one place to another. Do not pour water on vibrators.
When laying concrete mixture in a structure with a slope of 30° or more, concrete workers are equipped with safety belts.
When concreting according to continuous technologies(concrete paver, concrete pump) concrete workers must have clear and continuous communication with the driver.
When heating structures:
All workers involved in heating concrete structures are instructed and must have certificates of knowledge of labor safety rules.
When heating concrete structures, continuous monitoring of voltage, current and temperature is ensured. The temperature is measured every hour for the first 3 hours of warming up, and every 2–3 hours thereafter. The outside air temperature is measured three times a day.
Before concreting, the correct installation of the electrodes and their dimensions are checked. Before turning on the heating, the correct installation and connection of the electrodes, the reliability of contacts, the location of temperature sensors, and the quality of insulation are checked. The reliability of the contacts is checked after turning on the heating and switching the voltage.
For warming up, a voltage of no higher than 127 V is used. A voltage of 220 V is allowed for warming up unreinforced structures or separately standing structures, not associated with other general reinforcement.
Open fittings connected to the heated area are grounded. The warming up area is securely fenced and equipped with an alarm and locking system.
In damp weather and thaw, concrete should not be heated for open areas. You can water the concrete only after turning off the heating.
The presence of unauthorized persons and the conduct of other types of work are prohibited in the warm-up zone.
The concrete temperature when heating is turned on is measured only at a voltage not higher than 60 V; at higher voltages, heating is turned off for the duration of the measurement.
When performing work at subzero temperatures, it is necessary to prevent steam burns, electric shock, and calcium chloride poisoning.
All steam pipelines must be tested and passed according to the certificate. Areas where structures are heated are designated as a “danger zone” with appropriate inscriptions; During the entire supply of coolant (steam, electricity), these places are indicated by signal lights.
Source: Technology of construction processes. Snarsky V.I.
