Monolithic work technology. Concreting of monolithic concrete and reinforced concrete structures. Selection of assembly cranes
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Technology monolithic reinforced concrete
Production of monolithic concrete and reinforced concrete structures economically feasible when using industrial methods of construction production and the widespread use of inventory metal or wooden formwork.
A higher valuation score means that the performance of a particular technology is better compared to the original baseline. The figure shows the estimated characteristics of ready concrete based on high performance concrete technology, ready concrete based on ultra high performance concrete technology, precast concrete based on general concrete technology, precast concrete based on high performance concrete technology, and precast concrete based on high performance concrete technology, respectively.
Each column shows the minimum and maximum value of the evaluation score, as well as the standard deviation of certain values. The results of the evaluation show that the construction of a concrete structure using precast concrete elements is more beneficial than the traditional construction method using ready-mixed concrete, regardless of specific technologies. The preparatory construction method brings benefits during construction time, both labor and equipment needs on site, overall labor intensity of processes, impact on environment and effectiveness of management structures, respectively.
Distinctive feature the production of monolithic reinforced concrete lies in the fact that the main technological operations - installation of the formwork, laying reinforcement and concrete mixture into the formwork, compaction of the concrete mixture, hardening of molded products and concrete maintenance - are carried out at the construction site.
Depending on the configuration of the structure to be concreted, various types of formwork are used: stationary, collapsible-adjustable, sliding, moving in a horizontal direction, etc.
The excellent workability of fresh concrete reduces the number of workers required to process the concrete. On the other hand, the qualification of workers must be much higher, and the frequency and range of testing on the construction site is increasing. Thus, the overall labor content of the process increases.
The difference in views on the indicator of economic efficiency of advanced specific technologies is due to opposite resources and information. It is necessary to compare the cost with specific technological processes and, first of all, to determine the real relationship between the costs and the utility value of the structure, since the higher economic valuation of the improved cost of the utility of the structure directly affects the cost of profit. The total costs associated with material cost, labor cost, equipment cost, maintenance cost and other expenses should be taken into account.
Reinforcement is prepared in the reinforcement and welding shops of reinforced concrete plants and delivered to the place of installation in the formwork. The concrete mixture is prepared at mechanized (automated) concrete plants and delivered in the form of “ready-mixed concrete” (concrete mixture) to the place of its laying. For most monolithic reinforced concrete products and structures, the workability of the concrete mixture, characterized by the draft of a standard cone, ranges from 1-3 cm (foundations, retaining walls, mass blocks, etc.) to 6-8 cm (structures saturated with reinforcement, thin walls, slabs, columns of small section, etc.).
Improving the efficiency and confidence in sustainable development in construction depends on the wider application of advanced technologies, materials and modern construction methods in construction practice. General concrete has a long history in the production of precast elements. The benefits of precast construction are multiplied by the combination of modern concrete construction methods with advanced concrete technology. Therefore, the use of advanced concrete technologies in the assembly of prefabricated structures has significant potential to improve construction efficiency.
The concrete mixture is transported to the place of work by dump trucks, and at considerable distances - by concrete mixer trucks. In truck mixers, ready-made concrete mixtures do not become contaminated and do not delaminate and remain homogeneous, as they can be mixed during transsorting. The concrete mixture is often prepared directly in the mixer truck drum. Dry components in predetermined quantities are loaded into the drum at the central dosing unit of the concrete plant and the concrete mixture is prepared on the way 5-8 minutes before arrival at the work site.
A significant reduction in the weight and volume of structures leads to the elimination of the environmental impact caused by less material consumption. For a more complete assessment of the impact of application based on specific technologies on the efficiency of the construction process, it is necessary to prepare and analyze a wider set of input data from different construction projects implemented in different areas, except for Slovakia.
The authors declare that they have no competing interests. Fibers are used in cement to control cracking characteristics and reduce permeability. Fiberglass concrete is used for architectural products, while steel fibers are mainly used for paving and inside tunnels. This specific engineering guide will give you a variety of specific information, including some guidance for various situations. This works well for any type of construction, be it concrete, reinforced concrete or prestressed concrete. The manufacturing process has changed significantly since mason Joseph Aspdin first made Portland cement on his kitchen stove in England in the 19th century. Precast concrete is easy to work with, but its anti-earthquake performance falls short of expectations. Frequent failure of prefabs reinforced concrete beams and connections of precast concrete beams raised the question of its resistance to earthquakes. Without curing, concrete is also like a brittle mixture of various building ingredients that can break under excessive loads or even under normal loading conditions. Particular attention must be paid to underwater concreting, sub-zero curing of concrete and extremely hot temperatures.
- The surrounding concrete protects the steel used for reinforcement.
- Concrete is the basic building block of our everyday world.
- It is used in almost every type of structure we build today.
At the construction site, cranes, conveyors, pneumatic pumps and pneumatic blowers are used to transport and lay the concrete mix. The pneumatic method of supplying the concrete mixture to the place of laying is simple and allows it to be transported by compressed air through pipes over a distance of up to 150 m.
The concrete mixture is compacted in the formwork using mounted and portable surface or core vibrators.
It is about restoring an old recipe to remove the cement with the last of the Roman engineers, allowing the erection of works with a hardness like those that have continued to be admired for centuries. This search for compactness has driven theories and experiences among the promoters of this idea, scientists and entrepreneurs. Thus, over the next four decades there will be a real revolution in research, experience and testing. He uses it in various designs, among which stands out the church of Le Vesinet, which will be the last reason for its discrediting, since the appearance of stains cannot be eliminated on its surface.
Monolithic concrete and reinforced concrete structures are concreted continuously or in sections, blocks. Continuous laying of the concrete mixture is carried out when it is necessary to obtain increased solidity and uniformity of concrete in a structure or product. When concreting structures of a large area ( reinforced concrete floors) work is carried out in sections, providing for the construction of working seams in places of minimum stress.
Formwork production
Between the two inventions, patents move at a dizzying pace, driven by the desire to find new procedures that allow two materials other than iron and concrete to be combined in the same structural element. However, the new material, long dreamed of, tested and heavily licensed, cannot conquer the architectural environment governed by the academic rules that flow from traditional construction in stone and wood.
Classification of formwork by design features
Exceeded by events, with a boat and a barreos as the first realizations, concrete is not exhibited: it is submerged or used in those fragments of works that need reinforcement and strength, that is, forged, terraces or foundations. Lacking more joints than formwork, with a rough and blunt surface, the new conglomerate does not yet have own language, which many creators of the distinction do not have. Theorist Georges Gromot said: Concrete? But it's dirt! The molding nature of the concrete did not seem to be an advantage in delivering an image that should have been universal.
The quality of the concreted structure largely depends on the favorable temperature and humidity conditions for cement hydration and the formation of the reinforced concrete structure. Therefore, immediately after laying and compacting the concrete mix, concrete care begins. During the summer period of concreting, the surface of the freshly laid concrete mixture is protected from drying out, and during the first hours of hardening - from rain. To do this, the open horizontal surfaces of the structure are covered with a layer of wet sand, sawdust or moistened coarse weave fabric (burlap). In hot weather, the protective coating is kept wet until the concrete acquires at least 70% of the design strength. The vertical surfaces of the structure to be concreted are moistened with water after the formwork has been removed.
The commission of the church and Paul Cottancin's patent were at the same time, the reason why Bodo decided to use a method in which "armed cement" served as a link between hollow bricks, which worked as a permanent formwork. The result was a set of high, diagonal safes that emerged from thin walls and tree-shaped pillars. Brackets, protruding bodies, landscaped roofs, terraces and all manner of flying elements have turned this creation into a catalog of technical possibilities offered by its signature.
Preparation of concreting objects
Although it had grown more than ten years before, as it did not possess the constructive consistency of the latter, masking the material used. On the other hand, Perret's work has gained relevance and made his author a key figure in this process of aesthetic legitimization of reinforced concrete. The constructive skill of Charles Raboot, designing a seven-meter ledge extending over seventy-five, managed to impress the builders by inserting a beam and simply repositioning the armor.
When concreting structures with a large surface and length (aerodrome and road concrete pavements), various film-forming compounds that reflect the rays of the sun are used to preserve moisture. Laid concrete mixtures are often covered with polymer films (polyethylene, polyvinyl chloride, etc.), which retain moisture well and prevent the formation of temperature-shrinkage deformations. After the concrete reaches the design strength, the reinforced concrete structure is stripped and the actual (given) load is transferred to it.
But this simple combination had very important consequences. In fact, the work carried out by this firm has been the subject of much publicity thanks to photography, which has made it possible to better convey the technical and propaganda message. Sediments, bunkers, bridges, and hangars became an important part of this group of structures that facilitated the diffusion of reinforced concrete prior to the First World War. Its simple and monolithic appearance, associated with sustainable use models, became popular with new generations of architects and also became an icon of the pioneers of the modern movement.
Introduction
Concrete work must be carried out in compliance with the following operations: preparation and transportation of the concrete mix, concrete laying and concrete care during its hardening period. The quality of concrete is determined by many indicators: the quality, quantity and brand of cement used, the quality and quantity of aggregates, the correct selection of the ratio between the cement and aggregate used; the correct flow of water in the preparation of the concrete mixture; the quality of the concrete mix. Using various raw materials and technological methods for the preparation of a concrete mixture, it is possible to significantly change the properties of hardened concrete.
The Swiss craftsman was also the author of an ignited defense of the advantages of reinforced concrete: "We are in possession of an orthogonal means that has never had any age, is a means that will allow us to use geometry as a metropolitan environment of architecture", However, the main problem was related to the appropriateness between the constructive system and its formal system, a subject that has troubled many creators. Some argued for an architecture liberated at right angles, while others chose to identify with the idea that a way of working could only come from calculation.
The density of concrete can vary from 300 to 4500 kg / m3, compressive strength - from 1.5 to 80 MPa. This means that both load-bearing and enclosing heat-insulating structures can be made from concrete. Sand, gravel and crushed stone used in the preparation of concrete must be clean, without impurities, which can significantly reduce the strength of concrete. Cement is used of the grade that allows you to get concrete of the desired strength. The concrete mass is prepared in concrete mixers. It can be of different consistency (density). A rigid concrete mix requires a strong compaction when laying, and a plastic one needs less compaction. Cast moving mass almost by gravity fills the mold. The consistency of the concrete mixture depends on the amount of water, with an excess of which it delaminates, and the strength of the concrete decreases. Serve the concrete mixture to the place of laying in a bucket or a concrete paver. The descent of the concrete mixture from a height, in order to avoid delamination, is carried out in compliance with the following rules: The height of the free dropping of the concrete mixture into reinforced structures should not exceed 2 m; The descent of the concrete mixture from a height of more than 2 m should be carried out along vibrating chutes, which ensure the slow sliding of the mixture without delamination. The solidity of the concrete structure of the foundation is ensured by continuous concreting. If this cannot be done, work seams are arranged, by which they mean the plane of the junction between the hardened old and freshly laid concrete. Working seams can be horizontal and vertical, but they are never made oblique. It is possible to resume interrupted concreting if the concrete mixture has acquired a strength of at least 1 MPa, and also if the previously laid concrete mixture liquefies during vibration, that is, the process of its crystallization is still in its initial stage. Before starting concrete laying, the surface of the working joint is washed, and the cement film is cleaned with a steel brush. Freshly laid concrete should be covered with matting, burlap or other dense fabric, which is kept moist, periodically moistened with water. Formwork can be removed no earlier than 10 days after the completion of concreting. Load monolithic foundations with overlap and brickwork only after the concrete has completely set. A monolithic foundation, made according to this technology, ensures uniform shrinkage of the house without cracks and distortions.
He would try to cover large spaces at least possible material, looking for elegance in the balance between the control of forces and the image they receive. But the more you tried to correct the limit, the more you discovered the plastic potential of concrete, which made it dependent on the creator who worked it, almost as if it were an artist-shaped material.
As a starting point, the ideas put forward by van Aken, his compatriot Dominicus Behm, built a series of churches that used this ability of the material to create surfaces that are both a frame and a wall that surrounds the space, concentrating energy in the structure of the shell, the Church arouses interest to the broken shape of the walls of the presbytery, built by pouring concrete on a thin metal grid. Less dramatic was Bischofsheim's episcopal chapel, novel in its design and speed of execution, limited to four months.
1. Process Technology monolithic concrete and reinforced concrete
Concrete is widely used in the construction of most industrial, civil and agricultural buildings, as well as in other industries. The versatility and efficiency of reinforced concrete increases with the improvement of structural calculations and technological methods, the development of methods for high-strength and lightweight concrete, concrete with various additives, and the development of the theory of concrete structure formation. The expansion of the scope of concrete and reinforced concrete is facilitated by the further mechanization and automation of processes and works deployed on the basis of advanced technology, which ensures the production of a large number prefabricated structures. The factories produce not only ready-made prefabricated reinforced concrete structures, but also formwork sets, reinforcing cages and meshes, ready-mix concrete, dry mixes for concretes and mortars, various additives to concrete mixtures and mortars that allow controlling physical, mechanical and technological properties. Concrete work is carried out on the basis of a carefully developed project for the production of work, which indicates the physical and chemical processes occurring in the concrete mixture and in concrete, with the technological processes of concrete work, the features of the structures of the building or structure being erected, and also taking into account local conditions. General provisions for the construction of buildings using monolithic reinforced concrete.
The plant, long and narrow, was covered by a parabolic vault that started its journey from the same floor while holes were cut into it, resulting in an unreal space. You can see a certain tendency to offer rough, brutal material with surfaces that show primitive texture and make creases and volumes perfect readability. Paramenos illustrates the direct traces of the work's development operations, with its traces of formwork and the roughness of its skin.
Until the explosion of brutality in the 60s, the buildings that embraced the expressionist style looked like great sculptures, as if a giant hand was shaping the figure. But in the beginning, thick, opaque and sticky screens did not present an attractive feature, as they were associated with the thousand-year tradition of stone walls and the romantic sense of decoration between interior and appearance from which the concrete wanted to break free. Thus, constructions that conveyed the inertia of matter in sculptural forms were criticized with essays expressing a preference for the collapse of the "box", in parallel with plastic tendencies indicating the destruction of the usual hierarchies of volume.
At present, the construction of monolithic reinforced concrete using industrial methods of erecting buildings has become one of the directions for the further industrialization of housing and civil construction, complementing the prefabricated large-panel housing construction. This is due to the fact that today the construction of monolithic reinforced concrete is carried out by the industrial method. Using inventory, repeatedly wrapped formwork, reinforcing cages and factory-made meshes, you can get a high production effect. Mechanized supply, laying and compaction of the concrete mix make it possible to increase the level of mechanization of concreting structures up to 80-85%. The use of electrothermal treatment of concrete and various chemical antifreeze additives makes it possible to erect buildings and structures at any time of the year at any temperature. This trend in the development of monolithic reinforced concrete is also due to the following advantages: the possibility of construction in areas remote from the construction industry; less capital investment in creating a production base or expanding its capacity, in contrast to prefabricated housing construction; increased seismic resistance and crack resistance during construction in areas of mine workings and on subsiding soils. Monolithic housing construction has significant advantages in rural areas with mass building of individual houses, where the construction process is less dependent on the availability of a production base, and low-rise buildings open up wide opportunities for using local building materials, ash, slag and other industrial wastes, large-porous expanded clay concrete, etc. Currently under construction multi-storey buildings three main technological methods were determined, which are distinguished mainly by the structural and technological features of the formwork systems used: the construction of buildings in sliding formwork, in large-panel and block-panel formwork, and in volume-adjustable (tunnel) formwork. In low-rise construction from monolithic concrete, small-panel and large-panel formwork is used.
The complex technological process of building buildings and structures from monolithic concrete and reinforced concrete can be represented in the form of procurement and construction processes. The first of them is carried out at factories, outside the construction site, and the second, the construction process, is carried out directly at the facilities in a certain technological sequence, forming a complete production cycle, resulting in a monolithic concrete or reinforced concrete structure or structure. The complex process of production of monolithic concrete and reinforced concrete works consists in the mutually coordinated execution of all work processes according to the flow-speed method and includes transportation and installation of the formwork with its subsequent disassembly; transportation and installation of fittings; transportation, laying and compaction of the concrete mix; maintenance of concrete during its construction; quality control of the concrete mixture during its laying and compaction, as well as during its hardening. The leading process is the laying of the concrete mix, to which all other processes must be subordinated.
3. Formwork
Formwork is called forms, in which the design dimensions and outlines of the structures concreted in them are provided. The formwork consists of load-bearing, supporting and shaping elements made of various materials and different designs. Formwork, as a rule, is assembled from elements made at specialized factories or workshops. Formwork structures must be stable, immutable, rigid and durable, ensure the correct shape, the quality of the concrete surface, quickly assemble and disassemble, and not create difficulties when installing reinforcement, laying and compacting the concrete mixture. The formwork must be delivered to the construction site in the form of finished elements and reinforcement-formwork blocks. The formwork is calculated taking into account the main loads acting on it: the mass of the concrete mixture and reinforcement, its own weight and scaffolding, the mass of people working on the formwork and decking, mechanisms, wind effects, vibration, and lateral pressure of the concrete mixture. The formwork is classified according to its functional purpose, depending on the type of concreted structures and the accepted technology for the production of works. In this project, we use prefabricated formwork. This type of formwork is most widely used in construction and is used for the construction of a wide variety of monolithic structures with variable, small or repetitive sizes. After the concrete reaches a strength that allows stripping, the formwork elements are dismantled and rearranged to a new location.
4. Reinforcing work
Advantage monolithic construction largely determines the rational reinforcement of structures. For cast-in-situ reinforced concrete structures, the type of reinforcement is selected taking into account the features of the operation of these structures, their configuration and dimensions, technology and organization of work. When assigning reinforcement methods, the manufacturability of the reinforced aggregate device is taken into account, which determines labor costs, the amount of mechanized labor, and the intensity of work. The complexity of manufacturing and the cost-effectiveness of reinforced concrete structures largely depend on decisions taken for the reinforcement of structures. In the general cycle of work, the reinforcement of structures is 17-30% of the cost and 15-25% of the labor intensity. Steel, fibers from plastics, glass, basalt and organic materials are used as reinforcement. Reinforcing work consists of two main processes - the preparation of reinforcing products and their installation in the formwork of the concreted structure.
Reinforcing products, as a rule, are manufactured centrally at reinforcing and welding plants or workshops of construction industry enterprises, where manufacturing processes are mechanized as much as possible. Reinforcement manufacturing operations consist of acceptance and transportation of reinforcing steel, straightening, cleaning and cutting, bending of rods, welding of meshes and frames, their bending, assembly of spatial frames and transportation of finished products to a warehouse.
5. Laying and compacting the concrete mixture
Concreting of structures is one of the most critical processes in the construction of monolithic concrete and reinforced concrete structures and structures. The working operations included in the technological process of concreting can be divided into two groups: preparatory main and auxiliary. Preparatory operations include operations related to the preparation of the object, concreting blocks, mechanisms and tools. The main operations include the reception, distribution and compaction of the concrete mixture. These operations are carried out in a continuous technological sequence, and their implementation is carried out under the constant supervision of technical personnel. At the same time, a log of concrete work is kept, which indicates: the date of the start and end of concreting; name of the structure to be concreted; specified grades of concrete; working compositions of the concrete mixture, its temperature at the outlet of the concrete mixer and during laying; formwork type; mixture compaction method; date of stripping structures. Auxiliary operations associated with concreting is the installation, fixing and movement of transport devices and fixtures: vibratory feeders, vibration chutes, trunks, concrete pumps. Vibration is the main method of concrete mixture compaction, which is characterized by two parameters: frequency and amplitude of oscillations. According to the method of transmitting vibrations of the concrete mixture, vibrators are divided into internal (deep), immersed by the working body in the concrete mixture layer, surface, installed on the concrete mixture layer (on a vibrating beam or concrete platform) and external, fixed on the formwork.
6. Selection of mounting cranes
monolithic reinforced concrete formwork reinforcing
In the complex process of installation of building structures, machines play an important role, which are practically used to perform all the work that makes up the installation process. Depending on the work performed, the machines are divided into assembly machines used to perform the main operations of mounting, lifting and installing structures in the design position, and auxiliary machines and mechanisms used in preparatory and auxiliary work, unloading, pre-assembly, sealing joints, etc. . Mounting cranes are subject to increased operational requirements. They must have several operating speeds for lifting and lowering the load or smooth regulation of these speeds from a certain limit to a complete stop. These cranes must be adapted for quick change of booms, changing the length of booms by installing standard inserts, mounting jibs and picks. Mounting cranes are divided into the following groups: stationary, self-propelled jib, tower, gantry and special. Tower cranes move along specially equipped rail tracks and are widely used in the installation of structures of various buildings and structures. According to the constructive solution, tower cranes come with a fixed tower and a swivel head; with a turret and a counterweight located at the bottom, on the platform; with a rotary tower and a counterweight located at the top, with an arrow having a cargo trolley. Because the processes developed in the course project are associated with the work of the zero cycle, then for the selected erection crane only the required lifting capacity and the required crane outreach are determined.
Determination of the required lifting capacity of the crane
Q To ? Q uh +Q pr+Q gr (1)
where, Q To - lifting capacity of the crane, t; Q uh - mass of the heaviest mounted element, t; Q etc - mass of mounting devices, t; Q gr - mass of load-handling devices, t.
Qk = 10+0.1+0=10.1 t
Determination of the required reach of the crane boom
Lcr = +v+s (2)
where, a is the width of the crane runways, m; c - distance from the slope of the head of the undercarriage rails to the nearest protruding part of the building, m; c is the distance from the center of gravity of the mounted element furthest from the crane to the protruding part from the side of the building, m.
L cr= +2.7+9= 14.05m
Determining the hook height
H To = h O +h h +h e+h st (3)
where, h O - excess of the mounting horizon above the level of the tower crane, m; h h - height margin to ensure safe installation. (at least 1m), m; h uh - element height or thickness, m; h st - slinging height (from the top of the element to the crane hook, m), m.
Hk = 16.5+1+0.5+3=21m
According to the required parameters, we select the tower mobile crane BK-300.
Technical specifications crane:
) lifting capacity of the crane - 8-25t;
2) boom outreach - 30m;
3) hook lifting height - 50m.
Determining the volume of concrete work Labor costs for the installation of formwork and reinforcement and for the preparation of the concrete mixture are determined according to the calculated volume of work according to the ENiR standards. Next, the following parameters of the construction flow will be calculated: the total construction period T, the number of grips in each tier m + n
Steel consumption per 1 concrete in kg: For columns - 161 kg For crossbars - 155 kg For slabs - 21 kg We determine the complexity of all processes by tiers, this we find the volume of structures and formwork.
Formwork area for all columns
(0,4*4)*2,8*12*5=268,8
Concrete volume for all columns
4*2,8*0,4*12*5=26,8
Weight of reinforcement for all columns
*26.8=4314.8 kg. = 4.3 t
Formwork area for all crossbars
(0,5*2+0,4)*4,6*8*5+(0,5*2+1,4)*5,6*9*5= 862.4
Concrete volume for all crossbars
5*0,4*4,6*8+0,5*0,4*5,6*9= 17.44
Weight for all crossbars
*17.44= 2703.2 kg. = 2.7 t
Floor slab formwork area
Floor slab concrete volume
6*5,6*0,2*6*5= 154.56
Floor slab reinforcement weight
*154.56= 3245.76 kg. = 3.24 t
TOTAL: Formwork: 268.8 + 862.4 + 138 = 1269.2 Volume of concrete: 26.8+17.44+154.56= 198.8 Reinforcement weight: 4.3+2.7+3.24= 10.24 t Scaffolding installation: (10.0+18.0) *2*16.5= 924 924/4=231 pcs. 231*3.6= 831.6 m.
8. Bill of quantities for the construction of monolithic reinforced concrete structures
Table 1
№DescriptionUnit. Change Quantity Note1 Formwork works A) installation of formwork from prefabricated boards B) installation of scaffolding m 1269.2 831.62
Bibliography
Construction technology of buildings and structures: O.M. Terentiev
Technology and organization of building production: M.S. Danilkin, I.A. Martynenko, I.A. Karpalova
Technology and organization of construction: G.K. Sokolov
SNiP 3.02.01-87. Rules for the production and acceptance of work.
ENiR. Collection 4. Issue. 1. Buildings and industrial facilities. - M.: Stroyizdat, 1987.
ENiR. Collection 11. Insulation work. - M.: Stroyizdat, 1988.
Technology and organization of building production: S.K. Khamzin, A.K. Karasev.
Technology and organization of building production: S.K. Khamzin, A.K. Karasev
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