Types of reinforced concrete columns. Classification of columns of one-story industrial buildings, calculation methods. Species and types
Reinforced concrete columns are one of the most popular types of reinforced concrete products. They are vertically located building structures and are used as load-bearing frame elements: beams, crossbars, purlins, etc.
Such products are designed for a constantly high compressive load; they are also capable of bending, withstanding high wind loads. Our company produces reinforced concrete columns any size in compliance with high quality standards.
Features and Key Specifications
In production they use either standard sizes, if the building is being erected according to standard project, or custom sizes in accordance with the drawings. Most often, these structural elements are manufactured to implement a specific individual project, in this case they correspond to all the personal wishes of the customer and the provided working documentation.
Price reinforced concrete column determined by several key factors:
- The class of concrete used in terms of strength, frost resistance and water resistance. To reinforced concrete columns industrial buildings There are special requirements for strength; accordingly, they will cost more.
- Reinforced concrete column size. The length can be from 5.7 to 17 meters, as a rule, the height is equal to the height of two floors of the building.
- Type of reinforcement cage, presence of embedded parts. Products for industrial buildings are equipped with high-strength reinforcement to increase resistance to compressive and bending loads. For them, prestressed or unstressed reinforcement is used.
- Availability of standard metal equipment. Also, the final cost depends on the time allotted for the production of reinforced concrete products.
The key characteristic of reinforced concrete columns is load-bearing capacity. The lower it is located in the building structure, the higher its load-bearing characteristics should be; the highest requirements are placed on products installed in the technical underground and on the lower floors of the structure.
Types and materials for manufacturing
Reinforced concrete columns of one-story industrial and residential buildings are made from heavy grades of concrete M300-M600. Steel reinforcement provides the product with durability and high resistance to all destructive influences. The cross-section can be round, square or rectangular, it depends on the loads and the features of the structure.
For multi-storey residential buildings products with cantilever projections are used, used as a support for floor beams and become one of the main elements of the frame, since they have to withstand the main load.
Columns of the outermost and middle rows are also distinguished depending on their location in frame system building. Their connection with other frame elements is carried out by welding embedded elements, followed by concreting the joints. For the installation of reinforced concrete columns of industrial buildings, special column foundations glass or monolithic type.
Our company offers to place an order for any number of reinforced concrete columns,
In modern industrial construction, prefabricated reinforced concrete frames are mainly used, the structural elements of which are standardized.
Foundations
Foundations are placed under individual supports (columns of frame buildings, pillars), as well as under the walls of light buildings without basements. This is the cheapest and least labor-intensive type of foundation - it is 1.5-4 times cheaper than strip foundations.
Under the columns of one-story industrial buildings, mainly monolithic foundations are used, consisting of a kneecap and a one-, two-, or three-stage slab part (Fig. 9.18).
The height of the foundations is assumed to be 1.5 m and within the range of 1.8-4.2 m with an interval of 0.6 m. The dimensions of the ledges in plan and height are 0.3 or 0.45 m. All dimensions in plan are unified and are multiples of the module 0.3 m. The dimensions of a specific foundation are selected depending on the load transmitted by the column (columns), soil characteristics and solutions for the part of the building below the zero level.
The foundation for paired columns in places of expansion joints and junctions of spans is arranged in common (Fig. 9.20), except in cases where a settlement joint is required.
The edge of the foundations is most often located under reinforced concrete columns at minus 0.150, and under steel columns - minus 0.300 and below.
To install reinforced concrete columns in the body of the foundation sub-column, a recess is provided - a glass. The gap between the edges of the column and the wall of the glass is assumed to be 75 mm at the top, and 50 mm at the bottom (Fig. 9.18 d). For steel columns, anchor bolts are placed in the subcolumn to secure the columns to the foundation.
Rice. 9.18. Monolithic columnar foundations for prefabricated reinforced concrete columns of industrial buildings: a - single-stage; b - two-stage; c - three-stage; g - column support; d - top view
Prefabricated columnar foundations, depending on the size, can be solid from one block, from a block and slab, or from several different blocks and slabs (Fig. 9.26). Solid foundations are relatively small in size and weight. The use of ribbed and hollow elements makes it possible to reduce the material consumption of prefabricated columnar foundations.
Slabs (blocks) are laid on a preparation with a thickness of about 100 mm - crushed stone or sand for dry soils and concrete for wet soils. The elements are laid on top of each other using mortar and connected by welding embedded parts, outlets, anchors, etc.
Rice. 9.26. Prefabricated columnar foundations for columns: a-c - single-block pillars; g - column support on the slab; d - three-slab; e - column support on slabs in two rows; g - column support on perforated plates in two rows; h - column support on two ribbed slabs; and - ribbed column support on three slabs; k - high (hemp type) column support on a block and three slabs; l - pillar with recess into two slabs; m - ribbed; n - hollow column support on the slab; o - made of three hollow elements with a high column
To support external and internal self-supporting walls, foundation beams are used (Fig. 9.19), which transfer the load from the weight of the walls to the foundations. When supporting foundation beams on foundation ledges, it is recommended to install tides (concrete columns), the width of which is taken to be no less than the maximum width of the beam, and the top at minus 0.360 or 0.660 - respectively, for beam heights of 300 and 600 mm.
When heaving soils freeze, deformations may occur in foundation beams. To avoid this and to protect the floor from freezing, slag is poured along the walls from the sides and bottom of the beams (Fig. 9.20 c).
Rice. 9.20. Location of foundation beams:
a - side view; b - plan; c - section; 1 - foundation beam; 2 - tide or concrete column; 3 - row column; 4 - column at the expansion joint; 5 - column of the adjacent span; 6 - wall; 7 - filling with slag; 8 - blind area
Rice. 9.19. Foundation beams: a - sections of beams for buildings with a column spacing of 6 m; b - the same, 12 m; c - supporting beams on the foundation
Frame columns. The design of prefabricated reinforced concrete columns depends on the space-planning solution of the industrial building and the presence in it of one or another type of lifting and transport equipment with a certain load-carrying capacity. In this regard, prefabricated reinforced concrete columns are divided into two groups. Columns belonging to the first group are intended for buildings without overhead cranes, in craneless workshops and in workshops equipped with overhead lifting and transport equipment. Columns belonging to the second group are used in workshops equipped with overhead cranes.
According to the design solution, the columns are divided into single-branch and double-branch, according to location in the building - at the extreme, middle and located at the end walls.
Typical columns are designed for loads: from the coating and overhead lifting and transport equipment in the form of monorails or overhead cranes with a lifting capacity of up to 5 tons, and from the coating and overhead cranes with a lifting capacity of up to 50 tons. Solutions for prefabricated reinforced concrete two-leg columns for cranes with a lifting capacity of 75/20, 100/ have been developed. 20 and 125/20 t for spans of 24, 30 and 36 m with column spacing of 6 and 12 m. The height gradation of columns is set to a multiple of 600 mm module.
For buildings without overhead cranes, with a height from the floor to the bottom of the load-bearing structures of the coating up to 9.6 m, columns with sections of 400x400, 500x500 and 600x500 mm are used (Fig. 24.1, a). The middle columns with a cross-section of 400x400 mm in the place of support of the load-bearing structures have coverings on two side faces of the console. The choice of column section depends on the size of the span and their number, the pitch of the columns, the presence of rafter structures, suspended transport and the design of the coating.
Rice. 24.1. Prefabricated reinforced concrete columns: a – single-branch for craneless buildings; b – single-branch for crane buildings; c – two-branch for crane buildings; d – location of embedded steel parts in the column: 1 – steel sheet with anchors for fastening prefabricated reinforced concrete beams or farms; 2 – the same, for fastening crane beams; 3 – steel sheet for fastening crane beams to the columns on top, 4 – embedded parts for fastening vertical connections; 5 – embedded part for fastening wall panels. 6 – hole for slinging; 7 – support table
In cases where a craneless building must be greater than 9.6 m in height, columns for overhead crane buildings can be used. This solution allows you to expand the scope of application of standard columns without increasing the number of their standard sizes. For buildings equipped with overhead cranes with a lifting capacity of up to 20 tons, single-branch columns of rectangular cross-section are used (Fig. 24.1, b).
A column for a building equipped with overhead cranes consists of an over-crane and under-crane part. The over-crane part serves to support the supporting structure of the covering and is called the over-column. The crane part receives loads from the above-column, as well as from the crane beams, which are supported on the consoles of the columns, and transfers them to the foundation. The outer columns have a one-sided console, the middle ones have double-sided consoles.
The sections of the outer and middle columns at a step of 6 m are 400x600 and 400x800 mm, and at a step of 12 m – 500x800 mm. For cranes with a lifting capacity of up to 30 tons and a building height of more than 10.8 m, two-branch columns are used, which are more economical in material consumption than single-branch columns. They are stepped And stepped-cantilever(Fig. 24.1, c): the first are intended for the outer rows, the second for the middle ones.
The height of typical two-branch columns is 10.8-18 m. Columns with a height of 16.2 and 18 m are used in cases where it is appropriate for operational conditions and justified by economic considerations. The gaps between the branches are used to pass sanitary and technological communications. In some cases, reinforced concrete columns can be used for cranes with a lifting capacity of over 50 tons. In such two-branch columns, passages are arranged for workers, which are located at the level crane tracks.
The depth of the columns below the zero level depends on the type and height of the columns, the lifting capacity of the crane equipment and the presence of rooms or pits located below the floor level. The depth of columns in buildings with and without overhead transport is 0.9 m; rectangular columns used in buildings with overhead cranes - 1 m; two-branch columns with a height of 10.8 m - 1.05 m and the same columns with a height of 12.6-18 m - 1.35 m; two-branch columns for cranes with a lifting capacity of more than 50 tons - 1.6 m, and in the presence of technical undergrounds, channels or basements - 3.6-5.6 m. Such dimensions are due to the unification of the dimensions of prefabricated reinforced concrete structures. The columns are connected to the frame elements with bolts and welding of welded embedded parts (Fig. 24.1, d).
On the side surfaces of single-branch and double-branch columns in places where they are embedded in the foundation to absorb shear forces, dowels are provided in the form of triangular grooves 25 mm deep with a pitch of 200 mm.
Brands of columns for a certain type of building are selected from a catalog of prefabricated reinforced concrete products, depending on the lifting capacity of cranes, their operating mode, column spacing, span and height of the building, load from the coating and wind pressure.
Modern progressive structural solutions for columns include cylindrical columns made of centrifuged reinforced concrete, which are currently used on an experimental basis both for buildings without support cranes and with support cranes with a lifting capacity of up to 30 tons and in industrial buildings for various purposes. This solution makes it possible to reduce the consumption of concrete by 30-50% and steel by 20-30% (Fig. 24.2).
Rice. 24.2. Types of Cylindrical Columns
Foundations for columns. The volume of concrete going into the foundations for columns in an industrial building is 20-35% of the total volume of concrete consumed, and the cost of their construction is 5-20% of the total cost of the building. This suggests that right choice foundation design is essential and significantly affects the cost of the entire building.
The foundations are made monolithic and prefabricated. Precast concrete foundations can be made of a single block, a block and slab, or multiple blocks and slabs. Blocks and slabs are laid on a preparation 100 mm thick - crushed stone for dry soils and concrete (grade 50) for wet soils.
One foundation block can support from one to four columns (in places where expansion joints are installed). The area of the base and other dimensions of the foundation are determined by calculation depending on the load transferred to it and bearing capacity grounds.
Foundations in the form of individual blocks (Fig. 24.3) have a square or rectangular outline in plan. They are used for prefabricated reinforced concrete columns with a section of 400x400 and 500x500 mm. Single-block foundations weighing up to 12 tons are manufactured at factories of prefabricated reinforced concrete structures, and those weighing up to 22 tons are manufactured at landfills or they are made monolithic directly at the construction site. Single-block foundations - shoes are arranged in steps with the dimensions of the cups corresponding to the dimensions of the cross sections of the columns.
Rice. 24.3. Prefabricated foundations for columns: a – from one block; b – from block and slab: 1 – foundation slab; 2 – glass, 3 – lifting loops; 4 – risks; 5 – welds; 6 – leveling layer of solution; 7 – embedded parts and anchors; 8 – gas tubes
When large loads are transferred to the foundations, which causes their significant dimensions, and the mass of the block exceeds the lifting capacity of the cranes, and the use of a monolithic structure is not economically feasible, the need arises to use prefabricated foundations. Prefabricated foundations can be made of two elements - a block and a slab (Fig. 24.3, b) or several blocks and slabs (Fig. 24.4, a). The latter are used if the mass of blocks in a two-block foundation turns out to be greater than the carrying capacity of available transport and installation equipment. Prefabricated foundation elements are laid on mortar and fastened together by welding embedded steel parts.
Rice. 24.4. Prefabricated reinforced concrete foundations and supporting frame columns on them: a – from several blocks and slabs; b – the same, from blocks with voids; c – rigid embedding of the column into the glass: 1 – column; 2– shoe with glass (column support); 3 – intermediate block; 4 – slabs; 5 – base panel; 6 – column; 7 – foundation beam; 8 – assembly concrete: 9 – cement mortar; 10 – connection of embedded steel parts by welding
Precast foundations use large amounts of concrete and steel. To eliminate this drawback, the elements of a multi-block foundation can be made with vertical voids, obtaining a foundation as if in the form beam cage(Fig. 24.4 b). The blocks and slabs that form the foundation are packages of reinforced concrete elements connected by structural diaphragms.
The number, size and location of voids in the plan are chosen so that when foundation elements are laid on top of each other, wells are formed that pass through the entire foundation. Vertical voids can be of various shapes: round, square, rectangular, oval. If an eccentric load is transferred to the foundation, part of the vertical wells within the contour of the column can be reinforced and cemented.
The mark of the top edge of the foundation, regardless of ground conditions, should be 150 mm below the mark of the finished floor (Fig. 24.4, a). This solution makes it possible to install structures on the ground part of the building after the pits have been backfilled, preparation for the floors has been arranged and all communications have been laid, which is especially important in conditions of subsiding macroporous soils, when the ingress of water into the pits must be completely excluded.
To lay foundations to the depth required by geological conditions, one of the following methods is used, depending on economic feasibility: an additional cushion is arranged under the base of the foundation, the upper stage of the foundation is increased, the columns are installed at the same height (at the lowest foundation elevation), and in places where foundation elevations change foundations, inserts are used - pillars.
The connection of frame columns with foundations is usually carried out in the form of a rigid connection. With this connection, the columns are installed in glasses specially arranged in the foundations (Fig. 24.4, c). In this case, the gaps in the glasses between the columns and shoes are filled with concrete.
Foundation beams. The external and internal self-supporting walls of the building are installed on foundation beams, through which the load is transferred to the foundations of the frame columns. Foundation beams are laid on specially prepared concrete columns, installed on the edges of the foundations (Fig. 24.5, a).
Rice. 24.5. Supporting the foundation beams on the foundations: a – under the longitudinal wall; b – under the end wall: 1 – foundation beam; 2 – concrete column; 3 – column; 4 – self-supporting longitudinal wall; 5 – end wall; 6 – half-timbered column; 7 – foundation for the main column; 8 – foundation for a half-timbered column; 9 – slag filling; 10 – fatty clay; 11 – sand bedding; 12 – blind area; 13 – waterproofing
The main foundation beams are made with a height of 450 mm (for a column spacing of 6 m) and 600 mm (for a column spacing of 12 m) and a width of 260, 300, 400 and 520 mm. These dimensions correspond to the most common thickness of external walls in industrial buildings. In Fig. 24.5, b shows the location of the foundation beams for the end wall. The cross-section of foundation beams can be T-shaped, trapezoidal and rectangular. T-section beams are most widely used as they are more economical in terms of consumption of steel and concrete.
When freezing under the influence of heaving soils increasing in volume, deformations may occur in the foundation beams. To avoid this and to protect the floor from freezing along the walls, the beam is covered with slag from the sides and bottom. The upper edge of the foundation beam is placed 30-50 mm below the floor level of the room, which in turn is placed approximately 150 mm above the level of the ground surface planned around the building.
Waterproofing made of cement-sand mortar or two layers of rolled material on mastic is laid on top of the foundation beams. A blind area or sidewalk is installed on the surface of the ground along the foundation beams. Once the precast foundation beams are in place, the gaps between them and the columns are filled with concrete.
Strapping beams serve to support external walls in places where the heights of buildings differ, and when these beams are located above window openings, they act as lintels. The strapping beams are made as split beams. Their sizes and shape cross section taken depending on the thickness of the walls installed on them and the magnitude of the transmitted load.
Strapping beams are used when the walls of a building are made of brick or small blocks. The dimensions of the strapping beams are unified; for brick walls the width is 250 and 380 mm with a “spout”; for walls made of small blocks 190 mm thick, the strapping beams are 200 mm wide. The strapping beams are made 600 mm high and 6 m long (Fig. 24.6) and attached to the frame columns using mounting parts welded to the embedded parts in the beams and columns. In typical reinforced concrete columns, for these purposes, embedded parts are used, provided for fastening wall panels.
Rice. 24.6. Fastening the strapping beams to the reinforced concrete column: 1 – steel support console; 2 – embedded parts in the column; 3 – embedded part in the strapping beam; 4 – concrete on fine gravel
Reinforced concrete crane beams serve as supports for rails on which overhead cranes move. In addition, they provide longitudinal spatial rigidity of the building frame.
Reinforced concrete crane beams have limited use and can be split or continuous. The former are more widespread than the latter, as they are easier to install. When constructing continuous beams, the consumption of reinforcement is less, but the complexity of their manufacture is higher.
Depending on the position of the beams along the crane runway, middle and outer beams are distinguished, located at the transverse expansion joints and at the ends of the buildings. The latter have the same dimensions as the middle ones, however, the embedded parts in them, intended for fastening to columns, are located at a distance of 500 mm from the end of the beams.
Reinforced concrete crane beams can be of T-trapezoidal or I-section (Fig. 24.7), they are used for light and medium-duty cranes with column spacing of 6 and 12 m and a lifting capacity of overhead cranes up to 30 tons.
Rice. 24.7. Reinforced concrete crane beams: a – T-beams for cranes with a lifting capacity of 10–30 tons with a column spacing of 6 m; b – I-beam pop cranes with a lifting capacity of 10–30 tons with a column spacing of 12 m; 1 – holes for fastening trolley wires, 2 – holes for fastening crane tracks
After installation and alignment of the crane beams, they are fastened (Fig. 24.8) to the columns: at the bottom - with bolts and welding, at the top - by welding a vertically placed sheet to the embedded parts in the column and beam. When manufacturing reinforced concrete crane beams, gas tubes are placed in their body, which are necessary for passing the bolts for fastening the crane track and hangers for trolley wires.
Rice. 24.8. Fastening crane beams to frame columns: 1 – column; 2 – crane beam; 3 – embedded steel part of the column; 4 – supporting steel sheet of the column console; 5 – steel gasket with holes for bolts; 6 – lower embedded steel part of the crane beam; 7 – anchor bolts; 8 – upper embedded steel part of the crane beam; 9 – fastening vertically placed steel sheet; 10 – welding
The crane runway is installed in a certain sequence. A thin elastic lining made of rubberized fabric 8–10 mm thick with a double-sided rubber lining is placed on the top of the crane beam. Before laying it, the surfaces of the crane beam, rail and elastic lining are thoroughly cleaned of dirt and grease. The crane rail is installed and straightened on the elastic lining and then secured with clamping feet.
For cranes with a lifting capacity of 10-30 tons, special profile rails R-43, KR-70 and KR-89 are used. For cranes with a lifting capacity of 5-10 tons, wide gauge railway rails R-38 are also used. Within the temperature block, the rails are welded into one strand.
In highland buildings, stops for overhead cranes are installed on crane beams.
Load-bearing structures of coatings industrial buildings are divided into rafters, sub-rafters and load-bearing elements of the enclosing part of the covering.
In industrial buildings, the following types of truss load-bearing structures are usually used: flat - beams, trusses, arches and frames; spatial – shells, folds, domes, vaults and hanging systems.
Rafter structures are made in the form beams And farms, A bearing structures enclosing part of the coating - in the form large slabs. According to the unified dimensions of the space-planning elements of industrial buildings, the size of the transverse spans and longitudinal pitch of load-bearing structures is assigned as a multiple of the enlarged module of 6 m; in some cases, the use of a module of 3 m is allowed.
Reinforced concrete beams used for the installation of coverings in industrial buildings with spans of 6, 9, 12 and 18 m. The need for beam coverings with spans of 6, 9 and 12 m (spans of this size can also be covered with slabs) arises in the case of suspension of monorails or cranes to load-bearing structures.
Reinforced concrete beams can be single-pitched, double-pitched and with parallel chords (Fig. 24.9). Single-pitch beams are used in buildings with a column spacing of 6 m and external water drainage. Gable beams are installed both in buildings with external and internal water drainage. Beams with spans of 6, 9 and 12 m are installed only in increments of 6 m, and beams with a span of 18 m are installed in increments of 6 and 12 m. If there is overhead transport, regardless of the span, beams are installed in increments of 6 m.
Rice. 24.9. Reinforced concrete beams: a – single-pitched; b – gable; c – with parallel belts
In order to reduce the mass of beams and to allow communications through, holes of various shapes can be installed in their walls. Single-pitch beams are supported by standard reinforced concrete columns of different heights, which are a multiple of a module of 600 mm. In this regard, the slope of single-pitch beams with a span of 6 m will be 1:10, with a span of 9 m – 1:15, and with a span of 12 m – 1:20. The slope of the upper chord of the gable beams is 1:12.
The covering beams are connected to the columns with anchor bolts released from the columns and passing through the support sheet welded to the beam (Fig. 24.10, a, b). In longitudinal expansion joints, one of the beams is installed on a roller support; the beam located nearby is installed on a steel table located above the column (Fig. 24. 10, c).
Rice. 24.10. Installation of reinforced concrete beams: a – on the outer columns; b – on the middle columns, c – in the expansion joint for one column: 1 – anchor bolt; 2 – supporting steel sheet of the beam; 3 – supporting steel sheet of the column; 4 – column; 5 – reinforced concrete beam; 6 – semi-fine; 7 – skating rink; 8 – temperature seam
Reinforced concrete trusses They are usually used to cover spans of 18, 24 and 30 m; they are installed in increments of 6 or 12 m. Trusses with a span of 18 m are lighter than reinforced concrete beams of the same span, but are more labor-intensive to manufacture.
The use of 18-meter trusses is advisable in the case when it is necessary to place communication pipelines and ventilation ducts within the coverage or use the inter-truss space for the device technical floors. For spans of 24 and 30 m, the use of trusses is more advantageous compared to beam structures, since the mass (weight) of long-span trusses is 30-40% less than the mass (weight) of beams.
In modern industrial construction practice, trusses with a segmental outline and with parallel chords are most widespread (Fig. 24.11), both of which are included in the range of standard prefabricated reinforced concrete structures of factory production. Reinforced concrete trusses can be solid or composite; the latter are assembled from two half-trusses (shipping grades), or from blocks, or from casting elements.
Rice. 24.11. Unified prefabricated reinforced concrete trusses: a – segmental; b – with parallel chords (truss elements shown in dotted lines are installed if there is a suspended ceiling)
Segmental trusses with spans of 18, 24, 30 m included in the range of prefabricated reinforced concrete structures are assembled from prefabricated linear elements of the upper and lower chords and lattice. Linear elements have a length equal to the truss panel, and for the lower chord they sometimes take a length equal to the span of the truss.
The connection of linear elements to each other is carried out by welding the ends of the reinforcement with the installation of grease linings and subsequent concreting with quick-hardening concrete. The reinforcement in the lower chord is subjected to pre-tensioning, after which the channels in the nodes are filled with cement mortar, and the trays of the lower chord are filled with concrete. Reinforced concrete trusses make it possible to equip building spans with suspended transport with a load capacity of up to 5 tons (with a truss pitch of 6 m). It is possible to install light and aeration lantern structures along the upper chord of segmental trusses.
For buildings where it is necessary to use the inter-truss space for auxiliary rooms or communications, non-braced trusses with racks every 3 m are used (Fig. 24.12). With a flat surface, the truss posts are allowed to pass beyond upper belt; they serve as supports for the covering slabs (Fig. 24. 12, b). Separate racks are installed on the truss supports, which are secured by welding steel plates to the embedded parts located in the trusses and racks.
Rice. 24.12. Prefabricated reinforced concrete trusses: a – non-braced for buildings with a pitched roof; b – unbraced for buildings with a flat surface; c – general view of the covering with rafter structures; d – arched of two half-trusses: 1 – additional rack; 2 – covering slab; 3 – roof truss; 4 – rafter truss
Non-braced trusses make it possible to reduce the number of types of trusses; in addition, they are less labor-intensive to manufacture compared to trusses with a braced lattice.
In Fig. 24.12, c shows an example of a coating solution using 24-meter segmental unbraced trusses resting on 18-meter reinforced concrete segmental unbraced rafter trusses. In some cases, composite trusses are used to span large spans. In Fig. 24.12, d shows a reinforced concrete truss with a span of 45 m, designed for constructing a covering over the main building of the state district power plant. The truss is designed as a composite of two half-trusses, three tie-down elements, a lower chord and two hangers.
The trusses are attached to the frame columns with anchor bolts released from the column, and to increase the rigidity of the connections, the truss support sheets are welded to the embedded parts of the columns.
Reinforced concrete arches It is advisable to use for large spans (40 m or more). Arches are divided into three-hinged with hinges on supports and in the middle of the span, double-hinged with hinges on supports and hingeless. The outline of the center axis of the arches should coincide as much as possible with the pressure line, so that the arches mainly work for compression. The supports of the arches can be building columns or special foundations. For large spans, arches, as a rule, rest directly on the foundations.
In three-hinged arches, the middle key hinge complicates the design of the arch itself and the design of the enclosing structures of the roof covering. For these reasons, reinforced concrete three-hinged arches practical application currently do not have.
The most common are double-hinged arches, which are the easiest to manufacture and install. When exposed to temperature, they have the ability to bend, turning freely in hinges without a significant increase in stress in the arch sections. In double-hinged arches, the thrust is absorbed by the tension and transferred to the supports.
Hinged arches have the lightest structural solution, but to support them they require the construction of powerful foundations, and they are also sensitive to uneven settlements of the foundation soil. Hinged arches, when supported directly on foundations, are usually performed without tightening.
In construction practice, arches made of prefabricated elements are mainly used. Monolithic arches have not become widespread due to the high labor intensity of their construction. Prefabricated elements, in turn, are assembled from blocks. The cross-section of the arch can be rectangular, T-shaped, box-shaped and other shapes.
An example of a double-hinged arch resting on pile foundations is shown in Fig. 24.13, a. An example of a hingeless arch with a span of about 60 m, a height (in the middle part) of 40 m, resting directly on the foundations, is shown in Fig. 24.13 b. In this example, the arch is designed open, with a lightweight spatial type covering suspended from it using steel rods.
Rice. 24.13. Reinforced concrete arches: a – double-hinged; b – hingeless, supported on foundations; c – hingeless, supported on columns: 1 – arch link; 2 – supporting side beam; 3 – suspension; 4 – tightening; 5 – covering slab; 6 – frame colony, 7 – suspended covering of spatial type
A reinforced concrete arch made of prestressed elements with a span of 96 m, supported by columns with a pitch of 12 m, is shown in Fig. 24.13, at. The length of individual prefabricated links with an I-beam cross section does not exceed 17 m with a mass of up to 25 tons. The links are connected to each other by welding embedded steel parts. The hangers supporting the reinforced concrete tie of the tray section are made of metal corners. The arch takes the load from suspended transport - four suspended cranes with a lifting capacity of 5 tons.
Reinforced concrete frames they are arranged as single-span and multi-span, monolithic and prefabricated (Fig. 24.14). Frames are a rod structure, the geometric immutability of which is ensured by rigid connections of frame elements at nodes. The outline of the crossbars in the frame can be straight, broken or curved. Rigid connection of frame elements at nodes makes it possible to increase the size of the overlapped span.
Rice. 24.14. Reinforced concrete frames: a, c – single-span monolithic; b – multi-span team
The design solution of a single-span, double-hinged frame made of prestressed reinforced concrete with racks of variable cross-section and a box-section crossbar is shown in Fig. 24.14, a, a single-span reinforced concrete frame with racks rigidly embedded in the foundations, and with consoles for supporting crane beams under an overhead crane - in Fig. 24.14, at. In these examples, the frame posts protrude from the plane of the walls into outside, which gives the buildings a unique architectural design.
A prefabricated multi-span frame, mounted from outer L-shaped racks, middle T-shaped racks and pitched liners - crossbars, is shown in Fig. 24.14, b. The joints in the frame are located in places where they bend. moments occur only with wind and asymmetrical loads from snow.
1 0 11 12 ..Reinforced concrete columns of industrial buildings
Columns in the frame system carry vertical and horizontal permanent and temporary loads. Designed for mass industrial construction standard designs prefabricated reinforced concrete columns for buildings with supporting overhead cranes and for craneless buildings.
Reinforced concrete columns for buildings with overhead cranes have consoles for supporting crane beams. For craneless buildings, columns without consoles are used.
Based on their location in the building system, columns are divided into extreme (located at the outer longitudinal walls), middle and end (located at the outer transverse (end) walls).
For craneless buildings with a height of 3 to 14.4 m, columns of constant cross-section have been developed (Fig. 7). The cross-sectional dimensions of the columns depend on the load and length of the columns, their pitch and location (in the outer or middle rows) and can be square (300x300, 400x400 mm) or rectangular (from 500x400 to 800x400 mm). They are buried into the foundations by 750 - 850 mm.
Rice. 7. Types of reinforced concrete columns for craneless buildings
For buildings with supporting overhead bridge cranes of light, medium and heavy operating modes and a lifting capacity of up to 300 kN, columns of variable cross-section with a height of 8.4 to 14.4 m have been developed (Fig. 8), and for buildings with cranes with a lifting capacity of up to 500 kN, two-branch columns with a height of 10.8 to 18 m have been developed. (Fig.9).
The dimensions of columns of variable cross-section in the crane part range from 400x600 to 400x900 mm, in the over-crane part - 400x280 and 400x600 mm. The two-branch columns have dimensions in the crane part of 500x1400 and 500x1900, and of individual branches - 500x200 and 500x300 mm.
Rice. 8. Types of solid reinforced concrete columns for buildings with
overhead support cranes
Rice. 9. Types of two-leg reinforced concrete columns for buildings
with overhead support cranes
In buildings with three or more cranes in a span, for the safety of personnel servicing the cranes and crane tracks, through passage galleries are provided along the crane tracks at the level of the top of the crane beams measuring 0.4x2.2 m (Fig. 10).
Rice. 10. Two-branch reinforced concrete columns
with passages at the level of the crane tracks
Reinforced concrete columns have steel embedded elements for fastening truss structures, crane beams, wall panels (in outer columns) and vertical connections(in tie columns). In places where rafter structures and crane beams are supported through steel sheets missing anchor bolts.
In buildings with rafter structures, the length of the columns is taken to be 600 mm less (see Fig. 8,9,10).
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Reinforced concrete columns are one of the types of reinforced concrete products, which are used for the construction of frames of buildings and premises for industrial and administrative, residential and domestic purposes. When manufacturing this type of reinforced concrete products, control is carried out at many stages and strictly adhere to the requirements specified in GOST.
Reinforced concrete columns are made of heavy, durable concrete and specially reinforced reinforcement. They are used to support elements during the construction of structures of various sizes and complexity. The main use of columns is the construction of frames for buildings along with purlins, crossbars and other elements.
Most often, the length of reinforced concrete columns is designed so that it is equal to the height of two floors of the building.
Columns can be manufactured in heights of 5.7 m - 17 m.
Reinforced concrete columns are divided into types according to use:
K - for buildings without bridge support, overhead cranes and buildings equipped with overhead cranes.
KS - when covering building structures with sagging lower belt.
KKP - for building frames that are equipped with overhead electric support cranes.
KF - for half-timbered wall enclosures of buildings (half-timbered columns).
KD - for building frames that are equipped with electric support and suspension cranes, and buildings without cranes;
KDP - for building frames equipped with overhead electric support cranes.
KK - for building frames equipped with overhead electric support cranes.
KKS - at building structures coverings with a sagging bottom chord.
KR - for building frames that are equipped with overhead manual support cranes.
Characteristics of columns
In order not to make a mistake in choosing columns, you need to take into account a certain number of building parameters: the number of floors, the purpose of the building, the results of geological surveys, climate conditions in the region where the construction of the building or premises will take place, etc. The main characteristics of the columns are:
Resistance to various influences aggressive environments
. resistance to seismic activity
. column load-bearing capacity
. frost resistance
. moisture resistance
Reinforced concrete columns are also divided by application
Upper columns - used in the construction of upper floors
. Middle columns - used for middle floors
. Lower columns - used for lower floors
. Jointless columns - used along the height of the entire structure
Reinforced concrete columns can be single-, double- and non-cantilevered
The main characteristic used to separate the columns is the length of the trays supported on the columns: the first group - columns for trays, the length of which is 6 m; the second group is columns for trays, in which the length is 8 m.
The main document on which they rely when applying markings to columns under trays is GOST 23009-78.
The main documents regulating the standards for the manufacture of reinforced concrete columns in the Russian Federation are:
GOST 18979-90 "Reinforced concrete columns for multi-storey buildings. Technical conditions."
When using reinforced concrete columns for parabolic trays, the columns are divided into two types: K - post-column embedded in a glass-type foundation; SK - pile-column.
Conventional example of the designation of a reinforced concrete column type SK, length 4000 mm, width 200 mm and head width 450 mm, 1st in terms of bearing capacity of the column (for trays, length 6 m): SK 40.2.5-1 according to GOST 23899-79
There are also markings of this type:
3KND 3.33/20/-19/30
The number 3 means that the column is three-story; KND means that this double-cantilever column is intended for the lower floors; 3 - square section 300 mm; 33 - height typical floor 3.3 m; 20 - basement 2 m; 19/30 - maximum normal force - for top floor it is equal to 190 tf, for the lower floor this figure is 300 tf
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When designing columns, it is necessary to observe design requirements: the dimensions of the column sections must provide such flexibility that they do not exceed the ratio in any direction .
For a building with overhead cranes, the cross-sectional dimensions of the over-crane part of the outer columns are determined based on the conditions for placing crane equipment. The section height is 380 and 600 mm for solid columns. For the crane part of solid columns, the section height increases accordingly to 600...900mm.
The cross-sectional width of the column bс is taken from the manufacturing technology to be constant over the entire height of the column: for columns of the outer and middle rows with a step in the longitudinal direction B=6m - no less than 400mm; at H=12m - no less than 500 mm. In addition, based on the rigidity requirements bс(1/25)Н, Н is the height to the bottom of the rafter structure.
All columns are provided with embedded parts for installing rafter structures, wall panels and crane beams.
For the manufacture of columns, welded frames are used with working longitudinal reinforcement made of class A-III steel with a diameter of 16 mm, and transverse rods are made of steel classes A-I or Vr-I. When using high-strength concrete of classes B45...B60, it is advisable to reinforce the columns using non-tensioned reinforcement of classes A-IV and A-V, which allows reducing the consumption of metal by 20...40% and concrete by up to 20%.
In addition, from design experience it has been established that in flexible columns it is possible to use prestressed reinforcement of classes A-IV and A-V, which makes it possible to increase the rigidity and crack resistance of columns, improve the conditions for transporting long columns, as well as reduce transverse reinforcement and mechanize reinforcement work. In such columns, compared to columns made of conventional reinforced concrete, steel consumption is reduced by up to 40% and cost by up to 10%.
Columns of one-story industrial buildings are subject to all design requirements compressed elements. The thickness of the protective layer of concrete for working longitudinal reinforcement is taken to be at least 20 mm and not less than the diameter of the rod; for transverse reinforcement - not less than 15 mm and not less than the diameter of the transverse rod.
Longitudinal bars in reinforcement products at the ends must have protective layer concrete of at least 10 mm for a column length of up to 18 m and at least 15 mm for a column length of more than 18 m. For cross bars The ends of reinforcement products must have a protective layer of at least 5 mm.
Longitudinal working reinforcement is placed along the edges perpendicular to the bending plane of the column and concentrated in the corners of the section. If the distance between the axes of the working rods in the direction of the bending plane is more than 500 mm, it is necessary to install structural reinforcement with a diameter of at least 12 mm so that there is no more than 400 mm between the longitudinal rods.
Overlapping joints of longitudinal rods (without welding) are provided in places where the column cross-section changes, ensuring the length of the anchorage. In this case, in a stepped column, the longitudinal reinforcement of the crane part is brought beyond the edge of the spacer, also ensuring the length of the anchorage.
The diameter of the transverse reinforcement is assigned depending on the type of reinforcement frame and the largest diameter of the longitudinal working reinforcement and must be at least 0.25d (d is the largest diameter of the working longitudinal reinforcement), and in knitted frames, in addition, at least 5 mm.
