IN modern world Design engineers are increasingly faced with the need to strengthen existing structures in order to maintain or even increase their load-bearing capacity. Some of the reasons for these challenges are changes in the use of administrative and industrial buildings, increased traffic loads on bridges, structural changes and reduced bearing capacity due to corrosion of concrete and steel. There are many various methods reinforcements, such as adding prestressed and non-prestressed steel, installing external prestressing reinforcement, increasing the cross-section of concrete with or without additional reinforcement (concrete sprayed, conventionally applied or bonded in precast blocks), etc. It is necessary to consider whether the surface to be reinforced is subjected to compressive, tensile or shear loads and whether measures relating to stability, serviceability and/or fatigue safety are taken into account. The engineer’s task is to identify the ideal method of strengthening the structure being restored. Therefore, design engineers now have the opportunity to use adhesive reinforcement as an alternative to traditional reinforcement methods. The technology of connecting concrete and reinforced concrete blocks experiencing loads by gluing with reactive resins has proven itself to be reliable and is now being used wide application, especially since this method turns out to be more economical in some cases and is indispensable when space is limited.
Need for reinforcement building structures by installing external reinforcement elements made of high-strength and high-modulus material appears in the following cases:
- Damage to building structures, which led to a decrease in its load-bearing capacity, rigidity and crack resistance;
- Changes in operating conditions;
- Changing the design diagram of the supporting structure;
- The need to improve the reliability and durability of the structure.
To solve these problems, external reinforcement elements (ERA) made of high-strength and high-modulus fibers based on carbon and fiberglass, which have high strength characteristics and the ability to be installed even in the most inaccessible places, are actively used.
The effectiveness of tape reinforcement and the main areas of application of the method.
Gain Efficiency concrete structures composite tapes are very high. Depending on the type of lamellas, canvases, the number of their layers and the type of load, the maximum load-carrying capacity of the element can increase by 2 - 3 times compared to a non-reinforced element. This is especially true for beams. To achieve effective reinforcement using tapes and carbon sheets, it is necessary to strictly follow the technological regulations, primarily regarding the preparation of the surface of the reinforced element. Here we will only say that before gluing the tapes it is necessary to conduct a strength test concrete base for separation, i.e. "pull-off" test. The minimum value of the result of this test shall be 1.5 MPa.
Existing experience in the field of strengthening existing structures allows us to show the following areas of frequent and rational use of CARBODUR carbon fiber composite tapes and CARBOWRAP canvases in concrete objects:
- when reinforcement is required under normal loads on beams and slabs, then the tapes must be glued according to the envelope of bending moments, they come in different lengths and can be glued in 1 or more layers. Here there is an analogy to the scheme of reinforcement with rods in bending elements.
- when reinforcement is required to ensure cracking requirements for corroded prestressing elements of prefabricated or other beams - then tapes are glued “from support to support,” i.e. along the entire length of the element;
- when reinforcement is required due to shearing or main tensile stresses, then pieces of tape are glued in the directions of the bent rods.
Other applications of tapes, for example, for strengthening supports, pillars, floors and walls, are also justified, tested and repeatedly tested on numerous objects.
The effectiveness of this strengthening method has been repeatedly proven in practice and has been used in global construction for 40 years. In Russia, this technology has been used for 14 years and has become widespread in both civil and bridge construction. This strengthening technique is the most modern and “gentle” method of restoring and increasing performance characteristics designs.
The mechanical characteristics of EVA vary within:
- Elastic modulus E = 70,000 – 640,000 MPa
- Tensile strength R = 1700 – 4800 MPa
- Relative elongation at break 1.5%
Carbon fiber reinforcement
Carbon fiber is a high-strength, linearly elastic material that works effectively on reinforced concrete structures. Fiberglass has a lower modulus of elasticity and is used to strengthen brick structures. Since these EVA are fixed to the structure using mounting adhesive, they effectively respond to incremental deformation of the structure, large increments of force arise in them, and they immediately start working together with the structure.
Also, company employees took a direct part in the tests, scientific research and the development of technical regulations in the field of reinforcement in various construction institutes in Moscow, St. Petersburg, Yekaterinburg. Tests have shown that structures reinforced with EVA are able to withstand loads that are twice the design load, and elements that have undergone severe destruction restore their original characteristics by 70% - 95%.
Strengthening works are most often used in combination with structural repairs concrete and structural restoration using injection.
Reinforced concrete bending structures (beams, crossbars, crane beams, slabs, floors and coverings) are reinforced using the following fairly proven methods. When building up, the reinforced structure is increased in height or width (from below, from the sides and from above the reinforced element). A feature of this method is the perception of tangential stresses acting in the plane of contact of old concrete with new concrete, by special additional reinforcement welded to the reinforcement of the structure being strengthened.
Strengthening the existing structure, i.e. increasing its load-bearing capacity by building up leads to the joint work of the reinforced structure and the reinforcement structure, including them in the work in proportion to the rigidities. Extension is used to strengthen reinforced concrete structures, both monolithic (Fig. 3.2) and prefabricated (Fig. 3.3). Reinforcing bars are used 10 mm or more.
Reinforcement of bending elements instead of extension with clips is allowed only in case of significant damage, for example, due to corrosion of reinforcement, since the reinforcement of bending elements is taken depending on the protective layer and the diameter of the longitudinal and transverse reinforcement and usually does not exceed 100 mm. When reinforcing a monolithic ribbed floor with a clip, it is necessary to punch holes in the floor slab to allow passage of clamps and supply concrete mixture when concreting. Often, when constructing frames for beams, the slab is also concreted on top (Fig. 3.4, a).
The constructive solution in the form of a shirt, unlike a clip, is a concrete shell that is not closed on one side (see Fig. 3.4, a), in in this case with connection under the stove monolithic ceiling additional metal fin. Shirts are used in the same cases as clips, but only when it is not possible to cover the reinforced element from four sides.
Shirts are often used when strengthening monolithic beams ribbed floors. In this case, the clamps are brought out through the slab and anchored using longitudinal reinforcing bars. When reinforcing with a jacket only the damaged areas of the reinforced elements, it must be placed on undamaged parts of at least: the length of the anchorage of the longitudinal reinforcement of the jacket; five shirt wall thicknesses; edge width or diameter of the reinforced element and 500 mm. When reinforcing with jackets, reinforcement with a diameter of 8 mm or more is used for longitudinal rods and with a diameter of 6 mm for clamps.
In Fig. 3.5 and 3.6 compare methods of strengthening prefabricated and monolithic structures by building up and using a jacket. Sometimes, to increase the load-bearing capacity of reinforced elements by extension, it is enough just to increase the amount of main longitudinal reinforcement. To do this, the protective layer is removed to a depth of at least 0.5 diameters and additional reinforcement is built up by welding through short pieces of reinforcement 50...200 mm long. In the tensile zone, the shorts are placed every 200...1000 mm, in the compressed zone - at a distance of no more than 500 mm or 20 longitudinal reinforcement reinforcements. Reinforcement fittings are covered cement plaster or shotcrete.
In case of significant increase in cross-section, it is recommended to use specially welded connecting elements, for example 7 in Fig. 3.2 or 6 in Fig. 3.3. If reinforcing bars in bending elements break, it is recommended to restore them by welding prestressed overlays (Fig. 3.7). This operation requires preliminary strengthening of the structure with temporary supports. Welding of additional reinforcement is allowed only on steel classes A-I, A-II, A-III to existing fittings of the same classes.
Effective and sufficient in a simple way strengthening of bending structures is the installation of additional rigid supports in the form of struts (Fig. 3.8) or vertical elements(Fig. 3.9). However, these solutions are limited by the conditions of the technological process, which does not allow for limited dimensions production premises.
Since it is very difficult to completely avoid settlement of the supports when making rigid supports on independent foundations, in all cases it is advisable to install them on existing foundations (Fig. 3.8, c), even if it is necessary to strengthen them. In these cases, tough additional supports performed in the form of portals or in the form of struts. Reinforcement elements for rigid supports can be made of either reinforced concrete or metal.
If the reinforcement struts (Fig. 3.8, a and 3.8, b) are made of metal, in the lower nodes of the reinforcing system there are overhead metal parts connected by welding to the reinforcement of existing reinforced structures. After placing the struts in order to ensure a tight fit in the upper unit, the wedge is made using wedge-shaped spacers.
When making rigid supports in the form of connected racks with independent foundations (see Fig. 3.9), you should Special attention pay attention to reducing the settlement of these foundations, for which it is necessary to carry out preliminary compression of the soil under the sole. If the reinforced structure cannot be preliminarily unloaded, the installation of additional rigid supports must be accompanied by preliminary raising of the reinforced structure (see Fig. 3.8, b).
The reinforced structure is lifted different ways depending on the design of additional supports and the designs of reinforced elements. When strengthening a prefabricated hinged frame, which is assembled on site from individual elements, hinges in the nodes and elastic gaskets between the reinforced crossbar and the reinforcement frame ensure the occurrence of two unloading forces of equal magnitude applied from bottom to top (see Fig. 3.8, b). The frame is stressed by lifting its racks with jacks, after which special metal spacers are placed in the gap between the frame racks and the existing support, and the jacks are removed.
When reinforcing the crossbars with prestressed precast reinforced concrete half-braces (see Fig. 3.8, a), the reinforced crossbar is lifted using a jack horizontally located in the upper unit. To facilitate the movement of the expanding half-braces, metal shorts made of round reinforcing steel are placed in the gap between the reinforced crossbar and the half-braces. After lifting the reinforced structure, the half-braces are connected to one another with a spacer made of profile metal by welding, and the jack is removed. To avoid overloading the columns from below, the half-braces at the bottom are tied with a special metal tie.
In addition to rigid additional supports, elastic additional supports are used to strengthen the bending elements, which are less restrictive to the dimensions of production premises. Additional elastic supports are usually created using metal trusses fixed to the same supports on which the reinforced structure rests. The elastic support for the reinforced element is created by a spacer between it and the reinforcement structure (Fig. 3.10), and has less rigidity than the reinforced concrete element being reinforced. In multi-storey buildings, if it is necessary to strengthen the crossbar of one of the floors, when bearing structures the overlying floor have a sufficient margin of safety; prestressed suspensions can be used (Fig. 3.11).
The compliance of supports of this type occurs due to their longitudinal deformation. The reactive unloading force is created by prestressing the strands, first with tension nuts, and finally with tension couplings. The loads from the tie rods are absorbed by the frame of the upper tier, to the racks of which the tie rods are secured, welding them to pre-arranged metal clips made of sheet steel.
To reduce bending moments in the elements of a multi-span multi-tier frame, cross prestressed connections made of flexible metal strands can be used (Fig. 3.12). The tension of such connections is carried out using turnbuckles or using a thermal method. Anchoring is carried out using special anchor clamps made of sheet metal, fixed on columns. The specified connections may be installed along the height of the same frame only in different spans. For the same purposes, reinforcement with reinforced concrete braces with prestressed tie rods can be used (Fig. 3.13), when after installation of the brace the flexible metal ties are strained thermally on both sides the brace and the reinforcement element perceive both compressive and tensile forces.
To strengthen the bending elements of multi-span buildings, you can use the following solutions. Thus, when strengthening roof beams, outer pores are installed on intermediate supports (Fig. 3.14). To strengthen the bending elements, double-cantilever unloading brackets are also used, installed on intermediate supports (Fig. 3.15, 3.16).
When strengthening prefabricated beams, the branches of the brackets are triangular trusses. Their lower chord is usually made from an isosceles angle, and the upper chord and lattice can be made from either single angles or their round reinforcing bars (Fig. 3.15).
The height of the brackets is taken to be equal to the height of the supporting part of the reinforced beams, and the length of the cantilever parts of the brackets is 1/4...1/6 of the span of the reinforced beams. If the length of the cantilever parts is short, you can completely abandon the lattice elements. The support elements of the bracket can be either vertical metal sheet 20...30 mm thick and 300...400 mm high, welded from below to the horizontal distribution gasket, or in the form of saddle-shaped pads installed on top of the beams and connected by welding.
Design support device depends on the tension method. When tensioned with bolts, it is a rigid plate passed under the bottom of the reinforced beam and bolted to the branches of the bracket (see Fig. 3.15). When tensioned by a jack with tensioner Tension control is carried out using the jack pressure gauge. After tensioning, as a rule, fixing gaskets are installed. On intermediate supports, a bracket design can be adopted, assembled from two separate parts (see Fig. 3.16). After their installation, the upper stretched chords are welded over the support with overlays. Connections are created along the lower belt for the overall stability of the lower belt using special support pads. In case of anchorage violations, the extension of the longitudinal reinforcement of the support or bracket must be taken at a distance of at least 40 diameters of the rod reinforcement from the support sheet of the beam.
In cases where there is a need to carry out strengthening work without removing the temporary load, you can use a solution that involves installing additional prestressed reinforcement. Horizontal, truss, or a combination of both can be used as additional stressed reinforcement.
If anchor devices cannot be placed at the ends of the beams, they are welded in the support zone in places where the stresses in the reinforcement of the reinforced beam are low (Fig. 3.17). In this case, tension is produced thermally. To prevent sagging under the influence of their own weight, the reinforcement rods are secured using temporary hangers. After heating the rod, its free end is also welded. When reinforced with truss reinforcement, its tension is carried out mechanically, i.e. by screwing tension screws or laying into the gap of the package more gaskets (Fig. 3.18).
Both with the option of horizontal tension of additional reinforcement, and trussed or combined, it is possible to create tension in them by mutually tightening two or four rods with special tension bolts (Fig. 3.19, 3.20, 3.21). The coupling bolts have the form of a clamp with two threaded ends and a common washer. Tension is produced by simultaneously tightening the nuts at both ends of the clamps. Tension by mutual tightening does not require significant effort, since the stress in the tie bolts, which act as clamps, is 7...10 times less than the stress in the additional rods being tightened.
The advantage of this tension method, along with its simplicity, is the creation of uniform forces in all tightened rods as a result of self-regulation. Round rods of additional reinforcement are usually taken with a diameter of 18...40 mm. The perception of transverse forces when strengthening bending elements is mainly produced by increasing the cross-sectional area of transverse and inclined reinforcement.
Less in a labor-intensive way is reinforced with vertical overhead clamps (Fig. 3.22). To do this, holes are first punched in the ceiling on both sides of the beam, gaskets are placed from the corners and clamps are placed over them, which have threaded ends. A strip steel backing is placed on these ends and the nuts are tightened. When tightening the clamps, the nuts should be tightened at both ends simultaneously. An option for reinforcement with vertical clamps is reinforcement using prestressed clamps (Fig. 3.23).
The design of prestressed clamps consists of: upper fastening angles suspended from the floor slab with bolts, lower fastening angles connected by welding strips; an even number of clamps and tie bolts with locking washers. After securing the clamps at the bottom and top, pre-stress is created by mutually tightening each two adjacent rods with tie bolts. The rods are tightened simultaneously on both sides of the reinforced beam.
When reinforcing beams with inclined overhead clamps (Fig. 3.24), instead of strip steel pads, corner pads are used, which are welded to the lower longitudinal reinforcement using short bars. After tightening the clamps, the protective layer is restored.
The ribs of the prefabricated covering slabs are strengthened by installing vertical overhead clamps, which connect both ribs together (Fig. 3.25). When amplified a lot hollow core slabs With round and oval holes you can use voids. To do this, in the supporting sections of the slabs (1/4 of the span), holes are cut from above into which additional reinforcement cages are installed (Fig. 3.26), and the voids are concreted with plastic concrete on fine aggregate with or without the installation of an additional slab (Fig. 3.26, b) devices. To absorb both shear force and bending moment, the slabs are reinforced along their entire length.
When reinforcing hollow-core slabs on the outer supports, to prevent their shifting, the frames are installed so that they overlap the support. Then frames are installed along the ends of the slabs, which, after concreting, create a beam-frame, if necessary, along the perimeter of all walls. On intermediate supports, common frames are installed in the voids of the adjacent ends of the slabs.
The insufficient support area of ribbed prefabricated slabs can be compensated by installing metal ties on intermediate supports that interconnect the ribs of slabs of adjacent spans (Fig. 3.27, a), and on the outer ones - by lengthening the supporting parts of the ribs (Fig. 3.27, b). If necessary, short consoles of columns can be strengthened by installing additional prestressed inclined or horizontal ties or clamps (Fig. 3.28). The rods are attached to the console with metal fasteners and tightened by screwing in the nuts.
Strengthening the capitals of beamless floors, along with the installation of reinforced concrete jackets, can be carried out by installing prestressed metal
spatial trusses (Fig. 3.29). The structure of the truss consists of a lower corner frame resting on a reinforced concrete support frame; an upper corner frame covering the reinforced capital along the perimeter, and four struts connecting the frames to each other. The concreted support frame on the column and the lower frame mounted on it with welded struts are connected by welding to the heated upper frame, which, when cooled, shortens and creates a preliminary compression in the struts. The dimensions of the support clips and the heating temperature of the upper trim should be determined based on the load that the reinforcement must absorb. The design forces in the elements of a spatial truss should be calculated as in a spatial statically determinate truss under the action of a given load.
Strengthening of slabs supported on the contour, along with the concrete, is carried out by installing spatial prestressed metal trusses, brought from below under the reinforced slab and suspended in the corners to the load-bearing elements of the contour with four bolts and four transfer crossbeams. The springs are installed in two mutually perpendicular planes along the diagonals of the slab at the same level (Fig. 3.30).
The upper chords of the truss are tightly pulled to the lower surface of the reinforced slab, which allows them to be included in joint work when prestressing the lower chords using a thermomechanical method. All installation and prestressing work can be done without unloading the reinforced slab.
Crane beams are reinforced in two ways - with a metal clip and remote metal supports(Fig. 3.31) or a metal clip and truss, similar to the combined reinforcement option shown in Fig. 3.21. Strengthening the fastenings of crane beams to columns is carried out by plates connected by welding to the embedded parts of the column.
The embedded parts on the column can be secured either with metal clamps on spring washers (Fig. 3.32, a) or with metal clips (Fig. 3.32, b).
Strengthening reinforced concrete structures
Strengthening of reinforced concrete structures is carried out based on the results of a technical examination, maintainability and specific possibilities for restoring structures to ensure their normal operation as part of the building.
General rules carrying out work to strengthen reinforced concrete structures
1. Work should be carried out in compliance with safety regulations specified places according to schemes for strengthening technical solutions.
2. When strengthening damaged structures, it is recommended to use hammer drills with a power of no more than 0.8 kW and to avoid dynamic impacts on the building structure.
3. Weld leg Kf metal reinforcement elements are taken according to the smallest thickness of the elements being welded. Maximum weld length L = 85Kf.
4. Everything metal elements after installation in the designed position, the reinforcements are coated with a protective composition (primer GF-021) according to the application technology, welds thoroughly cleaned and primed 2 times.
Strengthening foundation structures with distribution belts
The main reasons for strengthening foundations belts:
Uneven settlement of the base;
Frost heaving of soils and foundation materials (unloaded foundations in the event of a long break in construction).
The main methods of strengthening the foundation with belts:
Installation of a metal distribution belt;
Construction of a reinforced concrete distribution belt.
Distribution belts are installed along the top of the foundation (see Fig. 6.10). The belt redistributes the emerging forces into existing structures and helps reduce tension in local areas.
Sequence of installation of reinforced concrete distribution belts (Fig. 6.10)
1. Clean the surface of foundations and walls (1), (2), moisten the foundation material with water two days before concreting.
2. Determine the sequence of work. It is recommended to carry out work symmetrically on both sides of the foundation using claws up to 2 m long.
3. Arrange fines for installing belts.
4. Drill holes in increments of 0.5-0.6 m to pass connecting rods (5) (class AIII reinforcement with a diameter of 10-12 mm). Install reinforcing bars.
5. Reinforcement frames of the belt are installed from class AIII reinforcement with a diameter of 10-12 mm, welded with connecting reinforcement. Fasteners provide a protective layer for the reinforcement.
6. Install the formwork for concreting the belt (6) 5-10 cm high.
7. Concrete of class no less than B15 is laid with vibration.
8. After the concrete has gained transfer strength, the formwork is removed.
Rice. 6.10. Distribution belt arrangement diagram strip foundations after a break in construction:
a - steel; b – reinforced concrete;
1 - wall; 2 - foundation; 3 - channel; 4 - steel bolt; 5 - connecting rod; 6 - reinforced concrete belt
Increasing the support area of reinforced concrete elements
During the construction of buildings, defects are often introduced - violations of the joints and assemblies of reinforced concrete elements. The covering slabs can be shifted relative to the crossbar, the crossbar can be shifted relative to the column consoles, etc. Horizontal shifts lead to a defect in support: the area of support is significantly reduced, which can provoke the collapse of frame structures. It is necessary to correct the support units by installing support posts or increasing the support area.
The main reasons for reducing the support area of elements:
Uneven deformations of foundation soils;
Dynamic impact on building frame structures.
Scope of application of the method:
In case of defects in the installation of building elements.
Basic ways to increase the support area:
Installation of a metal support table;
Suspension of support tables using ties.
As a result of correcting the support of reinforced concrete elements, the rigidity of the interface between the frame structures, horizontal disks of the floor and the coating is restored.
Before work is carried out to increase the support area of reinforced concrete elements, they develop technical solutions to design a correction scheme with calculations taking into account the identified defects and develop a technology for performing the work (routine map).
Below are diagrams of strengthening the nodes for supporting ribbed slabs on the crossbar (see Fig. 6.11) and the sequence of work to correct the nodes is given.
The sequence of correcting the support nodes of the coating slabs (Fig. 6.11)
1. Place supporting safety posts under the covering slabs (metal posts or timber on supports).
2. Clean the embedded parts (3) of the covering slabs (1) and crossbars (2) with metal brushes.
Rice. 6.11. Scheme for correcting the support nodes of ribbed floor slabs on the crossbar:
a - by welding support tables; b - suspension of support tables using cords;
1 - ribbed floor slab; 2 - reinforced concrete crossbar; 3 - embedded part of the crossbar; 4 - support table made of corners; 5 - stiffener; 6 - corner; 7 - support sheet; 8 - plate; 9 - cord; 10 - corner and washer
Rice. 6.12. Scheme for correcting the crossbar-column interface:
a - in frames of series 1.420-12; b - in frames of series 1.020-1;
1 - ribbed floor slab; 2 - reinforced concrete crossbar; 3 - column; 4 - coupling bolt; 5 - covering clamp from corners; 6 - thrust angle; 7 - additional support sheet; 8 - stiffeners
3. Install the support table from the corners (4) and (6) with stiffeners (5) according to the reinforcement diagram.
4. When correcting using ties, install the ties (9) in drilled holes in the body of the slab. To prevent destruction of the slab material, install a metal plate under its ribs (7) and on the upper edge of the crossbar (8).
5. Prime all reinforcement elements and paint with oil paint.
To strengthen the crossbar support unit on the column console, an additional support table is usually used, suspended from a clamp covering the column (see Fig. 6.12).
Strengthening reinforced concrete structures by building up produced when there is great physical wear of structural elements.
The main reasons for the increase reinforced concrete structures:
Reduced strength of concrete;
Corrosion of reinforcement, embedded parts and steel ties connecting elements to each other.
Increased load on structures.
Scope of application of the method:
With unfinished construction;
During a break in construction;
In case of defects in the material and connecting parts of reinforced concrete frame elements.
Basic methods of strengthening reinforced concrete structures:
Building up the concrete layer (see Fig. 6.13);
Reinforcement with dowels, tie bolts, rods (see Fig. 6.14);
Reinforcement with rolling elements (see Fig. 6.15);
Supply of unloading elements, trusses (see Fig. 6.16, 6.17);
Reinforcement with reinforcing bars (ties). Used to strengthen truss elements (see Fig. 6.18);
Reinforcement with reinforced concrete frame.
As a result of strengthening, the strength of reinforced concrete structures is restored.
Sequence of work on strengthening wall panels by extension (see Fig. 6.13)
1. Clean the surface of the walls (2), moisten the panel material with water two days before concreting.
2. Determine the sequence of work. Work should be carried out on one or both sides of the wall panels according to the reinforcement diagram.
3. Drill holes in increments of 0.5-0.6 m to install “blind” or “through” anchors (3), (4) (class AIII reinforcement with a diameter of 10-12 mm). Install anchors.
4. Install reinforcing mesh(5) from class AIII reinforcement with a diameter of 6-10 mm, welded with anchors.
5. Install formwork for concreting the surface of the walls (6) or gunite the surface.
Rice. 6.13. Scheme of strengthening wall panels by extension:
a - external on one side;
b - internal on both sides;
1 - hollow core slab; 2 - wall panel; 3 - “blind” anchor; 4 - “through” anchor; 5 - reinforcing mesh; 6 - concrete extension
Reinforcement of wall panels using rods is done in a similar way.
When reinforced with dowels and tie bolts, grooves are placed in the wall panels in increments of 0.3-0.5 m in height (see Fig. 6.14).
After installing the reinforcing elements (2), (4), (5), (6), the grooves are filled with lightweight concrete or porous mortar. The surface is plastered or a new finishing layer is installed.
Reinforcement of floor panels is carried out in case of great physical wear and insufficient load-bearing capacity of the slabs, or violation of the integrity of the horizontal disc of the floor.
Rice. 6.14. Scheme for fastening delaminated external wall panels:
a - dowels; b - coupling bolts; c – rods;
1 - wall panel; 2 - dowel; 3 - lightweight concrete or porous solution; 4 - coupling bolt; 5 - washer; 6 - nut; 7 - rods; 8 - washer-fixer made of wire; 9 - welded or woven mesh; 10 - wire harness; 11 - finishing layer
Sequence of reinforcement of floor slabs (Fig. 6.15)
1. Mark the reinforcement of the floor slabs (1).
2. Dismantle sections of slabs above the voids to allow passage of I-beams.
3. Install I-beams (2) into the punched voids.
4. Lay the reinforcing mesh (3) along the top of the floor slabs, weld the mesh to the I-beams.
5. Lay a layer of fine-grained concrete (4) compacted with a vibrating screed.
Rice. 6.15. Strengthening reinforced concrete hollow core slabs:
1 - floor slab; 2 - I-beam No. 16 through two voids; 3 - mesh made of AI reinforcement with a diameter of 8 mm with a pitch of 150x150 mm; 4 - fine-grained concrete class B20
Strengthening ribbed slabs coating can be done by supplying unloading elements (see Fig. 6.16).
In this case, work begins with opening the seams between the slabs and punching holes to allow the passage of tie bolts with a small seam width. Then reinforcement elements (3-7) are installed and painted with a protective composition.
Strengthening floor beams is carried out when there is great physical wear and insufficient load-bearing capacity of the beams.
Sequence of reinforcement of floor beams (Fig. 6.17)
1. Mark the reinforcement of the floor beam (1).
2. Install the reinforcement elements (3-8) in the design position, all connections are welded.
3. Put the studs (3) into operation by tightening the nuts (4) to the design value.
4. Paint the reinforcement elements with a protective compound.
Rice. 6.16. Strengthening reinforced concrete ribbed slabs by supplying unloading elements:
1 - ribbed plate; 2 - reinforced concrete beams; 3 - metal corners installed in cleared seams between slabs (continuous); 4 - rolled channel installed on cement-sand mortar; 5 - metal plates welded to the channel; 6 - coupling bolts installed in the seams between the plates (if the seam width is small, holes are drilled); 7 - strip-washers welded to the corners; 8 - seams filled with cement-sand mortar after the unloading beams are put into operation
Rice. 6.17. Strengthening a reinforced concrete beam with a straight sprengel:
1 - floor beam; 2 - columns of the building frame; 3 - stud made of rod reinforcement with thread; 4 - nut; 5 - reinforcing bar of class A I; 6 - part made of angle and metal plates for tensioning the stud; 7 - part for fastening the reinforcing bar (5) at the end of the beam; 8 - metal plate for fastening the part (7)
Rice. 6.18. Strengthening reinforced concrete roof truss installation of puffs:
1 - reinforced truss; 2 - tightening from prestressed reinforcement with a diameter of 25-40 mm, class A III; 3 - end support sheet; 4 - spacer (metal plate); 5 - clamp made of reinforcing steel; 6 - tightenings made of reinforcing steel; 7 - tension couplings; 8 - covering clamp made of sheet metal and connecting strips
Trusses are strengthened when there is significant physical wear and signs of loss of stability of truss elements in the form of cracks and flanges (see Fig. 6.18).
Technology of strengthening trusses with puffs
1. Mark the reinforcement of the truss elements (1).
2. Install the reinforcement elements (2-8) in the design position.
3. Tension the reinforcing steel tie (6) on the support sheet (3) using a torque wrench.
4. Use clamps (5) to increase the tension to the design value.
5. When strengthening the braces, weld the reinforcing bars to the female sheet metal clamps and connecting strips and put them into operation using turnbuckles (7).
6. Paint the reinforcement elements with a protective compound.
The most common way to strengthen reinforced concrete structures is to install a metal or reinforced concrete frame (jacket).
A metal clip is used when there is slight physical wear and insufficient load-bearing capacity, as a rule, for bending reinforced concrete elements (beams, trusses, etc.).
The advantage of a metal holder is that slight magnification the weight of the reinforced structure, the ability of the reinforced element to perceive large bending forces.
The main disadvantage is the high cost of materials and high costs labor.
A reinforced concrete casing (jacket) protects the reinforcement and increases the cross-sectional area of the reinforced element. It is used for significant damage to the material of reinforced concrete structures and corrosion of reinforcement. Reinforced concrete cage is used for compressed elements that can withstand small bending forces in aggressive environments ( high humidity, heat etc.) (see clause 6.1.6).
The advantage of a reinforced concrete cage is the ability to operate the reinforced structure in aggressive environments due to the introduction of various additives into the concrete of the cage.
The main disadvantage is a significant increase in the weight of the reinforced element.
Before work is carried out to strengthen the column with reinforced concrete casing, a calculation is made to determine the load-bearing capacity reinforced concrete column. They develop a design for strengthening the column, a scheme for reinforcing the cage, and assign a class of concrete and reinforcement. They are developing technology for a clip device.
Reinforced concrete cage technology
1. Clean the surface of the column, moisten the column material with water two days before concreting.
2. Mark the column reinforcement.
3. Install reinforcement cages, ensure verticality with clamps, pair the reinforcement with the outlets of the foundation reinforcement (if necessary).
4. Install the formwork, check the verticality of the installation.
5. Concrete is laid with layer-by-layer compaction, layer thickness no more than 0.5 m.
The choice of one or another method of strengthening building structures depends on the technical specifications for the reconstruction of a building or structure, which includes changes in space-planning solutions, loads and operating conditions. The main reasons for strengthening reinforced concrete structures are given in Table. 1, and ways to increase the load-bearing capacity of structures - in table. 2.
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Reasons for strengthening reinforced concrete structures | ||||||||||
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Increased loads on them as a result of replacement or strengthening of overlying structures (reconstruction of premises, addition of buildings) |
Modernization technological equipment in a building being reconstructed, change technological processes |
Operational wear (loss of load-bearing capacity) |
Structural defects and those resulting from improper operation of the structure |
Accidental damage (during dismantling and installation) |
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Table 1. The main reasons for strengthening reinforced concrete structures
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Ways to increase load-bearing capacity |
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Without changing their stress state or design diagram |
With a change in the stress state or structural design of structures |
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Reinforced concrete, metal frames, reinforced concrete jackets, extensions |
Pre-tensioned struts; metal beams supported on cantilever piles; |
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racks; struts; horizontal truss and combined tightening
Table 2. Ways to increase the load-bearing capacity of structures
One of the most effective ways to strengthen reinforced concrete columns is to install reinforced concrete and metal frames. In bending elements, clips are used when there is significant corrosion of the reinforcement.
A reinforced concrete frame consists of reinforcement and a thin layer of concrete covering the reinforced element on four sides (beams, crossbars, columns). Most simple type
are reinforced concrete cages with conventional longitudinal and transverse reinforcement without connection of the cage reinforcement with the reinforcement of the reinforced column. With this method of strengthening, it is important to ensure that the “old” and “new” concrete work together, which is achieved by thoroughly cleaning the surface of the concrete of the reinforced structure with a sandblasting machine, notching or treating with metal brushes, as well as pressure washing immediately before concreting. To increase adhesion and protection of concrete and reinforcement under aggressive operating conditions, the use of polymer concrete is recommended.
The thickness of the column casing is determined by calculations and design requirements (diameter of longitudinal and transverse reinforcement, size of the protective layer, etc.). As a rule, it does not exceed 300 mm. The area of working longitudinal reinforcement is also determined by calculation. At local amplification
the cage is extended beyond the damaged area by a length not less than the length of the anchorage of the reinforcement, as well as not less than double the width of the larger edge of the column, but not less than 400 mm. To improve the adhesion of “new” and “old” concrete, it is recommended to use adhesive coating made from polymer materials.
Additional longitudinal reinforcement is welded to the existing one using connecting shorts, which, in order to avoid burnouts, are made from class A-I reinforcement with a diameter of 10-16 mm and are placed at a distance from each other of at least 20 diameters of the longitudinal reinforcement in a checkerboard pattern.
If it is impossible to create a closed frame, for example, when a column is adjacent to a wall, it is recommended to install “shirts” - concrete shells that are not closed on one side. With this method of reinforcement, it is necessary to ensure reliable anchoring of the transverse reinforcement at the ends of the cross-section of the “shirts”. In columns this is done by welding clamps to the existing reinforcement.
When reinforcing local damaged areas with jackets, as well as when reinforcing with clips, they must be extended to undamaged parts of the structure for a length of at least 500 mm, as well as at least the length of the anchorage of the longitudinal reinforcement, at least the width of the edge of the element or its diameter, and at least five times thickness of the “jacket” wall.
The effectiveness of including a metal frame in the operation of a column depends on the tightness of the corners to the body of the column and the prestressing of the transverse strips. To ensure a tight fit of the corners, the surface of the concrete along the edges of the columns is carefully leveled by chipping off irregularities and caulking with cement mortar. Prestressing of the connecting strips is carried out thermally. To do this, the strips are welded on one side to the corners of the frame, then heated with a gas burner to 100-120°C and, while heated, the second end of the strips is welded. The closure of the planks is carried out symmetrically from the middle height of the belt column. When the planks cool, the cross sections of the column are compressed, which leads to an increase in load-bearing capacity.
The metal frame consists of corner profile posts, connecting strips, and support pads (Fig. 1).
Rice. 1. Reinforcement of the column with a metal frame:
1 - overlap; 2 - reinforced column; 3 - clip;
4 - angle to the i-rack; 5 - transverse strips; 6 - support bars
An effective means of strengthening external columns is the installation of prestressed metal struts. Single- or double-sided braces are metal cages with prestressed struts located on one or both sides of the columns. The former are used to increase the load-bearing capacity of eccentrically compressed columns with large and small eccentricities, the latter - for centrally and eccentrically compressed columns.
Prestressed one-way struts consist of two corners connected to each other by metal strips. In the upper and lower zones of the spacers, special strips with a thickness of at least 15 mm are welded, which transfer the load to the thrust angles and have a cross-sectional area equal to the cross-section of the spacers. The planks are installed in such a way that they protrude beyond the ends of the corners of the spacers by 100-120 mm, and are provided with two holes for tie bolts. The stop corners must be installed so that their inner edges coincide with the outer edge of the columns. To do this, the protective layer of concrete in the upper and lower zones of the column is chopped off and thrust corners are installed strictly horizontally on the cement mortar. Before installing the spacers in the design position, a cut is made in the side flanges of the corners in the middle of their height and they are slightly bent. The weakening of the cross-section of the corners at the cutout site is compensated by welding additional strips, which provide holes for tie bolts.
Prestressing of the spacers is created by giving them a vertical position by tightening the nuts of the tension bolts. In this case, it is necessary to ensure a tight fit of the corners to the body of the column, as well as their joint work, combining the spacers by welding metal strips to them. The pitch of the planks is taken equal to the minimum size of the column section. After welding the strips, the mounting bolts are removed, and the weakened sections of the struts are reinforced with additional metal plates.
To effectively include the spacers in the work, it is enough to create a preliminary stress in them of the order of 40-70 MPa, which is ensured by the calculated elongation when straightening the corners.
Building up - increasing the cross-section of structures being reinforced from above, below and from the sides with a layer of monolithic reinforced concrete (beam, crossbar, column, walls, floor slab).
Reinforcement of columns with concrete (Fig. 2) is performed in the following sequence:
Rice. 2. Strengthening the column with concrete: 1 - existing column;
2 - reinforced concrete “shirt”
Calculation determines the number and diameter of working reinforcement and clamps or spiral reinforcement. New reinforcement is connected to the old one;
Formwork is installed and concreting is carried out. For better adhesion of old and newly laid concrete, the surface of the column is thoroughly cleaned, notched and washed with water under pressure. The minimum thickness of the “jacket” must be sufficient to accommodate the reinforcement and protective layer (50 mm), and when shotcreting - 30 mm.
When strengthening reinforced concrete structures, a number of technological processes are performed: preparing the surface of the reinforced structure, installing reinforcement and formwork, laying and compacting the concrete mixture, maintaining the concrete during the period of achieving the required strength, and dismantling the formwork. The surface of the reinforced structure is prepared to ensure reliable adhesion of the concrete of the reinforcement layer to it. In this case, following operations: removing the surface of the protective layer and removing concrete delaminations; cleaning reinforcement from surface corrosion; blowing with compressed air and moistening the surface. Removal of the protective layer of concrete and removal of its delaminations is carried out using mechanized tools (electric jointing hammers IE-4207 and IE-4210, chipping hammers IP-4119, EP-1027, EP-1056, etc.).
It is recommended to clean the fittings from rust by waterjet treatment, using shotcrete equipment, and as a working mixture - quartz sand or sand-gravel mixture with a moisture content of up to 6%. When waterjet processing, the pressure ratio is observed compressed air(on the compressor receiver) and water supplied to the nozzle 4: 0.5. To clean reinforcement from rust when reinforcing structures in cramped conditions, it is effective to use a small-sized sandblasting machine with a vacuum gun operating on the ejector principle. For small volumes of work, pneumatic manual corner metal brushes IP-2104 are used to clean fittings from rust (brush weight 4 kg, compressed air pressure in the pneumatic system 0.6 MPa).
It is most advisable to lay the concrete mixture when reinforcing concrete structures using installations for pneumatic spraying of concrete: with a reinforcement layer thickness of up to 80 mm - shotcreting using a cement gun; when the thickness of the reinforcement layer for massive structures is up to 250 mm and its total surface is at least 10-15 m 2 - with sprayed concrete using concrete syringe machines. A special feature of these installations is the supply of dry concrete mixture through hoses using compressed air, which is mixed with water at the exit of the end nozzle. The concrete mixture is ejected from the nozzle at a speed of 50-70 m/s and forms a dense layer on the surface. The machines perform four processes simultaneously: transporting the concrete mixture to the placement site, mixing it with water, spraying and compacting. When using these installations, formwork work is completely eliminated, labor costs and work time are significantly reduced, which is especially important during reconstruction. Shotcrete has increased strength and adhesion, and also provides increased protective functions and improves the performance of structures compared to conventional concrete.
For shotcreting structures in cramped conditions, it is effective to use the SB-117 cement gun, and for applying sprayed concrete - the SB-67 and SB-68 units. The thickness of the sprayed concrete layer applied at a time is 50-70 mm, the distance between the nozzle and the concrete surface is 1-1.2 m. To perform sprayed concrete work, concrete syringe machines and cement guns are equipped with a mobile compressor with a working pressure of 0 .9 and 0.6 MPa (for SB-117), a water tank, mobile scaffolding or auto-hydraulic lifts for working at heights. Dry concrete mixtures are supplied centrally: for work volumes up to 2.5 m 3 - in bags, for large volumes of work - in specialized containers.
As the load on the column consoles increases, they are reinforced with horizontal or inclined ties (Fig. 3).
Rice. 3. Reinforcement of consoles with cords:
1 - reinforced console; 2 - supporting elements; 3 - corner stops; 4 - strands;
5 - anchors; 6 - stops made of channels
Prestress is created by screwing in nuts or tightening clamps together. They also use unloading of consoles using additional metal brackets or special supports in the form of channels (corners), which are attached to the column using prestressed ties.
STRENGTHENING Rafter STRUCTURES
With additional load on sub-trusses and beams, there is often a need to strengthen them as a whole or individual elements and assemblies. Most effective ways the gains are shown in Fig. 12.
The reinforcement consists of two identical (hinged-rod) chains on both sides of the structure, anchor devices in the upper zone on supports, round steel pendants or racks made of profile metal located in places where the branches of the chains bend.
Branches are usually made from corners, the vertical flanges of which are cut at the places where the chains bend, as well as from reinforcing bars with a diameter of up to 36 mm or ropes made of high-strength wire. Anchors are made of sheet or profile steel. Reinforcing elements are of classes A-I, A-P, A-III, K7, K19, metal structures made of VStZsp, VStZps and VStZkp steels. Prestressing of the hinge-rod system is carried out by tightening the nuts with a wrench or a jack.
Rice. 1. Methods of strengthening metal coating trusses:
a) pre-stressed hinge-rod chains by tightening the nuts;
b) strengthening of truss nodes with metal clamps made of sheet steel or reinforced concrete;
c) trussed tightening from angles or I-beams and angles;
1 - single-tier reinforcement within the height of the trusses; 2 - the same below the truss belt; 3 - hinge-rod chains; 4 - horizontal strands; 5 - reinforcement clamps; 6 - concrete;
7 - truss; 8 - support device; 9 - spacer; 10 - tension screws
Rice. 2. Methods of strengthening roof beams:
a) by placing unloading racks, frames, struts, etc.:
1 - reinforced beam; 2 - additional support; 3 - support element made of channel;
4 - metal wedges for putting the stand into operation;
6) reinforced concrete extension:
1 - reinforced beam; 2 - reinforced concrete extension; 3 - longitudinal reinforcement reinforcement; 4 - reinforcement shorts; 5 - exposed beam reinforcement (in increments of 1 m);
c) installation of a reinforced concrete cage:
1 - reinforced beam; 2 - reinforced concrete slabs; 3 - reinforced concrete frame; 4 - beam surface prepared for concreting (cleaning, notching, washing with water);
5 - holes punched in the flanges of slabs for laying concrete
Reinforcement of compressed truss chords is carried out by installing metal clips made of sheet or profile metal. Reinforcement of the lower belt is carried out with pre-stressed puffs. The supporting parts of the anchor tightening devices are made of plates 10-24 mm thick, reinforced with ribs. To enable the tie rods into the operation of the trusses, it is necessary to create a preliminary stress of about 15-20 MPa in them. The anchor devices must fit tightly to the supporting parts of the trusses, for which in some cases a layer of grade 25 cement mortar is placed between the supporting plates and concrete.
The stretched truss braces are reinforced with prestressed ties, which are fastened to the truss nodes by welding to shaped parts or support corners. The end sections of the puffs are equipped with threaded shorts, and the diameter of the shorts must exceed the diameter of the puffs by at least 4 mm.
The metal clips of the compressed elements of the trusses are put into operation due to the expansion forces that arise when additional load is applied to the truss. If it is necessary to unload compressed truss elements, pre-stressed one-sided or two-sided struts are used. The spacers rest against special sheet steel cages installed in the truss nodes.
To strengthen rafter beams, truss ties made from angles or I-beams and angles are recommended. Prestressing of the truss is necessary for reliable inclusion of the truss in the operation of the beam. The truss tie includes two side angles, which are attached to anchor boxes installed on cement mortar at the ends of the beam (Fig. 3). Pre-stressing of the truss is carried out by mutually tightening the horizontal corners of the lower chord using special bolts.
Rice. 3. Reinforcing the rafter beam with prestressed truss from the corners:
I - reinforced element; 2 - inclined rod; 3 - corner of the lower belt; 4 - compensating pads; 5 - mounting hangers; 6 - horizontal strand of sprengel
The lower horizontal part of the truss can be made of an I-beam or channel. In this case, pre-stressing of the truss is carried out by pulling the I-beam away from the beam using tension screws, and first the screws in the places where the strands are bent are simultaneously tightened, and then the middle bolt. After tightening, the bolts are welded to the lower chord of the truss to prevent them from unwinding.
Prestressing can also be carried out using hydraulic jacks suspended from the truss at the bend points of the strands.
Fixation of prestress is carried out by filling the gap between the lower chord of the beam and the I-beam with cement mortar or special linings made from pieces of strip steel.
After reinforcement, all metal parts are painted with protective varnish or enamel.
The sequence of strengthening reinforced concrete structures is shown in Fig. 4.
Rice. 4. Sequence of reinforcement of reinforced concrete structures
Strengthening reinforced concrete trusses located in in emergency condition, is carried out by unloading them and transferring forces to additional steel trusses installed on both sides of the emergency truss using mounting beams (winches, blocks).
The load is transferred from the covering slabs to the installed trusses by means of uniform wedging, which eliminates the gaps between the support posts of the installed trusses and the longitudinal ribs of the covering slabs. Wedging is carried out simultaneously along both trusses from the middle to the edges. Next, gaps are formed between the covering slabs and the emergency truss.
STRENGTHENING PLATE STRUCTURES
Monolithic floor slabs can be reinforced using the extension method, i.e. concreting an additional reinforced concrete slab on top of the existing one, as well as placing additional supports in the form of monolithic reinforced concrete or metal beams.
Precast concrete hollow core slabs can be strengthened using voids. From above, in the area where the channel is located, a shelf is broken through and a reinforcement frame is installed. Then the channel is filled with plastic concrete on fine crushed stone and the slab is calculated taking into account additional reinforcement (Fig. 10).
Rice. 10. Strengthening prefabricated hollow-core floor slabs:
I - reinforced slab; 2 - support; 3 - additional reinforcement cage;
4 - concrete reinforcement
When strengthening only the supporting part of the slab, the frames are located on part of its span, and if it is necessary to strengthen along the normal and inclined sections, along the entire length of the slab.
Strengthening the supporting parts of hollow core slabs when their support area is insufficient is recommended to be carried out according to the following schemes:
For extreme supports - by installation in channels reinforcement cages with their removal beyond the ends of the slabs to the required length, subsequent installation of vertical frames parallel to the ends of the slabs, concreting the anchor beam and supporting sections of the slab voids;
For intermediate supports - by installing common vertical frames into pre-punched holes in support zones, adjacent slabs and subsequent concreting of channels with additionally installed reinforcement. In this case, the slabs work as continuous structures.
The longitudinal ribs of prefabricated reinforced concrete ribbed slabs are reinforced by adding additional metal supports that reduce the span of the ribs, additional metal beams, which are included in the work using a wedge; trussed structures.
An effective way to strengthen the longitudinal ribs of slabs along normal sections is to install additional reinforcement cages in the seams between the slabs and concreting the seams.
It is possible to build up longitudinal ribs with additional reinforcement while ensuring its connection with the existing working reinforcement.
If it is impossible to make concrete to strengthen slabs supported along the contour, it is recommended to place a pre-stressed spatial truss under the slabs (Fig. 11), which consists of two flat trusses mutually intersecting at the same level, the upper chords of which are tightly fitted to the lower plane of the slab, and the lower ones The belts are pre-stressed mechanically or thermo-mechanically.
During operation, the sprengel must be protected from corrosion, and, if necessary, covered with a suspended ceiling.
Rice. 11. Strengthening a prefabricated slab supported along the contour,
spatial truss:
1 - reinforced plate; 2 - element of the supporting contour; 3 - spatial truss;
4 - upper belt; 5 - lower belt; 6 - intermediate racks; 7 - central pillar;
8 - bolts for hanging the sprengel; 9 - transfer traverses
To strengthen the support of prefabricated floor and roof slabs on crossbars and building structures, it is recommended to place metal tables from corners under the supports, securing them with ties or clips to adjacent structures or the upper chord of crossbars and rafter structures (Fig. 12, 13).
Rice. 12. Options for arranging support tables, if available
embedded parts:
1 - crossbar; 2 - plate; 3 - embedded part in the crossbar; 4-support table
Rice. 13. Strengthening the support of the slabs:
1 - crossbar; 2 - plate; 3 - fastening the rod to the plate; 4 - inclined rod; 5 - thrust table; 6 - stiffeners; 7 - clamps; 8 - corner "of the support table
INSTALLING ADDITIONAL EMBODIED PARTS AND REINFORCING JOINTS
It is often necessary to install additional embedded parts or restore those missed during the manufacture of structures.
In this case, it is necessary to distinguish between structural embedded parts to which large loads are not transferred, and those that perceive significant bending moments and tearing forces.
The first group includes embedded parts for fixing elements that are installed on load-bearing structures (coating slabs on beams and trusses, beams and trusses on columns, self-supporting walls and Wall panels to columns, etc.). These embedded parts experience compressive or slight shearing forces and are easily fixed using a special metal clamp.
For example, to fix a supporting metal sheet on the surface of a reinforced concrete element (Fig. 14), it is enough to chop off the protective layer of two corner reinforcing bars, weld round shorts or ribs made of strip steel to them, and to the latter - a sheet (corner) of a new embedded part.
Rice. 14. Installation of parts on the upper plane:
I - chipped concrete zone; 2 - short lining made of a round rod;
3 - welds; 4 - additional embedded part; 5-corner
element reinforcement; 6 - transverse frame rods
If necessary, make the embedded part flush with the concrete surface in protective layer a groove is cut out, the width of which exceeds the width of the embedded part by 10-20 mm, and the depth exceeds the thickness of the plate by 5-10 mm. The plate is pressed into the fresh cement mortar and is welded through short linings to the working reinforcement of the frame.
A less labor-intensive method for installing structural embedded parts using metal clamps (Fig. 15), although it requires more steel consumption. Such embedded parts are made on site from pre-prepared and fitted elements.
Fig. 15. Installation of parts using clamps:
1 - side strips of the clamp; 2 - front strap of the clamp; 3 - welds; 4 - coupling bolt; 5 - stiffeners; 6 - hole in the beam wall for passing pre-cast concrete
When constructing rigid joints between crossbars and columns, as well as in case of defects in the outlets of the reinforcement (misalignment, reduction in diameter and quantity of reinforcement), female clamps are recommended, the area of which is equal to the design cross-section of the joint. During reconstruction, there is often a need to anchor additional reinforcement or install new embedded parts in an existing reinforced concrete structure. In these cases, it is recommended to drill holes in concrete with a perforator to a depth of at least 20 reinforcement diameters and embed reinforcement in them epoxy glue or by vibrocaulking with a rigid cement mixture. Using epoxy adhesive, you can attach smooth and periodic profile reinforcement to the horizontal and vertical planes of concrete, as well as to the lower plane located at an angle of 45° to the horizontal. It is allowed to fix reinforcement with cement mortar only on the horizontal plane of concrete. A washer is welded to the end of the anchor short, and the well is caulked with cement mortar using a special vibration compactor. The anchoring of rods in the concrete body is carried out at a distance of at least 5 diameters from each other and at the same distance from the concrete edge.