In repair and construction works, technical operations with columns are performed quite often. This is due to the large loads that fall on this structural element, wearing out its structure. The most common repair and restoration operation of this type can be called strengthening of columns, for which a wide range of methods is used.
When is it necessary to strengthen the wellbore?
The need for additional strengthening of building structures usually arises after the formation of defects. The column is mainly used as a bearing architectural and construction element, so it is characterized by various kinds of damage. The most common problems are:
- Cracks. The most common type of damage to a column structure, which can have different forms and manifestations. As for the causes, deformation cracks can occur as a result of building shrinkage, increased loads, corrosion of reinforcement in the shaft, a decrease in the strength of concrete andetc.
- Chipped. An equally dangerous defect, the formation of which may be associated with mechanical or fire effects on the structure, as well as with the loss of the original properties of metal bearing rods.
- Peel off. This kind of damage also occurs due to fire effects, corrosion of reinforcement and pressure of neoplasms - ice crust or alkalis.
- Peeling. As a rule, it is a consequence of contact with aggressive media. Cyclic processes of moistening/drying or freezing/thawing usually lead to the complete destruction of the structure.
Structure deformation factors can influence the choice of tactics for repair and restoration activities. But most often, column reinforcement technologies are selected based on the physical and operational qualities and parameters of the wellbore. Before proceeding with the review of specific methods for solving the task, it is worth familiarizing yourself with the universal rules for organizing work.
General advice from experts in the course of work
In reinforcing technical operations that are carried out in relation to load-bearing structures and structures, various supports, linings and corner support elements are often involved. When using such devices, it is important to consider two rules:
- The number of levels or layers of the reinforcing bandage should not be less than three. The cross strapping is completely superimposed in four layers.
- An overlap of about 20-30 cm is maintained. Butt joints are usually excluded.
If it is planned to use methods of strengthening columns with surface treatment of the trunk with composite agents and polymers, then the following conditions should initially be taken into account:
- Concrete moisture should be at least 4%. This coefficient is checked by a moisture meter.
- Condensation must be removed from the surface of the column.
- An epoxy layer is applied to the barrel before the polymer is directly applied.
- The temperature of the structure should vary between +10…+45 °С. This is the normal mode for working with resin formulations.
Regardless of the method used to strengthen the column shaft, the surface should be cleaned and dedusted. It must be free from dirt, grease stains, and laitance. Such tasks are solved with a grinding tool - manual or machine, depending on the area.
Clip Reinforcement Technology
The use of a combined casing to strengthen the shafts of the columns makes it possible to ensure the stability of the structure, both in front of dynamic and static loads. The standard version of this method is considered to be the reinforcement of columns with a metal clip, but experts recommend initially calculating the addition of the frame with reinforced concrete inserts with closed steel clamps.
Before performing installation operations, notches should be made in the structure of the trunk up to 5 mm deep. The surface of the column is also cleaned of foreign particles and protected from corrosion. The basis of the frameclips will be a structure of transverse strips and longitudinal metal corners. Longitudinal components are seated on a cement-sand mortar and clamped with clamps. Further, along the entire length of the trunk to the corners, it is necessary to weld the transverse strips by spot welding, maintaining a step of about 50-60 cm.
The advantages of strengthening columns with steel clips include the speed of installation and the structural flexibility of the fastening scheme. Immediately after the installation of the frame is completed, the trunk will be ready to accept the design loads, and in the future, if necessary, the frame can be modified by introducing additional fasteners. But the clip can perform the main task of strengthening only if the screeds and planks with corners fit snugly to the surface of the column. The quality of fixation is determined by the smoothness of the barrel and its geometry.
Section extension technology
Typical construction of a building column consists of two structural parts - concrete and reinforcing elements. If the strengthening of the columns with clips is oriented towards increasing the rigidity of the bearing metal skeleton of the barrel by the external method, then the increase in the section aims to expand the area of the bearing surface. The main concrete mass is increased, which makes the structure more stable and durable.
This method is used in cases where, in principle, it is possible to increase the technical zone at the site of the column operation. The best way can be a one-sided increase in the section - in width,length or depth of the structure. From a technological point of view, the main task of the master will be to ensure a sufficiently strong bond between the new concrete layer and the old one. For this, methods of strengthening columns with metal clips are used. But the frame in this case does not perform the function of an independent bearing element, but acts as an auxiliary reinforcing crate, which will allow you to connect two concrete levels. The same longitudinal reinforcement with notches and corners is mounted. Ideally, if possible, it should be welded to the main reinforcement in the barrel with metal shorts. Then the concrete mortar is directly built up with masonry.
Composite Reinforcement Technology
Today, in many areas of construction and production, metal parts are being replaced by products made of composites and carbon fiber. This option of strengthening the columns is advantageous in that, with a smaller mass and dimensions of the element, it allows to provide the same functional tasks. Lightweight carbon fiber itself does not overload the column (especially important for structures of dilapidated cultural monuments), but shows resistance to loads like steel. Moreover, the tensile strength of some composites is 4-5 times higher than that of reinforced concrete reinforcement.
The technique of strengthening the columns in this case will consist in gluing composite or carbon fiber lamellas perpendicular to the surface of the trunk. Typically, the calculation is made for the relief of vertical loads with an emphasis onbending moment. To achieve this reinforcement effect, the plates are glued along the line of action of the load moment. As for the adhesive composition, polymer building mixtures can be used, which will also perform auxiliary tasks of external reinforcement of the structure, moisture protection and heat resistance - the set of adhesive properties will depend on the conditions of its use. Among the advantages of this method, the absence of structural changes in the column, the possibility of decorating the trunk by painting the lamellas and durability stand out.
Reinforcement of reinforced concrete columns
For this type of architectural trunks, it is recommended to use steel jacket reinforcement methods. Since we are talking about a massive structure with a large mass, the reinforcing frame must fit tightly into the structure of the column. At the same time, it is undesirable to overload the bearing shaft, since this will lead to a higher effect of mechanical fatigue not only for the column, but also for the lower floor. It would be optimal to use a steel clip with corners on a cement-sand mortar. As in the classical scheme, reinforced concrete columns are reinforced with transverse strips and transition inserts welded to the internal reinforcement of the shaft.
Before welding, it is important to consider one technological trick. Experts recommend heating the wallpaper strips to 100-120 ° C, and only after that proceed with the connection. When the element cools down, its dimensions will become smaller, which will provide a positive effect of prestressing. Also, in strengthening reinforced concrete structures, it will not be superfluous to use additionalsafety devices. It is most convenient to mount spacers formed by two channel corners. They are connected with planks and fastened according to the principle of support with tension bolts.
Reinforcement with heated clamps
If the columns do not experience large design loads and do not require a major strengthening of the structure, then you can get by with an optimized technique for installing strip steel linings. It turns out a kind of strapping clamps, which are mounted along the entire height of the trunk. As a result, building materials with fittings are saved, and the column design remains intact. The technological complexity of such a solution lies in the preheating of the metal strips and the correct crimping of the column. Theoretically, clamps can be used to reinforce reinforced concrete columns with round, rectangular and square sections. But in each case there will be its own crimping scheme, for which the appropriate strip gripping method is selected.
Blanks for overlays are heated in a furnace building or with a burner to about 300 ° C. Further, using a special jig or clamps, it is necessary to tightly compress the trunk with a clamp in the previously established zone. Some time after the strapping, the clamp will cool down, and the metal, as a result of temperature reduction, will press even more tightly against the surface of the column. Again, the result is not so much an independent reinforcing frame as an auxiliary reinforcement.
Strengthening metal columns
Compared to reinforced concrete shafts, full metalstructures exclude the possibility of a monolithic build-up of the structure by means of a frame or concrete masonry. Therefore, braces, tightenings, spacers and prestressing devices are more often introduced. A very practical and functional option is to reinforce the steel column by expanding or strengthening the structural shoe adjacent to the floor or foundation. On the lower tier, the possibility of creating a concrete screed is allowed, which will increase the vertical stability of the column.
Small shaft structures are recommended to be reinforced with prestressed members. In this capacity, inventory and telescopic trusses with rigid struts are used, the parameters of which can be changed depending on the current load. By the way, such strengthening of reinforced concrete columns will be difficult due to insufficient structural rigidity, but metal shafts allow the use of jacking tools. That is, the user can change the height and position of the structure by wedging and connecting it with clamps.
Slots and grooved recesses are made in the supporting sections for additional insurance, and restrictive temporary plates with circular slots for reinforcement are mounted. After that, a reinforcing bar is installed, and the supporting zone is concreted. When the poured screed gains enough strength, the reinforcement bar is strained with anchor hardware and bolts - they can be built into the holes from the side of the lower faces. It turns out a capital method of structural reinforcement of columns,which is used only when it is technically possible to reconstruct the adjacent site.
Strengthening compressed columns
Eccentrically compressed trunks are strengthened by a combination of technical means, including reinforcing bandages, profiled metal corners and cross bars. Complex strengthening allows in this case to provide constrained deformation and mutual operation of the strapping elements with ceilings. That is, the load moments are not redistributed, but are directly transferred from the upper concrete structure to the lower one.
The basis of the reinforcing system is formed by several transverse bandages, which are interspersed with single reinforcing inserts made of steel or carbon fiber. But if the reinforcement of the column with a reinforced concrete cage is made with the addition of a sand-cement mortar, then the bandage with overlays is calculated only for hardware fasteners. In particular, the same concrete is replaced by anchoring with longitudinal elements through the floors. The main difficulty of mounting such a system comes down to the need to maintain axial symmetry when installing longitudinal gripping and fastening elements.
Conclusion
The nature of the application of one or another method of strengthening a vertical architectural structure will largely depend on the characteristics of the parts of the structure associated with it. For example, reinforcement of reinforced concrete columns under heavy loads may involve both the installation of a metal frame with concrete expansion and the installation of spacers. But only if it allowslower overlap - the limitation may be due to the excess of the design loading mass. Such restrictions become especially acute in situations of amplification of group column compositions. As a rule, massive and heavy frames and screeds are not allowed in such cases, and the developers of the technical project are faced with the task of detailed calculation for the installation of additional connections by integrating rigid prestressed supports.
