The cost of covering a house for any purpose usually reaches 50% of the cost of a typical residential building. The technical condition of these structural elements is one of the main factors that determine the need for the reconstruction of civil and residential buildings.
Replacing floors is a rather expensive and very time-consuming process. In terms of cost, it reaches 20% of the amount of one-time costs for reconstruction. These works include a whole range of measures aimed at restoring the bearing capacity of the ceiling and individual parts.
What provides for reinforcement of floors
Strengthening the floor slabs may involve reducing the load and providing reliability for the duration of the work. The cross section of the bearing elements must be increased in this case. The design scheme of work should be changed.
Restoration and strengthening may include the identification of margins of safety. The design is recalculated according to new standards, which take into account the nature of the floor work. Depreciation during such work should not exceed 40%. The structure may be overloaded. To do this, heavy backfills and lubricants are changed to modern materials that reduce the own weight of the floor. In this case, wear at the stage of work should not exceed 60%.
Additional measures
Strengthening floor slabs may involve an increase in the section of structural elements. Manipulations involve attaching additional elements to existing sections. These nodes will take on part of the load. In the case of reinforced concrete floors, clips are installed, as well as metal clamps. In the first case, such additions are also called shirts.
Adding elements
Strengthening floor slabs is sometimes accompanied by the inclusion of new elements in the work. In this case, beams that stand on supports are brought up. They are installed between existing structures. New structural elements can take on the load partially or completely. Structural schemes can be changed to achieve the goals. Efforts are redistributed, in some cases spans are reduced.
Use supports
Sometimes additional supports may be installed. Wear should vary from 40 to 60%. Strengthening floor slabs using this technology is expressed in the transformationbeams for one span in a multi-span continuous structure. The technique may involve the installation of prestressed metal braces and puffs, which must be prestressed.
Reinforcement of monolithic and prefabricated slabs
Monolithic slabs are reinforced by extension technology. An additional slab is concreted over the existing one. Supports are installed in the form of metal or monolithic reinforced concrete beams.
Reinforced concrete floor slabs can be precast concrete. Such structures are hollow and are reinforced using all the same voids. In the channel zone, a shelf is punched from above, where the reinforcing cage is installed. Work can only be carried out on the supporting part of the slab. In this case, the frames will be located on part of the span. Sometimes there is a need for reinforcement along inclined and normal sections. The frames in this case will be located along the entire length of the plate.
When reinforcing reinforced concrete floor slabs using this technology, the channel is filled with a plastic solution, closed on fine gravel. The slab must be calculated taking into account the reinforcement. If the work is to be done with a multi-hollow prefabricated slab, then the channels can be monolithic. This technique is used when there are cracks in the wall between the voids, and also if it is necessary to increase the bearing capacity of the structure.
Preparation
Reinforced concrete slab is reinforced according to a certain algorithm. The surface must first be cleaned of floor elements. A furrow is made along the slab, the width of which canbe equal to 70 to 100 mm. The surface must be blown with compressed air. Next, reinforcing cages oriented vertically are installed. It will also be necessary to install a reinforcing mesh. The next step will be the placement of lighthouse rails. Next, you can lay concrete with compaction.
Reinforced concrete slab can be reinforced from below with metal ties, which are embedded in the supporting parts of the flooring and panels. Reinforced concrete beam ceilings can be reinforced by reinforcing and concreting beams. However, most often, sprengels are used for this, which are located on both sides of the beam. From below, these elements are pulled together to give them tension and enable them to work.
Use Sprengel
If you reinforce reinforced concrete floor slabs by transverse tightening of the sprengel, this will not allow you to get the desired effect, which will cause concrete collapse on the side faces of the beam. For this reason, sprengels are used today, which are made up along the length and stretched in the longitudinal direction.
Alternative solutions
Reinforcement will be effective if you use a hinged-rod chain. This technique can be compared in nature to reinforcement with sprengels. The connections will be hinged. In the chain, it is necessary to make intermediate nodes, the number of which will depend on the span of the beam. This method of strengthening the floor slabs involves the installation of hangers on different sides of the reinforced concrete beam. The connection is made from below.
When the chain is tensed, themiddle suspension tension. For uniform reinforcement, it sometimes takes several attempts to tension the suspensions. The required degree of unloading or the amount of reinforcement can be determined by taking into account the actual strength. If you have chosen such a design, then you can improve its operation by bringing the channel under the suspension. In this case, it is necessary to install tense clamps at the ends of the beam. The work of the suspensions can be combined with a channel lining. At this stage, it is necessary to eliminate the compression of the concrete under the hangers, while the clamps will reinforce the beam by a shear force.
Using carbon fiber
Strengthening floor slabs with carbon fiber is a new technique for Russia, which was first implemented in 1998. The technology consists in sticking a high-strength material to the surface, which takes part of the effort, increasing the bearing capacity of the element. The adhesives are structural adhesives based on epoxy resins or mineral binders.
If you want to reinforce hollow core slabs, you can consider carbon fiber, whose physical and mechanical characteristics are quite high. This allows you to increase the bearing capacity of the structure without losing the usable volume of the room. The self-weight of the building will not be increased either, as the thickness of the reinforcing elements used varies from 1 to 5 mm.
Carbon fiber is a material, not a finished product. Materials are made from it by the type of grids, lamellas and carbon tapes. Coating slabs (GOST28042-2013) are reinforced by gluing carbon fiber in places where the zones are most stressed. This is usually the center of the span at the bottom of the structure. Manipulations allow to increase the bearing capacity for bending moments.
To solve the described problems, you can use different types of carbon materials. If we are talking about beams, then they are reinforced in the support zones, where it is possible to increase the bearing capacity. It is in these areas that the transverse forces act. In the described case, U-shaped clamps in the form of stickers are used.
Lamels and tapes are sometimes used in combination, because the methods of their installation are similar. But if you decide to use carbon meshes, then this will eliminate the use of lamellas and tapes, because you will have to carry out wet work.
Coating slabs, the GOST of which was mentioned above, are reinforced using a technology that provides for marking the structure at the first stage. It will be necessary to outline the zones where the reinforcement elements will be located. These areas are cleared of finishing materials, cement laitance and pollution. You should reach a coarse concrete aggregate. To do this, use an angle grinder or water sandblaster.
The compatibility of the structure with reinforcement elements will depend on how well you prepare the base. Therefore, at the preparation stage, it is necessary to make sure that the surface is even, its strength and the integrity of the materials in the base, as well as the absence of dust and pollution. The surface must not bedamp, and the temperature must be within acceptable limits. Carbon materials are being prepared. They are supplied packed in polyethylene. It is important to exclude the contact of elements with dust, which is very abundant after grinding concrete. Otherwise, the elements cannot be impregnated with a binder.
You will have to cover the working area with polyethylene, along which it is convenient to unwind the carbon material to the desired length. You can use a clerical knife, angle grinder or metal scissors when cutting.
Calculation of the reinforced concrete structure before reinforcement
Verification calculations consist in comparing the forces in the elements with their bearing capacity. First, it is necessary to determine the actual forces in sections. Dimensions, stiffness, value, location and nature of the load are taken according to the results of the survey. At the final stage, conclusions are drawn and recommendations for strengthening are made.
The choice of structural and reinforcement resistances is of particular importance. These values are taken from the results, which must comply with the rules. The cross-sectional area of the reinforcement should be taken taking into account its reduction due to corrosion. When performing verification calculations, you must perform static calculations. Bending and torsional moments, transverse and longitudinal forces must be determined, taking into account the points established by the survey.
When there is a change in the ratio of span and support moments, it is necessary that in the beam sections the sum of the span moment and the share of support moments is equal to the moment in a single-span beam. This convictioncan be expressed as follows: l a M l b M0=М pr + M A + B, (1.14). Here M0 is the bending moment determined for a single-span beam; but M pr is the bending span moment, taking into account deformations. The abbreviations M A and M B denote the reference moments in the diagram. Whereas a, b is the step to the section from the left and right supports. The span length here is denoted by the letter l.
