Building reinforcement is a branch of civil construction. According to statistics, some of the old houses built in the 1950s and 1960s on the mainland have to be reinforced because they have exceeded the design benchmark period, about 1/3 of the residential safety reserves are insufficient, and the residential structure of the city has gradually entered an aging and needs to be strengthened and repaired. At the same time, the state limits the investment in structural construction, from the perspective of cost saving, the use of old structures and old buildings for reinforcement is increasing, and the number of projects that need to be reinforced is gradually increasing. The following is an introduction to several reinforcement methods and technical points for your reference.
Reinforced with adhesive steel
The adhesive steel reinforcement method is a reinforcement method that uses special building structure glue to paste steel plates on the surface of reinforced concrete structural components to improve the bearing capacity of structural components. The effect of bonded steel reinforcement mainly depends on the quality of the bonding construction. The construction of adhesive steel reinforcement should be carried out in strict accordance with the process flow for professional construction.
Surface treatment→ (unloading, gluing) paste→ fixing and pressurizing→ curing→ inspection→ anti-corrosion treatment.
1. Surface treatment
Surface treatment includes reinforcement component joint surface treatment and steel plate lamination surface treatment, is the most critical process, should be carefully treated concrete component joint surface, according to the degree of new and old part of the component surface, degree of solidity, degree of dry and wet, respectively, according to the following four situations.
1) For the bonding surface of the component, the high-efficiency detergent should be dipped in a hard brush first, the surface oil and dirt should be brushed off, and then rinsed with cold water, and then the adhesive surface should be sanded off 2 to 3mm until the new surface is completely exposed, and the powder particles are blown off with oil-free compressed air. If the surface is seriously uneven, it can be repaired with high-strength resin mortar.
2) If the concrete surface is not very dirty, you can directly sand the adhesive surface, remove the surface layer of 1 to 2mm, remove the dust with compressed air or rinse it with water, and wipe the surface with degreasing cotton with acetone after complete drying.
3) For the new concrete bonding surface, first use a wire brush to brush off the loose scum on the surface, and then use a hard brush to dip the detergent to wash the surface, or rinse with water, and then completely dry.
4) For concrete components with large humidity or concrete components with an age of less than 3 months, because the bond strength of the general resin adhesive on the wet base layer will be greatly reduced, in addition to meeting the above requirements, manual drying treatment must also be carried out.
2. The steel plate lamination surface of the steel plate should be treated according to the degree of corrosion of the steel plate according to the following two methods.
1) If the steel plate is not rusted or slightly rusted, it can be sandblasted, sandblasted or flat grinding wheel until a metallic luster appears. The larger the rough grinding, the better, and the grinding pattern is as perpendicular to the direction of the steel plate force. It is then wiped clean with a degreasing cotton dipped in acetone.
2) If the steel plate rust is serious, it must first be soaked with moderate hydrochloric acid for 20 minutes to make the rust layer fall off, and then rinse with lime water to neutralize the acid ions, and finally use a flat grinding wheel to grind out the grain.
3. Unloading. In order to reduce and eliminate the stress and strain lag phenomenon of the post-adhesive steel plate, the appropriate amount of the components should be unloaded before the adhesive steel plate.
4. Glue. At present, the adhesives for various structural reinforcement are basically A and B components, which must be temporarily formulated on site during use. In principle, the preparation should be carried out in accordance with the provisions of the product instruction manual, but due to the strong time limit of the glue, the on-site trial matching should also be carried out before use, and appropriate adjustments should be made according to the local temperature conditions and storage time at that time, and the mechanical indicators should be selected as the optimal ratio. According to the selected proportion of the scale, the A and B groups are poured into a clean container, and the same direction is stirred mechanically until the color is completely uniform.
5. Paste. After the adhesive is prepared, use a spatula to apply at the same time on the treated concrete surface and the steel plate lamination surface, in order to make the glue can be fully infiltrated, infiltrated and diffused, adhered to the bonding surface, it is advisable to first use a small amount of glue to scrape back and forth on the bonding surface several times, and then add 1 to 3mm, the middle thick edge is thin, and then the steel plate is pasted in a predetermined position. If the façade is pasted, in order to prevent flowing, a layer of dewaxed glass cloth can be added. After the steel plate is pasted, the hand hammer gently taps the steel plate along the pasting surface, if there is no cavitation sound, it means that it has been pasted densely, otherwise the steel plate should be peeled off, glued, and re-pasted.
6. Fixation and pressurization. Immediately after the steel plate is pasted, it is fixed with fixtures, supports or expansion bolts, etc., and pressurized appropriately so that the glue is just extruded from the edge of the steel plate. Expansion bolts generally double as permanent additional anchoring measures for steel plates, and their buried holes should be drilled together with the steel plate before gluing.
7. Solidify. Several of the structural adhesives mentioned earlier are cured at 20 ° C, the fixture or support can be removed at 24h, and the force can be used in 3d. If the temperature is lower than 15 °C, artificial heating should be taken, generally heated with infrared rays. The steel plate must not be disturbed in any way during the curing period.
8. Anti-corrosion treatment. The external adhesive steel reinforced steel plate should be treated with anti-corrosion treatment according to the design requirements. When the external plaster protects the anti-corrosion, in order to facilitate the bonding of the rake pulp, it can be bonded or wrapped in a layer of lead wire mesh or a layer of bean stone on the surface of the steel plate, and a concrete primer can be brushed in plastering.
Carbon fiber reinforcement
Compared with the traditional increased concrete section or bonded steel concrete reinforcement, carbon fiber has the characteristics of space saving, simple construction, no need for on-site fixed facilities, easy to ensure construction quality, basically no increase in structural size and self-weight, corrosion resistance, good durability and so on. In addition, the use of this method can greatly improve the service life of the building and reduce the cost of reinforcement. Therefore, carbon fiber is favored and concerned as an epoch-making reinforcing material.
1. Concrete surface treatment
1) Remove the defective and damaged parts of the surface of the concrete components.
2) Repair and restore the missing parts of the components that have been chiseled, cleaned and exposed.
3) Crack repair. Cracks with a seam width of less than 0.2 mm are sealed with epoxy resin for surface brushing; cracks larger than 0.2 mm are caulked with epoxy resin.
4) Grinding. The protruding part of the surface of the component (the junction of the concrete component, the joint of the formwork, etc.) is polished and smoothed, and the surface of the repaired component is as smooth as possible.
5) Clean the surface of the polished component and make it dry sufficiently.
2. Apply primer to the defective area
The compounding primer (binder) is applied evenly over the concrete surface of the defective part.
3. Repair of defective surfaces of components
The repair of defective surfaces of the component surface with epoxy putty is a very important step, and the main points are as follows.
1) Putty main agent, curing catalyst, curing agent according to the prescribed proportion of accurate weighing, into the container, with a stirrer to stir evenly.
2) The concave parts of the surface of the component are filled with epoxy putty and repaired to a flat surface. When using epoxy putty in defect repair, it is necessary to work under conditions of temperature above -5 °C and relative humidity of less than 85%. After the putty is scraped, the surface is still concave and convex and rough, and it should be sanded and smoothed with sandpaper.
4. Brush the primer. The compounding primer (binder) is applied evenly with a roller to the surface of the concrete to be bonded.
5. Paste the carbon fiber. Before pasting the carbon fiber material, first confirm that the pasted surface is dry. When the temperature is above minus 10 °C and the relative humidity RH > 85%, construction shall not be carried out without effective measures. To prevent damage to carbon fiber, carbon fiber materials are transported, stored, cut and pasted. The use of steel ruler and wallpaper knife according to the specified size to cut off the carbon fiber material, the length of each section is generally not more than 6m is appropriate. In order to prevent damage to the material during the storage process, the amount of cutting of the material should be based on the amount of cutting on the day. Carbon fiber longitudinal joints must be lap more than 20cm. This part should be coated with more resin, and the carbon fiber does not need to be lapted laterally. The key points of its construction process are as follows.
1) The main agent, curing urger and curing agent of the paste resin should be weighed accurately in accordance with the prescribed proportions, loaded into the container, and stirred evenly with a stirrer. The amount of one reconciliation shall be based on the use of the usable time.
2) When pasting, try not to have air between the carbon fiber and the resin. Roller (special tool) can be used to roll on the carbon fiber material several times in the direction of the fiber, so that the resin can be infiltrated into the carbon fiber.
6. Conservation
After pasting the carbon fiber material, it needs to be naturally cured for 1 to 2 hours to achieve initial curing, and it should be ensured that there is no external interference and collision during the curing period.
7. Painting
If the reinforcement component needs to be fireproof, the refractory coating can be applied after the resin has cured. The coating should be carried out after the resin has initially cured and should comply with the relevant standards and construction regulations of the paint used.
Prestressed reinforcement
The prestress reinforcement method has the triple effect of reinforcement, unloading and changing the internal force of the structure, which is suitable for the reinforcement of large-span structures, as well as the reinforcement of large structures under higher stress strain states that cannot be reinforced by general methods or the reinforcement effect is not ideal.
1. Loft positioning
1) Lofting positioning of slider pad and anchor support position
Measure the center position and span of the slider pad (along the beam bottom from the actual center of the anchor, that is, the projection point to the mid-span direction), and then mark the sides of the bottom of the beam respectively, and then draw the flat size of the pad on the bottom of the beam, and mark the hole position of the bolt. Among them, in the gasket lofting, the deflection effect of the beam is negligible.
2) Loft positioning on anchor points
When the anchoring point on the beveled rib is located at the top of the beam or the end of the beam, the distance between the anchoring point and the end of the beam is measured along the longitudinal bridge with the longitudinal axis of the top (end) of the single girder as the reference.
When the anchoring point is located at the end of the beam, the vertical distance between the anchoring point and the bottom of the beam or the top surface of the beam should be taken, and then the transverse distance of the anchoring point is taken along the symmetry of the cross-bridge direction to mark the theoretical position of the anchoring point. Since there are reinforcement bars in the top plate and web of the beam, especially the stress reinforcement, when the anchoring point is lofted, the anchoring point position can be adjusted appropriately to avoid these reinforcements, and it is important to remember that they should not be cut off.
2. Set on anchor points
When the upper anchoring point is located at the top of the beam and the top surface of the beam end, it is necessary to drill through two bevel holes with the same angle as the ribs on the bridge deck or the top surface of the beam according to the designed diagonal ribs. First of all, the bridge deck paving layer is chiseled, the concrete protective layer on the top surface of the beam is chiseled to expose the steel bar, and then the concrete at the anchor pad is finely chiseled. Make a chisel frame according to the design angle of the bevel hole, put the drill pipe of the rock drill into the groove of the chisel frame, align the center of the drill bit with the theoretical anchoring point, and then drill the hole in order to chisel the inclined hole. After the upper anchor hole is chiseled, the concrete on the top surface of the beam is cleaned and the concrete debris is removed. The excavated concrete surface is then coated with an epoxy glue and then flattened with epoxy cement mortar. Finally, when the upper anchor is placed at the top of the beam, the upper surface of the anchor pad should be ensured to be flush with the top surface of the beam, or slightly lower, to ensure that there is as thick a concrete protective layer as possible on the anchoring point.
3. Steering device
The steering device is an important component to achieve external cable reinforcement, and its transmission method and its own performance are also the key to affecting the effect of prestress application. The prestressed ribs of the in vitro prestressed concrete structure must be redirected by means of a steering device, thus forming the curved form of the prestressed ribs of the design. In the area of contact between the steering device and the prestressed ribs, due to the squeezing effect of friction and lateral forces. If the steering device is not designed or the construction measures are improper, the prestressed steel is prone to local hardening and excessive friction loss. The design of the steering device requires that the position of the prestressed ribs at the bend point must be highly accurate to avoid additional stress, and the steering device should not have any damage to the prestressed steel during the life of the structure. In addition, the processing of the steering device should be carried out in the processing plant, it is strictly forbidden to process on site, on-site installation, to be carried out strictly according to the drawings, in the transportation and welding process, measures should be taken to prevent welding deformation, before threading the bundle should be pulled to determine whether the installation is appropriate.
4. Installation and tension of prestressed ribs
Before installing the prestressed ribs, first check whether the various anchors can work properly, especially the matching of the screw and nut of the thick reinforcement, try to twist one by one, and each silk head should be screwed to the whole process without force.
For horizontal ribs and diagonal ribs, where two thick reinforcement bars or bevel rods are used as section steel, the diagonal ribs are first fixed together with the horizontal slider, and the upper anchoring point of the diagonal ribs is fixed. Position the slider in the position of its pad with a temporary bracket before penetrating the horizontal ribs. When wearing ribs, ensure that both ends of the horizontal ribs have equal head length, check the position of the slider and reserve the amount of slip. In order to prevent difficulty in tightening the nut when tensioning the anchor, tighten the nut of the two horizontal ribs, and at the same time ensure that the center of the horizontal rib is aligned with the slider anchor hole.
In the system of transverse tightening of the horizontal rib to produce prestress, the bevel rod is first welded to the U-shaped anchor plate at the end of the beam according to the inclination requirements of the inclined rib, and the horizontal rib is welded on the beveled rib by clamp rod welding. Every 2 to 2.5 m, the horizontal tie rod is lifted with a wooden block, and then a locking device is installed to reduce the sag. In case of tensioning, place the column at the beginning of the bend, and then install the bracing rod and tightener according to the design position.
5. Depression
After the tensile is completed, the local bonded section of the grouting work is a very important process, first of all, before the construction to carry out a 1:1 model test, in the case of ensuring that the grout is dense and full, the adhesion force of the local bonded section can reach 108% of the design tension. In the project, the grouting construction was carried out within 24 hours after the completion of the tensioning to meet the anchoring requirements. The grouting adopts a manual grouting machine to ensure the uniform stability of the grouting process and the requirements of the grouting pressure. In addition, the degree of compactness of the grout will directly affect the bonding effect, so the water-to-ash ratio should be strictly controlled in the grouting and the pressure should be kept uniform.
Replacement concrete reinforcement
Operational points of replacement concrete reinforcement construction.
1. When the building structure needs to be reinforced by the replacement concrete reinforcement method, the following 8 operation preparations should be made before the replacement concrete operation to ensure the quality of the replacement concrete reinforcement.
1) Before concrete pouring, in addition to the acceptance of the formwork and its support, the following items should also be accepted for concealed engineering. Quality of interface treatment and primer brushing. The brand, grade, specification, quantity, location, etc. of the reinforcement or stirrup reinforcement. The connection method and quality of the rebar and the original rebar.
2) According to the design and construction organization plan, unload or partially remove the load on the reinforced member.
3) Complete the technical review of the template system, check and clean up the residual debris in the supported template, and it is best to rinse with water.
4) The shelves and horse tracks for pouring concrete have been erected and passed the inspection.
5) Cement, sand, stone and admixtures are inspected to meet the requirements of relevant standards; According to the design requirements for concrete strength grade, durability and working, and in accordance with the current industry standard JGJ 55-2011 "Ordinary Concrete Mix Ratio Design Regulations" and the relevant provisions of local standards, the concrete construction mix ratio design is completed, and a notice has been issued.
6) Concrete mixers, vibrators and other machinery have been inspected, maintained and put into trial operation; Measuring instruments are regularly checked.
7) Check the construction power supply and line.
8) The foreman has made a comprehensive construction technical presentation to the operation team according to the construction plan.
2. Replacement concrete reinforcement construction of local rejection and interface treatment.
1) When removing the concrete to be replaced, it should be carried out according to the prescribed methods, steps and requirements. No damage to steel bars and concrete without replacement during the removal process; If the reinforcement or concrete is damaged, the construction unit should propose a technical treatment plan, and the treatment can only be carried out after being approved by the design and supervision unit.
2) The interface treatment of new and old concrete should be carried out in accordance with the design requirements and the provisions of relevant specifications.
3) When the design does not require the use of the surfacy, paint a silicate or ordinary Portland cement slurry on the original concrete surface chiseled and cleaned the interface, and the cement strength level of the pulp should not be lower than 42. Level 5; When using a surfactant, spray the chemical surfactant according to the method of the product instruction manual.
3. Concrete construction
1) Install and weld reinforcement and stirrup in accordance with the design regulations; If the original steel bar is injured during welding, it will be treated immediately with the design unit.
2) When using ordinary concrete replacement, refer to the relevant ordinary concrete replacement requirements for construction.
3) When using shotcrete replacement, refer to the relevant requirements of shotcrete replacement for construction.
4) After the concrete pouring is completed, it should be maintained in time according to the construction technical plan; The maintenance measures should comply with the provisions of the current national standard GB 50204-2015 "Concrete Structure Engineering Construction Quality Acceptance Specification".
5) When the strength of the concrete reaches the strength level specified in the design, the bottom mold and formwork of the replacement member are removed.
4. Bracket removal
When the bracket is disassembled, the concrete strength should meet the design requirements. The disassembly sequence, displacement control or stress control of disassembly shall comply with the requirements of the design regulations and the construction technical scheme.
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