Excellent reinforcement scheme is embodied in four characteristics: convenient construction, advanced construction technology, good economic effect and high reinforcement quality.
1. Good constructability is one of the conditions that must be considered in the reinforcement project scheme.
The advantages and disadvantages of the reinforcement project plan should first be based on the convenience of construction, and the lack of good constructability is an obstacle to the reinforcement project construction. Although some reinforcement schemes are feasible to solve the problems, they increase the construction difficulty in the construction process, resulting in the disadvantages of long construction period, large manpower and low safety factor, which affects the reinforcement quality. For example, the beam of a construction site has serious cracks and needs reinforcement. There are two construction schemes for concrete reinforcement design: simple repair method (that is, the brittle concrete at the crack of the beam is chiseled, and the corroded steel bar is derusted and sealed with epoxy mortar after the steel bar is exposed, so as to achieve the purpose of reinforcement) and enlarged section reinforcement method (that is, the strength and rigidity of the member are improved by increasing the cross section and reinforcement).
Through the analysis of design schemes, these two schemes have the advantages of low project cost, but they also have the following disadvantages: 1) poor technical feasibility. Due to the large span of this beam, the concrete beam needs to be chiseled in sections, and a large number of temporary supports are needed for safety protection, resulting in unnecessary waste of turnover materials; 2) the labor intensity is high, and only one meter can be chiseled when the concrete beam is chiseled, so the labor intensity is doubled; 3) Low work efficiency, a lot of repetitive work and backward construction methods delay the construction period, which leads to the decline of labor efficiency; 4) The safety is poor, because all girders must be chiseled with steel chisels, and the bearing capacity of girders is reduced. Always pay attention to whether the protective measures are in place during construction, and accidents are prone to occur if you are slightly careless; 5) The output value benefit is small, which wastes a lot of turnover materials and labor costs, increases production costs and reduces production benefits; 6) The enlarged cross section affects the appearance and space size of the house.
Based on these reasons, after consultation with Party A and the design institute, we changed the reinforcement scheme, adopted the advanced steel-clad reinforcement construction method, and strengthened these girders with QR-type bonding and anchoring technology. Due to advanced technology, good reinforcement performance, small occupied space, short construction period, less material consumption and simple and safe technology, the labor intensity is reduced and the reinforcement quality is improved. Good comprehensive benefits have been achieved.
2. Analysis of different types of reinforcement projects and reinforcement schemes.
Generally speaking, the commonly used methods in reinforcement engineering include increasing cross section, wrapping steel bars, applying prestress and changing the way of structural force transmission. With the continuous progress of science and technology, the application of new technologies, new materials and new processes to engineering reinforcement methods, such as chemical grouting, steel-bonded anchorage and carbon fiber reinforcement, came into being and began to be widely used in various reinforcement projects. The concrete scheme can best reflect the characteristics of short, flat, fast and economical required by the reinforcement project, and the reinforcement scheme should be comprehensively determined according to the conditions of the components to be reinforced.
(1) Taking the reinforcement of frame beams as an example, I personally think that the more reasonable, economical and technologically advanced reinforcement schemes are bonded steel anchorage method and carbon fiber reinforcement method. The former is obviously superior to the section method and prestressed reinforcement method because of its low cost, simple construction and good reinforcement effect, while the latter has various advantages besides high material cost, the important performance is that the material itself hardly increases weight; High strength, the strength of cured carbon fiber is ten times higher than that of steel; The labor intensity is low, and only one or two people are needed to operate a working face; The construction period is short, and skilled workers can complete nearly 200m2 per person per day. However, the reinforcement effect in negative bending moment area is not as good as that in steel plate.
(2) Taking the reinforcement of frame columns as an example, the common reinforcement method is steel-clad reinforcement, that is, steel is wrapped around concrete columns for reinforcement, which will not increase the section size of concrete, but also greatly improve the bearing capacity of concrete columns. The concrete methods are divided into dry operation and wet operation: the dry reinforcement method is to directly wrap the steel bar (usually angle steel) around the concrete column to be reinforced, and there is no connection between the steel bar and the concrete because there is no connection between the steel bar and the concrete. One of the wet reinforcement methods is to paste the angle steel on the concrete column with latex cement slurry or epoxy resin chemical grouting, and the other is to leave a certain distance between the angle steel and concrete and pour concrete in the middle, so as to realize the combination of steel and concrete.
Compared with the two operation methods, the dry operation method is simpler, lower in cost and shorter in construction time, but the bearing capacity is not as good as the wet operation method. In the scheme selection, the appropriate scheme should be reasonably selected according to the reinforcement requirements and the original components. For example, due to the function change of Taihe Hotel in Xinxiang City, the original design of the first floor column adopts dry reinforcement scheme, and the column body is wrapped with L 100×6 angle steel and connected with wooden strips, which fully meets the reinforcement requirements. However, the columns on the fourth and fifth floors of a mechanical and electrical engineering school in Xinxiang City were corroded and cracked, so the wet reinforcement scheme was adopted. High-grade cement mortar and epoxy mortar mixed with quartz sand are used for local column angles. The two reinforcement methods have achieved good results.
In addition, for reinforcement projects, there are welding reinforcement, stirrup reinforcement, shotcrete reinforcement, chemical grouting repair, steel bar bonding reinforcement, carbon fiber reinforcement and so on. Each reinforcement method has its own characteristics and scope of application. As long as it is effective and technically mature, it can meet the reinforcement requirements, and it is economical and practical.
3. The reinforcement project plan should write articles on new technologies, new materials and new technologies.
Excellent reinforcement project scheme should reflect the feasibility, scientificity and advancement of its construction method. Personally, chemical reinforcement method is the first choice in reinforcement engineering at present. As we all know, some reinforcement projects need a lot of manpower, material resources and time to adopt outdated reinforcement methods, which can no longer meet the requirements of quality, time limit, safety and economy of current reinforcement projects, and chemical reinforcement methods are increasingly becoming the first choice in reinforcement projects because of their obvious advantages. For example, in the reinforcement part of Nanning Zoo 10# workers' residential complex, which I am in charge of, chemical reinforcement is used, and QR structural adhesive is applied to reinforce the frame beams of the fifth and sixth floors, which meets the normal use requirements of the residential complex under the condition of increased load and fully demonstrates the application results of new technologies, new materials and new technologies in the reinforcement project.
Among the chemical reinforcement methods, carbon fiber reinforcement technology is an advanced reinforcement method besides sticking steel. Compared with other general reinforcement technologies, it has the characteristics of moisture resistance, strong corrosion resistance, light weight, high strength, convenient construction and good quality, and its reinforcement performance is superior to other reinforcement methods at present.
It can be seen that the selection of reinforcement project scheme should be targeted, and different reinforcement projects should take corresponding reinforcement measures. It is necessary to reflect the scientific and advanced nature of the technology when formulating the price ratio, performance ratio and quality ratio. Such a reinforcement scheme is a good reinforcement scheme.
4. Engineering construction requirements of several typical reinforcement methods
The purpose of engineering reinforcement is to repair, reinforce and improve the bearing capacity, enhance the use function and meet the use requirements through reinforcement construction. Therefore, the fundamental purpose of selecting reinforcement scheme is to improve the quality of reinforcement project. Different reinforcement schemes have different construction methods and quality evaluation standards. According to several typical reinforcement methods in Technical Specification for Strengthening Concrete Structures (CECS 25: 90) and construction experience, different reinforcement methods should be emphasized in construction.
4. 1 steel-clad reinforcement method
Surface treatment, including the treatment of steel bar joint surface and steel plate joint surface, should be the key in the process of steel bar construction. During the construction of dry reinforcement, in order to make the angle steel cling to the surface of the component, the concrete surface must be polished smooth and free of sundries and dust. When mixed reinforcement is used for construction, the treated angle steel and concrete surfaces should be painted with latex cement slurry or prepared with epoxy resin chemical grouting material, and the steel plate should be derusted, the concrete should be dedusted, the steel plate and concrete surfaces should be cleaned with propylene or xylene, and then glued and poured.
4.2 Prestressed reinforcement method
When prestressed tie rods are used for reinforcement, the tie rods must be straightened and adjusted in advance before installation, and the size and installation position of the tie rods must be accurate. Before tensioning, the quality of welded joints, screws and nuts should be checked to ensure the correct and reliable force transmission of the pull rod, so as to avoid fracture or sliding during tensioning, resulting in safety and quality accidents. When prestressed stay bars are used for reinforcement, attention should be paid to the quality inspection of buried force-transmitting weld between angle steel at the end of stay bars (and its hot plate) and concrete members. After passing the inspection, both ends of the strut are temporarily fixed with bolts, and then filled with epoxy mortar or high-strength cement mortar. Strengthened strut limbs, connecting plates, slats and tension bolts shall be coated with antirust paint for corrosion protection.
4.3 Reinforcement method by changing the way of structural force transmission
If wet connection is used to increase the fulcrum, the contact surface between the beam and column at the joint and the concrete of post-cast strip should be chiseled to remove scum and moistened with water, and micro-expansive concrete should generally be poured. If the steel hoop is dry-connected, cement mortar should be applied between the steel hoop and the contact surface of the beam. After the steel hoop and the pillar are welded firmly, all joints should be plugged and filled with dry mortar. For wedge jacking method, after jacking, all wedges shall be welded and sealed with epoxy mortar.
4.4 External Bonding Steel Reinforcement Method for Concrete Members
This method is simple in construction, but first of all, we need to pay attention to the surface treatment of concrete and steel plate. For the bonding surface of old and dirty concrete members, we should first dip a hard brush in an efficient detergent to brush off the oil and dirt on the surface, then rinse with water, and then polish the bonding surface, remove the surface layer with a thickness of 2~3mm, expose a new surface, level off and remove dust; If the concrete surface is good, you can directly polish the bonding surface, remove the 1~2mm thick surface layer to make it smooth, remove dust, and then wipe the surface with acetone. The surface treatment of steel plate should be based on its embroidering corrosion, and it can be polished by sandblasting, emery cloth and grinder to make the steel plate appear metallic luster. The polished grain should be perpendicular to the stress direction as far as possible, and then it can be cleaned with acrylic.
Secondly, we should pay attention to the choice of adhesive. At present, the domestic building structural adhesive market is mixed, so we must be careful in the choice of adhesives. Third, we should pay attention to the details in the process of dispensing and pasting. The adhesive should be prepared in strict accordance with the proportion required in the instructions. In particular, it is necessary to master the dosage of curing agent and mix it evenly. At the same time, when pasting, ensure that the pasting surface is full and dense. Finally, it should be noted that the steel plate should not be disturbed during the curing stage.
At present, these concrete structure reinforcement technologies need to be further explored in practice. With the continuous progress of building science and technology, new building materials are constantly emerging, and better reinforcement construction methods will also be expanded. Therefore, the selection scope of reinforcement construction scheme will also have a broader space.
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