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Theory and application analysis of building detection, appraisal and reinforcement

Through the overview of building inspection and reinforcement engineering, this paper introduces the implementation procedures of building inspection and reinforcement engineering, and expounds various reinforcement methods and construction techniques. Finally, the theory of reinforcement engineering is applied through an engineering example, which realizes the combination of theory and practice and deepens the understanding of detection and reinforcement engineering.

Keywords: detection, identification, reinforcement method, construction technology

1 Building detection, appraisal and reinforcement project

Building reinforcement engineering refers to the reinforcement engineering when the reliability of the building structure cannot meet the design or use requirements for various reasons. The reliability of building structure refers to the ability of the structure to complete the predetermined function under normal design, construction and use conditions within the specified design reference period, and it is the general name of structural safety, applicability and durability. Structural reliability appraisal is a process of evaluating the "three characteristics" of the actual structure through investigation, detection, analysis and judgment. Structural inspection mainly includes material strength, structural cracks, structural deformation, structural defects, structural corrosion, load conditions and structural geometric dimensions. By analyzing the causes of structural damage and its harm to the structure, the appraisal conclusion is made, and finally the treatment opinions should be put forward to determine whether it is necessary to strengthen the existing building. If the safety reserve in the design can be used, if the repair can solve the problem, don't reinforce it, so as to avoid the aggravation of structural damage or the emergence of new problems in the reinforcement process. Structural damage affects the safety of the structure and threatens the safety of people's lives and property, but it has the value of restoration and preservation or is more economical than demolition and reconstruction, so it should be reinforced in time. Reinforcement should not be carried out blindly, but should be carefully designed, comprehensively designed, set out from reality, adapt to local conditions, be practical, and draw detailed and complete construction drawings. In a word, the detection is scientific, the appraisal is legal, the reinforcement and reconstruction reflect the economy, the detection provides data for the appraisal, and the appraisal provides the basis for the reinforcement and reconstruction.

2 building inspection, appraisal and reinforcement procedures

3 building reinforcement methods

There are many reinforcement methods for building reinforcement projects. In actual selection, we should choose the best scheme according to specific projects, local conditions, multi-scheme comparison and the principle of advanced technology, reliability and economy. The following briefly introduces several commonly used reinforcement methods.

3. 1 chemical reinforcement by planting steel bars This technology is widely used for reinforcement rooting and bolt anchorage in building storey adding, building reconstruction and reinforcement, glass curtain wall, elevator derrick, equipment installation and other installation projects. The scope of application is steel bars or bolts with a diameter of 46 (inclusive). After anchoring, the load can completely reach the ultimate load of steel bars or bolts. This method is suitable for the reconstruction and reinforcement of concrete load-bearing structures with concrete strength grade of C20~C60. It is not applicable to the above-mentioned severely weathered structures and lightweight structures.

Construction process of chemical bar planting: positioning-drilling-hole cleaning-reinforcement treatment-mixing and injecting glue-anchoring and reinforcement-fixed maintenance-inspection and acceptance.

3.2 Bonding steel reinforcement technology for structures is suitable for general flexural and tensile members subjected to static force. The weight of the reinforcement member increases or decreases; At the same time, it does not affect the use clearance of the structure and does not change the shape of the component; And the stress on the joint is uniform, and stress concentration will not occur. Sticking steel plates to strengthen the structure is fast, and there is no wet operation or only a small amount of plastering on site, which has little influence on production and life, and has no obvious influence on the appearance and original clearance of the strengthened original structure, but the reinforcement effect depends largely on the sticking technology and operation level; It is suitable for the reinforcement of flexural or tensile members under static action and normal humidity environment.

Construction technology of structural steel bonding reinforcement: positioning and setting-out, surface treatment of concrete and steel bars, unloading, pre-pasting, configuration of structural adhesive, bonding and pasting of steel members, crimping and fixing, curing, maintenance, inspection, acceptance and anti-corrosion treatment.

3.3 The technology of sticking carbon fiber cloth on the concrete surface with matching bonding resin and strengthening and repairing the concrete structure with fibrous materials (carbon fiber cloth, carbon fiber board, aramid fiber and glass fiber) plays the role of structural reinforcement and seismic reinforcement. It is widely used in the reinforcement of building beams, slabs, columns and walls, bridges, tunnels, chimneys, silos and other civil engineering.

The construction process of strengthening by sticking carbon fiber cloth: positioning and setting out-surface treatment-painting primer-carbon fiber sticking-surface protection, infiltration-acceptance.

3.4 shotcrete reinforcement shotcrete is a fast and effective reinforcement method from roadway support technology to ground structure reinforcement, which has its unique advantages: shotcrete is formed by spraying a certain proportion of mixture through high-pressure pipeline, with the help of spraying machinery and compressed air as the driving force, at high speed. The spraying speed of the concrete nozzle reaches 60m ~ 80m/s, and the repeated and continuous impact of cement and aggregate during the high-speed spraying makes the concrete compact. Due to the small water-cement ratio (0.4-0.5), the bonding strength with concrete, masonry and steel bars is high. When it is used with steel mesh, it can transfer the tensile stress and shear stress on the joint surface well, with high mechanical properties and good durability, which can greatly improve the bearing capacity of masonry and enhance the integrity. At the same time, under the condition of high-speed shotcrete, mortar can enter the pores and cracks of steel bars, so that the original structure can be restored to a certain extent.

Concrete spraying technology: coarse aggregate, fine aggregate, cement, accelerator-dry material mixer-sprayer-nozzle-spraying surface.

4 engineering cases

4. 1 Project Overview: Schwab Building has one basement and seven floors above ground, and its structure is a frame structure with a total construction area of about 13000 square meters. The building has a total height of 25.3 meters, a total longitudinal length of 80 meters and a total transverse length of 20 meters. The design and use reference period is 50 years, and the seismic fortification intensity is 6 degrees. The site category of the frame structure is Class II, the safety level is Class II, and the seismic level of the frame is Class IV. According to the geotechnical investigation report and construction design, the characteristic value of the treated foundation bearing capacity is 220kPa. The strength grade of the foundation concrete is C30, and the concrete grade of the first to third floors of the underground beam slab column is C35. The concrete grade of beams and columns with more than four floors is C30. The reinforcing bars are HPB235 and HPB335. MU 10 ordinary clay brick is used as the masonry material below 0.000, and M7.5 cement mortar is used as the mortar; KP 1 non-load-bearing porous brick (bulk density 10kN/m3) is used for mortar above 0.000, and M7.5 mixed mortar is used for mortar.

Theory and Application Analysis of Building Detection, Appraisal and Reinforcement (Ⅱ)

4.2 The main content of detection and appraisal is to detect the appearance damage of beam components, understand the damage status of damaged components through the appearance detection of building structural components, and make a preliminary investigation on the location and degree of damage of components. On the other hand, it is a special inspection of damaged beam members. Through the special inspection of structural components, we can master the material characteristics and defect state of the structure, detect the exact cause and degree of structural damage, and judge the technical state of relevant parts and main components accordingly.

4.2. 1 Evaluation of damage degree of concrete members According to the engineering characteristics and the general survey results of beam members, the damaged state of members is classified and rated.

① The surface of beam member is damaged, but there is no exposed reinforcement-slight damage.

② The surface of the beam member is damaged, and the main reinforcement/stirrup is exposed, but the steel bar is not damaged-generally damaged.

(3) Not only the surface of the beam member is damaged, and the main reinforcement/stirrup is exposed, but also the steel bars are damaged to a certain extent, and some steel bars are slightly rusted-more serious damage.

(4) Not only the surface of the beam member is damaged, and the main reinforcement/stirrup is exposed, but also the steel bar is seriously damaged, and some steel bars are corroded-seriously damaged.

4.2.2 Reliability Appraisal of Damaged Beam Components Through theoretical calculation and design comparison, the service bearing capacity, service condition, safety and reliability of structural components are comprehensively analyzed, and the performance and function of structural components are comprehensively evaluated.

When evaluating the safety of concrete structural members according to the bearing capacity, the grades of each inspection item are evaluated respectively, and then the lowest grade is taken as the safety grade of structural bearing capacity.

4.3 Inspection and appraisal conclusions and suggestions

4.3. 1 appraisal conclusion of damaged beam members 177. In the first case, the surface damage points of beam members without exposed tendons account for 34% of the total; In the second case, not only the surface of the beam member is damaged, but also the main reinforcement/stirrup is exposed, but the number of unbroken steel bars accounts for 49% of the total; In the third case, not only the surface of the beam member is damaged, but also the main reinforcement/stirrup is exposed, but the number of points with a certain degree of damage to the reinforcement and slight corrosion of some reinforcement accounts for12% of the total; In the fourth case, not only the surface of the beam member is damaged, but also the main reinforcement/stirrup is exposed, but the number of points with serious reinforcement damage and partial reinforcement corrosion accounts for 5% of the total.

Test results of protective layer thickness of steel bars: The protective layer thickness is one of the important indexes to evaluate the durability of structures and whether concrete and steel bars work together effectively. In this experiment, the protective layer thickness of 83 beam members with five to seven floors was measured. The design requires that the thickness of concrete protective layer of tension member is 30mm, and the measured thickness of reinforced concrete protective layer is 25mm, with the maximum thickness of 35mm. It can be seen from the test data that the thickness of the protective layer basically meets the requirements of the design and relevant specifications.

According to the appearance inspection results, special inspection results and corresponding specifications, the bearing capacity, safety and reliability of damaged beam members are evaluated according to the Reliability Appraisal Standard for Civil Buildings (GB50292- 1999). The conclusion is that there are 83 damaged beam members, of which 35% are B-class members and 46% are C-class members. Grade D accounts for 19% of the damaged beam members, among which 52% of the five-story damaged beam members are Grade B, 36% are Grade C, 12% are Grade D, and the six-story damaged beam members 19% are Grade B, and 50% are Grade C and Grade D..

4.3.2 The treatment scheme of damaged beam members is suggested to be based on the inspection and appraisal conclusion, and it is suggested to repair and reinforce the damaged beam members according to different evaluation grades.

Used for beam members with damaged surface but no exposed reinforcement. Repair the damaged parts with fine stone expansive concrete, high-strength grouting material or epoxy mortar. The fluidity of the new concrete for repair should be larger, and the strength grade should be one grade higher than that of the original concrete, and not less than C25. In order to enhance the bonding ability between the new concrete and the original foundation concrete, the concrete residue in the damaged part must be removed before repairing, the bonding surface should be coated with epoxy resin or concrete interface agent, and the new concrete should be poured before the initial setting of epoxy resin or interface agent. Some beams with Grade C and Grade D should be strengthened with carbon fiber according to the calculation results, and the construction measures should be carried out in strict accordance with the National Architectural Standard Design Atlas "Reinforcement Structure of Concrete Structures" (06SG311).

For beam members with damaged surface and exposed main reinforcement/stirrup, and beam members with damaged steel bars to a certain extent and slight corrosion of some steel bars. Repair the damaged parts with fine stone expansive concrete, high-strength grouting material or epoxy mortar. The fluidity of the new concrete for repair should be larger, and the strength grade should be one grade higher than that of the original concrete, and not less than C25. In order to improve the durability of damaged beam members, mixed rust inhibitors (powder or water solution) should be added to new concrete to repair and protect the steel bars in damaged beam members. In order to enhance the bonding ability between the new concrete and the original foundation concrete, the concrete residue in the damaged part must be removed before repairing, the bonding surface should be coated with epoxy resin or concrete interface agent, and the new concrete should be poured before the initial setting of epoxy resin or interface agent. Some beams with Grade C and Grade D should be strengthened with carbon fiber according to the calculation results, and the construction measures should be carried out in strict accordance with the National Architectural Standard Design Atlas "Reinforcement Structure of Concrete Structures" (06SG311).

The surface is damaged, the main reinforcement/stirrup is exposed, the steel bar is seriously damaged, and some steel bars are corroded. Repair the damaged parts with fine stone expansive concrete, high-strength grouting material or epoxy mortar. The fluidity of the new concrete for repair should be larger, and the strength grade should be one grade higher than that of the original concrete, and not less than C25. In order to improve the durability of damaged beam members, mixed rust inhibitors (powder or water solution) should be added to new concrete to repair and protect the steel bars in damaged beam members. In order to enhance the bonding ability between the new concrete and the original foundation concrete, the concrete residue in the damaged part must be removed before repairing, the bonding surface should be coated with epoxy resin or concrete interface agent, and the new concrete should be poured before the initial setting of epoxy resin or interface agent. Finally, the beam members with this degree of damage (both Grade C and Grade D) should be strengthened with carbon fiber, and the construction measures should be carried out in strict accordance with the national building standard design atlas "Strengthening Structure of Concrete Structures" (06SG3 1 1- 1).

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