Wall cracks reinforcement method introduction

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Concrete cracking is a common form of disease in housing diseases, and its appearance will not only reduce the impermeability of the house and affect the use function of the house, but also cause the rust of steel bars, the carbonization of concrete, reduce the durability of materials, and affect the bearing capacity of buildings.

Wall cracks are divided into the following three categories according to the causes caused:
1. Temperature cracks
Cracks caused by changes in temperature inside and outside the concrete. It often occurs in hydraulic large-volume concrete with poor heat dissipation conditions.
2. Settlement cracks
Uneven settlement of the foundation will cause the masonry to be pulled and sheared, creating cracks in the masonry.
3. Force crack
When the internal force generated by the load on the masonry structure is greater than the bearing capacity of the masonry structure, the cracks generated in the masonry structure are force cracks.

Cracks are patched
1) Surface closure method
For individual cracks or mesh cracks with a crack width of ω≤0.2 mm, the crack channel can be closed with a repair glue with good permeability (such as XQ Xin Ball edge banding glue). For floor slabs and other parts that need to be impermeable, it is advisable to paste fiber materials on the surface of the cracks to enhance the sealing effect.
2) Pressure perfusion method
For crack widths of 0.1mm≤ω≤1.5mm, low-viscosity structural adhesives (such as XQ-GF Xin ball grout glue) can be injected by pressure perfusion method for repair. The repair of cracks is mainly completed by embedding the nozzle, sealing the cracks, and filling the crack repair glue.

3) Pressure perfusion + paste carbon fiber cloth reinforcement

For cracks with a crack width of ω≥ 1.5 mm, and the cracks appear in the trans-intermediate region, it is determined to be a structural crack, and on the basis of pressure perfusion, a carbon fiber cloth is pasted along the vertical direction of the crack to increase the tensile bearing capacity of the structure.

The repair of concrete cracks can prevent the further development of cracks, and the concrete caused by further rust of steel bars continues to deteriorate. It has a significant effect on improving the durability of concrete. As a material for crack repair, its performance is directly related to the long-term performance of crack repair.

Zhejiang -Multi-storey frame structure office building

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50 years service life for multi-storey frame structure office building addtional layer reinforcement

 

Project Name: A multi-storey frame structure office building in Zhejiang

Year of Strengthening: 2021

Method: Concrete Section Expansion / Steel Jacketing / Chemical Anchoring



 

Description:

This building was built in August 2014, the building as a whole is “L” shaped layout, the original design is a 6-story local 7-story frame structure, in the construction process the owner requested to add a layer, after adding layers, it is now a 7-story local 8-story frame structure, and the building function does not change. The current office building is 34. 20m, width 27. 70m, construction area of about 4700 square meters. 1, 2 layer height are 4. 50m, 3 ~ 7 layer height are 3. 60m, local 8 layer height is 4. 20m, building height 27. 45mThe foundation of the office building is a manually dug-hole pile, the pile diameter is 800mm ~ 1100mm, the foundation pile holding layer is a weathered sandstone layer, and its limit end resistance standard value is 3000kPa. The strength grade of frame concrete is C30 and the strength grade of poured pile concrete is C35. During the construction of the structure, the deformation and bearing capacity after adding a layer do not meet the requirements of the specification, and the seismic structure does not meet the requirements of the specification, and the overall reinforcement treatment of the structure is required.

 

After the office building structure is fully reinforced by the structure, the maximum elastic inter-layer displacement angle in the X direction and Y direction meets the requirements of the specification, the bearing capacity of the frame column and the frame beam meets the design bearing requirements, and the axial pressure ratio of the underlying column meets the specification requirements, so the structural reinforcement is reasonable and effective, and the reinforcement goal is achieved, which meets the design requirements of 50 years after reinforcement.

 

Through the engineering practice of structural bearing capacity appraisal and calculation, structural reinforcement calculation analysis and reinforcement design after the addition of the office building, the dynamic characteristics of the structure after engineering reinforcement are significantly improved, the deformation of the structure meets the requirements of the specification, and the bearing capacity of the overall structure meets the design bearing requirements, which can meet the design requirements of the subsequent 50 years of use. The outer steel method reinforces concrete components using viscose glue for bonding, because the subsequent service life is 50 years, so the viscose glue needs to use the “Technical Specification for safety identification of engineering structural reinforcement materials” (GB 50728-2011) requires the design of structural adhesives with a service life of 50 years.

Improve bridge reinforcement by steel jacket bonding method

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Steel jacket bonding method reinforces bridges by attaching special epoxy adhesive to bond steel plates, improve the bearing capacity of damaged structural components, and reinforce damaged components, which is a new, convenient and effective reinforcement method to improve the bearing capacity of damaged reinforced concrete.

 

Steel plate jacket bonding reinforcement method:

The use of epoxy resin adhesives, the steel plate is pasted in the weak part of the tensile area of the reinforced concrete structure, so that it forms a whole with the structure, which is used to replace the reinforced steel bar that needs to be added, and through the joint action of the steel plate and the reinforcing structure, improve its stiffness, limit the development of cracks, improve the stress state of the reinforcement and concrete, and improve the bearing capacity of the beam to achieve the reinforcement effect.

 

Advantages of the steel jacket bonding method

1. Durability 

The repaired structure by the steel jacket bonding reinforcement method can restore the ultimate bearing capacity of the original damaged components, improve the durability of the damaged components, and extend the service life of the damaged components.

2. Fast processing

The biggest advantage of the steel jacket bonding reinforcement method is that the construction is no need to stop and the processing is fast. Compared with the traditional method, the steel jacket bonding method can shorten the construction period and basically does not affect the use of components during the construction period.

3. Simple and lightweight

The whole process of construction can be kept dry construction, the environmental pollution is little, the construction is extremely convenient, because in order to meet the requirements of the use of the steel plate than the concrete quality is much smaller, so the steel jacket bonding method can reduce the structural weight after maintenance, and do not change the connection form between the structure before and after the construction.

4. Flexible and diverse

Through the flexible use of the steel jacket bonding method, it can deal with a variety of engineering problems, has a strong usability and scope of application, and provides a good idea for the construction party.

5. Economical and reasonable

The cost has been significantly reduced, reflecting the economic advantages of the steel jacket bonding method. The first is that the delay due to construction is reduced, and the second is that the cost of the method is relatively low, so it is quite reasonable in economic terms.

Disadvantage

(1) There is a stress lag phenomenon in the force of the pasted steel plate, and the larger the load of the original structure during construction, the more stress lag.

(2) The quality and durability of the adhesive are the main factors affecting the reinforcement effect, and are significantly affected by the construction quality.




How to improve the effect of steel jacket bonding reinforcement

There are many factors affecting the reinforcement effect of viscose steel, mainly from the selection of materials, construction technology and other aspects to optimize, this time we summarized the following 5 points:


Construction process

According to the design requirements, the cracks in the bottom of the beam plate are first sealed or irrigated, and then the position of the pasted steel plate is released at the bottom of the beam plate, and the surface of the pasted bridge is chiseled with an automatic chiseling machine, and fresh concrete is leaked out, and a flat rough surface is formed. Remove the concrete that has been loosely pasted at the bottom of the beam plate, blow away the surface dust with oil-free compressed air, or rinse it with clean water, and when it is completely dry, wipe the pasted surface with a degreasing cotton dipped in acetone.

Plate selection

1. The thickness of the steel plate using direct glue paste should not be greater than 5mm; The thickness of the steel plate is greater than 5mm, and it should be bonded with low-pressure injection glue.

2. When reinforcing the positive section of the curved members of reinforced concrete, the steel plate should be pasted with strips, and the width-to-thickness ratio of the steel plate should not be less than 30

Plate bonding adhesive quality

The quality of steel plate bonding adhesive often determines the quality of reinforcement, so we need to pay attention to the following points when choosing high-quality viscose glue:

1. Select high-quality steel plate bonding adhesive, according to GB 50728-2011 “Technical Specifications for Safety Identification of Engineering Structural Reinforcement Materials” 3.0.1 clear requirements: All engineering structural reinforcement materials and products involving engineering safety must pass safety appraisal in accordance with the requirements of this specification. The tensile strength is required to be more than 30MPa, and the measured value of Xinchor is above 33MPa, which meets the requirements of the national standard. Steel-to-steel tensile shear strength, the national standard stipulates 15MPa, and the measured value of Xinchor is 17MPa, which is in line with national standard 4. The tensile shear strength of steel-to-steel is tested according to GB/T7124-2008. T impact peel length is an important indicator to measure the toughness of structural glue. It can be used as a standard for evaluating structural adhesives for building reinforcement in seismic fortification areas. Simply put, the smaller the peel length, the better the toughness of the structural glue and the better the seismic performance.

Xinchor high-temperature resistant Steel Bonding Adhesive STEELCHOR 501 has a unique patented formula design, in the case of performance to meet the requirements of the national standard, can meet the normal curing of the colloid within 25 -125, strength development. It can be seen that a number of inspection items of Xinchor steel bonding adhesive not only meet the national standards, but also far exceed the national standards.

2, the use of suitable adhesives, in case of some special construction environments, you must choose customized products. For example, for steel jacket bonding  reinforcement in a high-temperature environment, it is necessary to choose a special high-temperature resistant bonding adhesive for construction, and cannot still use conventional adhesives, otherwise it will cause bonding failure and affect the quality of the project.

Anchor bolt installation

GB 50550-2010 “Construction Quality Acceptance Code for Building Structural Reinforcement Projects” clearly stipulates that the anchor bolt reinforced by the adhesive steel should be chemical anchor bolt, and the expansion bolt shall not be used.

Anchor bolts should be used for direct gluing and pasting steel plates, and the anchoring depth should not be less than 6.5 times the diameter of the anchor bolts. The spacing of the anchor arrangement should meet the following requirements:

1. The maximum spacing of the anchor bolt center is 24 times the thickness of the steel plate; The minimum spacing is 3 times the anchor bolt bore diameter.

2. The maximum distance between the center of the anchor bolt and the edge of the steel plate is 8 times the thickness of the steel plate or the smaller of 120mm. The minimum distance is 2 times the anchor bolt bore diameter.

3. The anchor bolt is used for steel plate positioning or pasting and pressurization, and is not limited by the above description.

The choice of construction unit

Steel jacket bonding reinforcement is a relatively traditional reinforcement method, the process requirements are high, and it requires rich experience to ensure the quality of the project and improve the construction effect. To improve the effect of adhesive steel reinforcement, it is necessary to select high-quality, suitable adhesives, steel plates, anchor bolts and other materials, as well as the selection of professional construction personnel, and in strict accordance with the construction guidelines, in order to achieve a more ideal reinforcement effect.


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What Is The Shelf Life And Storage Method For Chemical Anchors?

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The shelf life of each chemical anchors is different based on the material. For new and unused GU-100 polyester is 12 months from manufacture date and 18 months for GU-500 GU-600 epoxy acrylate, and GU-2000 vinlyester. Reuse of the cartridges is possible until the final expiration date. To make the chemical anchors stay in good quality, we suggest to store the chemical anchors in a room where the temperature is between 15-25℃ degrees. Do not store the chemical anchors in locations where there is direct sunlight or heat.