House crack structure safety inspection and identification process - Database & Sql Blog Articles

The process of detecting and identifying the safety of cracks in houses:
The building crack structure safety inspection and identification process, the building must meet the requirements of safety, applicability and durability. The destruction and collapse of houses begins with the emergence and development of cracks. Therefore, people often have a fear of cracks in houses. The leakage of houses not only interferes with the daily life of people living and working in buildings, but also affects the use of houses. The function, and the water and other gases and liquid media that penetrate into the structure also pose a threat to the durability of the structure. For concrete components, the cracks will also accelerate the carbonization rate of the concrete and the corrosion of the steel. This requires us to analyze the location and cause of the cracks in actual work to determine which cracks are harmful, which need to be controlled and reinforced; which allow cracks and do not affect the normal use of the house. Our company is specialized in building quality inspection and safety appraisal, seismic identification, plant safety inspection, steel structure inspection, road, bridge, traffic construction engineering inspection and identification, ancient building inspection and identification, dangerous house identification, indoor environmental inspection Testing and other services, providing customers with test reports issued by the national authorities. At the same time, it focuses on the reinforcement of building structure, carbon fiber reinforcement, steel structure reinforcement, building rectification, foundation reinforcement, building reinforcement design, building materials sales and so on. The company advocates the enterprise spirit of “professional, pragmatic, efficient and innovative” and has a good internal mechanism. The excellent working environment and good incentive mechanism have attracted a group of high-quality, high-level and high-efficiency talents. Have a sound technical research and development strength and a mature team. Our aim is: "In exchange for service and sincerity in exchange for your trust and support, mutual benefit and create a win-win situation!

Shenzhen crack test structure safety inspection and identification process, Shenzhen Zhongzheng Engineering Technology Co., Ltd. dedicated to serve you, to undertake the national business scope, provide free technical consulting services, contact telephone, 15999691719 Li Manager

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The crack detection structure safety inspection and identification process -

Example of safety detection of crack structure in houses:

1 A high-rise residential building is a 28-story cast-in-place reinforced concrete frame shear wall structure that has been completed and put into use. The concrete strength rating of this building is C30. The building has a through crack at the 2nd to 4th axis/axis to the shaft area of ​​the 17th floor. In order to understand the cause of the crack and the impact of the crack on the safety of the structure, the 17th floor is targeted. Detecting, analyzing the causes of cracks, judging the impact of cracks on structural safety, and proposing treatment opinions.
2 on-site inspection
2. 1 The crack inspection is carried out by detecting the cracks at the 2nd floor to the 4th axis/axis to the axis area of ​​the 17th floor of the building. The cracks in the floor are mainly irregular cracks, and the crack width is 0. 05 mm ～ 0. At 08 mm, the length of the crack is about 3 700 mm, which is mainly through the crack. No other cracks are found in the main and secondary beams of the frame.
2. 2 Structural layout inspection According to the design drawings, the 17-story beam and slab structure layout system of the building was checked. The inspection results show that the 17-story beam and slab structure layout system of the building meets the design drawing requirements.
2. 3 Concrete strength test The core strength method is used to test the concrete strength of the 17-story slab of the 17-story floor of the building. The concrete strength of the slab is designed to be C30. According to the test results, the concrete strength of the slab with cracks appears. The estimated value is 30. 4 MPa, meeting the design strength level requirements.
2. 4 Floor thickness inspection site The thickness of the 17-story floor of the building was sampled. The thickness of the floor design was 130 mm. According to the test results, the thickness of the floor slab with cracks ranged from 125 mm to 134 mm, meeting the design drawings and concrete construction acceptance specifications. Claim.
2. 5 Floor slab reinforcement test site The steel bar configuration of the 17-story slab of the 17-story slab of the building was sampled. According to the test results, the diameter, spacing and thickness of the slab reinforcement with cracks were Meet the requirements of design drawings and concrete construction acceptance specifications.
2. 6 Concrete raw material inspection According to the cement physical property test report of the building, the physical properties such as fineness, stability, setting time and strength of the cement used for the slab concrete are qualified; According to the admixture test report and fly ash inspection of the building Report, gravel or pebbles inspection report, sand physical property inspection report, all tested items meet the standard technical requirements; According to the concrete mix design report of the building, the concrete mix ratio physical property meets C30 pumping concrete trial design technology Claim.
2. 7 Concrete internal defect detection The internal defects of concrete in the 17-story to 4-axis/axis-axis-axis area of ​​the 17-story floor of the building were tested by ultrasonic method. The results show that the concrete quality of the floor members with cracks is uniform, no honeycomb, no holes. And other defects.
2. 8 Floor slab bearing capacity calculation According to the test results on site, the bearing capacity of the 17-story slab of the 17-story slab/axis/axis-axis area of ​​the building is checked. The thickness of the slab in the calculation is taken according to the measured results. The strength of the steel bar is taken as follows: I grade steel 210 N/mm2 and grade II steel 300 N/mm2. The main load standard values ​​are as follows: Dead load: 4. 0 kN/m2 ; Live load: 2. 0 kN/m2 ; According to the verification results, the floor reinforcement configuration meets the bearing capacity requirements.
3 Analysis of cracks The structural layout of the 17-story slabs of the 17-story slabs of the building with the cracks in the building meets the design requirements. The strength of the slab concrete meets the design requirements. The thickness of the slabs and the configuration of the steel bars meet the design requirements. The slab steel bar configuration meets the bearing capacity requirements, and the possibility of cracks due to insufficient bearing capacity can be eliminated. According to the relevant inspection report, the concrete raw materials testing items all meet the technical requirements; the concrete quality of the floor slab members is uniform and the construction quality is good. Through analysis, it is inferred that the crack in the floor is caused by deformation changes, that is, caused by factors such as temperature, shrinkage, and uneven settlement. Judging from the use of the building, there is no basic feature of cracks caused by uneven settlement, which can be ruled out. It is thus determined that the crack in the floor is mainly a concrete shrinkage deformation crack. This kind of crack is mainly caused by temperature change and shrinkage. When the temperature and humidity around the structure change, the beam and slab will be deformed. The main cause of cracking is shrinkage. The shrinkage of the slab is larger than the rib or beam, which will inevitably cause the inside of the slab. The tensile stress is easy to cause cracking and cause cracking through the crack; it cannot be ruled out due to the influence of construction and maintenance factors, because the concrete is poorly maintained during construction, the surface is dried too fast, and the internal humidity changes little, and the concrete with fast surface shrinkage is slow to shrink. The internal concrete constraint will produce greater stress resistance on the concrete surface, and cracks will occur when the tensile stress exceeds the ultimate compressive strength of the concrete.
4 Conclusions and treatment opinions The comprehensive structure test results and crack cause analysis can be concluded that the cracks in the floor are mainly concrete shrinkage cracks. Such cracks have little effect on the bearing capacity of the floor members and have an impact on the structural durability. Oxygen resin grouting is carried out for sealing treatment.

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The crack detection structure safety inspection and identification process -

Causes of cracks in the floor

1. 1 Calculate errors or cut corners of conventional two-way boards, such as floors in offices, bedrooms, and living rooms. These boards have large bidirectional dimensions that are basically in accordance with calculation assumptions. Generally speaking, such floors have cracks due to the floor. The actual strength is seriously insufficient. There are two reasons for this. One is the calculation error during design; the other is the work-scraping behavior during construction (such as less steel reinforcement, inferior steel, thinner slab thickness or insufficient concrete strength). The two-way plate with a large proportion of long and short sides has cracks parallel to the long side, which is also caused by the above reasons. Therefore, as long as the designer carefully calculates, the construction unit can avoid the occurrence of such cracks according to the construction of the figure and not cutting the work.
1. 2 improper installation of power supply bushings According to the regulations, the power supply bushing should be laid between the steel bars under the floor. It is placed under the steel bar at the bottom of the plate, forcing the bottom ribs to lift up, which will reduce the effective height of the slab. Under normal circumstances, allow The slab has a certain working crack (the crack width is less than 0.3 mm). Since the casing (generally a plastic casing) is inside the concrete protective layer of the slab reinforcement, the crack may first appear along the casing. As the load increases, The crack continues to expand until it runs up and down. In a project, although the individual slabs of the bedroom and the bathroom are not spanned, cracks along the casing appear. As can be seen from the figure, the crack extends along the casing from the corner of the plate to the center of the plate. Therefore, construction When making sure to place the casing between the steel bars under the floor. If there are more pipelines at the local location, the thickness of the building board should be added.
1. 3 premature demoulding and poor support According to the regulations, the general span of the slab can be demoulded after its concrete strength is greater than 75% of the design strength. When the effect of the construction load is greater than the board's bearing capacity, it must be checked and added. Temporary support is provided. Some projects are blindly on the road. The mold is removed too early in the construction process, and the construction load greatly exceeds the capacity of the floor. This will lead to early cracks in the floor. According to the author's experience, the demoulding time can be based on the pouring floor. The strength of the test block produced by the laboratory is determined. However, the design unit should be checked and approved. If the construction load is greater than the load used, the design unit can be increased to increase the design load and re-fit the rib. It can be considered to adopt the method of back support after demoulding. , but need to design unit approval.
1. 4 When the building is damaged, there are often some cement mortar falling on the floor and forming a block. In order to remove these mortar blocks, often several workers chat with the coarse steel rods to hit the mortar block. Although the mortar is removed. The block, the floor was knocked out of the crack.
1. 5 The design of the hole is not considered in the opening of the hole (gas) hole and the corresponding wall load. During the construction, the hole is not reserved according to the drawing, and the additional steel bar is not installed. When installing the water pipe Drilling the floor, often lead to cracks in the floor. Especially in the bathroom and kitchen, temporary addition of air ducts or chimneys. This often requires the opening of a large hole, breaking the bottom of the steel and support steel, the hole edge Brick wall. This not only reduces the strength of the floor but also increases the load. The floor is prone to cracks. Ventilation (smoke) The hole is usually located in the corner of the wall. Therefore, the diagonal cracks often occur (Fig. 4). Therefore, the design When specifying the location of the hole according to the construction requirements, and adding additional steel bars. If the hole is large, the wall load should also be considered, and the flange beam or secondary beam should be added.
1. 6 Shrinkage crack Concrete condensation and changes in working temperature will cause the floor to shrink or stretch. If the stress caused by shrinkage is greater than the tensile strength of the floor, cracks will appear on the floor. During construction, the water-cement ratio or working temperature difference is greater. This phenomenon is more serious. One-way plates (especially long and narrow plates such as ladder roofs) or two-way plates with large proportions of long and short sides often have cracks perpendicular to the long sides. This is mainly caused by the shrinkage of concrete.

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The crack detection structure safety inspection and identification process -

In order to improve the quality of identification, it is necessary to have a rich understanding of the structure of the house. It is necessary not only to fully understand the transmission and deformation of the force, but also to pay attention to the accumulation and impact of the damage. Most of the damage of houses is related to cracks, and the causes of cracks are very complicated, and their shapes are ever-changing. Therefore, correct understanding of cracks is of great significance to improve the quality of identification. Cracks can be divided into load-bearing cracks and non-loading cracks. According to relevant statistics, most of the cracks in houses in engineering practice are non-loaded cracks, accounting for about 80%, and load cracks only account for about 20%. The load cracks are closely related to the internal forces of the load-bearing members. The internal forces of different members and different properties have obvious characteristics, which are easier to judge, and have been described in detail in textbooks and other materials. The following only analyzes and summarizes the non-loaded cracks often encountered in actual work.
4.1 Shrinkage cracks (1) Masonry: There are often two kinds of cracks. One crack occurs in the plaster layer, and a few can extend into the interior of the masonry. Generally, a crack is formed along the length of the wall surface. Another crack Irregular cracks or radioactivity, the crack width is small, only occurs in the plaster layer, and the drum sound is easily hit by hand.
(2) Concrete: There are generally two types of cracks, one is irregular chaotic or radial cracks on the surface of the component, and the other is a crack at every other distance when the length of the member is large. As for the whole house, affected by factors such as structural type, body arrangement (facade and plane), stiffness distribution, etc., different constraints will be generated between the relevant components. When the internal force of the restrained production is greater than the ultimate bearing capacity of the component, Cracks will occur in the weak link.
4.2 Cracks caused by foundation deformation The cracks caused by uneven deformation of the foundation are complex and have different shapes. They have common characteristics and laws, and have their special characteristics. Generally speaking, the cracks are heavy, the upper layer is light, and the vertical wall is heavy. The cross-wall is light, the outer wall is heavy, the inner wall is light, and most of them are oblique cracks. The oblique direction of the oblique crack is inclined and developed from the bottom of the small settlement to the large settlement side. The main reason is the local base. When the deformation difference exceeds the limit deformation of the relevant member, the house will crack. Brick-concrete structures are prone to the following damage:
(1) When the central part of the house sinks, the wall is mostly positively cracked.
(2) When the two sides of the house sink, the wall is often inverted with eight characters.
(3) When the height of the house is relatively large, vertical cracks may appear in the wall.
(4) When the window is narrow, it is easy to produce horizontal cracks at the window. When the upper part of the settlement unit of the house is subjected to the resistance, the window wall is subjected to a large shear stress. When the shear stress is greater than the shear strength of the masonry, the level of the mortar of the horizontal gray joint is lower, so that the gray seam is produced. Horizontal crack, at this time, the crack at one end of the large settlement is below, and the crack at the end of the small settlement is above.
(5) When the window hole is large, it is easy to produce oblique cracks or vertical cracks in the corners and middle portions of the first layer window hole (the upper end is wide and the lower end is narrow). The load on the window wall is large, and the wall below the window hole is less stressed. It is easy to cause uneven settlement of the foundation between the window wall and the window hole, so that the wall below the window hole has an upward bending tendency. When the foundation is rigid, Insufficient strength. If the bending tensile stress is greater than the tensile limit of the masonry, vertical cracks will occur. When the deformation of the foundation on both sides of the window is too large, oblique cracks will occur.
4.3 Temperature cracks When the external temperature changes, due to the mutual restraint between the roof, the floor and the wall, the temperature deformation between them is uncoordinated, resulting in temperature stress. When the temperature stress exceeds the tensile or shear resistance of the member, the member A temperature crack will occur. Temperature cracks usually have the following characteristics and laws: that is, the top layer is heavy, the lower layer is light, the ends are heavy, the middle is light, the sun is heavy, the back is light, the cast-in-place weight, prefabricated light, and changes with temperature. Most of the oblique cracks occur at the top ends of the top layer, especially in the upper and lower corners of the door and window holes. Most of the horizontal cracks occur at the intersection of the concrete roof (beam, plate) and the masonry. According to the relevant data, the surface temperature in summer is up to 55-65 °C due to the influence of solar radiation, and the indoor temperature is generally 25-35 °C, that is, the temperature difference between 20 and 40 °C inside and outside the roof, when the roof insulation measures owe When it is reasonable or invalid, the relevant components will produce large temperature deformation. The linear expansion coefficient of the reinforced concrete members is 10×10-6/°C, and the brick masonry is 5×10-6/°C. The deformation between the two is definitely Inconsistent, even if it is the same reinforced concrete, different components have different deformations due to different constraints, and it is easy to crack in weak places, such as the intersection of beams, plates and brick walls, door and window openings or roof panels 45°. Cross-angle cracks, etc.
4.4 Steel corrosion crack

Affected by various unfavorable factors (carbonization depth, external humidity, concrete protective layer thickness, chloride ion content, etc.), the cracks caused by the corrosion of the steel bars in the components are generally the same as the ribs, such as along the longitudinal ribs or the stirrups. Cracking, when the thickness of the concrete protective layer is thin, the surface of the component may first appear yellowish and then crack. Such severe cracks will destroy the bond between the steel and the concrete, and at the same time reduce the effective cross-section of the steel, thus affecting the bearing capacity of the member.

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The process of testing and appraising the safety of cracks in houses – the company undertakes the following national business scope:

1. Quality inspection before rental housing rental

2. Historical legacy testing (structure inspection before property ownership) and seismic testing of old buildings

3. Industrial plant floor bearing capacity test

4. Housing change use safety detection and change function detection

5. Pre-opening, pre-transfer and pre-qualification housing safety inspections in public places such as hotels, hotels, Internet cafes, mobile roaming art cities, bars, KTV, cinemas, schools, kindergartens, shops, etc.

6. Safety inspection before house demolition

7. Dangerous houses and various emergency tests

8. Building structure safety inspection after fire

9. Building foundation bearing capacity and seismic detection

10. Pre-decoration safety inspection

11. Building life test

12. Damage detection of subway and construction surrounding houses

13. Concrete long-term and durability testing

14. Indoor environmental testing for civil construction projects

15. Building material testing

16. Structural deformation and settlement detection

17. Building reinforcement, layering, transformation testing

18. Judicial arbitration commission

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