In construction projects, the quality and safety of the main structure directly determine the quality and safety of the entire building project, so testing it is a way to grasp the quality condition of the overall building and thus provide a reliable reference basis for the next step.

One. Importance of inspection

Within the specified period of use of the building, based on the specified conditions, such as normal design, construction, use, and maintenance, it is necessary to meet the requirements of durability, safety, and applicability. However, in reality, there are many reasons why a building cannot meet the expected functional requirements, including poor design, quality problems in construction, irregularities in use, and large changes in the environment. To determine whether the performance of the main structure of the building can meet the requirements, it is necessary to do a series of testing and appraisal of the main structure, and according to the results of the testing and appraisal of the reliability of the main structure to be a comprehensive evaluation, and then provide a reference basis for the subsequent maintenance and reinforcement treatment, so as to ensure the overall safety of the main structure and effectively extend the service life of the structure.

It can be seen that not only the project quality supervision, the main structure of the building testing and identification, to ensure the safety of the building use phase also has a vital role, and the main structure testing is a relatively complex and highly professional work required

Second, the scope of detection and classification

The main structure of the building inspection can be broadly divided into the following two categories.

First, the main structure of the building project is under construction inspection.

Second, the main structure of the existing building project testing.

The above two categories are basically the same in terms of testing content, the main difference is that the main structure of existing buildings may have to face more aging and damage and other aspects of the problem, compared to the relatively more difficult. The quality of the main structural work of a building under construction should be tested immediately if one of the following conditions is encountered.

(1) The actual number of test pieces, test blocks, or materials related to structural safety is small.

(2) the quality of construction of the main structure after random inspection, the results failed to meet the design requirements.

(3) When there are doubts about the construction quality of the main structure, the structural reliability should be determined by testing.

(4) When an engineering accident occurs, the cause of the accident and its possible impact on the stability and reliability of the structure should be determined immediately through testing.

If one of the following conditions is encountered, the main structure of the building in use should be tested immediately for each performance.

(1) when the main structure of the building is for periodic safety assessment.

(2) the main structure of the building for regular seismic evaluation.

(3) in the building before the start of major repairs to the reliability of identification.

(4) When the use of the building has changed, or for renovation and expansion.

(5) when the main structure of the building has reached its design life but must continue to use

(6) when the main structure of the building needs to be identified under the influence of environmental violations and natural disasters

(7) when there are doubts about the quality of the main structure of existing buildings.

 Third, testing methods and precautions 

1 . Concrete structure testing

(1) raw material performance testing

① for concrete raw materials, their quality, and performance in accordance with the following methods for testing: if there are still raw materials used in the construction of the structure at the site, it can be directly in accordance with the relevant standards of the product, combined with the provisions of the test; if there are no raw materials used in the construction of the structure at the site, it is necessary to take samples in the structure, and then tested according to the provisions of the test.

② for reinforcement raw materials, their quality and performance in accordance with the following methods of testing: if the site and the structure of the raw materials used in construction, then directly in accordance with the relevant product standards, combined with the provisions of the test or the implementation of chemical composition analysis; if the site does not have the structure of the raw materials used in construction, it is necessary to intercept a section of steel in the structure, and then according to the provisions of the test or the implementation of the test Chemical composition analysis.

(2) Strength testing

For the concrete structure, its strength testing mainly refers to the detection of compressive strength, commonly used testing methods are: rebound hammer concrete test, ultrasonic rebound method, and core drilling method. In the actual testing process, it is necessary to strictly follow the technical provisions of each method.

①When using the rebound method for testing, the quality of the surface layer to be inspected must have a good representation, while the compressive strength and age should be within the range allowed by the specifications.

② When using the ultrasonic rebound method for testing, the quality of the internal and external inspection can not be significantly different, while the compressive strength and age should be within the range allowed by the specification.

③If the quality of the surface layer at the place to be tested is not well represented, it should be detected by the drilling core. If the compressive strength and age at the place to be tested are not in the range allowed by the specification, they should also be detected by the drilling core, or the results should be corrected by the drilling core method.

④When using the rebound method or ultrasonic rebound method for testing, if the conditions allow, the results obtained after testing by the above two methods can be corrected by drilling core testing, and can also use the standard test block formed after maintenance under the same conditions, the compressive strength test results for correction.

(3) Appearance quality and defect detection

Common appearance defects, including honeycomb, pockmarked, cracked, exposed tendons, holes, etc., the appearance of the detection method to visual inspection and footage; internal defects detection to non-destructive methods, such as impact reflection method and ultrasonic detection method; in case of necessity, through local damage to verify and correct the test results.

(4) reinforcement detection

The reinforcement testing project includes reinforcement position testing, protective layer thickness testing, reinforcement diameter testing, and reinforcement quantity testing. Among them, the configuration position, protective layer thickness, and quantity of reinforcement can be detected by using the reinforcement detector, and in case of necessity, the concrete at the place to be inspected can be chiseled away to detect and verify the internal reinforcement.

2. Masonry structure detection

(1) masonry block testing

The testing items include strength and strength level testing, dimensional deviation testing, appearance quality testing, frost resistance testing and block species testing. Among them, strength and strength grade testing methods include sampling method and rebound hammer method, etc.; dimensional deviation testing methods include sampling method and field testing method, etc.; block performance testing should be carried out according to the product standards using appropriate methods to ensure the authenticity and accuracy of the test results.

(2) Masonry mortar testing

The testing items include strength testing, species testing, frost resistance testing, and the actual content of harmful elements testing. Among them, strength testing is the key content, and its testing methods include the rebound method, penetration method, and point load method, etc. The actual testing operation must meet the requirements of the current relevant technical standards. Other testing items, are based on product standards using appropriate methods to ensure the authenticity and accuracy of the test results.

(3) masonry strength testing

Masonry strength testing method for the sampling test method and field in situ method. For ordinary brick masonry, its compressive strength testing method to rebound method and in situ axial compression method; shear strength testing method to in situ double shear method or single shear method; in the specific testing operation process, need to strictly comply with the relevant technical standards proposed by the provisions.

For existing masonry components, the quality and structure of the test should be carried out after the surface plaster is chiseled clean, if the masonry quality is problematic, the masonry strength should be reduced; when the span of the roof frame is relatively large, the surface plaster should also be chiseled clean after the test; when the span of the door and window openings is relatively large, should be indirectly detected through the measurement of the actual situation of the over-beam reinforcement, and then by chiseling the surface plaster to verify the results of indirect detection.

(4) Deformation and damage detection

The detection items include ultrasonic crack detection, tilt detection, foundation settlement detection, environmental erosion damage detection, natural disaster damage detection, and man-made damage detection. The operation methods of the above inspection items are roughly the same as those of the previously mentioned concrete structures.

Four  Conclusion

To sum up, the main structure of the building inspection is an important means of project quality supervision, in the supervision and assessment of project quality to provide a reference basis and structural reinforcement and maintenance to provide the correct guidance and other aspects of the importance of self-evident. To ensure the authenticity and accuracy of the test results, different testing methods should be used for different types of structures, and attention should be paid to each matter to give full play to the role and function of the main structure testing.