If the cantilever beam is classified into the enclosure structure component, it may lead to the low comprehensive proportion of the calculated dangerous components, which will affect the final assessment of the risk level of the building and cause certain safety hazards.
Therefore, the author thinks that in this case, considering the importance of cantilever beams, we can first grade cantilever beams as a component of the upper load-bearing structure in accordance with the Reliability Appraisal Standard for Civil Buildings GB50292-2015, and also take it into account when rating the load-bearing part of the envelope structure.
The reason is as mentioned above.
There have been many accidents of balcony slab collapse causing casualties across the country, It is probably worth discussing that such members should be classified as load-bearing members of the enclosure structure.
In terms of the possibility of accidents, the probability of cantilever beam is far greater than that of frame beam, and the consequences are not necessarily smaller than that of ordinary frame beam.
Is the importance of the cantilever beam less than the side beam or the center beam? The author doesn’t think so.
Since the load-bearing components of the enclosure system are the concepts proposed in the Standard for Reliability Appraisal of Civil Buildings, the author has searched the contents of the two versions of the Standard for Reliability Appraisal of Civil Buildings (GB50292-1999 and GB50292-2015), and has not found which components should be included in the load-bearing parts of the enclosure system specified in the standard.
Of course, considering the safety appraisal and rating in the General Code for the Appraisal and Strengthening of Existing Buildings (GB55021-2021), the rating of the secondary subsystem of the second floor only considers the two subsystems of the foundation and the main structure, and cancels the subsystem of the bearing system of the retaining structure, so it is not too big whether the cantilever beam belongs to the bearing system of the retaining structure.
Considering that the definition and classification of structural components in the Standard for the Appraisal of Dangerous Buildings JGJ125-2016 are basically consistent with the Standard for the Appraisal of the Reliability of Civil Buildings, Chen found the Standard for the Appraisal of Dangerous Buildings JGJ125-2016, and found such a provision in it: I’m afraid that is the source of this question asked by this netizen.
The center beam is 1.9, the side beam is 1.4, and the component of the enclosure structure is 1.0.
Fortunately, the article description in Article 7.1.1 of the Standard for Reliability Appraisal of Civil Buildings (GB50292-2015) gives the following sentence: This means that although the cantilever beam can be considered as a load-bearing member of the enclosure structure in the Standard for Appraisal of Dangerous Buildings (JGJ125-2016), it can also be considered as a load-bearing upper structure in the Standard for Reliability Appraisal of Civil Buildings (GB50292-2015).
(Click here to view) Recently, an enthusiastic netizen asked the author, “If the load-bearing components of the enclosure system include cantilever beams, then all the cantilever components belong to the load-bearing components of the enclosure system, such as beam-type balconies and cantilevered outer corridors in commercial buildings”.
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But since the netizen asks so, there must be a source.
Rather, the Standard for the Identification of Dangerous Buildings JGJ125-2016 should carefully consider whether it should be included in the load-bearing components of the enclosure structure.
Because when assessing the comprehensive proportion of the dangerous components of each floor in the hazard standard, the calculation coefficients of the number of center beams, side beams and the number of the components of the enclosure structure are different.
Seeing this, the author thinks that there is a problem that the cantilever beam is used as the load-bearing component of the enclosure structure in the Identification Standard for Dangerous Buildings.
When I first saw this problem, the author felt a little confused.
In the author’s concept, the cantilever beam should be an important load-bearing member of the superstructure, and its importance is even higher than that of the frame beam, because its unique stress mode (statically determinate structure) means that a serious collapse accident will occur once it fails, while the frame beam is generally an statically indeterminate structure, and the probability of failure is relatively much smaller due to the redistribution of internal forces.