Cracks appear in the middle of the bottom of the cantilever beam of the seven story balcony because

Construction errors.

The structural column cannot be constructed at one time with the main body, otherwise it is not a structural column. The structure is completely changed by force. The cantilever beam design is all negative bending moments. The structural columns were constructed together and became supports. Reinforcement is completely different.

In addition, the vertical load on the structural column is transmitted downward from each layer, resulting in a large concentrated force. The cracking of the seventh layer should be the reason.

The top of the structural column should be filled with sand. The structural columns are poured together with the masonry to form a whole.

In this regard, it is first necessary to determine that the balcony is indeed a cantilevered beam. This involves the theory of structural mechanics, theoretically speaking, the middle part of the cantilever beam bears the concentrated load of the superstructure column, but the maximum shear force and the maximum bending moment of the balcony cantilever beam are at the support, that is, the anchor end of the balcony cantilever beam, and the connection with the wall. And the upper part is tensile, and the lower part is compressed.

Therefore, if it is a structural column effect, theoretically the crack should appear near the wall of the upper part of the balcony cantilever beam, near the wall of the building, and not directly below the structural column. If the crack is in the middle of the XL, it could be something else. The structural columns are poured along with the wall, of course, not all at once, and most of the ones I have encountered are poured at one time to the end of the floor slab on the previous floor, reserving the column socket.

The structural column is a secondary structure and cannot be constructed together with the main body.

And the connection between the top end of the structural column and the superstructure must be softly connected, and the support cannot be formed. That is, the concrete at the top of the structural column cannot be poured to the top, leaving 1 2cm, and filling it with extruded plastic board foam board or foaming agent.

The reason for the problem is that the construction unit does not understand the structural knowledge and the construction procedure is wrong; No problem with the design!

Take measures: 1. Disconnect the hard connection between the top of the structural column and the bottom of the pick beam from top to bottom, and change it to a soft connection. 2. Reinforcement and treatment of the quality problems of the beams on the seventh floor

It can be reinforced with adhesive steel and carbon fiber; The treatment plan must be submitted to the design institute for review and approval or the design institute must be entrusted to prepare treatment measures. Reinforcement must be entrusted to a qualified unit.

The reason for the problem of the project is very obvious: there is a structural column at the end of the sixth floor as the support of the end of the seventh floor of the beam, and the beam on the seventh floor becomes a simply supported beam (similar), the bottom of the beam is generally configured with structural steel bars, and the reinforcement ratio is very small, and there is a large amount of load in the middle of the beam (after the upper beam is dismantled due to gravity, there will be a downward deformation process, resulting in a downward load).

First of all, the structural column belongs to the follow-up pouring is best not to be poured with the main body, generally there are decorative columns on both sides of the balcony, the original decorative column is not bearing, only its own load, if it is cast in situ with the main beam plate, the decorative column will definitely be stressed, affecting the XL own stress structure, so there will be all kinds of problems!There is a way is that before construction, it is best to make a design change, to see whether the decorative column can be cast with the main body, if agreed, its own reinforcement, concrete and no problem, that is the design of the problem!

The load of the cantilevered part and this layer is borne by the cantilevered structure of this layer, so the structural column is only located in this layer and cannot be connected with the upper or lower layer.

If it is contacted, the lowest cantilever beam will crack when it can't bear it, and it will affect the upper layer and the upper layer, causing this part to be damaged.

The structural column is a measure of the secondary structure, and the main structure only cooperates with the pre-throwing reinforcement. Structural columns should only generate loads in this layer and transfer them to the lower beams or shear walls and columns.

It is deliberately reserved for cracks during construction!