Variable cross-section cantilever beam, construction method and application

Abstract

The invention provides a variable cross-section cantilever beam, a construction method and application, and belongs to the technical field of building construction.The variable cross-section cantilever beam comprises a shear wall and a cantilever beam body, the fixed end of the cantilever beam body is fixed to the shear wall, the free end of the cantilever beam body is overhung outdoors and used for supporting a balcony structure, and the cantilever beam body 2 is divided into a first section of cantilever beam body and a second section of cantilever beam body which are continuous in the length direction; the sectional areas of the first section of cantilever beam and the second section of cantilever beam keep consistent in respective section, the sectional area, close to the fixed end, of the first section of cantilever beam is larger than that, close to the cantilever end, of the second section of cantilever beam, and the sectional area mutation is formed between the first section of cantilever beam and the second section of cantilever beam; the change position of the section area mutation is located at the staggered position of balcony structure arrangement; the structure is simple and compact, the stress arrangement is reasonable, the stress requirement of the enlarged balcony can be effectively met on the whole, meanwhile, the engineering cost is saved, and the structure has important significance on safety and stability of the structure and cost control.

Description

Technical Field

[0001] The present invention relates to the technical field of building construction, and particularly relates to a variable cross-section cantilever beam, a construction method and an application thereof. Background Art

[0002] In recent years, with the rapid development of social economy, people's requirements for living space have been increasing day by day, which has given rise to the concept of "fourth-generation housing". The fourth-generation housing is a housing form that integrates "sky gardens", "vertical greening", etc., and is also known as courtyard houses, three-dimensional garden ecological housing or urban forest gardens. This housing model not only greatly enriches the ecological elements of the living environment, but also provides residents with more possibilities to get close to nature and enjoy life by increasing the balcony space of the building.

[0003] However, the traditional balcony structure usually adopts the cantilever method. When the balcony space is increased to meet the residents' demand for a more spacious leisure space, the cross-sectional area of the corresponding cantilever beam structure will also increase rapidly. In addition, the current design schemes of the fourth-generation housing generally adopt the method of setting concrete supports under the cantilever balconies. This not only affects the aesthetics of the building visually, but also occupies valuable indoor usable space. More importantly, it significantly increases the project cost.

[0004] Therefore, there is an urgent need for a variable cross-section cantilever beam structure that can be applied to the large cantilever forest gardens of the fourth-generation housing. Summary of the Invention

[0005] Object of the Invention: The object of the present invention is to provide a variable cross-section cantilever beam, a construction method and an application thereof in view of the deficiencies of the prior art. The structure is simple and compact, the layout of the forces is reasonable, and it can effectively meet the force requirements of the enlarged balcony as a whole. At the same time, it saves the project cost, which is of great significance for the safety and stability of the structure and cost control.

[0006] Technical Solution: The variable cross-section cantilever beam described in the present invention includes a shear wall and a cantilever beam. The fixed end of the cantilever beam is fixed on the shear wall, and the free end of the cantilever beam projects outside for supporting the balcony structure. The cantilever beam 2 is divided into a continuous first-segment cantilever beam and a second-segment cantilever beam along the length direction. The cross-sectional areas of the first-segment cantilever beam and the second-segment cantilever beam are consistent within their respective segments. The cross-sectional area of the first-segment cantilever beam near the fixed end is larger than the cross-sectional area of the second-segment cantilever beam near the cantilever end. A sudden change in cross-sectional area is formed between the first-segment cantilever beam and the second-segment cantilever beam, and the change point of the sudden change in cross-sectional area is located at the staggered position of the balcony structure layout.

[0007] The present invention designs the cross-sectional area according to the force conditions at different positions of the cantilever beam. The first section near the fixed end needs to bear a large bending moment and shear force, so the cross-sectional area is larger to enhance its bearing capacity. While the second section near the cantilever end is subject to relatively smaller loads, so the cross-sectional area can be reduced. On the premise of meeting the force requirements of the balcony, the reasonable optimization of the structure is realized. The first section of the cantilever beam is fixedly connected to the shear wall. Through this connection method, the loads borne by the beam (including the self-weight of the balcony structure and the live loads during use, etc.) are transmitted to the shear wall, and the shear wall then transmits these loads to the foundation and other structures of the building, thus ensuring the stability of the entire structure. The second section of the cantilever beam projects outdoors and directly supports the balcony structure, providing sufficient bearing space for the balcony.

[0008] Further, the cross-sectional area of the first section of the cantilever beam near the fixed end is twice that of the second section of the cantilever beam near the cantilever end. When the cross-sectional area increases by 1 time, the shear resistance capacity is improved synchronously, ensuring a reduction in the risk of shear failure; stress redistribution is achieved through the stiffness mutation point, i.e., the cross-section change point, to avoid stiffness redundancy at the far end.

[0009] Further, the length of the cross-section change point of the cross-sectional area mutation from the fixed end of the shear wall is 30%-50% of the total cantilever length. The cross-section mutation will cause a stiffness mutation. If the position is too close (<30%L), the length of the small cross-section segment is too long and the stiffness at the far end is insufficient, which is likely to cause vibration problems; if it is too far (>50%L), the large cross-section segment is redundant and materials are wasted. Therefore, the range of 30%-50% balances the stiffness transition and material economy.

[0010] Further, a reinforced steel bar skeleton is arranged along the axial direction in both the first section and the second section of the cantilever beam. The main reinforcement ratio of the first section of the cantilever beam is 20%-30% higher than that of the second section of the cantilever beam; the first section of the cantilever beam bears the largest bending moment and shear force, and the load of the second section of the cantilever beam is smaller. Reducing the reinforcement ratio can reduce the amount of steel bars used and avoid stiffness redundancy at the same time.

[0011] Further, a shear key and a mechanical anchoring device are arranged at the connection node between the cantilever beam and the shear wall; the shear force is transmitted through the mechanical engagement of the shear key (such as a trapezoidal steel plate or a concrete rib), and embedded anchor bolts or welded steel plates are used to resist the pulling force.

[0012] A construction method for a variable cross-section cantilever beam includes the following steps: Step 1: According to the balcony structure plan layout drawing, determine the spatial position of the cross-sectional area mutation of the cantilever beam to ensure that this position coincides with the axis at the intersection with the balcony structure.

[0013] Step 2: Determine the cross-sectional dimension parameters of the first section and the second section through moment analysis and calculation. The segmented variable cross-section design can reduce the amount of concrete used.

[0014] Step 3: Embed the cantilever beam connectors during the construction of shear walls; the embedded parts can form a tight whole between the cantilever beam and the shear wall. By means of anchor bars or anchor bolts, etc., the force of the cantilever beam can be effectively transmitted to the shear wall, enhancing the integrity and stability of the structure; when the cantilever beam bears the load, the embedded parts can evenly disperse the stress and transmit it to all directions of the shear wall, avoiding stress concentration, thereby improving the bearing capacity and anti-deformation ability of the cantilever beam.

[0015] Step 4: Use a segmented formwork system to pour the cantilever beam to ensure the construction accuracy of the cross-section mutation of the first-section cantilever beam and the second-section cantilever beam; the segmented formwork system ensures that the geometric deviation at the cross-section mutation is ≤5mm through adjustable formwork (adjustment accuracy ±2mm), avoiding stress concentration.

[0016] Step 5: Arrange the main reinforcement bars in the first-section cantilever beam and the second-section cantilever beam to ensure that the reinforcement ratio of the first-section cantilever beam is 20%-30% higher than that of the second-section cantilever beam.

[0017] Step 6: First pour the first-section cantilever beam, and remove the side formwork after the strength reaches 70%; then pour the second-section cantilever beam, and use slightly expanded concrete to control the joint shrinkage. The expansion strain generated by the slightly expanded concrete during the pouring of the second section can compensate for the joint shrinkage and eliminate the risk of cracks.

[0018] The application of a variable cross-section cantilever beam is used for large cantilever buildings.

[0019] Furthermore, the large cantilever building includes the large cantilever forest garden of the fourth-generation residence.

[0020] Beneficial effects: Compared with the prior art, the advantages of the present invention are as follows: (1) In the present invention, the first section with a larger cross-sectional area can effectively bear larger bending moments and shear forces, strengthening the bearing performance of the cantilever beam near the fixed end, enabling the entire cantilever beam structure to better adapt to the stress requirements of the balcony structure, and ensuring the safety of the structure under various loads; (2) By adopting the design of different cross-sectional areas at different positions of the cantilever beam in the present invention, on the premise of ensuring structural safety, material waste is avoided. The cross-sectional area of the second section near the cantilever end is reduced, reducing unnecessary concrete and steel usage, lowering the construction cost, and at the same time reducing the structural self-weight, which has a positive impact on the structural performance of the entire building; (3) The cross-section change of the present invention is located at the staggered intersection of the balcony structure layout. This design can flexibly adjust the cross-section change position of the cantilever beam according to the specific layout requirements of different balconies, enabling the cantilever beam structure to better match various balcony layouts, and improving the adaptability and flexibility of the structural design. Description of the drawings

[0021] Figure 1It is a schematic plan view of the variable cross-section cantilever beam structure of the large cantilever forest garden of the fourth-generation residence in Embodiment 1; Figure 2 It is a schematic cross-sectional view of the first cantilever beam of the large cantilever forest garden of the fourth-generation residence in Embodiment 1; Figure 3 It is a schematic cross-sectional view of the second cantilever beam of the large cantilever forest garden of the fourth-generation residence in Embodiment 1; In the figure: 11 - the first cantilever beam, 12 - the second cantilever beam, 2 - shear wall, 31 - forest garden, 32 - terrace structural surface. Specific implementation manners

[0022] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings, but the protection scope of the present invention is not limited to the described embodiments.

[0023] Embodiment 1 A variable cross-section cantilever beam in this embodiment is applied to the large cantilever forest garden of the fourth-generation residence, and includes a shear wall 1 and a cantilever beam 2. The fixed end of the cantilever beam 2 is fixed on the shear wall 1, and the free end of the cantilever beam 2 projects outdoors to support the balcony structure. The cantilever beam 2 is divided into continuous first cantilever beam 11 and second cantilever beam 12 along the length direction. The cross-sectional areas of the first cantilever beam 11 and the second cantilever beam 12 are consistent within their respective segments. The cross-sectional area of the first cantilever beam 11 near the fixed end is larger than the cross-sectional area of the second cantilever beam 12 near the cantilever end. A cross-sectional area mutation is formed between the first cantilever beam 11 and the second cantilever beam 12, and the change point of the cross-sectional area mutation is located at the staggered position of the balcony structure layout. In the variable cross-section cantilever beam, the first cantilever beam supports the terrace structural surface 32, and the second cantilever beam 12 supports the forest garden 31.

[0024] As Figure 2 and Figure 3 shown, the cross-sectional area of the first cantilever beam 11 near the fixed end is 2 times the cross-sectional area of the second cantilever beam 12 near the cantilever end. The length from the change point of the cross-sectional area mutation to the fixed end of the shear wall 2 is 30% - 50% of the total cantilever length. Reinforcing steel bar skeletons are arranged along the axial direction in both the first cantilever beam 11 and the second cantilever beam 12, and the main reinforcement ratio of the first cantilever beam 11 is 20% - 30% higher than that of the second cantilever beam 12. Shear keys and mechanical anchoring devices are arranged at the connection node between the cantilever beam 1 and the shear wall 2.

[0025] The construction method of the variable cross-section cantilever beam in Embodiment 1 includes the following steps: Step 1: According to the balcony structure plan layout drawing, determine the spatial position of the cross-sectional area mutation of the cantilever beam, and ensure that this position coincides with the axis of the balcony structure staggered position; Step 2: Determine the cross-sectional dimensions of the first section 11 and the second section 12 by bending moment analysis. Step 3: Pre-embed cantilever beam connectors during the construction of shear wall 2; Step 4: Use a segmented formwork system to cast the cantilever beam to ensure the structural accuracy of the cross-sectional mutation between the first segment 11 and the second segment 12; Step 5: Arrange main reinforcement in the first cantilever beam 11 and the second cantilever beam 12, ensuring that the reinforcement ratio of the first cantilever beam 11 is 20%-30% higher than that of the second cantilever beam 12; Step 6: Cast the first section of cantilever beam 11 first, and remove the side formwork after the strength reaches 70%; then cast the second section of cantilever beam 12, using micro-expansive concrete to control joint shrinkage.

[0026] Because the first cantilever beam 11 has a larger cross-sectional area, it can withstand significant bending moments and shear forces, resulting in a strong load-bearing capacity, thus meeting the load requirements of the terrace structure 32. While the second cantilever beam 12 has a smaller cross-sectional area and relatively weaker load-bearing capacity, its proximity to the cantilever means it receives less load, thus meeting the load requirements of the forest garden balcony. Furthermore, the cross-sectional change is located at the intersection of the balcony structure, making the load distribution of the cantilever beam more rational.

[0027] During the specific implementation, the cross-sectional change position of the cantilever beam is first determined according to the layout of the balcony of the large cantilevered forest garden of the fourth-generation residence; then, the cross-sectional area and size of the first section of the cantilever beam 11 and the second section of the cantilever beam 12 are determined according to the force analysis and structural design requirements; finally, the first section of the cantilever beam 11 is fixedly connected to the shear wall 2, and the second section of the cantilever beam 12 is cantilevered outdoors to support the balcony structure of the forest garden.

[0028] As described above, although the present invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the present invention itself. Various changes may be made to it in form and detail without departing from the spirit and scope of the present invention as defined in the appended claims.

Claims

1. A variable cross-section cantilever beam, comprising a shear wall (1) and a cantilever beam (2), wherein the fixed end of the cantilever beam (2) is fixed on the shear wall (1), and the free end of the cantilever beam (2) projects outdoors for supporting a balcony structure, and is characterized in that: The cantilever beam (2) is divided into a continuous first-section cantilever beam (11) and a second-section cantilever beam (12) along the length direction. The cross-sectional areas of the first-section cantilever beam (11) and the second-section cantilever beam (12) are consistent within their respective sections. The cross-sectional area of the first-section cantilever beam (11) near the fixed end is larger than the cross-sectional area of the second-section cantilever beam (12) near the cantilever end. A cross-sectional area mutation is formed between the first-section cantilever beam (11) and the second-section cantilever beam (12), and the change of the cross-sectional area mutation is located at the staggered position of the balcony structure layout.

2. The variable cross-section cantilever beam according to claim 1, wherein: The cross-sectional area of the first-section cantilever beam (11) near the fixed end is 2 times that of the second-section cantilever beam (12) near the cantilever end.

3. The variable cross-section cantilever beam according to claim 1, characterized in that: The length from the change of the cross-sectional area mutation to the fixed end of the shear wall (2) is 30%-50% of the total cantilever length.

4. The variable cross-section cantilever beam according to claim 1, wherein: Reinforcing steel bar skeletons are arranged along the axial direction in both the first-section cantilever beam (11) and the second-section cantilever beam (12). The main reinforcement ratio of the first-section cantilever beam (11) is 20%-30% higher than that of the second-section cantilever beam (12).

5. A variable cross-section cantilever beam according to claim 1, characterized in that: Shear keys and mechanical anchoring devices are provided at the connection node between the cantilever beam (1) and the shear wall (2).

6. A construction method for a variable cross-section cantilever beam as described in any one of claims 1 to 5, characterized in that It includes the following steps: Step 1: According to the balcony structure plan layout drawing, determine the spatial position of the cross-sectional area mutation of the cantilever beam, and ensure that this position coincides with the axis of the staggered position of the balcony structure. Step 2: Determine the cross-sectional dimension parameters of the first section (11) and the second section (12) through moment analysis and calculation. Step 3: Embed the cantilever beam connecting pieces during the construction of the shear wall (2). Step 4: Use a segmented formwork system to pour the cantilever beam to ensure the construction accuracy of the cross-sectional mutation structure of the first section (11) and the second section (12). Step 5: Arrange the main reinforcement in the first-section cantilever beam (11) and the second-section cantilever beam (12), and ensure that the reinforcement ratio of the first-section cantilever beam (11) is 20%-30% higher than that of the second-section cantilever beam (12). Step 6: First pour the first-section cantilever beam (11), and remove the side formwork after the strength reaches 70%; then pour the second-section cantilever beam (12), and use slightly expanded concrete to control the joint shrinkage.

7. An application of a variable cross-section cantilever beam as described in any one of claims 1 to 5, characterized in that: It is used for large cantilever buildings.

8. The application of the variable cross-section cantilever beam according to claim 8, characterized in that: The large cantilever building includes the large cantilever forest garden of the fourth-generation residence.

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