Shear-resistant structure for intermediate landing of pure cantilever concrete staircase and its construction method

Abstract

The present invention relates to a shear-resistant structure for the intermediate landing of a pure cantilevered concrete staircase and its construction method. The shear-resistant structure is buried in the intermediate landing and includes a shear-resistant frame, prestressed diagonal braces, and strengthening units. The shear-resistant frame includes a pair of side edges arranged in the same direction as the flight of stairs, which are divided into an upper side edge and a lower side edge. One end of the upper side edge far from the upward flight of stairs is lower than the end close to the upward flight of stairs. One end of the lower side edge far from the downward flight of stairs is higher than the end close to the downward flight of stairs. The strengthening units are sleeved on the outside of the near edge and are welded and fixed to the near edge. The prestressed diagonal braces are arranged inside the shear-resistant frame and include an upper layer diagonal brace and a lower layer diagonal brace. The upper layer diagonal brace connects the higher end of the upper side edge to the higher end of the lower side edge, and the lower layer diagonal brace connects the lower end of the upper side edge to the lower end of the lower side edge. Compared with the prior art, the present invention solves the problems in the prior art that the embedded steel sections are subject to large concentrated forces, are prone to deformation and shear failure, and the concrete is prone to cracking and spalling after the deformation of the steel sections.

Description

Technical Field

[0001] The present invention relates to a cantilever staircase, and particularly to a shear-resistant structure for an intermediate landing of a pure cantilever concrete staircase and a construction method thereof. Background Art

[0002] During the building design process, adding vertical members will to a certain extent affect the building function layout, and the vertical members will affect the line of sight of building users, making the building look "bulky" and "heavy". Therefore, during the building design process, it is generally desired to reduce the arrangement of vertical members, and the pure cantilever staircase emerges as the times require. As the name implies, the pure cantilever staircase does not have a ladder column at the intermediate landing, and only the frame beam at the floor elevation projects the stair tread slab and the intermediate landing. This kind of pure cantilever staircase is generally applied to outdoor environments or atria with large openings, and has a good sensory effect.

[0003] Since the cantilever section of the pure cantilever staircase has no vertical support, its own weight and the permanent and live loads it bears have to be borne by itself. Therefore, the load it bears is extremely large, and a large internal force requires more materials to resist. Generally speaking, the slab thickness of the stair tread slab and the intermediate landing of the concrete cantilever staircase is very large. From the force analysis, it can be seen that the upper stair tread slab can be simplified as a tension rod, the lower stair tread slab can be simplified as a compression rod, and the intermediate landing is the node of the tension and compression rods. Moreover, the tensile force and the compressive force of the tension rod form a couple of forces, and the resultant force of this couple of forces in the vertical direction is used to resist the self-weight of the member, the surface load and the live load of the people on the staircase, while the component force in the horizontal direction will form a large shear force on the intermediate landing. Generally speaking, the design angle of the staircase is less than 45°, so it can be qualitatively judged by force decomposition that the shear force is greater than the vertical load.

[0004] In view of this problem, the prior art is to add steel sections on one side of the intermediate landing close to the flight slab, and bury another steel section in each of the upper and lower flight slabs to form a "╞" steel frame to resist shear force. However, there are several problems with this solution: 1. The tensile or compressive force of a normal flight slab on the intermediate landing is a uniform force along the width of the flight slab. The stiffness of the steel section is greater than that of concrete. Therefore, after adding a steel section in the flight slab, the force exerted by the flight slab on the intermediate landing is closer to a concentrated force. Under the action of the same external force, the structure is more disadvantaged when subjected to a concentrated force than a uniform force. 2. The smaller the shear span of a beam, the more prone it is to shear failure. Moreover, in the prior art, the steel sections in the flight slab are arranged on one side close to the stairwell, which results in a relatively short distance between the two steel sections in the flight slab. Even when the shear force is the same, the steel section in the intermediate landing is more likely to cause shear failure. In addition, there is a problem that the deformation of this steel section causes the concrete near it to crack. 3. The steel section in the flight slab is not horizontal, and its direction is along the flight slab with a certain angle. Therefore, the external force exerted by the steel section in the flight slab on the steel section in the intermediate landing is not along the horizontal plate surface direction of the intermediate landing. This results in not only in-plane deformation but also out-of-plane deformation perpendicular to the plate surface of the steel section in the intermediate landing. Compared with the plate surface direction, the concrete thickness in the plate thickness direction is relatively thin, and the concrete will crack or even spall as soon as the steel section deforms slightly.

[0005] Therefore, it is urgent to solve the above problems. Summary of the Invention

[0006] The purpose of the present invention is to provide a shear-resistant structure and its construction method for the intermediate landing of a pure cantilever concrete staircase to solve at least one of the above problems, so as to solve the problems in the prior art that the embedded steel sections are subjected to large concentrated forces, are prone to deformation and shear failure, and the concrete is prone to crack and spall after the steel section deforms, and to achieve good shear resistance of the intermediate landing of the cantilever concrete staircase and limit the development of cracks.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] The first aspect of the present invention discloses a shear-resistant structure for the intermediate landing of a pure cantilever concrete staircase. The intermediate landing is connected with a parallel upward flight and a downward flight on the same side. The upward flight is higher than the intermediate landing, and the downward flight is lower than the intermediate landing;

[0009] The shear-resistant structure is buried in the intermediate landing and includes a shear-resistant frame, a prestressed diagonal brace, and a strengthening unit;

[0010] The shear-resistant frame includes a pair of side edges arranged in the same direction as the flight of stairs, divided into an upper side edge and a lower side edge. Among them, the upper side edge is the side edge of the shear-resistant frame on the side of the ascending flight of stairs, and the lower side edge is the side edge of the shear-resistant frame on the side of the descending flight of stairs; one end of the upper side edge far from the ascending flight of stairs is lower than the end close to the ascending flight of stairs; one end of the lower side edge far from the descending flight of stairs is higher than the end close to the descending flight of stairs; the shear-resistant frame further includes a near edge arranged close to the flight of stairs and a far edge arranged far from the flight of stairs, and the near edge and the far edge are respectively connected to the upper side edge and the lower side edge to form the shear-resistant frame.

[0011] The reinforcing unit is sleeved on the near edge and fixedly welded to the near edge.

[0012] The prestressed diagonal bracing is arranged inside the shear-resistant frame, including an upper-layer diagonal bracing and a lower-layer diagonal bracing. The upper-layer diagonal bracing connects the higher end of the upper side edge to the higher end of the lower side edge, and the lower-layer diagonal bracing connects the lower end of the upper side edge to the lower end of the lower side edge.

[0013] Preferably, the shear-resistant frame is a steel section frame, and the prestressed diagonal bracing is a steel diagonal bracing.

[0014] Preferably, the shear-resistant frame is fixedly welded by full penetration welds, and the prestressed diagonal bracing and the shear-resistant frame are fixedly welded by full penetration welds.

[0015] Preferably, the projection of the shear-resistant frame is a rectangle, and the projection of the prestressed diagonal bracing is the diagonal of the rectangle.

[0016] Preferably, the reinforcing unit is a double-layer casing, which is composed of an outer casing, an inner casing, and a connecting plate connecting the outer casing and the inner casing.

[0017] Preferably, the reinforcing unit is fixedly welded to the near edge by full penetration welds.

[0018] Preferably, several reinforcing units are arranged at intervals and are arranged according to the shear force distribution of the near edge.

[0019] Preferably, the reinforcing units are arranged in a denser manner at the stairwell.

[0020] Preferably, the connecting plate is fixedly welded to both the outer casing and the inner casing.

[0021] In the second aspect of the present invention, a construction method for the shear-resistant structure of the intermediate landing of a pure cantilever concrete staircase as described in any one of the above is disclosed, including the following steps:

[0022] S1: Prefabricate the upper side edge, the lower side edge, the near edge, the far edge, the upper-layer diagonal bracing, the lower-layer diagonal bracing, and the reinforcing unit according to the design dimensions;

[0023] S2: Sheath the strengthening unit on the near edge and weld it in place.

[0024] S3: Weld the upper side edge, lower side edge, near edge and far edge in sequence to form a shear-resistant frame.

[0025] S4: Tension the upper diagonal brace and lower diagonal brace according to the designed stress in sequence, and weld the upper diagonal brace and lower diagonal brace inside the shear-resistant frame under the tension state to form a shear-resistant structure.

[0026] S5: Place the shear-resistant structure between the steel bars of the intermediate landing, and then pour concrete.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) In the present invention, the upper diagonal brace and lower diagonal brace can apply an inward pulling force F to the four corner points of the rectangular shear-resistant steel frame. Furthermore, the rectangular steel frame can restrain the concrete, making the concrete in a state of biaxial confining pressure, which is beneficial to improving the shear resistance of the concrete and can also improve the crack resistance of the concrete.

[0029] (2) Since the upper diagonal brace and lower diagonal brace are welded to the shear-resistant frame through full-penetration welds, a stable triangular structure is formed, which can have a large stiffness. Therefore, when this structure is subjected to the shear force transmitted from the upper and lower flight of stairs, the structure itself can not only bear the shear force, but also ensure less deformation.

[0030] (3) If the upper side edge is in the same inclination direction as the upward-sloping upward flight of stairs, it can ensure that when the upper side edge is subjected to the pulling force transmitted from the corresponding flight of stairs, the profiled steel is basically in a state of axial tension; if the lower side edge is in the same inclination direction as the downward-sloping downward flight of stairs, it can ensure that when the lower flight of stairs is subjected to the pressure transmitted from the corresponding flight slab, the profiled steel is basically in a state of axial compression; in this way, there will be no (or very few) component forces perpendicular to the direction of the intermediate landing, reducing the force on the concrete, and thus being able to reduce the generation of cracks.

[0031] (4) The shear force received by the shear-resistant frame is not evenly distributed. Among them, the shear force is the largest at the position close to the flight slab, and the shear force on the near edge close to the flight slab is even greater at the position of the stairwell and its nearby areas. After welding the strengthening unit formed by double-layer steel pipes to the near edge close to the flight slab through full-penetration welds, the stiffness of the profiled steel of the near edge will be further increased, and the deformation under the action of the shear force will be reduced. In addition, after the hollow and transparent double-layer steel pipe strengthening unit is connected to the near edge and concrete is poured, the mechanical biting force between the component and the concrete can be enhanced, further increasing the integrity of the structure. Description of the Drawings

[0032] Figure 1 It is a schematic structural diagram of a conventional staircase;

[0033] Figure 2 It is a structural schematic diagram of a pure cantilever staircase;

[0034] Figure 3 It is Figure 2 a top view structural schematic diagram of the pure cantilever staircase of;

[0035] Figure 4 It is Figure 2 a simplified force analysis diagram of the pure cantilever staircase of;

[0036] Figure 5 It is Figure 2 a force analysis diagram of the intermediate landing in the pure cantilever staircase of;

[0037] Figure 6 It is Figure 5 a shear force analysis diagram of the intermediate landing of;

[0038] Figure 7 It is a top view structural schematic diagram of an existing steel frame;

[0039] Figure 8 It is Figure 7 a simplified force analysis diagram of the steel frame of;

[0040] Figure 9 It is Figure 7 a structural schematic diagram of the deformed steel frame of;

[0041] Figure 10 It is Figure 7 a structural schematic diagram of the concrete crack of the intermediate landing in the deformed steel frame of;

[0042] Figure 11 It is a structural schematic diagram of the intermediate landing of the present invention;

[0043] Figure 12 It is Figure 11 a side view structural schematic diagram of the A-A side of;

[0044] Figure 13 It is Figure 11 a side view structural schematic diagram of the B-B side of;

[0045] Figure 14 It is a structural schematic diagram of the shear-resistant structure of the present invention;

[0046] Figure 15 It is a schematic diagram of the relative height relationship of the corner points of the shear-resistant structure of the present invention;

[0047] Figure 16 It is a shear force distribution schematic diagram of the shear-resistant structure of the present invention;

[0048] Figure 17Schematic diagram of the strengthening unit of the shear-resistant structure of the present invention arranged according to the shear force distribution;

[0049] Figure 18 Schematic diagram of the strengthening unit of the present invention;

[0050] Figure 19 Schematic cross-sectional structure diagram of the strengthening unit of the present invention;

[0051] Figure 20 Schematic diagram of the tensile force of the prestressed diagonal brace received by the shear-resistant frame of the present invention;

[0052] In the figure: 1 - shear-resistant frame; 11 - upper side; 12 - lower side; 13 - near side; 14 - far side; 2 - prestressed diagonal brace; 21 - upper-layer diagonal brace; 22 - lower-layer diagonal brace; 3 - strengthening unit; 31 - outer sleeve; 32 - inner sleeve; 33 - connecting plate. Detailed implementation manners

[0053] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0054] During the building design process, adding vertical members will affect the building function layout to a certain extent, and vertical members will affect the line of sight of building users, making the building look "bulky" and "heavy", as Figure 1 shown. Therefore, during the building design process, it is generally desired to reduce the arrangement of vertical members, and the pure cantilever staircase came into being. As the name implies, a pure cantilever staircase does not have a ladder column at the intermediate landing, and only relies on the frame beam at the floor elevation to cantilever the stair tread slab and the intermediate landing, as shown in Figure 2 . This kind of pure cantilever staircase is generally applied to outdoor environments or atrium parts with large openings, and has a good effect in terms of perception.

[0055] Since the cantilever section of the pure cantilever staircase has no vertical support, its own weight and the permanent and live loads it bears have to be borne by itself. Therefore, the load it bears is extremely large, and a large internal force requires more materials to resist. Generally speaking, the thickness of the stair tread slab and the intermediate landing slab of the concrete cantilever staircase is very large. From Figure 4 the force analysis diagram, it can be seen that the upper stair tread slab can be simplified as a tension rod, the lower stair tread slab can be simplified as a compression rod, and the intermediate landing is the node of the tension and compression rods. In the top view ( Figure 3 , Figure 5 ), it can be seen that the tensile force and compressive force of the tension rod form a couple of forces, and the resultant force of this couple of forces in the vertical direction is used to resist the self-weight of the member, the surface layer load and the live load of the people on the stairs, while the horizontal component of the force forms a large shear force on the intermediate landing ( Figure 6 ). Generally speaking, the angle of the staircase is less than 45°, so through the decomposition of forces, it can be qualitatively judged that this shear force is greater than the vertical load.

[0056] In response to this problem, the prior art is to add steel profiles on one side of the intermediate landing close to the flight slab, and bury one steel profile in each of the upper and lower flight slabs to form a steel frame to resist shear force, as shown in Figure 8 . This solution has the following problems: 1. The tensile or compressive force of a normal flight slab on the intermediate landing is a uniform force along the width of the flight slab. The stiffness of the steel profile is greater than that of concrete. Therefore, after adding the steel profile in the flight slab, the force exerted by the flight slab on the intermediate landing is closer to a concentrated force, as shown in Figure 7 and Figure 8 . Under the action of the same external force, the structure is more disadvantaged when subjected to a concentrated force than a uniform force. 2. The smaller the shear span of a beam, the more prone it is to shear failure. Moreover, in the prior art, the steel profiles in the flight slab are arranged on the side close to the stairwell, which results in a relatively close distance between the two steel profiles in the flight slab. Even when the shear force is the same, the steel profile in the intermediate landing is more likely to deform, thus causing shear failure, as shown in Figure 9 . In addition, the deformation of this steel profile causes the problem of concrete cracking near it. 3. The steel profile in the flight slab is not horizontal, and its direction is along the flight slab with a certain angle. Therefore, the external force exerted by the steel profile in the flight slab on the steel profile in the intermediate landing is not along the horizontal plate surface direction of the intermediate landing. This results in not only in-plane deformation but also out-of-plane deformation perpendicular to the plate surface of the steel profile in the intermediate landing. Compared with the plate surface direction, the concrete thickness in the plate thickness direction is thinner. Once the steel profile deforms slightly, the concrete will crack or even spall, as shown in Figure 10 .

[0057] Embodiment 1

[0058] A shear-resistant structure for an intermediate landing of a pure cantilever concrete staircase, as shown in Figures 11 - 20 . The intermediate landing is connected with a parallel upward flight and a downward flight on the same side. The upward flight is higher than the intermediate landing, and the downward flight is lower than the intermediate landing;

[0059] The shear-resistant structure is buried in the intermediate landing and includes a shear-resistant frame 1, a prestressed diagonal brace 2, and a strengthening unit 3;

[0060] The shear-resistant frame 1 includes a pair of side edges arranged in the same direction as the flight of stairs, divided into an upper side edge 11 and a lower side edge 12. Among them, the upper side edge 11 is the side edge of the shear-resistant frame 1 on the side of the upward flight of stairs, and the lower side edge 12 is the side edge of the shear-resistant frame 1 on the side of the downward flight of stairs; one end of the upper side edge 11 away from the upward flight of stairs is lower than the end close to the upward flight of stairs; one end of the lower side edge 12 away from the downward flight of stairs is higher than the end close to the downward flight of stairs; the shear-resistant frame 1 further includes a near edge 13 close to the flight of stairs and a far edge 14 away from the flight of stairs, and the near edge 13 and the far edge 14 are respectively connected to the upper side edge 11 and the lower side edge 12 to form the shear-resistant frame 1.

[0061] The strengthening unit 3 is sleeved outside the near edge 13 and welded and fixed to the near edge 13.

[0062] The prestressed diagonal brace 2 is arranged inside the shear-resistant frame 1, including an upper layer diagonal brace 21 and a lower layer diagonal brace 22. The upper layer diagonal brace 21 connects the higher end of the upper side edge 11 and the higher end of the lower side edge 12, and the lower layer diagonal brace 22 connects the lower end of the upper side edge 11 and the lower end of the lower side edge 12.

[0063] More specifically, in this embodiment:

[0064] In this embodiment, a shear-resistant structure with a rectangular projection is arranged inside the intermediate landing, which is specifically composed of a rectangular shear-resistant frame 1 and a prestressed diagonal brace 2 with a projection as the diagonal of the rectangle.

[0065] Combined Figures 11 - 15 , the shear-resistant frame 1 can be further divided into a near edge 13 close to the flight of stairs, a far edge 14 away from the flight of stairs, an upper side edge 11 on the side of the upward flight of stairs (higher than the intermediate landing, the flight of stairs going up from the intermediate landing), and a lower side edge 12 on the side of the downward flight of stairs (lower than the intermediate landing, the flight of stairs going down from the intermediate landing). The near edge 13 and the far edge 14 are a pair of long sides of the rectangle, and the upper side edge 11 and the lower side edge 12 form a pair of short sides of the rectangle, and the joints are welded and fixed with full penetration welds. Among them, the upper side edge 11 is inclined, and the end close to the upward flight of stairs is higher than the end away from the upward flight of stairs, forming a high point and a low point; the lower side edge 12 is also inclined, and the end close to the downward flight of stairs is lower than the end away from the upward flight of stairs, forming a low point and a high point; since this embodiment is for a double-run folded staircase, that is, the upward flight of stairs and the downward flight of stairs are parallel and on the same side of the intermediate landing, the inclination directions of the upper side edge 11 and the lower side edge 12 are always opposite. The near edge 13, the far edge 14, the upper side edge 11 and the lower side edge 12 of the shear-resistant frame 1 are all made of section steel.

[0066] The prestressed diagonal brace 2 includes an upper layer diagonal brace 21 and a lower layer diagonal brace 22, as Figure 14As shown, the upper diagonal brace 21 connects the high point of the upper side 11 and the high point of the lower side 12, and the lower diagonal brace 22 connects the low point of the upper side 11 and the low point of the lower side 12. Figure 15 , and thus the prestressed braces 2 form a diagonal connection within the shear frame 1.

[0067] like Figure 16 , the shear force distribution of the shear structure is quite different, the shear force is smaller on the side far from the staircase, and larger on the side close to the staircase; in addition, the shear force on the near side 13 is also different, among which the shear force at the corresponding stairwell position is the largest and decreases towards both sides. Therefore, in order to strengthen the rigidity of the near side 13 and reduce its deformation under the action of shear force, a reinforcement unit 3 is also set. Figure 17 As shown, on the near side 13, according to the shear force distribution, a number of reinforcement units 3 are arranged at intervals, and are densely arranged at the ladder shaft position, forming a distribution that is concentrated in the middle and scattered on both sides. Figure 18 , 19 It is a double-layer steel casing, the outer casing 31 and the inner casing 32 are welded and fixed by a connecting plate 33 to form a concentric cylinder; the reinforcement unit 3 is sleeved on the outside of the near edge 13 and is welded and fixed to the near edge 13 by full penetration weld.

[0068] like Figure 20 As shown, in the intermediate rest platform using the shear structure, the prestressed diagonal brace 2 applies an inward pulling force F to the four corners of the shear frame 1, and the shear frame 1 can constrain the concrete, so that the concrete is in a state of two-phase confining pressure, which is beneficial to improving the shear resistance of the concrete and the crack resistance of the concrete. In addition, since the prestressed diagonal brace 2 and the shear frame 1 can form a triangular structure with relatively large rigidity, it can also maintain a small deformation when subjected to shear force.

[0069] Since the upper side 11 and the lower side 12 in the shear structure are consistent with the inclination direction of the stair section, when transmitting tension, the steel sections of the upper side 11 and the lower side 12 can be in an axial tension or axial compression state, which can avoid the generation of a component force perpendicular to the middle rest platform as much as possible, thereby reducing the stress on the concrete and reducing the generation of cracks.

[0070] A construction method for a shear-resistant structure of a rest platform in the middle of a pure cantilevered concrete staircase comprises the following steps:

[0071] (1) Prefabricate the upper side 11, the lower side 12, the proximal side 13, the distal side 14, the upper diagonal brace 21, the lower diagonal brace 22 and the reinforcing unit 3 according to the designed dimensions;

[0072] (2) Slip the double-layer steel pipe sleeve strengthening unit 3 over the 13-shaped steel near the edge of the flight of stairs, and weld the two together using full penetration welds. Additionally, denser arrangements are required near the hoistway location.

[0073] (3) Weld the upper side 11, lower side 12, near side 13, and far side 14 together using full penetration welds to form the steel shear frame 1.

[0074] (4) Tension the lower diagonal brace 22 according to the design stress.

[0075] (5) While maintaining the tensioned state of the lower diagonal brace 22, weld it to the underside of the two low points of the steel shear frame 1 using full penetration welds.

[0076] (6) Tension the upper diagonal brace 21 according to the design stress.

[0077] (7) While maintaining the tensioned state of the upper diagonal brace 21, weld it to the upper side of the two high points of the steel shear frame 1 using full penetration welds to form the shear structure (steel frame embedded in the intermediate landing).

[0078] (8) Place the fabricated embedded steel frame between the upper and lower layer of steel bars of the intermediate landing.

[0079] (9) Pour concrete.

[0080] Since the strengthening unit 3 is a double-layer sleeve, and the outer sleeve 31 and the inner sleeve 32 are connected by a connecting plate 33, there are a large number of voids. Therefore, after pouring concrete, some concrete will solidify in the voids. The interaction between the concrete and the strengthening unit 3 can enhance the mechanical interlocking force between the strengthening unit 3 and the concrete, and further enhance the integrity of the structure.

[0081] The above description of the embodiments is for the convenience of those of ordinary skill in the art to understand and use the invention. Those skilled in the art can obviously make various modifications to these embodiments easily and apply the general principles described herein to other embodiments without creative labor. Therefore, the present invention is not limited to the above embodiments, and all improvements and modifications made by those skilled in the art without departing from the scope of the present invention according to the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. Shear resistance structure of the intermediate landing of a pure cantilever concrete staircase, characterized in that, The intermediate rest platform is connected with parallel upward and downward flight segments on the same side. The upward flight segment is higher than the intermediate rest platform, and the downward flight segment is lower than the intermediate rest platform. The shear-resistant structure is buried in the intermediate rest platform and includes a shear-resistant frame (1), prestressed diagonal braces (2) and strengthening units (3). In the shear-resistant frame (1), there are a pair of side edges arranged in the same direction as the flight segment, which are divided into an upper side edge (11) and a lower side edge (12). Among them, the upper side edge (11) is the side edge of the shear-resistant frame (1) on the side of the upward flight segment, and the lower side edge (12) is the side edge of the shear-resistant frame (1) on the side of the downward flight segment. One end of the upper side edge (11) far from the upward flight segment is lower than the end close to the upward flight segment. One end of the lower side edge (12) far from the downward flight segment is higher than the end close to the downward flight segment. The shear-resistant frame (1) also includes a near edge (13) arranged close to the flight segment and a far edge (14) arranged far from the flight segment. The near edge (13) and the far edge (14) are respectively connected to the upper side edge (11) and the lower side edge (12) to form the shear-resistant frame (1). The strengthening unit (3) is sleeved on the outside of the near edge (13) and welded and fixed to the near edge (13). The prestressed diagonal braces (2) are arranged inside the shear-resistant frame (1) and include an upper layer diagonal brace (21) and a lower layer diagonal brace (22). The upper layer diagonal brace (21) connects the higher end of the upper side edge (11) and the higher end of the lower side edge (12), and the lower layer diagonal brace (22) connects the lower end of the upper side edge (11) and the lower end of the lower side edge (12). The shear-resistant frame (1) is a steel section frame, and the prestressed diagonal braces (2) are steel diagonal braces.

2. The shear-resistant structure of the intermediate landing of a pure cantilever concrete staircase according to claim 1, wherein, The shear-resistant frame (1) is welded and fixed by full penetration welds, and the prestressed diagonal braces (2) and the shear-resistant frame (1) are welded and fixed by full penetration welds.

3. The shear-resistant structure of the intermediate landing of a pure cantilever concrete staircase according to claim 2, characterized in that, The projection of the shear-resistant frame (1) is a rectangle, and the projection of the prestressed diagonal braces (2) is the diagonal of the rectangle.

4. The shear-resistant structure of the intermediate landing of a pure cantilever concrete staircase according to claim 1, characterized in that, The strengthening unit (3) is a double-layer sleeve, which is composed of an outer sleeve (31), an inner sleeve (32) and a connecting plate (33) connecting the outer sleeve (31) and the inner sleeve (32).

5. The shear-resistant structure of the intermediate landing of a pure cantilever concrete staircase according to claim 4, characterized in that, The strengthening unit (3) is welded and fixed to the outside of the near edge (13) by full penetration welds.

6. The shear-resistant structure of the intermediate landing of a pure cantilever concrete staircase according to claim 4, characterized in that, A number of the strengthening units (3) are arranged at intervals and are arranged according to the shear force distribution of the near edge (13).

7. The shear-resistant structure of the intermediate landing of a pure cantilever concrete staircase according to claim 6, characterized in that, The strengthening units (3) are arranged in a denser pattern at the stairwell.

8. The shear-resistant structure of the intermediate landing of a pure cantilever concrete staircase according to claim 4, characterized in that, The connecting plate (33) is welded and fixed to both the outer sleeve (31) and the inner sleeve (32).

9. A construction method for the shear-resistant structure of the intermediate landing of a pure cantilevered concrete staircase as described in any one of claims 1-8, characterized in that, It includes the following steps: S1: Prefabricate the upper side edge (11), lower side edge (12), near edge (13), far edge (14), upper layer diagonal brace (21), lower layer diagonal brace (22) and strengthening unit (3) according to the design dimensions. S2: Sleeve the strengthening unit (3) on the near edge (13) and weld and fix it. S3: Weld and fix the upper side edge (11), lower side edge (12), near edge (13) and far edge (14) in sequence to form the shear-resistant frame (1). S4: Tension the upper diagonal braces (21) and the lower diagonal braces (22) in sequence according to the design stress, and connect the upper diagonal braces (21) and the lower diagonal braces (22) inside the shear-resistant frame (1) in the tensioned state to form a shear-resistant structure; S5: Place the shear-resistant structure between the steel bars of the intermediate landing platform, and then pour concrete.

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